<%BANNER%>
HIDE
 Title Page
 Table of Contents
 Energy use in developing count...
 Fundamentals of fluid flow
 Analysis of flat plate collect...
 Solar thermal electric systems
 Biogas
 Improved stoves and solar...
 End-use matching
 The cost of renewable energy...
 Conclusions
 References
 Units


PETE



Notes on selected topics in alternative energy technologies for developing countries
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/AA00008142/00001
 Material Information
Title: Notes on selected topics in alternative energy technologies for developing countries
Physical Description: 224 p. : ill. ; 28 cm.
Language: English
Creator: Bush, M. J
Publisher: Training in Alternative Energy Technologies, Solar Energy Laboratory, University of Florida
Place of Publication: Gainesville, Fla
Publication Date: 1982
 Subjects
Subjects / Keywords: Renewable energy sources -- Developing countries   ( lcsh )
Power resources -- Developing countries   ( lcsh )
Biogas -- Developing countries   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references.
Statement of Responsibility: M.J. Bush.
General Note: "August 1982."
 Record Information
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 662517857
ocn662517857
Classification: lcc - TJ807.9.D44 B87 1982
System ID: AA00008142:00001

Table of Contents
    Title Page
        Title Page
    Table of Contents
        Table of Contents 1
        Table of Contents 2
    Energy use in developing countries
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
    Fundamentals of fluid flow
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
    Analysis of flat plate collectors
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
    Solar thermal electric systems
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
        Page 87
        Page 88
        Page 89
        Page 90
    Biogas
        Page 91
        Page 92
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
        Page 98
        Page 99
        Page 100
        Page 101
        Page 102
        Page 103
        Page 104
        Page 105
        Page 106
        Page 107
        Page 108
        Page 109
        Page 110
        Page 111
        Page 112
        Page 113
        Page 114
        Page 115
        Page 116
        Page 117
        Page 118
        Page 119
        Page 120
        Page 121
        Page 122
        Page 123
    Improved stoves and solar cookers
        Page 124
        Page 125
        Page 126
        Page 127
        Page 128
        Page 129
        Page 130
        Page 131
        Page 132
        Page 133
        Page 134
        Page 135
        Page 136
        Page 137
        Page 138
        Page 139
        Page 140
        Page 141
        Page 142
        Page 143
        Page 144
        Page 145
        Page 146
        Page 147
        Page 148
        Page 149
        Page 150
        Page 151
        Page 152
        Page 153
        Page 154
        Page 155
        Page 156
        Page 157
        Page 158
        Page 159
        Page 160
        Page 161
        Page 162
        Page 163
        Page 164
        Page 165
        Page 166
        Page 167
        Page 168
        Page 169
    End-use matching
        Page 170
        Page 171
        Page 172
        Page 173
        Page 174
        Page 175
        Page 176
        Page 177
        Page 178
        Page 179
        Page 180
        Page 181
        Page 182
        Page 183
        Page 184
        Page 185
        Page 186
        Page 187
        Page 188
        Page 189
        Page 190
        Page 191
        Page 192
        Page 193
        Page 194
        Page 195
        Page 196
        Page 197
        Page 198
        Page 199
        Page 200
        Page 201
        Page 202
        Page 203
        Page 204
        Page 205
        Page 206
    The cost of renewable energy systems
        Page 207
        Page 208
        Page 209
        Page 210
        Page 211
        Page 212
        Page 213
        Page 214
        Page 215
        Page 216
        Page 217
        Page 218
        Page 219
        Page 220
        Page 221
    Conclusions
        Page 222
    References
        Page 223
    Units
        Page 224
Full Text










____


ALTERNATIVE ENERGY TECHNOLOGIES

FOR

DEVELOPING COUNTRIES


NOTES ON SELECTED TOPICS


M.J. Bush

Training in Alternative Energy Technologies Program

University of Florida


August 1982









NOTES ON SELECTED TOPICS IN ALTERNATIVE ENERGY TECHNOLOGIES
FOR DEVELOPING COUNTRIES.




CONTENTS PAGE


ENERGY USE IN DEVELOPING COUNTRIES 1
Commercial energy 3
The traditional fuels 14
Rural energy use 19
Animal energy 24
Urban and industrial energy use 25
The modern sector 26
Future energy supply 27
Oil a dwindling resource 30
Prospects for the traditional fuels 32
Renewable energy resources 34

FUNDAMENTALS OF FLUID FLOWi 41
Basic concepts 41
Flow in pipes 48
Sizing pipes 51
Thermosyphon systems 53

ANALYSIS OF FLAT PLATE COLLECTORS 57
Efficiency factor 59
Heat removal factor 60
Overall loss coefficient 62
Minimizing thermal losses 69
Energy gain 70
SOLAR THERMAL ELECTRIC SYSTEMS 74
Distributed collector systems 75
Central receiver systems 79
BIOGAS 91
The digestion process 91
Carbon-nitrogen ratio 93
PH level 93
Temperature effects 97
Sludge utilization 99
Gas utilization 100
Indian gobar gas plants 102
Economics of biogas systems 107
Socio-economic impacts 111
Chinese biogas systems 113
Construction details, materials and costs 116















CONTENTS


PAGE


IMPROVED STOVES AND SOLAR COOKERS 124
The Lorena stove 128
On the boiling of a pot of water 131
Stove configurations 135
Technology extension 145
Solar cookers 147
Advanced solar cookers 149
Heat transfer systems 150
Ovens and food warmers 161

END-USE MATCHING 170
Introduction 170
Systematic end-use matching 173
Characterization criteria 178
Scale 182
System flexibility 187
Socio-cultural factors 188
Examples of end-use matching 196

THE COST OF RENEWABLE ENERGY SYSTEMS 207
Small-scale water pumping 207
Village electrification 216

















ENERGY USE IN DEVELOPING COUNTRIES

Developing countries use considerable amounts of energy but generally
much less than the industrialized nations. However, both the pattern of
energy supply and use, and the types of fuels utilized in the developing
countries show significant and important differences when compared to the
industrialized countries. There are also enormous differences between coun-
tries that are all loosely classified as developing countries. At one end
of the scale there are very poor countries with little economic activity
beyond subsistence agriculture and livestock tending; at the other end of
the scale are countries such as Brazil, Korea, and Mexico which are indus-
trialized to a very substantial degree. And in between lie a large number
of countries with widely differing resource bases, economic activities, and
energy supply and use patterns.

Despite such important inter-country differences, it is useful to
compare the developing countries, both as a group and broadly disaggregated
by region, with the industrialized countries. Figure 1 shows the per capital
energy consumption levels fo~r each of the developing country regions and for
the group as a whole, contrasting them with the industrial countries and
with aggregate global data. The wide bars distinguish between energy
consumption from commercial sources (oil, gas, coal, hydroelectricity, and
nuclear power) and traditional sources (firewood, charcoal, dung, and
agricultural residues). Human and animal energy inputs are not included,
which, in many developing countries, make significant contributions to total
energy supply. In addition to the sharp contrast in energy use per capital
between developing and industrial countries, there is a striking difference
in the degree of reliance on traditional fuels which in Africa account for
the major part of energy use. It is also notable that per capital energy
consumption in Latin America is roughly twice that of Asia and nearly three
times per capital consumption in Africa.




















4,500 447

4.1

Traditional
4,00 suraPopulation
Commercial
sources

3,500 .(energy in kilograms oil
equivalent; population

3,076
3,000 -:



2,500~ iil
2,32 4





1,634~
132 ii
1,500

1.14 F~i3 n~1,143

I,000 1291


520 lii3578 j
500 431 409 119 344ii 159




Africa ~Asia Latin Devloping ` Industrial Worl
America countries countries
Figure 1, Per Capita Energy Consumption and Population, by Region, 1978. Traditional
energy data for 1973 from Jyoti K. Parikh, "Energy and Development," World Bank
Public Utilities Report No. PL1N 43 (Washington, D.C., August 1978), recalculated on
the assumption that per capital traditional energy consumption remained unchanged
between 1973 and 1978. Commercial energy data for 1978, except for Taiwan, from
United Nations, World Energy Supplies, 1973-1978, Series 3, No. 22 (New York, 1979),
with data on hydroelectricity and nuclear energy recalculated on basis of thermal
generation primary energy equivalents. Data for Taiwan from an oral communication
from the Coordination Council for North American Atfairs to Lincoln Gordon. Population
data from Population Reference Bureau, 1978 World Population Data Sheet (Washington,
D.C., 1979). Ci7










COMMERCIAL ENERGY

The pattern of current energy consumption and its future demand in the
developing countries depends strongly on their overall economic structure
and other related socio-demographic factors. It is useful to classify the
developing countries into five relatively homogeneous groups according to
their degree of development as indicated by per capital income, extent of
industrialization and urbanization, as well as by the characteristics of
their economic and resource bases.

Table 1 shows a division of 88 developing countries into five groups
classified as follows:

I Industrialized

In this group, the industrial sector accounts for the largest share of
Gross Domestic Product (GDP). There is relatively more industry and less
traditional handicraft production compared to the other groups. However,
their modern and predominantly urban industrial sectors usually exist
independently from the traditional urban and rural sectors. These countries
have the highest fraction of their populations located in urban areas (60%)
and, not surprisingly, the highest commercial energy consumption per capital.
All are coastal nations with significant trade activities. In common~ with
the other oil importing groups, all the industrial developing countries
consume more energy than they produce [4].

II Oil Exporters

Countries in this group have a set of common choices confronting them:
the rate of development and use (domestic or export) of their oil resources,
and the pattern of investment of their export earnings. Most of these
countries face sizeable short-term debt service and/or domestic public
spending needs. This group can be expected to grow over the next few years
as developing countries receive relatively more emphasis on oil exploration.

III Balanced Growth Economies

This group of countries is characterized by an industrial structure
that is relatively well developed but which does not account for the largest
share of GDP. Most of the members of this group have already completed the
primary and intermediate phases of import substitution and are attempting to
become self-sufficient in the heavy industrial sector.

All of the countries in this group are still essentially agrarian
societies in that agriculture is the principal activity of a large part of
the population. For example, agricultural production still absorbs well
over half of the total work force in India, Turkey, and Pakistan. Apart
from direct agricultural work, the rural sector provides employment oppor-
tunities in the service and traditional industries sectors, so that the vast
majority of the population resides in and is dependent on the rural economy.







TABLE 1



DEVELOPING COUNTRY GROUPS


V-a. Agricultural Exporters


II. Oil Exporters

Angola
Bolivia
Congo
Egypt
Indonesia .
Malaysia
Mexico
Dman
Syrian Arab Republic
Trinidad and Tobago
Tunisia

III. Balanced Growth Economies


I. Industrialized


Argentina
Brazil
Chile
South Korea
Singapore
Spain
Taiwan
Uruguay
Yugoslavia


Costa Rica
Dominican Republic
Gambia
Guatemala
Honduras
Ivory Coast
Senegal
Sri Lanka
Thailand


V-b. Other Agricultural

Afghanistan
Bangladesh
Benin
Burma
Burundi
Cameroon
Central African Empire
Chad
Cyprus
El Salvador
Equatorial Guinea
Ethiopia
Fiji
Ghana
Haiti
Jordan
Kenya
Lebanon
Lesotho
Madagascar
Malawi
Mali
Mauritius
Mozambique
Nepal
Nicaragua
Niger
Papua New Guinea
Paraguay
Rwanda
Somalia
Swazi land
Sudan
Tanzania
Ug anda
Upper Volta
Yemen Arab Rep.


Colombia
Greece
India
Pakistan
Panama
Peru
Philippines
Turkey


IV. Primary Exporters

Botswana
Guinea
Guyana
Jamaica
Liberia
Mauritania
Morocco
Sierra Leone
Surinam
Togo
Zaire
Zambia


Source [2, 3]
















IV Primary Exporters

As a group, the primary exporters vary considerably from the indus-
trialized LDCs and those with balanced economies. Their mean GNP per capital
figure is considerably lower than the industrialized developing countries of
group I, and they also use considerably less commercial energy than that
group. Although these countries are, on the whole, not large energy con-
sumers they still consume more than they produce.

V Agricultural

In this group, the agricultural sector clearly dominates the GDP.
This group can be further sub-divided into Agricultural Exporters: coun-
tries dependent on the export of one or two -ag 97~u~~r~;j:icultua cmmodties and
Other Agricultural: countries largely characterized by subsistence/
taming. The group is generally without significant commercial quantities
of mineral resources. Many of these countries are among the poorest of the
world. The bulk of energy consumption by these countries is of traditional
fuels, primarily wood with some crop residues and animal wastes.

From the energy use point of view, the utility of this classification
lies in the relative homogeneity of the energy consumption patterns found in
each group. In group I, the industrial sector, here dependent on commercial
fuels, dominates the energy use structure while at the other extreme, in
group V, energy use in rural households -- mainly food preparation using
traditional fuels -- is the principal mode of energy consumption. Table 2
shows commercial energy use, the contribution of petroleum, and its
sectoral distribution for each of the five groups. To a first
approximation, the growth in per capital commercial energy consumption
follows reasonably closely the rise in GNP per capital. Also apparent is the
way oil consumption increases as a fraction of commercial energy use from
category I to V, suggesting the extreme dependence of the poorer
agricultural countries on petroleum products for their entire commercial
energy supply. One should note that the figures for category III are
distorted by the inclusion of India which is a major consumer of coal.

As far as oil consumption is concerned, it is instructive to note that
the industrial and transportation sectors account for roughly equal amounts
of this fuel but that, taken together, these two sectors only account for
about 70% of total oil consumption.

Tables 3 through 9 show per capital energy consumption patterns for
seven developing countries: South Korea, Indonesia, Pakistan, Turkey,
Dominican Republic, Thailand, and Sudan. There is at least one represen-
tative from each of the developing country groups listed in Table 1.




















Table 2

DEVELOPING COUNTRY GROUP CHARACTERISTICS


Fraction Oil
by Sector (2)
Industry Transport

0.35 0.24

0.25 0.45

0.25 0.45

0.6 0.3

0.2 0.3-0.5


Number of
Countries

9

10

8

13

45


Population
(Millions)

262

134

784

61

398


GNP/cap
($/cap)

1120

740

221

313

162


Energy/cap
GJ/cap(1)

43

36

21

19

16


Fraction Oil
of Commercial

0.67

0.69

0.41

0.73

0.90


Group

Industrialized

Oil Exporters

Balanced Growth

Primary Exporters

Agricultural


I

II

III

IV

V


Notes: (1) Commercial energy: not including the traditional fuels.

(2) There is a great deal of variability in these numbers depending on the energy resource base and
industrial structure. The data are based on Palmedo [2, 3] and are from 1975.















I


Table 3

PER CAPITAL ENERGY CONSUMPTION

Group I


SOUTH KOREA

BY SECTOR AND RESOURCE 1973 (GJ/YR)

Industrialized


Non-**
Commercial

4.34

0.48


TOTAL
Direct Use

18.53

9.29

4.24

0.25

12.91

45.22


Oil

1.57

6.06

4.22

0.24

5.38

17.47


Gas a Coal

8.97

1.11

0.02



0.45

10.55


H~ydro*










12.38


Electricity

3.65

1.64



0.01

(5.30)


Residential-Commercial

Industry

Transportation

Agriculture

Electricity Generation

TOTAL


----

4.82


* Taken as fossil fuel equivalent

** Crop residues, fuelwood, charcoal, dung

% of oil consumption in total commercial energy consumption 43.2

% of oil consumption in total energy used for electricity generation 29.6


Source: Palmedo, P.F., et. al. [2]
1973 population: 34 million; 53% rural





Table 4

PER CAPITAL ENERGY CONSUMPTION

Group II


INDONESIA

BY SECTOR AND RESOURCE 1973 (GJ/YR)

Oil Exporters


Non-**
Commercial

8.00


TOTAL
Direct Use

9.02

0.78


Gas ar Coal



0.28


Hyd ro*


Electricity

0.05

0.02





(0.07)


Oil

0.97

0.48

1.15



0.22

2.82


Residential-Commercial

Industry

Transportation

Agriculture

Electricity Generation

TOTAL


1.15



0.30

11.25


----

0.15


8.00


0.28


* Taken as fossil fuel equivalent

** Crop residues, fuelwood, charcoal, dung

% of oil consumption in total commercial energy consumption 86.7

% of oil consumption in total energy used for electricity generation 58.4


Source: Palmedo, P.F., et. al. [2]
1973 population: 130 million; 81% rural












Table 5 PAKISTAN

PER CAPITAL ENERGY CONSUMPTION BY SECTOR AND RESOURCE 1974 (GJ/YR)

Group III Balanced Growth Economies

Non-** TOTAL
Oil Gag a Coal Hydro* Electricity Commercial Direct Use

Residential-Commercial 0.67 0.11 ---- 0.07 4.77 5.62

Industry 0.14 1.71 ---- 0.16 ---- 2.01

Transportation 1.16 ---- ------- ---- 1.16

Agriculture 0.16 ---- ---- 0.06 ---- 0.22

Electricity Generation 0.13 0.74 0.86 (0.29) ---- 1.44

TOTAL 2.26 2.56 0.86 ---- 4.77 10.45


* Taken as fossil fuel equivalent

** Crop residues, fuelwood, charcoal, dung

% of oil consumption in total commercial energy consumption 39.7

% of oil consumption in total energy used for electricity generation 7.5


Source: Palmedo, P.F., et. al. [2]
1974 population: 69 million; 73% rural~












Table 6 TURKEY

PER CAPITAL ENERGY CONSUMPTION BY SECTOR AND RESOURCE 1975 (GJ/YR)

Group III Balanced Growth Economies


Residential-Commercial

Industry

Transportation

Agriculture

Electricity Generation

TOTAL


Non-**
Commercial

6.39


TOTAL
Direct Use

10.30

4.52

5.93

1.05

2.98

24.78


Oil

2.63

2.55

5.39

1.05

1.53

13.15


Gag a Coal

0.90

0.97

0.53


Hyd ro*


Electricity

0.38

1.00

0.01



(1.39)


1.10

3.50


1.74

1.74


6.39


* Taken as fossil fuel equivalent

** Crop residues, fuelwood, charcoal, dung

% of oil consumption in total commercial energy consumption 71.5

% of oil consumption in total energy used for electricity generation 35.0


Source: Palmedo, P.F., et. al. [2]
1975 population: 40.2 million; 57% rural












Table 7 DOMINICAN REPUBLIC

PER CAPITAL ENERGY CONSUMPTION BY SECTOR AND RESOURCE 1977 (GJ/YR)

Group V-a Agricultural Exporters


Non-**
Commercial

2.69

5.34


TOTAL
Direct Use

4.35

12.05

3.71

0.32

4.76

25.19


Oil

0.96

6.29

3.71

0.32

5.32

16.60


Gag ac Coal


Hydro*


Electricity

0.70

0.42


Residential-Commercial

Industry

Transportation

Agriculture

Electricity Generation

TOTAL


0.56

0.56


(1.12)


8.03


* Taken as fossil fuel equivalent

** Crop residues, fuelwood, charcoal, dung

% of oil consumption in total commercial energy consumption 96.7

% of oil consumption in total energy used for electricity generation 90.5


Source: Palmedo, P.F., et. al. [2]
1977 population: 4.98 million; 56% rural




































* Taken as fossil fuel equivalent

** Crop residues, fuelwood, charcoal, dung

% of oil consumption in total commercial energy consumption 86.6

% of oil consumption in total energy used for electricity generation 52.3


Source: Palmedo, P.F., et. al. [2]
1976 population: 42.6 million; 83% rural





Table 8 THAILAND

PER CAPITAL ENERGY CONSUMPTION BY SECTOR

Group V-a Agricultural


AND RESOURCE 1976 (GJ/YR)

Exporters


Non-**
Commercial

10.49

0.88







11.37


TOTAL
Direct Use

11.47

3.21

3.92

0.94

1.94

21.48


Oil

0.72

1.78

3.92

0.94

1.40

8.76


Gay a Coal



0.08


Hyd ro*


Electricity

0.26

0.47





(0.73)


Residential-Commercial

Industry

Transportation

Agriculture

Electricity Generation

TOTAL


1.11

1.11


0.16

0.24












Table 9 SUDAN

PER CAPITAL ENERGY CONSUMPTION BY SECTOR AND RESOURCE 1975 (GJ/YR)

Group V-b Other Agricultural


TOTAL
Direct Use

16.51

0.58

1.33

0.48

0.38

19.28


Non-**
Commercial

16.18

0.15







16.33


Electricity

0.07

0.08



0.02

(0.17)


Oil

0.26

0.35

1.33

0.46

0.21

2.61


Gap ar Coal


Hydro*


Residential-Commercial

Industry

Transportation

Agriculture

Electricity Generation

TOTAL


0.34

0.34


* Taken as fossil fuel equivalent

** Crop residues, fuelwood, charcoal, dung

% of oil consumption in total commercial energy consumption 88.5

% of oil consumption in total energy used for electricity generation 38.4


Source: Palmedo, P.F., et. al. [2]
1975 population: 15.6 million; 87% rural














THE TRADITIONAL FUELS

About 25% of the energy consumed in developing countries is provided by
the traditional fuels, and approximately half the world's population rely
primarily on traditional fuels for their direct energy needs. The tradi-
tional fuels include:

1. Wood fuels -- firewood and charcoal
2. Animal wastes -- dung from cattle and other animals
3. Crop residues -- such as straw and bagasse.

Wood is the principal fuel in the rural areas of developing countries.
Charcoal is generally more popular in urban areas because of its convenience
and ease of transportation. Crop residues and dung are usually only
resorted to when wood fuels are unavailable or are too costly. In countries
in the early stages of industrial development the traditional fuels may
constitute 80-90% of total energy consumption.

Since most traditional fuels are not traded in commerce, estimates of
their consumption are necessarily very approximate. The FA0 estimates wood
and charcoal consumption in all developing countries at over 1 billion cubic
metres per year. The use of animal dung as a fuel amounts to about 400
million tons annually. Reliance on traditional fuels is heavier in poorer
countries and in rural areas, among the urban poor relative to the urban
non-poor, and geographically in Africa and Asia. Table 10 gives a general
picture of the extent of national reliance on traditional fuels.

The traditional fuels are, of course, renewable sources of energy. But
these fuels are rUpt available in unlimited quantities. Deforestation is now
a serious problem in many of the poorer developing countries where reliance
on fuel wood and charcoal as energy sources is heaviest. Part of the
problem with the traditional fuels is that they are used very inefficiently,
so the amount of fuel consumed to cook food, or heat or light a dwelling is
very much more than is theoretically required. The introduction of more
efficient cookstoves, charcoal kilns, lamps and heating devices could
substantially reduce the pressure on forest biomass resources.

Tables 11 and 12 show the contribution that traditional sources of
energy make to six Central American countries and five Asian countries. The
data for Bangladesh and India show the significant contribution that human
and animal labour make in these countries, chiefly in agricultural produc-
tion. Table 13 shows the sectoral distribution of energy consumption for
one of the poorest of the developing countries -- Nepal. This country, with
95% of its population in the rural areas, is almost completely dependent on
firewood as a source of energy.























Table10. Estimated NatOioa Rellance on Traditional Fuels, 1976
(each group arranged in ascending order of per capital GNP) 1(63
Medium reliance
(approximately
Modest reliance one-half to Heavy reliance
(less than half) three-quarters) `(three-quarters or more)


Pakistan (22)
Mauritius (2)
Morocco (22)
Rhodesia (Zimbabwe) (36)
China (9)
N. Korea (<1)
S. Korea (8)
Philippines (<1)
Ec~iador (20)
Albania (24)
Algeria (4)
Tunisia (25) .
Iran (1)
Lebanon (2)
Argentina (3)
Chile (14)
Cuba (5)
Dominican Republic (19)
Guadaloupe (19)
Mexico (4)
Panama (29)
Peru (20)
Uruguay (13)
Fiji (2) <
Cyprus (NA) .
Malta (NA)
Portugal (3)
Romania (2)
Turkey (18)
Yugoslavia (4)
Libya (Sy
Hong Kong (NA)
Israel (NA)
Singapore (NA)
Bahamas (NA)
Venczuela (8)


Togo (67)
India (28)
Indonesia (62)
Sri Lanka (55)
'Vietnam (55)
Gabon (44)
Liberia (53)
SMauritania (63)
Senegal (63)
Zambia (45)
Thailand (34)
Bolivia (45)
Colombia (37)
El Salvador (53r
Guatemala (60)
Honduras (64)
Malaysia (25)
Mongolia (25)
Brazil (38)
Costa Rica (50)
Nicaragua (47)


Benin (86)
Burundi (89)
Cameroon (82)
Cape Verde (NA)
Central African Empire (91)
Chad (94)
Ethiopia (93)
Gambia (73)
Guinea (74)
Guinea Bissau (87)
Kenya (74)
Lesotho (NA)
Madagascar (80)
Malawi (82)
Mali (97)
Mozambique (74)
Niger (87)
Rwanda(96)
Sierra Leone (76)
Somalia (90)
Sudan (81)
Tanzania (94)
Uganda (91)
Upper Volta (94)
Zaire (76)
Afghanistan (76)
Bangladesh (63)
Bhutan (NA)
Burma (85;)
Cambodia (93)
Laos (87)
Nepal (96)
Yemen (NA)
Haiti (92)
Angola (74)
Botswana (NA)
Congo (80)
Eq. Guinea (86)
Ghana (74)-
Nigeria (82)
Swaziland (NA)
Paraguay (74)
Papua New Guinea (66)


Notes: Country Reliance classified according to wood fuels plus estimated dung and crop wastes
as a percentage of total energy consumption. Figures in parentheses are wood fuels alone as a
percentage of total energy consumption in each country. Egypt. Iraq, Syria. Bahrain, Brunei.
Kuwait, Oman, Qatar, Saudi Arabia, United Arab Emirates were not classi~ed. NA = not available.

















COSTA RICAL NICARAGUA HONDURAS GUATEMALA EL SALVADOR PANAMA
1978 1977 1977 1977 1978 1977
ENERGY SOURCE

Commercial 26.0 17.4 10.2 8.6 11.5 43.1

Traditional* 9.8 8.2 Z.0 7.2 6.7 7.9

TOTAL (GJ) 35.8 25.6 17.2 15.8 18.2 51.0


*Bagasse, firewood and agricultural wastes. Does
not include human and animal power.

Table i. Approximate Annual Energy Use Per Capita


in Six Central American Countries (Gigajoules)


Source: adapted from reference 5.














CHINA BANGLADESH INDIA SRI LANKA THAILAND
1977 1978 1978 1978 1977
ENERGY SOURCE

COMMERCIAL SOURCES


Coal and lignite 0.1 3.4 0.02 0.2

Oil and gas 1)12.5 1.2 1.6 2.4 9.1

Hydro and nuclear 0)I .1 0.2 0.2 1.0

TOTAL (Commercial) 12.5 1.4 5.2 2.6 10.3


TRADITIONAL SOURCES


Firewood and charcoal 1.7 1.3 1 4.8 10.9
7.0
Other biomass 3.0 ~ 5.5 1)i --- 1.2
Human labour 1.3 1.0 1.3----

Animal labour --- 0.5 3.3----

TOTAL (Traditional) 6.0 8.3 11.6 4.8 12.1



TOTAL ENERGY USE (GJ) 18.5 9.7 16.8 7.4 22.4


Table 12. Approximate Annual Energy Use Per Capita
in Five Asian Countries (Gigajioules)


Source: Revelle, adapted from reference 7.













PER CAPITAL ENERGY CONSUMPTION AND DISTRIBUTION IN NEPAL, 1978-79


FUEL C 0NSUMPTI 0N G J/ YR
PERCENTAGE TOTAL
SECTOR OF FIREWOOD CROP ANIMAL COAL AND PETROLEUM ELECTRICITY SECTORAL
TOTAL USE RESIDUES DUNG COKE FUELS USE


TRANSPORTATI ON 2.2 --- --- --- 0.01 0. 18 --- 0 19


DOMESTIC 95.0O 7.92 0. 16 0. 06 --- 0 09 0.02 8. 25


AGRICULTURAL 0.2 --- --- --- --- 0.01 --- 0.01


COMMERCE IAL/
I NDUSTRIAL 2.4 0. 06 --- --- 0 10 0. 03 0. 02 0. 21


OTHER/LOSSES 0.2 --- --- --- --- --- 0 02 0.02


TOTAL FUEL USE 7.98 0.16 0. 06 0. 11 0. 31 0. 06 8. 68




SOURCE: Country paper of Nepal, Submitted to the U.N. Conference on New and Renewable Sources
of Energy, Nairobi, 1981. Figures do not include human and inanimate energy. The
population of Nepal is 15 million, 95% of the population live in the rural areas.


Table 13















RURAL ENERGY USE

A most important distinction between the industrialized and developing
countries concerns the structure of energy supply and the pattern of energy
consumption in rural areas. In the industrialized nations there is very
little difference TE the type of energy used in rural as opposed to urban
areas. All areas generally have access to the principal fuels: elec-
tricity, gasoline, diesel fuel, heating oil and fuel gas; only the intensity
of use changes since industrial activity is predominantly an urban
phenomenon.

This relative homogeneity is not the case in the developing nations.
The structure of energy supply, the sources of energy utilized, and the
tasks for which the energy is used, all show marked differences when the
urban areas are compared with the rural. These regional differences have
important implications for energy policy.

Most energy in rural communities is locally produced from human and
animal labour, wood fuels, and animal and crop residues, with commercial
fuels being used on a limited.scale. Traditional fuels are usually gathered
by family members, although rdealthier families may purchase charcoal, dung
cakes, or wood, and the poor may have to pay with services for the privilege
of gathering firewood or residues on land that is privately owned. Much
firewood is gathered, not from forests, but from trees scattered along roads
and fields, intercropped with agricultural crops, or in gardens and yards.

Table 14 clearly illustrates the differences between the urban and
rural sectors, and between the traditional and commercial fuels, for India
and Bangladesh. ,Although per capital energy use is higher in the urban areas
(as one might expect), it is in the rural areas that the greater part of the
total energy consumption occurs. G-rEtrmore, the energy sources utilized
ItE~T~e rural areas are dominated by the traditional fuels.

This last characteristic is illustrated further in Tables 15 and 16.
In all cases, except that of Northern Mexico, the principal sources of
energy used in the rural areas are the traditional fuels. In addition,
Table 16 shows that most of the energy consumed is taken by the domestic
sector, principally for cooking. Again, the exception to this generali-
zation is Northern Mexico a relatively developed region.

Finally, the most detailed analysis of energy supply and consumption in
the rural areas of India is provided by Table 17. Fully 64% of total energy
use is consumed by domestic activities and of this amount 98% is traditional
fuels. Agriculture accounts for 22% of total energy use and more than
three-quarters of this is supplied by animate energy human and bullock
work.

Commercial energy account for 10.5% of total energy; mainly for agri-
culture (mostly for fertilizers) and for lighting.













ENERGY USE IN INDIA AND BANGLADESH


INDIA BANGLADESH


per capital total use per capital total use
SECTOR GJ/yr EJ/yr GJ/yr EJ/yr


UR BAN


Commercial 23.2 2.55 3.9 0.02

Traditional 7.5 0.82 5.4 0.03

TOTAL 30.7 3.37 9.3 0.05


RU RAL


Commercial 1.1 0.47 0.5 0.04

Traditional 9.1 3.99 7.0 0.48

TOTAL 10.2 4.46 7.5 0.52


Table 14


BY SECTOR AND


FUEL TYPE


SOURCE: Revelle, adapted from reference 10.

















Tablel5. Estimated Per Capita Use of Energy in Rural Areas of Seven
Developing Countries (GJ)


INDIA CHINA, TANZANIA NORTHERN NORTHERN BOLIVIA BANGLADESH
HUNAN NIGERIA MEXICO


Human Labour 1.0 1.0 1.0 0.9 1.1 1.1 1.0

Animal Work 1.5 1.5 --- 0.2 2.0 2.8 1.5

Fuel Wood 4.5 1~ 123.0 15.7 14.8 34.9 1.4

Crop Residues 1.8 120.9 2.5

Dung 1.0 I 0.9

TOTAL TRADITIONAL 9.8 23.4 24.0 16.8 17.9 38.8 7.3


Coal, Oil, Gas and 0.8 3.1 --- 0.03 30.3 --- 0.4
Electricity

Chemical 0.3 0.5 --- 0.08 8.2 --- 0.2
Fertilizers


TOTAL COMMERCIAL 1.1 3.6 --- 0 .11 38.5 --- 0.6


TOTAL ALL SOURCES 10.9 27.0 24.0 16.9 -56.4 38.8 7.9


from reference 10.


Source: Revelle, adapted






22











Table 16. Characteristics of Energy Use in Rural Areas of Seven
Developing Countries (GJ)




INDIA CHINA, TANZANIA NORTHERN NORTHERN BOLIVIA BANGLADESH
(per capital) HUNAN NIGERIA MEXICO

Total use 1 0.9 27.0 24.0 16.9 56.4 38.8 7.9

Domestic uses 7.4 21.3 23.4 16.0 18.1 35.3 5.5

Non-domestic uses 3.5 5.7 0.6 0.9 38.3 3.5 2.4

Domesti c/non- 2.1 3.7. L 37.4 18.4 0.47 10.1 2.2
domestic uses

Traditional/ 8.5 6.3 1 57.3 0.47 13.0
commercial



*no commercial energy used.


Source: Revelle, adapted from reference 10.










Table 17. Estimated Energy Use in Rural India
(Gigajoules per year per capital)

Pottery Transportation
Domestic brick making and other
Source of energy Agriculture activities Lighting metal work uses Total Percentage


Note: Dashes = not applicable. Figures may not reconcile exactly due to rounding.
Sou rce: Adapted from Revelle, reference 10.


Traditional sources:
Human labor
Bullock work
Firewood and
charcoal
Cattle dung
Crop residues .
Total traditional

Commercial sources:
Petroleum and
natural gas
Fertilizer
Fuel
Soft coke
Electricity:
Hydro
Thermal
Total commercial

TOTAL RURAL ENERGY USE

Activities as a percentage
of total energy consumption


0.09
0.25


1.03
1.53
4.37

1.77
1.02
9.72




0.33
0.48
0.13

0.04
0.16
1.14

10.86

100.0


9.5
14.1
40.3

16.3
9.4
89.5




3.1
4.4
1.2

0.4
1.5
10.5

100.0

100.0


0.37



6.45

6.82






0.13



0.13

6.95

64.0


--- 0.01



---3 0.71
--- 0.72





0.40 --


0.01 --
0.05 --
0.46 --


0.56
1.28




1.84




0.33
0.08


0.03
0.11
0.55

2.40

22.0


---
0.34


0.46

4.0


0.72

7.0


0.34

3.0















ANIMAL ENERGY

In a number of countries, principally in Asia, a large part of rural
energy use is in the form of animate energy animal and human labour. This
is particularly true in the agricultural sector, where the majority of
people in developing countries are employed. Table 18 shows the livestock
population of some developing countries in Asia [9].


Table 18 1978 LIVESTOCK POPULATION (MILLIONS)

Cattle Horses Asses and Mules

India 180.3 0.9 1.1
China 64.0 6.9 12.1
Pakistan 14.4 0.4 1.9
Bangladesh 28.0 0.04 n.a
Burma 7.3 0.1 n.a
Afghanistan 3.7 i 0.4 1.3
TOTAL 297.7 8.7 16.4

n.a. = not available


Animals are used for plowing, lifting water, irrigation, sugarcane
sugarcane crushing, chaff-cutting, oil extraction, and similar tasks.
Animals represent a considerable source of power. On average, approximately
1/2 hp or 375 Wlrcan be obtained continuously over an 8 hour period from a
medium-sized bullock or buffalo. Assuming about a quarter of the animals
listed in Table 18 are work animals then the peak power output is of the
order of 30,000 MW. Unfortunately, this significant, decentralized source
of power is used very inefficiently.

An important consideration in countries with large numbers of livestock
is the potential utilization of animal dung in anaerobic digestors to pro-
duce biogas. In some Asian countries, notably China and India, biogas makes
a very significant contribution to rural energy supplies.

















URBAN AND INDUSTRIAL ENERGY USE

Small rural and urban industries, some large modern sector industries,
and the urban poor are also important users of traditional fuels. In urban
households, commercial fuels are commonly used together with traditional
fuels, both of which are sold in organized markets. Charcoal is generally
-preferred to wood in cities because of its convenience, compactness, and
cleaner burning, and surveys in Asia and Africa have found per capital con-
sumption of wood fuels (including charcoal) in towns to be higher than in
the countryside, probably because of relatively higher incomes in urban
areas. In low-income urban areas, per capital demand for wood fuels can be
quite high, caused by the greater use of charcoal, which usually requires a
larger raw material input. As incomes rise, however, commercial fuels are
generally substituted for wood fuels in urban areas.

Industrial use of traditional fuels is also quite extensive. Estimates
of non-household consumption of wood for energy in surveyed areas of Africa
and Asia vary from 2 to 25% of total wood consumption. As Table 19 below
shows, in a number of countries industrial consumption of traditional fuels
is not only large but risingiboth in absolute terms and also as a share of
traditional fuel use. The share of traditional fuels in total industrial
energy consumption, however, has generally decreased, reflecting the
expansion of modern industry. Some industries, sensitive to price changes,
are likely to continue to rely on or even revert to the use of traditional
fuels if the price of commercial fuels increases.



Tablet?. Industrial Consumption of Traditional Fuels in Selected Countries, 1967-1977
(absolute figures in thousand metric tons oil equivalent (Ltte))
1%7 1973 1976
Percent Percent Percent Percent
total total total Percent total total Percent total
traditional industrial traditional industrial traditional industrial
Countries ttoe fuels* energy ttoe fuels* energy (toe fuels* energy
Argentina 1,070 51 20 1,532 69 22 3,700 80 38
Brazil 2,825 12 28 4,459 19 23 4,166 15 17
Colombia 197 3 73 267 555 309 6 29
Egypt 120 84 17 189 87 '21 190 87 14
India ..778 3 S 1.316 5 4 1,661 5 4
Indonesia 203 1 58 289 I 46 455 2 40
Iran 151 29 9 215 45 2 215 31 2
Mexico 796 26 5927 30 4 894 30 3
Thailand 153 52 20 456 84 19 869 93 28
Venezuela 131 8 3 277 14 4 300 14 4
Source: International Energy Agency/Organisation for Economic Co-operation and Development. Workshop on Energy Datea ofDeveloping Countries. vol. 11 Basic
Energy Statistics arnd Energy Balances of Developing Countries. 1967-1977 (Paris, OECD. 1979). Many of these figures must be treated with caution; a relatively large
proportion of consumption of many fuels is often not allocated by sector.
*The percentage of all traditional fuel consumption that is consumed by the industrial sector.
ThWe percentage of all industrial sector energy consumption that is traditional fuels.

















Wood and charcoal are used in brick and tile making, cement and metal
industries, crop drying, bread baking and fish curing. Tobacco curing
appears to account for 17% of total annual energy consumption in Malawi, or
1 million cubic metres of fuelwood a year. The Ugandan tea industry and
railways in Thailand are also heavy users of wood fuels. Other important
industries using traditional fuels are some steel mills in Brazil, Argentina
and the Philippines, which use charcoal rather than coal, and sugar mills
(and in some cases, sugar refineries), which are able to be self-sufficient
in energy by using bagasse to provide heat for evaporation and sometimes to
produce electricity.

THE MODERN SECTOR

In contrast to the traditional sector of developing countries, the
modern sector has always depended on commercial fuels for its principal
sources of energy. Almost every developing country has at least a small
modern sector, typically including its administrative capital, its ports,
and some industrial activity in mining, plantation agriculture, food proces-
sing, and manufacture of light consumer goods. The more industrialized
developing countries have large urban-industrial complexes, manufacturing
both consumer and capital good and providing an array of commercial services
that make their modern sectors strikingly similar to those of the industrial
countries.

The rapid pace of economic development in most of the developing world
since the 1950's has been accompanied by an even greater increase in the use
of commercial energy. The developing countries have greatly outpaced the
industrial countries in the growth of energy consumption since 1965 and
especially since 1973. The vast portion of the increase, moreover, was in
the form of oil. Between 1960 and 1978, the share of oil in the commercial
energy supplies of developing countries rose from 24 to 42 percent, and when
China and North Korea are excluded, from 56 to 62 percent [1]. Natural gas
is currently a significant source of energy only for developing countries
with substantial associated oil production--nainly members of OPEC.
Hydroelectricity supplies only a modest share overall, but provides a
substantial proportion of total electricity output and is particularly
important in some major countries such as Brazil and India.

The sharp increases in commercial energy consumption are natural
concomitants of the changes in economic structure involved in development.
In the early stages, these changes typically include the commercialization
of agriculture, the introduction of industry for processing raw materials
and supplying light consumer goods, the shift of labour from agricultural to
industrial and urban service occupations, the growth of urban settlements
and the mechanization of transportation. Most of the activities connected
with these growing sectors usually require the use of commercial as opposed
to traditional fuels.












FUTURE ENERGY SUPPLY

The rapid increase in world oil prices beginning in the early 1970s
marked the start of a major transition in energy supply and use patterns.
This transition must be expected to culminate ultimately in the widespread
use of renewable energy technologies based on hydropower, biomass, wind
energy, solar energy and perhaps nuclear power. At the present time, these
technologies make only a small contribution to commercial energy supply in
the industrial countries. It will require several decades before new and
renewable sources of energy account for a dominant portion of their energy
supply structure. According to one scenario [12] during the- next twenty
years one can anticipate:

*Economic growth will be significantly lower than in the
1965 to 1973 period and slightly lower than the 1973 to
1979 experience. Adjusted for inflation, the world
economy as a whole is expected to grow about 3 percent
annually between 1979 and 2000, compared to more than 5
percent per year between 1965 and 1973.

*Real energy costs are likely to rise throughout the
period as a result of a limited supply of conventional
oil and the high cost of most alternate energy sources.

World energy demand is expected to grow about 2 1/2
percent per year, less than world economic growth rate.
Even at this lower growth rate, world energy demand will
increase substantially by the year 2000.

Only a modest increase in world production of conven-
tional oil is anticipated. Volumes available for inter-
national trade are projected to show a net decline as
oil-exeorting countries increase domestic consumption.
Consequently, neither the industrial countries, nor the
developing countries, can rely on conventional oil for
increases in their energy requirements.

Most of the growth in the industrial, re s ident ial and
commercial sectors, where consumers have a choice of
fuels, is projected to come from coal and from nuclear
energy.

*Oil use will be concentrated increasingly in specialized
applications, including transportation, specialty pro-
ducts, such as lubricants, and some other demands for
which large-scale substitution of other fuels is not yet
considered practical.

*Production of synthetic fuels, especially liquids, will
be needed during the late 1980s and in the 1990s to meet
demands for transportation and other uses for which fuel
substitution opportunities are limited.












For many years prior to 1973, oil and gas provided most of the
growth in world energy supply. Oil penetrated all sectors of the world
economy. Between 1965 and 1973, oil supply grew almost 8 percent per
year and gas more than 7 percent, rates much higher than the rate at
which total energy supply was increasing. By 1973, oil and gas accounted
for two-thirds of total world energy supply.

Developments since that year have set in motion a dramatic transition
in the mix of primary fuels, as illustrated in Figure 2 .Conventional
oil supply is expected to grow less than 1 percent per year through
2000 resulting in a decline in oil's share of energy supply from 47
percent in 1979 to 31 percent by the year 2000. Most future energy
growth will have to be supplied from other energy sources. All non-oil
energy sources have projected growth rates above that for total energy
supply, as shown in the table below.

ENERGY SUPPLY GROWTH, PERCENT PER YEAR

1965- 1973- 1979-
1973 1979 2000
Oil 7.7 2.2 0.4
Synthetics & VHO --- 13.8
Gas 7.3 3.6 2.6
Coal 1.0 2.4 2.8
Nuclear 27.8 20.9 10.0
Hydro & Other 3.9 4.6 3.5
Total 5.3 2.9 2.4


Conventional natural gas supply is projected to keep pace with overall
energy use, maintaining its share of world energy supply at about 20
percent. In the'1990s, projected growth in world gas supply will require
the development of reserves in remote areas and the construction of
expensive distribution systems to bring the gas to markets. Given favorable
prices and supportive government policies, the necessary volumes should
be available. Indeed, world gas reserves in the 1990s would probably
be sufficient to support consumption above projected levels, should
conditions prove to be favorable.

Coal, which grew slowly between 1965 and 1973, is projected to be a
major source of energy supply growth. Coal is expected not only to meet
a substantial share of new energy demand,but also to replace oil and gas
in major industrial and electric utility markets. Coal use is projected
to grow almost 3 percent per year, increasing its share of world energy
supply from 26 percent in 1979 to 28 percent by 2000. (If the coal con-
verted to synthetic oil and gas were included here, coal's share would
increase to 30 percent by 2000.) At that level, coal will rival oil
as the single largest source of energy, but world coal resources still
would be large relative to production rates. Coal use is expected to be
constrained by the growth in demand rather than by the availability of
supply.





Most coal will continue to be consumed in the country in which
it is produced, with the largest increases occurring in the United
States and the centrally-planned economies. Some countries, however,-
particularly in Europe and East Asia-are likely to import substantial
volumes of coal. Exports from Australia, South Africa, Colombia, the
U.S. and other coal producers are likely to increase rapidly. Sea-
bourne coal trade is expected to quadruple by 2000 to over 600 million
tons per year.











FIGURE 2.

WORLD ENERGY SUPPLY


i--;QILV~ZJ` IgOb~F:~C~CZl~ir~j~I~~
4%
;:r
ri ..
j :r'T~7P~'~'
37% ./ 1 .=5-~` -~.c"r--r5rm'
.C 5 "" 'd. r ;
~I Zk r:' 'LY. I )~-
'' I'.
. r ... '' :'I'
~~ ~t'~lUI~UY' ' ." I 1
' .:.~
It .
154b; - -~ ..
'' ~-.- ` 38b 31~a
.i 47% ' '
r 1 '
....u ~. I-)i-r.
. r.,r~
.-'i ~. /I.jrr-~*rrU ~CLI*r;9rr I 'i: ::L: ~: :l~.Y*r - --- ~I-r I;_:~_ ~~~. .~ i ~II
4206 ~ '' . "C _'.'L:' I j 1:~: r~ ~
-~ .:r
.' ~...i 1... -..P ''I
'" '' ~,..Y~ ii '
"r~: ll~1 '1-. .~Ll


196S 1970
MILLION BARRELS DAY OIL EQUIVALENT


1980 1990


2000













OIL-- A DWINDLING RESOURCE

For some years now, the world has been consuming more oil than it
has been finding. During the quarter of a century prior to 1970,
substantial discoveries, principally in the Middle East, had built
the world's inventory of discovered reserves, as illustrated in Figure
3 In the early 1970s, however, the situation reversed. Smaller
discoveries and a continuing rise in oil production caused the
inventory of discovered reserves to decline. This pattern is expected
to continue in the future, despite a much slower rate of growth in oil
consumption and the increased incentives to discover oil provided
by rising energy prices.

There is little doubt that finding and developing the world's
as yet undiscovered oil reserves will be progressively more difficult
and costly. Many prospects are in remote locations or harsh operating
environments, such as the Arctic, which will be technologically demanding
and will require long lead-times for development. Fields remaining
to be discovered in areas where production already exists are anticipated
to be somewhat smaller, on average, than past discoveries. Moreover,
the number of unexplored areas is steadily diminishing.


FIGURE 3.


RAlTE OF DISCOVERY OF WORLD OIL RESERVES


1930 1940
BILUON BARRELS tYEAR


1950


1960 1970 1980


1990 2000











Thus, even with an active exploration effort, the average oil
discovery rate for the outlook period is likely to be well below the
expected production of 24 to 25 billion barrels per year and, conseauently,
the world's inventory of discovered oil reserves will continue to
decline. Since production cannot increase indefinitely in the face
of declining discovered reserves, it seems reasonable to expect that
conventional oil production will reach a plateau some time shortly
after the turn of the century.

Until the early 1970s, world oil demand expanded rapidly, growing
at a rate substantially greater than for total energy demand. Since
1973, however, growth has averaged only about 2 percent per year and
demand is expected to increase at less than one percent per year over
the next twenty year period. This reversal will be most pronounced
in the industrial countries which, in the past, were chiefly responsible
for the rapid expansion in oil demand. As shown in Figure 4 oil demand
in the major industrial countries is projected to decline as a result
of conservation, efficiency improvements, and substitution of alternate
liquid fuels.

However, the noteworthy feature of this projection is the significant
demand for oil expected to be exerted by the developing countries.


FIGURE .4.


MILLION BARRELS CA

















PROSPECTS FOR THE TRADITIONAL FUELS

Besides the difficulty and expenses of securing adequate supplies of
oil, the other problem with energy supply for the developing countries
concerns the traditional fuels principally fuel wood.

In most cases, people only burn crop or animal residues when fuel wood
is unavailable or expensive. Because wood cannot usually be economically
transported over long distances, large demands for wood fuels by urban
peop le and industrial users can rapidly stress forest resources in the
locality.

The fuel wood situation is already critical. Although globally, about
97 million hectares, or 2 percent of existing forests were added between
1965 and 1975, tropical forests are under much greater stress. The tropical
forest areas are being lost at a rate of about 20 million hectares each
year. The preliminary results of a study of fuelwood supply and needs indi-
cate that about 100 million people in developing countries live in areas
where there is already an acute shortage of fuel wood. Another 1 billion
are able to meet their minimum fuel wood requirements only by cutting in
excess of the sustainable yield. According to this report [13], with
current trends of population growth, of fuel wood demand, and rates of
depletion of tree resources, over 2 billion rural people in developing
countries will need to be provided with large supplies of traditional fuels
within two decades.

However, ittis more likely that the overall rate of deforestation in
the developing countries will decline before the turn of the century, for
the simple reason that the people who are doing most of the cutting will
eventually run out of forests to cut. Populations and forest resources are
not evenly distributed. Some countries cleared all their forest lands
accessible to them years ago (Afghanistan, for example), other densely
populated nations that still have substantial forest resources will have
lost most of them before the year 2000 (Indonesia and Thailand, for
example), and some sparsely populated nations with very large areas of
forest will still have vast forests in the year 2000 (G;abon and Congo, for
example) [14].

Table 20 below summarizes the forecast for forest resources by global
region for the year 2000. It should be noted that these figures are
considered a "mildly optimistic" scenario [14].










Table 20 WORLD FOREST RESOURCES

REGION 1978 2000 Chang
(million hectares) (percent)
DEVELOPED COUNTRIES
USSR 785 775 -1
North America 470 464 -1
Europe 140 150 +7
Australia, Japan,
and New Zealand 69 68 -1
TOTAL 1464 1457 0

DEVELOPING COUNTRIES
Latin America 550 329 -40
Asia and Pacific 361 181 -50
Africa 188 150 -20
TOTAL 1099 660 -40


WORLD TOTAL 2563 2117 -17



The depletion of fuelwood supplies has causes other than the constant
demand for cooking fuel. Thelispread of agriculture is in fact the principal
cause of deforestation. As populations grow, larger areas of forest will be
cleared to create land for cultivation or grazing. The results, particu-
larly in densely settled areas, include soil erosion, flash flooding, drying
up of previously perennial streams, and eventual desertification.

The problem is further compounded by the substitution of animal dung
and crop residues for scarce fuelwood supplies. Because commercial fertil-
izers are unavailable or too expensive for most villagers, the diversion of
dung and crop residues from the land contributes to declining agricultural
productivity. Yields diminish thus creating additional pressure to bring
more land under cultivation for subsistence crops. This involves felling
more trees and the cycle is perpetuated.













RENEWABLE ENERGY RESOURCES

All countries utilize renewable sources of energy to some extent. In
the industrial countries the contribution of the renewable energy sources
to total energy consumption is generally small--less than 5 percent--and is
predominantly hydropower. In the developing countries the contribution
made by renewable sources of energy is much higher. On the average, about
30% of the total energy supply in the developing countries is derived from
renewable energy sources, principally biomass: fuelwood, charcoal, and
animal and crop residues. Some countries have a very high dependence on
renewable energy sources. Nepal, for example, gets fully 94% of its total
energy supply from biomass sources.

The degree to which the renewable sources of energy will make a
contribution to the energy supply in the developing countries in the future
is very hard to predict. So much will depend on government policy,
commitment, initiative, and innovation; not to mention the price of
petroleum. What we can at least do here is to ascertain, to a first
approximation, whether the renewable energy resources are available, since
without on adequate resource base the renewable sources of energy are
hardly likely to make a significant impact on future energy supply. Table
21 indicates the potential of biomass and hydropower to supply energy in
the developing countries. Also shown are data on commercial energy and
traditional fuel consumption. Table 22 compares current energy consumption
with the potential renewable energy supply from biomass and hydropower.
Approximately 80% of the developing countries listed could provide all
their current energy requirements from these two renewable energy sources.7
When one further considers the very large potential contribution of direct
solar thermal energy, the increasing utilization of photovoltaic systems,
and the possibility in many developing countries of exploiting the wind,
the immense potential of the renewable sources of energy becomes strikingly
clear.









Table 21 Potential Annual Energy Supply From Biomass and Hydropower and Annual Energy Consumption


Potential Potential Total
Potential energy energy potential Annual Estimated Estimated Estimated
energy from from from energy output at fuelwood and animal and CommercialI totalI
forest an imalI crop from Hydro 50t% p lant charcoa l crop res idue energy energy
growth manure res dues b iomass Potent ialI factor cons umpt ion cons umpt ion consumption consumption
Country (PJ/yr) (PJ/yr) (PJ/yr) (PJ/yr) (MW) (PJ/yr) (PJ/yr) (PJ/yr) (PJ/yr) (PJ/yr)


CENTRAL AMERICA
Bel ize
Costa Rica
Cuba
Dominican Republic
El Salvador
Guatemala
Haiti
Honduras
Jamaica
Mexico
Nicaragua
Panama
Puerto Rico
SOUTH AMERICA
Argentina
Bolivia
Brazil
Chi le
Columbia
Ecuador
French Guinea
Guyana
Paraguay
Peru
Surinam
Uruguay
Venezuela
AFRICA
Algeria
Angola
Benin
Botswana
Burundi
Cameroon
Central African Rep.
Chad
Congo


20-200
20-200
20-200
10-100
10-100
60-600
2-20
70-700
10-50
400-4,000
60-600
40-400
2-20

600-6,000
470-4,700
3,200-32,000
50-500
780-7,800
180-1,800
90-900
180-1,800
210-2,100
870-8,700
150-1,500
10-50
480-4,800

20-200
730-7,300
90-900
110-1,100
3-30
300-3,000
280-2,800
160-1,600
270-2,700


31.6
105.0
39.6
20.8
41.2
30.6
34.2
7.2
645.0
45.5
24.4
10.6

1,128.0
82.7
1,950.0
86.2
408.0
67.8

6.2
88.5
142.0
0.8
232.0
248.0

57.7
52.7
18.8
41.4
0.5
55.2
9.6
69.1
1.1


16,4
328.0
61.6
22.4
41.3
22.7
12.0
22.8
405.0
17.4
14.1
19.1

414.0
26.7
948.0
37.7
163.0
22.4

28.7
16.6
85.9
4.3
25.5
46.4

34.2
12.0
6.2
0.1
15.8
9.9
3.1
1.1
4.1


20-200
68-250
450-630
110-200
53-140
140-680
55-70
120-750
40-80
1,500-5,100
120-660
80-440
32-50

2,100-7,500
580-4,800
6,100-35,000
170-620
1,400-8,400
280-1,900
90-1,900
210-1,800
310-2,200
1,100-8,900
160-1,500
270-310
1,000-5,400

110-290
800-7400
120-930
150-1,100
30-45
370-3,100
290-2,800
270-1,700
280-2,700


300
4,326


900
1,176

4,800

20,334
3,600
2,400


48,120
18,000
90,240
15,780
50,000
21,000
233
12,000
6,000
12,500
260
2,512
11,644

4,800
9,664
1,792
2,984

22,960
11,040
3,440
9,040


9
136


28
37

151

641
114
76


1,518
568
2,846
498
1,577
662
7
378
189
394
8
79
367

151
305
57
94

724
348
108
285


24
16
19
35
56
42
33
0.02
86
24
15


38
39
1,023
33
209
21

0.2
33
63

10
77

14
73
26
8
10
77
22
38
20


3
310
340
97
31
47
4
22
117
2,239
31
45
3358

1,360
54
2,340
302
488
98
4
25
15
303
31
91
1,028

370
32
4

1
19
2


3
54
356
116
66
103
46
55
122
2,362
55
60
338

1,553
93
3,537
335
710
119
4
25
48
366
31
101
1,118

384
105
30
8
11
96
24












PotentialI Potentilal TotalI
Potent ial energy energy potent ialI An nual E st mated Est mated Est imated
energy from from from ener gy output at fue wood and an imalI and Commercial totalI
forest animal crop from Hydro 501C plant charcoalI crop residue energy energy
growth manure res idues b Iomass Potent ial1 factor cons umpt ion cons umpt ion consumrption consumption
Country (PJ/yr) (PJ/yr) (PJ/yr) (PJ/yr) (MW) (PJ/yr) (PJ/yr) (PJ/yr) (PJ/yr) (PJ/yr)


Table 21 Potential Annual Energy Supply From Biomass and Hydropower and Annual Energy Consumption


(Continued)


AFRICA
Dj ibouti
Egypt
Equatorial Guinea
Ethlopia
Gabon
Gambia
Ghana
Guinea
Guinea-Bissau
Ivory Coast
Kenya
Lesotho
Liberia
Libya
Madagascar
Malawi
Mall
Mauritania
Morocco
Mozambique
Namibia
Niger
Nigeria
Rwanda
Senegal
Sierra Leone
Somalia
Sudan
Swazi land
Tanzanla
Togo
Tunisia
Uganda
Upper Volta
Zaire
Zambia
Z imbabwe


98.3
0.2
586.0.
0.5
5.4
29.9
26.6
5.7
14.8
149.0
16.9
2.1
15.5
167.0
13.0
89.3
51.9
27.0
26.5

66.5
277.0
14.1
53.0
5.7
98.9
327.0
11.2
217.0
8.8
30.5
76.5
39.3
29.6
1.8
73.8


182.0
0.2
67.1
0.4
0.4
17.1
11.3
0.8
16.5
37.6
2.6
4.1
10.3
46.7

3.2
0.1
5.3
22.3

1.8
79.2

3.4
9.1
3.5
20.5
10.8
96.1
4.8
41.6
15.6
1.6
31.9
9.6
32.1


280
10-100
980-4,000
250-2,500
7-16
170-1,200
210-1,700
17-110
220-1,900
200-400
20
31-260
31-75
330-1,400
98-730
110-490
52
82-530
710-6,600
100-1,000
110-470
700-35,800
22-67
110-560
18-45
100-120
770-4,500
22
700-4,200
53-450
75-100
110-290
76-390
1,900-18,000
380-3,700
390-2,900


2
537
1
272
32
4
167
41
6
109
180

36
122
71
41
35
10
172
127

29
823
44
48

39
306
5
431
16
95
17
46
46
122
181


10-100
330-3,300
250-2,500
1-10
120-1,200
170-1,700
10-100
190-1,900
20-200
2- 5
25-250
120-1,200
70-700
40-400

50-500
660-6,600
100-1,000
40-400
340-3,400
5-50
50-500
3-30
2-20
420-4,200

390-3,900
40-400
3-30
20-200
35-350
1,800-18,000
370-3,700
280-2,800


3,800
2,400
9,214
17,520

1,615
6,400
120
.,780
13,440
490
6,000
160
64,000
100
3,520
2,000
975
11,290
1,200
9,600
1,515

4,400
3,000
240
16,000
700
20,800
480
29
12,000
12,000
132,000
3,834
5,000


120
76
291
553

51
202
4
25
424
15
189
5
202
3
111

31
356
38
303
48

139
95
8
505
22
656
15
1
378
378
4,163
121
158


1

250
12
3
120
29
5
53
115

15
4
55

30
6
30
90

25
645
42
25
27
35
230
5
400
10
19
0.50
43
0.30
40
60













Potent ialI Potential TotalI
Potent ia l energy energy potent i al Annual Est mated Est mated Est imated
energy from from f rom energy output at fuelwood and an ima l and Commerc ialI totalI
forest animal crop from Hydro 508 plant charcoal crop residue energy energy
growth manure res idues b iomass Potent ia l f actor cons umpt ion cons umpt ion consumption consumption
Country (PJ/yr) (PJ/yr) (PJ/yr) (PJ/yr) (MW) (PJ/yr) (PJ/yr) (PJ/yr) (PJ/yr) (PJ/yr)


Table 21 Potential Annual Energy Supply From Biomass and Hydropower and Annual Energy Consumption


(Continued)


NEAR EAST
Afghanistan
Bahrain
Iran
Iraq
Jordan
Kuwait
Lebanon
Oman
Qatar
Saudi Arable
Syria
Turkey
U.A.E.
Yemen (AR)
Yemen (P.D.R.)
EAST ASIA
Bangladesh
Bhutan
Brunel
Burma
China
India
Indonesia
Khmer Rep.
Korea N.
Korea S.
Laos
Malaysia
Mongolia
Nepal
Pakistan
Phi lippines
Sri Lanka
Taiwan
Thaliand
Vietnam


64.0

21
0.1
0.03

0.7



0.5






150


210
1,500
1,237
1,162
44
50
77
33
61
15
96
93
250
46

27
180


24
93
1,459
245
43
278
46
16
70


88
93
1,489
245
43
278
47
16
70


7-70

40-400
15-150


1-10
1-10

12-120
5-50
180-1,800


26-260

23-230
30-300
4-40
450-4,500
800-8,000
750-7,500
1,250-12,500
130- 1,300
90-900
70-700
150-1,500
240-2,400
150-1,500
50-500
20-200
160-1,600
20-200
20-200
290-2,900
70-700


124.0,
0.1
261.0
98.4
4.7
1.1
3.7
2.3
0.4
24.6
11.5
417.0

52.5
5.4

492.0
4.0
0.5
173.0
3,350.0
4,250.0
219.0
47.2
23.3
40.1
33.1
20.7
113.0
184.0
494.0
177.0
41.9

205.0
143.0


44.1

276.0
48.7
2.5

3.0
0.1

6.5
74.4
679.0

12.9
0.6

369.0
7.6
0.1
176.0
5,096.0
3,043.0
559.0

108.0
206.0
16.2
40.2
10.9
60.1
450.0
289.0
24.3

308.0
13.5


180-250

580-940
160-300


8-17
3-12

43-150
91-140
1,300-2,900

65
32-300

880-1,100
42-310
5-41
800-4,800
9,200-16,000
8,000-15,000
2,000-13,000
180-1,300
220-1,000
320-950
200-1,500
300-2,500
280-1,500
290-740
960-1,100
630-2,100
86-270
20-200
800-3,400
230-860


6,000

10,196
1,900





900
I,000
15,200


466
*


2,717
3,150
19

*
*
"

*

6


1,307


75,000
330,000
70,000
30,000

2,000
5,514

1,319

80,000
20,000
7,504
1,180
1,632
6,242
54,000


41


2,365
10,407
2,208
946

63
174

42

2,523
631
237
37
51
197
1,703


77

74
44
17,293
3,896
892

1,462
1,072
6
206
51
4
384
421
42

387
169


693

74
254
21,510
8,283
2,073
44
1,512
1,149
39
267
66
100
477
671
88

780
349











Table 22 Potential for Renewable Energy Sources in Developing Countries

Potent ialI Potent ialI Potent ialI Est Imated Ratio of potential
energy energy energy from total renewable energy
from from biomass and energy supp ly to current
b iomass hydropower hyd ropower consumpt ion energy consumpt ion

Country (PJ/yr) (PJ/yr) (PJ/yr) (PJ/yr)


CENTRAL AMERICA
Belize
Costa Rica
Cuba
Dominican Republic
El Salvador
Guatemala
Haiti
Honduras
Jamaica
Mexico
Nicaragua
Panama
Puerto Rico
SOUTH AMERICA
Argentina
Bol ivia
Brazil I
Chile
ColIumibla
Ecuador
French Guinea
Guyana
Paraguay
Peru
Sur inam
Uruguay
Venezuela
AFRICA
Algeria
Angola
Benin
Botswana
Burundi
Cameroon
Central African Rep.
Chad
Congo
Dj bout i
Egypt
Equator ialI Gu inea
Ethiopia
Gabon
Gambia
Ghana
Guinea
Guinea-Bissau
Ivory Coast
Kenya
Lesotho
Liberia
Li bya
Madagascar
Malawi
Mall
Mauritania


20-200
68-250
450-630
110-200
53-140
140-680
55-70
120-750
40-80
1,500-5,100
120-660
80-440
32-50

2,100-7,500
580-4,800
6,100-35,000
170-620
1,400-8,400
280-1,900
90-1,900
210-1,800
210-2,200
1,100-8,900
160-1,500
270-310
1,000-5,400

1PO-290
800-7,400
120-930
150-1,100
30-45
370-3,100
290-2,800
270-1,700
280-2,700

280
10-100
980-4,000
250-2,500
7-16
170-1,200
210-1,700
17-110
220-1,900
200-400
20
31-260
31-75
330-1,400
98-730
110-490
52


9
136


28


151

641
114
76


1,518
568
2,846
498
1,577
662
7
378
189
394
8
79
367

151
305
57
94

724
348
108
285

120
76
291
553

51
202
4
25
424
15
189
5
202
3
111
63


29-209
204-386
450-630
110-200
81-168
177-717
55-70
271-901
40-80
2141-5741
234-774
156-516
32-50

3618-9018
1148-5368
946-37846
668-1118
2977-9977
942-2562
97-1907
588-2178
499-2389
1494-9294
168-1508
349-389
1367-5767

261-441
1105-7705
177-987
244-1194
30-45
094-3824
638-3148
378-1808
565-2985

400
86-176
1271-4291
803-3053
7-16
221-1251
412-1902
21-114
245-1925
624-824
35
220-449
36- 80
532-1602
101-733
221-601
115


3
54
356
116
66
103
46
55
122
362
55
60
2338

553
93
537
1335
710
3119
4
25
48
366
31
101
108

384
1105
30
8
11
96
24
41
26
2
537
1
272
32
4
167
41
6
109
180

36
122
71
41
35
10


9.7 69.7
3.8 7.1
1.3 1.8
0.9 1.7
1.2 2.5
1.7 7.0
1.2 1.5
4.9 16.4
0.3 0.7
0.9 2.4
4.3 14.1
2.6 8.6
0.1

2.3 5.8
12.3 57.7
2.5 10.7
2.0 3.3
4.2 14.1
7.9 21.5
24.3 -476.8
23.5 87.1
10.4 49.8
4.1 -25.4
5.4 -48.6
3.5 3.9
1.2 5.2

0.7 1.1
10.5 73.4
5.9 -32.9
30.5 -149.3
2.7 4.1
11.4 -39.8
26.6 -131.2
9.2 -44.1
21.7 -114.8

0.7
86-176
4.7- 15.8
25,1- 95.4
1.8- 4
1.3- 7.5
10.0- 46.4
3.5- 19.0
2.2- 17. 7
3.5- 4.6

6.1- 12.5
0.3- 0.7
7.5- 22.6
2.5- 17.9
6.3- 17.2
11.5









Table 22 Potential for Renewable Energy Sources in Developing Countries

Potent ialI Potent ialI Potent ialI Est mated Ratio of potential
energy energy energy from total renewable energy
from from biomass and energy supp ly to current
biomass hydropower hydropower consumption energy consumption

Country (PJ/yr) (PJ/yr) (PJ/yr) (PJ/yr) (Continued)


63
31
356
38
303
48

139
95
8
505
22
656
15
1
378
378
4163
121
158

189

322
60






28
32
479





41


2365
10407
2208
946

63
174

42

2523
631
237
37
51
197
1703


115
113-561
1066-6956
138-1038
413-773
748-3848
22-67
249-699
113-140
108-128
1275-5005
44
1356-4856
68-465
76-101
488-668
454-768
6063-22163
501-3821
548-3058

369-439

909-1262
220-360


8-17
3-12

71-178
123-172
1779-3379

65
32-300

921-1141
42-310
5-41
3165-7165
19607-26407
10208-17208
2946-13946
180-1300
283-1063
494-1124
200-1500
342-2542
280-1500
2813-3263
1591-1731
867-2337
123-307
71-251
997-3597
1933-2563


10
172
127

29
823
44
48
36
39
306
5
431
16
95
17
46
46
122
181

88
93
1489
245
43
278
47
16
70
515
167
874
89
8
17

693

74 .
254
21510
8283
2073
44
1512
1149
39
267
66
100
477
671
88

780
349


11.5
0.7 3.3
8.4 54.8

14.2 -26.7
0.9 -4.7
0.5 1.5
5.2 -14.6
3.1 -3.9
2.8 -3.3
4.2 -16.4
8.8
3.1 -3.9
4.3 -29.1
0.8 1.1
28.7 -39.3
9.9 -16.7
131.8 -481.8
4.1 -31.3
3.0 -16.9

4.2 5.0

0.6 0.8
0.9 1.5
0.2
<0. 1
0.2 -0.4
0.2 0.8

0.1 -0.3
0.7 1.0
2.0 3.9

8.1
1.9 17.6

1.3 1.6

0.1 0.6
12.5 28.2
0.9 1.2
1.2 2.1
1.4 6.7
4.1 -29.5
0.2 0.7
0.4 1.0
5.1 38.5
1.3 9.5
4.2 22.7
28.1 -32.6
3.3 3.6
1.3 3.5
1.4 3.5

1.3 4.6
5.5 7.3


Mauritania
Morocco
Mozamb ique
Namibia
Niger
Nigeria
Rwanda
Senegal
Sierra Leone
Somal ia
Sudan
Swazi land
Tanzania
Togo
Tunisia
Uganda
Upper Volta
Zaire
Zambia
Zimbabwe
NEAR EAST
Afghanistan
Bah rain
Iran
Iraq
Jordan
Kuwait
Lebanon
Oman
Qatar
Saudi Arabia
Syria
Turkey
U.A.E.
Yemen (AR)
Yemen (P.D.R.)
EAST ASIA
Bangladesh
Bhutan
Brunel
Burma
China
India
Indonesia
Khmer Republic
Korea N.
Korea S.
Laos
Malaysia
Mongolia
Nepal
Pakistan
Phil ippines
Sri Lanka
Taiwan
Thailand
Vietnam


52
82-530
710-6600
100-1000
110-470
700-3800
22-67
110-560
18-45
100-120
770-4500
22
700-4200
53-450
75-100
110-290
76-390
1,900-18000
380-3700
390-2900

180-250

580-940
160-300


8-17
3-12

43-150
91"-140
1300-2900

65
32-300

880-1,100
42-310
5-41
800-4,800
9,200-16,000
8,000-15,000
2,000-13,000
180- 1,300
220- 1,000
320-950
200- 1,500
300- 2,500
280- 1,500
290- 740
960- 1,100
630- 2,100
86-270
20-200
800-3,400
230-860











REFERENCES

1. Dunkerley, J., et. al., "Energy Strategies for Developing Nations",
Resources for the Future, Washington, D.C., 1981.

2. Palmedo, P.F., and Baldwin, P., "The Contribution of Renewable
Resources and Energy Conservation as Alternatives to Imported Oil
in Devel opi ng Countri es" En ergy/ De vel opme nt Internat ional Port
Jefferson, N.Y., 1980.

3. Palmedo, P.F., et. al., "Energy Needs, Uses, and Resources in Devel-
oping Countries", Brookhaven National Laboratory, BNL 507-84, 1978.

4. U.N. World Energy Supplies 1971-1975, 1977.

5. "Energy and Development in Central knerica", MITRE Corporation,
Vols. I and II, 1980.

6. Knowland, W., and Ulinski, C., "Traditional Fuels: Present Data,
Past Experience, and Possible Strategies", U.S. AID., Was h ington,
D.C., 1979.

7. Revelle, R., "Energy Dilemmas in Asia: The Needs for Research and
Development", Science, Vol. 209, 4 July 1980.

8. "Prospects for Traditional and Non-Conventional Energy Sources ih
Developing Countries", Staff Working Paper, No. 346, World Bank,
Washington, D.C., 1979.

9. Kashkari, C., "Effective Utilization of Animal Energy in Developing
Countries", in Changing Energy Use Futures, Proceedings of the 2nd
International Conference on Energy Use Management, Los Angeles, 1979.

10. Revelle, R., "Requirements for Energy in the Rural Areas of Developing
Countries", in "Renewable Energy Resources and Rural Applications in
the Developing World", (ed. N.L. Brown), AAAS Symposium 6, Washington,
D.C., 1978.

11. Revelle, R., "Energy Use in Rural India", Science, Vol. 192, 4 June
1976.

12. "World Energy Outlook", Exxon Background Series, December 1980.

13. UNCNRSE Conference News No. 7. (U.N. Conference on New and Renewable
Sources of Energy), New York, 1981.

14. The Global 2000 Report to the President, Volume 2, Government Printing
Office, Washington, D.C.












FUNDAMENTALS OF FLUID FLOW

It is useful to review some basic concepts:

Pressure Relationships

Pressure is force divided by area
F Newtons
i.e. P-
A m2
1 N/m2 is called a Pascal (Pa)

105 Pa is equal to 1 bar which is about equal to atmospheric
pressure. More precis y, 1 standard atmosphere is equal to

760 mm Hg = 14.7 psi = 101325 Pa
=1.01325 bar

The difference in pressure between any two points at different levels
in a liquid is given by

Pp2 1 = pg(h2 bl) Pa (1)
Pressure may also be expressed in terms of a pressure head as

h = E- metres (2)
pg

In these expressions

h = fluid height, metres
p =fluid density, kg/m3
g = acceleration due to gravity, nominally 9.81 m/s2
p = pressure, Pa

For ideal gases
p1 1 2v2
-mR (3)
T1 T2

or pl p2
R (4)
P1T1 P2T2

where p = absolute pr:~ePessure, Pa

m =mass, kg
p = density, kg/m3
T = absolute temperature in degrees Kelvin (273 + OC)

for air R = 287.1 J/kg K














Equation of Continuity
The equation of continuity follows from the principle of conservation
of mass. For steady flow, the mass of fluid passing all sections per unit
of time must be the same.

Therefore
plA1V1 = p2A2V2 = constant (5)
For incompressible fluids and where density may be considered constant the
flow rate Q is given by

Q = A1V1 = A2V2 = constant (6)

Bernoulli's Equation

Just as the continuity equation is a mass balance, so Bernoulli's
equation follows from the principle of conservation of energy. For steady
flow of an incompressible fluid in which there is negligible change in
internal energy:

P+V1+ z1 + HA HL HE 2+V2+ z2 (7)
pg 2g pg 2g


where z = elevation above any datum level, metres
p = fluid density, kg/m3
g = acceleration due to gravity, m/s2
V = average fluid velocity, m/s
HA = energy added, metres
HL = head losses due to friction, metres
HE = energy extracted, metres
P = pressure, Pa

The units used in Equation (7) are J/N or metres of the fluid. It is
usual to identify the elements of the Bernoulli equation as 'heads', i.e.

static pressure head p/Pg
velocity head V2/2g
potential head z










Since the fluid velocity in a conduit is not uniform with respect to cross
section, the velocity head should in theory be corrected by a kinetic-
energy correction factor a.

for turbulent flow a = 1.02 1.15
for laminar flow a = 2

Generally, a may be taken as 1 without serious error since the velocity
head is usually only a small part of the total head. Practically all
problems dealing with flow of liquids utilize the Bernoulli equation as the
basis of solution.


Energy Line

The energy line is a graphical representation of the energy at each
section. With respect to a chosen datum, the total head in metres of fluid
can be plotted at each representative section, and the line so obtained is
a valuable tool in many flow problems. The energy line will slope down-
wards in the direction of flow except where energy is added by mechanical
devices such as pumps.


Hydraulic Grade Line

The hydraulic grade line lies below the energy line by an amount equal
to the velocity head at the section. The two lines are parallel for all
sections of equal cross section area. The ordinate between the centre of
the stream and the hydraulic grade line is the pressure head at the
section.


Power

Energy may be added to or exracted from a fluid. Power is calculated
as

P = H~g Watts (8)

where H = total head added or extracted, metres
m = mass flow, kg/s
g = acceleration due to gravity, m/s2









Example 1

A pipe carrying oil of relative density 0.877 changes in size from 150 mm at
section A to 450 mm at section B. Section A is 4 m lower than 8 and the
ps assures are 0.9 bar and 0.6 bar respectively. If the discharge is 0.15
m s determine the lost head and the direction of flow.


Q = 0.15 m3/s


=0.6 bar


4 m


0.15 m
0.9 bar


Solution:

The velocity of the fluid at sections A and B is given by Equation (6), i.e.
0.15
V ==8.5 m/s
A w(0.15)2/4


0.15
V =
B w(0.45)2/4


=0.94 m/s


Using point A (the lowest) as the datum plane, the total
section is given by Bernoulli's equation:


head at each


PA V2A
-+ + zA HL
pg 2g


SPB V2
+ -- -- 2
pg 2g


so 0.9 X 105 4
877 X 9.81


_(8.5)2
2 X 9.81


+0 HL 0.6 X 105
877 X 9.81


14.1 HL = 11.0


HL = 3.1 metres.


(0.,94~2_ + 4
2 X 9.81


Note that the head at
an amount equal to HL.


A (14.1 m) is greater than the head at 8 (11.0 m) by
The oil, therefore, must flow from A to 8.











Example 2

For the system shown below, pump BC rmst deliver 0.16 m3/s of oil (762
kg/3) o rseroirD. ssuingthat the head loss between A and 8 is 2.5
m, and from C to D is 6.5 m, ()dtriehwmc oe h upms
supply to the system, and (b) plot the energy line.








EL15.0 60


Solution


(a) The velocity of the fluid at surfaces A and D will be very small. We
neglect the velocity heads at these surfaces. Taking BC as the datum
level, and applying Bernoulli's equation from A to D:


+ -+ zA + HA HL
2g


+" z
2g


Patm
Pg


= Patm
pg


Most of the terms drop out leaving


zA + HA HL

12 + HA (2.5 + 6.5)


=zD
=57


therefore


HA = 54 metres


From Equation (8),

P = 54 X 0.16 X 762 X 9.81

=64.6 kW

This is the power delivered to the fluid; the power delivered to the pump
will depend on its efficiency.










(b) The energy line at A is at elevation 15 m above datum zero. From A to
8 the energy loss is 2.5 m and the energy line drops by this amount,
the elevation at 8 being 12.5. The pump adds 54 m of head and the
elevation at C is therefore 66.5 m. Finally, since the loss of energy
between C and D is 6.5 m, the elevation at D is 66.5 6.5 = 60 m.
The energy line is shown below. Note that the pump has supplied a head
sufficient to raise the oil 45 m, but it has also had to overcome 9 m
of losses in the piping. Therefore, 54-m is delivered to the system.






El. 66.5





EL 15.0 ,A







47




Example 3
Water flows through the turbine shown below at a rate of 0.2 m3/s and the
pressures at A and 8 respectively are 1.5 bar and -0.3 bar. Determine the
power delivered to the turbine by the water. Neglect head losses.








1.0ml Trbine

ir 0.6 m


Solution:


0.2
wAr(0.32)/4
0.2
wB (0.6)2/4


= 2.8 m/s


= 0.7 m/s


Applying Bernoulli's equation with point 8 as the datum level:


pA A
-+ + zA HE
Pg 2g


(2.82+1-HE
(,22 X 9.81 +lH


Be y28
= -+-+ zg
Pg 2g


1.5 X 105 4
1000 X 9.81


-0.3 X 105
1000 X 9.81


2X 9.81 +


=19.7 metres


or HE


Power


=Hing


=19.7 X 1000 X 0.2 X 9.81


=38.7 kW to turbine









Flow in Pipes

Flow in pipes is generally laminar or turbulent. If the flow is
laminar the viscosity of the fluid is dominant and suppresses any tendency
to turbulent conditions. The Reynolds number, Re, is the ratio of inertial
forces to viscous forces.

Laminar flow: Re < 2100
Turbulent flow: Re >6000

where Re = VDp (9


V = fluid velocity, m/s
D = pipe diameter, metres
p = fluid density, kg/m3
S= viscosity, Pa s

For non-circular cross-sections an equivalent diameter (or hydraulic dia-
meter) is used where
D=4 X cross-section area (10)
wetted perimeter

The Darcy-Weisbach forrml~a is the basis for evaluating the lost head
for fluid in pipes and conduits:

HL =f~ V metres (11)

where L = length of pipe
D = hydraulic diameter
f = friction factor

*For laminar flow f is a simple function of the Reynolds number:

f = 64/Re (12)

For turbulent flow the situation is more complex. Graphs are available
which show the relationship between friction factor f, Reynolds number Re,
and the relative roughness of the pipe, C/. A typical chart is shown
overleaf in Diagram 1.

Other Losses of Head

It is common practice to express all losses in terms of a velocity head
V2/2g. That is, Equation 11 is written as

29


and K is evaluated from tables according to the actual structure of the flow
system. Tables 1 and 2 give values of K for common pipeline items.

























dll o -- Il




LTS 81818 %114-g


N


6
ar,

v,
I

i
rr,

N
V) i
W
O


Ilfl 12I


Imlol'PU I 1 1 1 I~_10


-I; q
74 /








0:,

N l l1 1111111III 1 I II I I Y ~ i I I I IIII 1~
0Y '''''''' '`' '' "''Ie~H cC)C+-H-


I/3



O)V


w19
11


Ln


D O


o" s


CP
V)


m
J


V)
g
it






II


ar
cw
zl
NO
ti
4:
I'


Ill


r
9


E"
oL
* '3 .
UY
u- u.


COD


~- ~C)LO~
~ ~ am oh q 9 9















Item Average Lost Head

1. From Tank to Pipe flush connection (entrance loss) 0.50-
2g

projecting, connection 1.00
2g

rounded connection 0.05-
2g.

V:
2. From Pipe to Tank (exit loss) 1.00--
2g

3. Sudden Enlargement
2g


4. Gradual Enlargement (see Table 2) K~f


5. Venturi Meters, Nozzles and Orifices ~- 1:2


6. Sudden Contraction (see Tabl 2) K,-
2g

V2
7. Elbows, Fittings, Valves K-
2g
Some typical values of K are:
45* Bend ...........................0.35 to 0.45
90. Bend ................... ..........0.50 to 0.75
Tees ................... .............. 1.50 to 2.00
Gate Valves (open) ................... about 0.25
Check Valves (open) ................... about 3.0




TABLE 2

VALUES OF; K*
Conltractions and Enlalrgements


Suddetin Gradual Enlargement for Total Angles of Cone

dtdz K, 4* 10' 15" 20" 30' 50" 60'

1.2 0.08 0.02 0.04 0.09 0.16 0.25 0.35 0.37
1.4 0.17 0.03 0.06 0.12 0.23 0.36 0.50 0.53
1.6 0.26 0.03 0.07 0.14 0.26 0.42 0.57 0.61
1.8 0.34 0.04 0.07 0.15 0.28 0.44 0.61 0.65
2.0 0.37 0.04 0.07 0.16 0.29 0.46 0.63 0.68
2.5 0.41 0.04 0.08 0.16 0.30 0.48 0.65 0.70
3.0 0.43 0.04 0.08 0.16 0.31 0.48 0.66 0.71
4.0 0.45 0.04 0.08 0.16 0.31 0.49 0.67 0.72
5.0 0.46 0.04 0.08 0.16 0.31 0.50 0.67 0.72


*Values from Kingsr "Handbook of Hydraulics"- McGraw-Hill Book Company.


TABLE 1

TYPICAL LOSS OF HEAD ITEMS
(Subscript 1 = Upstream and Subscript 2 = Downstream)











Sizing Pipes

In designing any fluid flow system one generally seeks the lowest cost
system that will operate reliably over a projected lifetime. A reduction in
pipe diameter will mean a lower system capital cost but the pressure drop
will increase thus raising pumping costs. The economic pipe diameter is
therefore the diameter which minimizes total costs, i.e., amortized capital
plus operating costs.

Note also from Equation 11 that head loss may be written as


HL ) 2 =f (14)

and that therefore the pressure drop varies inversely with the fifth power
of pipe diameter. Clearly, pumping requirements may become excessive if
conduits are undersized.

In the absence of any firm economic data, pipes may well be sized on
the basis of a maximum permissible system pressure drop.





Example 4


Water at 600C is to flow at a
iron pipe 20 metres long with a
density and viscosity for water
4.71 X 10'4 Pa.s respectively.
diameter.


rate of 10 litres/s through a galvanized
head loss not to exceed 0.5 metres. The
at this temperature are 983.3 kg/m;3 and
Determine the minimum acceptable pipe


Solution


A trial-and-error approach is required. One way to start is to guess the
friction factor, f, which is usually quite close to 0.03. This allows us to
calculate a first estimate of the pipe diameter.


DS = 8fLQ2


From Equation 14


,2


D5 = 8 x 0.03 x 20 x
0.5 x 9.81 x

D = 0.10 metres


To check our guess at the
number.


friction factor we need to calculate the Reynolds


Re =


pV = 4p


Since


Re =4 x 983.3 x 0.01
4.71 x 10-4 x ax 0.1


We have


=2.66 x 105


From Diagram 1

so

So from Diagram 1


E = 0.15 mm (G.I. pipe)

E/D = 0. 00015/ 0. 1 = 0. 0015


f = 0.022


Recalculating the pipe diameter:

D5 = 8 x 0.022 x 20 x (0.01)2
0.5 x 9.81 x wr2

gives D = 9.4 cm


So we would choose an available pipe equal or larger than this diameter.











Thermosyphon Systems


The tendency of a less dense fluid to r-ise above a more dense fluid can be
exploited in a simple, natural circulation solar water-heating system called
a thermosyphon. The sketch below shows the arrangement of a typical system.


Cold water supply


hot water


mixing
Svalve


air vent


P-T relief Mvalv


soa prehel an


dra~n


When the sun shines on the collector, it heats the water present in the
tubes. This water becomes less dense than the colder water in the tank and
downcomer and therefore rises to the highest point in the assembly, the top
of the storage tank. A natural circulation flow pattern thus becomes estab-
lished. Since the driving force in a thermosyphon system is due to small
density differences and not the presence of a pump, friction losses through
the system must be kept to a minim~um. In general, one pipe size larger than
would be used with a pump system is satisfactory. Most commercial systems
use 1-inch inside diameter pipe. The flow rate through a thermosyphon sys-
tem is about 1 gal/ft2.hr (40 litres/m2.h) in bright sun.

After sunset, a thermosyphon system can reverse its flow direction and lose
heat to the environment during the night. To avoid reverse flow, the top of
the collector should be at least 2 feet (10.6 m) below the bottom of the
storage tank.







54




Example 5
A simple thermosyphon system is shown below. The water in the tank is at
1400F (density 983.3 kg/m3), and leaves the collector at 1800F (density
970.2 kg/m3). The pipes are smooth copper, I.D. = 2.5 cm. The pressure
drop through the collector is estimated at 5 velocity heads. The total
length of piping is approximately 8 metres. The viscosity of water may be
assumed constant at 4 x 10-4 Pa~s. Determine the flow rate of the water.


0.6m


-L- i,5 m
9.


collecto~-


Solution

Estimate the pressure drop through the system from Table 1.


2

1.35
0.75


= 0.45)


3 x 45* bends (K


1 90* bend (K = 0.75)
tank to pipe
pipe to tank
collector (given)


5.0


8.6

From Equation 11 the head loss is therefore:

HL = ( L + 8.6) -










We will have to guess the friction factor, f, since we don't know the
velocity V. A good rule-of-thumb is that f is about 0.03.

so HL = 0.03 x 8 + 8.6) V2-098 2mte
0.025 2g


This gives us the head loss as a function of velocity. As the water in the
solar collector heats up the fluid begins to circulate: the warmer fluid,
being less dense, tends to rise. The fluid velocity will increase until the
head losses resulting from the fluid motion become equal to the driving
force caused by the density differences in the hot and cold legs of the
system. We now calculate the driving force.


Cold Leg

Taking the temperature of the cold leg as 1400F and the height as 1.1 metre
we have

P = pgh = 983.3 x 9.81 x 1.1
= 10610.8 Pa


Hot Leg

We assume that the temperature of the fluid in the collector is the mean of
the inlet and outlet temperatures, i.e. 160aF. At this temperature the
density of water is 977.3 kg/m3. So the pressure at the base of the hot
leg is given by:

P = 977.3 x 9.81 x 0.5 + 970.2 x 9.81 x 0.6
=10504.3 Pa


The driving force is 10610.8 10504.3
=106.5 Pa.

The head loss of 0.928 V2 metres of water, is equivalent to a pressure
loss of
PL = pgh = 977.3 x 9.81 x 0.928 V2
=8897.0 V2 Pa.

The fluid velocity will be such that the forces balance, i.e.

8897 V2 = 106.5
or V = 0.109 m/s





However, we must now check that the estimated friction factor of f = 0.03
was reasonable.

We therefore compute the Reynolds number.

Re = -L 1 = 977.3 x 0.109 x 0.025
11 4 x10-4
=6658

So the flow is barely turbulent.

from Diagram 1 we find f = 0.034
(smooth pipe)

Recalculating the head loss gives

HL 0.034 x 8 + 8.6) V2 -0.993 V2
0.025 2g


equivalent to a press

PL =



At steady state

9520.2 V2 =
or V =


The flowrate is given

Q =


ure loss of

977.3 x 9.81 x 0.993 V2
9520.2 V2 Pa.



106.5
0.106 m/s


by
VxA
0.106
0.052


m3/s
x + x (0.025)2/4
litres/sec.





































Fioute 1. Energy balance over collector.


ANALYSIS OF FLAT PLATE COLLECTORS

Although solar energy is sometimes portrayed as a 'simple' technology,
the thermal analysis of a solar collector is, in fact, quite complex. Flat
plate collectors can be designed for applications requiring energy at moder-
ate temperatures, up to about 1000C. They absorb both beam and diffuse
solar radiation, do not need to track the sun, and generally require little
maintenance.




Insolation IAre



Useful energy, QU


Energy lost to the
environment, QL


In the steady state, the heat balance over the collector may be written

Qu = IA re QL (1)

where Qu = useful energy transferred from the absorber plate to the
working fluid.

QL = heat losses from the collector.
I = incident solar radiation.

A = area of the collector.

e = overall transmittance of the collector covers.

a = absorptance of the absorber surface.











The instantaneous efficiency of the collector,r would then be defined as


Qu
n = -- (2)


In practice, this is not a useful parameter since it varies continually with
time. The average efficiency ~iis then:


In Equation (1) the heat losses from the collector QL can be written as a
function of the overall heat loss coefficient UL as follows:


QL = ULA(Tp T,)


where Tp is the mean plate temperature and T, is the ambient temperature.
Equation (1) becomes


Qu = A[Ira UL(Tp T,)]


The problem here is that the temperature of the asbepltT is
difficult to calculate or measure since it is a function of the collector
design, the incident solar radiation, and the entering fluid conditions.



To help in the thermal analysis of flat plate collectors, and to get around
the fact that the absorber plate temperature T in Equation (5) is not
known, it is conventional practice to introduce wo new variables into the
analysis. These variables are the Collector Efficiency Factor and the Heat
Removal Factor.


Q udt
" Aldt














1/UL


+ 1+ 1
I ( w-jh


0.0



0.0











0 05 1.0 1.


Figure 2 Fin emciency for tube and sheet solar collectors.


Collector Efficiency Factor


The collector efficiency factor F' is given by the following expression


F' =


1
WULLD + (W D)F+( )F


where UL
W

D
F
Cg
Di
hf


= the collector overall heat loss coefficient.
= the distance between tubes centres on the absorber
plate.
= the outside diameter of the tubes.
= the fin efficiency.
= the bond conductance.
= the inside diameter of the tubes.
= the inside convective film coefficient for the
fluid.


Figure 2 below may be used to estimate the fin efficiency, F, or it may
be calculated directly from

F= tanb [m(W D)/2] (7)
m (W D)/2


where m=U~l


where 6
k


= absorber plate thickness.
= thermal conductivity of the plate.










The bond conductance, Cg, can be estimated from a knowledge of the bond
thermal conductivity, k, the bond average thickness,Y and the bond width,
8. On a per unit length basis

CB B- (9)


The bond conductance can be very important in accurately describing collec-
tor performance. Simple wiring or clamrping of the tubes to the absorber
plate may result in a significant loss of performance.

The collector efficiency factor is essentially a constant for any collector
design and fluid flow rate.


Collector Heat Removal Factor


The collector heat removal factor, FR, may be determined from the follow-
ing expression.

FR = F'C(1 e-1/C) (10)

where C is a dimensionless collector capacitance equal to

C = L4 (11)
AULF

S= fluid mass flow rate, kg/s
Cp = specific heat of the fluid, J/kg K
A = collector area, m2
UL = overall heat loss coefficient, W/m2 K
F' = collector efficiency factor

It now becomes possible to write a simple expression for the useful energy
collected by a flat plate collector.


Qu = FRA [Ina UL(Tin -T,)] (12)

This is a rmch more useful expression than Equation 5, since both Tin*
the inlet temperature of the fluid, and the ambient temperature, Ta, are
usually known. The heat removal factor, FR, may be computed once UL has
been determined, and Iera, the radiation striking the absorber plate, will
also be available.





8(0.01 + 0.14 X 0.937)


Example 1


Calculate the collector efficiency factor, F', and the collector heat
removal factor, FR, for the following system:

Overall loss coefficient 8 W/m2 K
Tube spacing 150 mm
Tube I.D. 10 mm
Plate thickness 0.5 mm
Plate conductivity 385 W/m K
Heat transfer coefficient inside tubes 300 W/m2 K
Bond resistance 0
Flow rate 0.03 kg/s
Specific heat of water 4190 3/kg K
Dimension 1 X 2 m


Solution


Determine the fin efficiency, F, from Equations 7 and 8.


8 1/2
m = ( ----~ )
385 X 5 X 10 4


=6.45


F=tan h 86.45(0.15 0.01)/2]
6.45(0.15 0.01)/2

=0.937


The collector efficiency factor, F', is then given by Equation 6.


F'


1
a X 0.01 X 300


0.15


=0.84


To find the
capacitance,


heat removal factor,
C, from Equation 11.


FR, we first determine the dimensionless


C=0.03 X 4190
2 X 8 X 0.84


= 9.35


so from Equation 10

FR = 0.84 X 9.35(1 exp(-1/9.35)
=0.797











The Calculation of the Overall Loss Coefficient UL

A basic calculation is to determine the overall collector heat transfer
coefficient UL. The thermal network for a two-cover flat plate collector
is shown overleaf in Figure 3. It is clear that


R1 1(13)
hc2 + br2

R2 = (14)
bc1 + hrl

R = (15)
3hc + h

R4 = Ax/k (16)

R5 (17)
bcb + hrb

and UL 11(18)
1 R1 + ,R2 + R3 R4 + RS


In some texts, a 'top loss' coefficient, Ut, and a 'back loss' coefficient
Ub are specified, where
U = (19)
SR1 + R2 + R3

Ub =1
b R4 + R5 (20)


In general, it is possible to assume Rg is zero and that all resistance
to heat flow is due to the insulation. However, it may also be necessary
to consider edge losses. In a well designed system the edge loss should be
small. It is recommended that edge insulation should be about the same
thickness as that on the back of the collector. In this case edge losses
can be included with the back loss to give


Ub = x (1 + Ae/Ac) (21)

where Ae is area of the edge. This formulation assumes RS is zero and
that the back and edges are insulated in a similar manner. Edge losses for
well constructed large collector arrays are usually negligible, but for
small collectors the edge losses may be significant.



























-cver Z


1/hct


r, -- - -- cover F


1/h p


---'aac~c


Ilhb


f.

1
U,

Lr4


Figure 3. Thermal
terms of conduction,
resistances between
coefficient.


network for a two-cover flat-plate collector, (a) in
convection, and radiation resistances, (b) in terms of
plates, (c) in terms of an overall heat transfer


he = convective heat transfer coefficient
h, = radiative heat transfer coefficient










The procedure for determining the loss coefficient UL is an ite rati ve
process. First, a guess is made of the unknown absorber plate and cover
temperatures. This permits the calculation of the heat transfer coeffi-
cients and therefore the resistances to heat transfer. The value of UL
then follows from Equation 18. The absorber plate temperature is then
recalculated from

Qu,/A
T =I T. + -- -(1 -F )(2
P Tin+~~~IR ULFR

A new temperature is then calculated for the first cover. This cover temp-
erature is used to find the next cover temperature and so on. For any two
adjacent covers, the new temperature of cover 2 can be expressed in terms of
cover 1 as

Ut(TD Ta)
T2 = T1 (23)
bc1 + hr1

When the absorber plate temperature and the cover temperatures have been
recalculated, the overall loss coefficient, UL, is calculated once again.
This iterative procedure continues until calculated and estimated plate and
cover temperatures remain the same.

However, the calculation of UL depends on estimating the radiative and
convective heat transfer coefficients (h, and he resp ect ivel y) for the
heat transfer between the absorber plate and the first cover, between the
covers if there is more than one, and between the outer cover and the envi-
ronment. The equations used to determine these coefficients are given
below.

A) PLATE TO COVER


* Radiation: h, = o(1 + T+Tl m2K (24)
1/Ep + 1/E1 -
whr p = absorber plate temperature, K
T1 = innermost cover temperature, K
EP = absorber plate emittance
E1 = cover emittance
a = Boltzmann's constant
= 5.67 X 10-8 W/ 2K4

Convection: he = /2K (5

where k = thermal conductivity of air, Wm/K
d = distance between the surfaces
N = a dimensionless number (the Nusselt number)
which may be determined here as


z]*[1 z(sin 1.88)1.6] + [0.664z-1/3 1]'


N = 1 +1.44 [1 -


(26)









In this equation the meaning of the + exponent is that only the positive
values of the term in the square brackets are to be used, (i.e. a value of
zero is used if the term is negative).


Also


z = 1708/R cos6


(27)


where B is the angle between the collector and the horizontal, R is another
dimensionless number, the Rayleigh number and is given by


R = gAT d3e2 Cp/vkT


(28)


=acceleration due to gravity, 9.81 m/s2
= temperature difference between the surfaces,K
= distance between the surfaces,mn
= density of air, kg/m3
= specific heat of air at constant pressure, ;r/kg K
= viscosity of air, kg/m.s
= thermal conductivity of air, Wm/K
= the average temperature of the air between the surfaces, K


and here g

d

CP

k
T


B) COVER TO COVER


Radiation:


Same as Equidtion (24) except that the equation is now
applied to the two cover surfaces.


Convection: Same as for the plate-to-cover situation.


C) OUTER COVER TO SKY


h, = co(T2 + T2)(T2 + Ts)


(29)


Radiation:


= emittance of outer cover
= cover temperature, K
= sky temperature, K
= Boltzmann's constant
=5.67 X 10-8 W/m2K4


where e
T2
Ts
o


W/m2K


Convection: he = 4.5 + 2.9 u


(30)


The calculation of heat transfer coefficients for flat heated surfaces
exposed to wind is not yet well established. For smooth surfaces Equation
(30) is a reasonable approximation. The average wind speed, u, must be in
metres per second.









Example 2
Calculate the overall loss coefficient for a collector (single cover) with
the following specifications:


Plate to cover spacing
Plate emittance
Ambient air and sky temperature
Wind heat transfer coefficient
Mean plate temperature
Collector tilt
Glass emittance
Back insulation thickness
Insulation conductivity
Collector array dimensions


25 mm
0.95
100C (283 K)
10 W/m2 K
10000 (373 K)
450
0.88
50 mm
0.045 W/m.K
10 X 3 X 0.075 m


Solution


Estimate the cover temperature as 350C (308 K).
the absorber plate temperature has been specified.


In this example


A) PLATE TO COVER


Radiation:


From Equation (24),

(T 2 + T 2)(T + T)
h = P p 1p 1'
rP1/ +1 1-1


=5.67 X 10-8 X (3732 + 3082)(373 + 308)
1/0.95 + 1/0.88 1

= 7.60 W/m2 K


Convection:


=kN/d


where Equations 26, 27 and 28 are to
be used.


g AiT d3p2C
R =
ukT


=100 + 35 =
2


from Table 1 at T


67.50C


=340.5 K


= 1.032 kg/m3
=1.0084 X 103 J/kg K
=2.0575 X 10-5 kg/ms
=0.02931 W/m K
=100 35 = 65 K
=0.025 m









so R =9.81 X 65 X 0.0253 X 1.0322 X 1008.4
2.0575 X 10-5 X 0.02931 X 340.5

=52110


From Equation 27,


Z = 1708/52110 X cos 450 = 0.0464


and (sin 1.88)1.6 = 0.98


[0.664(0.0464)-1/- 1]


so N = 1 + 1.44 [1 0.0464][1 0.0464(0.98)] +


=3.159


0.02931
=3.159 X =
0.025


3.70 W/m2 K


hence h p


B) COVER TO SKY


= co(T12 + Ts2)(T1 + Ts)
= 0.88 X 5.67 X 10-8(3082 + 2832)(308 + 283)

= 5.16 W/m2 K


Radiation:


hr1


(given)


Convection:


hc1 = 10 W/m2 K


=7.60 + 3.70
=0.0885 m2 K/W


5.16 + 10
=0.0660 m2 K/W


so resistance, plate to cover


and resistance, cover to sky


so U = 1
soU 0.0885 + 0.0660


6.47 W/m2 K


This is the first estimate of the top loss coefficient. We now check the
first estimate of the cover temperature. From Equation 23

T1 = T -Ut(Tp Ta)
P hp + b~

= 10 6.47(100 10_)
7.6 + 3.70


=48.50C










The procedure now is to recompute
estimate of the cover temperature.
but the results are:

h =
rp


all the film coefficients using this new
We do not repeat the calculations here,

8.03 W/m2 K
3.52 W/m2 K
5.53 W/m2 K


=10 W/m2 K


as before


1 1 )-1
so Ut = (8.03 + 3.52 5.53 + 10)
=6.62 W/m2

The third estimate of the cover temperature, T1, is therefore

6.62(100 10)
T1 = 100 8.03 + 3.52
=48.4*C

so the calculation is acceptable.

Once the top loss coefficient has been determined, the back loss coefficient
can be quickly found.


Ub = (1 + )


from Equation 21


0.045 2(10 + 3) X 0.075,
so Ub 0.05 [1 + 10 X 3
=0.96 W/m2 K


C so UL = Ut + Ub =


6.62 + 0.96


=7.58 W/m2 K











Minimizing Thermal Losses


Assuming the collector to be adequately insulated (including the edges),
there remain two principal modifications to further reduce heat losses from
the collector. The first is to add additional covers or glazings, the
second is to incorporate a selective absorber plate. Figure 4 below shows
the effect on thermal losses of double glazing and selective surfaces. The
cover temperatures and the heat flux by convection and radiation are shown
for one and two glass covers and for selective and non-selective absorber
plates. Note that radiation between the inside surfaces is the dominant
mode of heat transfer in the absence of a selective surface. When a selec-
tive surface having an emittance of 0.10 is used, convection is the dominant
heat transfer mode between the selective surface and the cover, but radia-
tion is still the largest term between the two covers in the double-glazed
system.


----------------- T = 48.4

9 co,,,=182 q na = 414




9 Wind~ = 2324 Rad
T = 33.2

9co,=124 9m,, = 227
------- -T= 70.3

9con \~,\\\, = 90 q u\\ = 261


q ,,,,, = 2 14 ,a 10
--- ------- ------ T = 31.4







T =24.7

-- -----------------T =50.8

9 c.\\\\,\\\\\\,,, = 12 9 R


Figure 4 Cover temperature and upward heat loss for nat-plate colicctors operating at 100 C
with ambient and sky temperatures of 10 C, plate spacing of 25 mm, tilt of 45", and wind heat
transfer coeffcient of 10 W/m' "C. (All heat nux terms in W/mL.) (a) one cover, plate emittance =
0.95, U, = 6.6 W/m'C; (b) one cover, plate emittance = 0. 10 U, = 3.6 W/mZ C; (c) two covers, plate
emittance = 0.95, U, = 3.9 W/m'C; (d) two covers, plate emittance = 0.10; U, =- 2.4 W/m'C.










Energy Gain from Flat Plate Collectors

It is now possible to evaluate all the terms necessary to compute the
amount of useful energy delivered by a flat plate collector. This quantity,
Qu watts, is found from Equation 12, after FR and UL have been deter-
mined in the manner illustrated by Examples 1 and 2. However, equation 12
is time-dependent since I, the incident solar radiation, obviously varies
through the day. In order to determine, therefore, the useful energy deli-
vered by the collector and its mean efficiency it is necessary to compute
Qu for short time increments over the period of a day. The procedure is
illustrated by the following example.

Example 3

Calculate the daily useful gain and efficiency of a bank of 10 solar collec-
tors installed in parallel. The hourly radiation on the plane of the col-
lector, I, and the hourly ambient temperature, T,, are given in the table
below. Assume that the combined ro coefficient is 0.85, the overall loss
coefficient, 2UL,2 is 6.6 W/m2K, and the heat removal factor is 0.8. Each
collector is 2 2in area. If the fluid inlet temperature is 4000 and the
flow rate through each collector is 0.03 kg/s, what is the fluid temperature
rise and how does it vary during the day?

Time T, I
.OC W/m2
7 8 20 5.6
8 -9 24 119.4
9 10 25 275.0
10 11 28 788.9
11 12 31 833.3
12 1 33 913.8
1 2 31 866.7
2 3 '30 644.4
3 4 29 336.1
4 -5 26 13.9
4797.1 W hr/m2
Solution

We wish to calculate the useful energy delivered from Equation 12 and
the mean efficiency from Equation 3. For each time increment we have:

Time I o UL(Tin Ta)u/
W/m2 W/m2 W/m2
7 8 4. 5 132. 0 0
8 9 95.5 105.6 0
9 10 220.0 99.0 96.8
10 11 631.1 79.2 441.5
11 12 666.6 59.4 485.8
12 1 731.0 46.2 547.8
1 2 693.4 59.4 507.2
2 3 515.5 66.0 359.6
3 4 268.9 72.6 157.0
4 5 11.1 92.4 0
2595.7 W hr/m2











EQu/A
the mean efficiency n =

=2595.7 =05
4797.1

The energy delivery by the 20 m2 array over the day is

2595.7 X 20 X 3600 = 186.9 MJ


The temperature rise for the water will vary according to the period. The
smallest positive temperature rise is between 9 and 10; the highest between
12 and 1.

taking Cp = 4195 J/kg K
and = 0.03 kg/s for each 2 m2 collector.
Qu
then AT=


so from 9 10: AiT = 9. .c
0.93 X 4195

547.8 X 2 = 8.7*C
and from 12 1: AT=
0.03 X 4195


Performance Characteristics

The performance characteristics of flat-plate collectors are often presented
graphically.
Since the instantaneous efficiency is given by
Qu
IA

and since Qu = FRA[Ira UL(Tin Ta)]
the efficiency may be expressed as a function of the fluid inlet
temperature, Tin, as
nI = -FRUL Tin T") +FR~a (31)

If n~ is plotted against (Tin Ta)/I then a straight line results with
a negative slope of FRUL. The intercept on the abscissa is equal to
FR~a. A number of typical plots are shown overleaf. It is clear that, in
practice, there is considerable data scatter and that, moreover, the plots
are slightly non-linear. However, a straight line drawn through the data
points and intercepting the abscissa presents a very convenient indication












of collector performance. It will be necessary to calculate or estimate the
transmittance of the covers, and the absorptance of the collector plate
surface a. The intercept divided by the product, r ct, gives the value of
FR, the collector heat removal factor. The slope of the line divided by
FR then gives UL, the overall heat loss coefficient.


0 I i .
0 0.02 0.04 0.06 0.08 0.10



Experimental collector efficiency data measured for a type of liquid heating collector
with one cover and a selective absorber. Sixteen points are shown for each of five: test sites. The curve
represents the theoretical characteristic derived from points calculated for th~e test conditions.


80 1-


Efficiency curve
for a double-glazed flat-plate
liquid-heating solar collector with
a selective coating on the absorber.
m ,= 0.0136 kg/sec m';
Ta = 29*C; T in = 38-101"C;
I = 590-977 W/cm'; wind
= 3.1 m/sec. (The tests were run
indoors using a solar simulator.)


IIIIII
0.02 0.04 0.06 0.08 0.1 0.12
T in T,
(K m' /W)


0 0.1 0.20



Experimental thermal effciency curves for two air heaters operated outdoors.
Absorbing surface was flat black paint.







73


TABLE 4 Properties of Dry Air at Atmospheric Pressures between 250
and 1000 Ka



Tbp cp (kg/m ec (m' /sec k (m' /sec
(K) (kg/m') (kJ/kg K) X 10s) X 10') (W/m K) X 10') Pr

250 1.4128 1.0053 1.488 9.49 0.02227 0.13161 0.722
300 1.1774 1.0057 1.983 15.68 0.02624 0.22160 0.708
350 0.9980 1.0090 2.075 20.76 0.03003 0.2983 0.697
400 0.8826 1.0140 2.286 25.90 0.03365 0.3760 0.689
450 0.7833 1.0207 2.484 28.86 0.03707 0.4222 0.683
500 0.7048 1.0295 2.671' 37.90 0.04038 0.5564 0.680
550 0.6423 1.0392 2.848 44.34 0.04360 0.6532 0.680
600 0.5879 1.0551 3.018 51.34 0.04659 0.7512 0.680
650 0.5430 1.0635 3.177 58.51 0.04953 '0.8578 0.682
700 0.5030 1.0752 3.332 66.25 0.05230 0.9672 0.684
750 0,4709 1.0856 3.481 73.91 0.05509 1.0774 0.686
800 0.4405 1.0978 3.625 82.29 0.05779 1.1951 0.689
850 0.4149 1.1095 3.765 90.75 0.06028 1.3097 0.692
900 0.3925 1.1212 3.899 99.3 0.06279 1.4271 0.696
950 0.3716 1.1321 4.023 108.2 0.06525 1.5510 0.699
1000 0.3524 1.1417 4.152 117.8 0.06752 1.6779 0.702

aFrom Natl. Bureau Standards (UI.S.) Circ. 564, 1955.
bSymbols: K= absolute temperature, degrees Kelvin; u= y/p; p= density; ep= specific heat
capacity; a= cpp/k; = viscosity; k =thermal conductivity; Pr =Prandtl number, dimensionless.
The values of pc, k, cp, and Pr are not strongly pressure-dependent and may be used over a fairly
wide range of pressures.






TABLE 2 Properties of Water (Saturated Liquid) between 273 and 533 Ka"


aAdapted from Brown, A. I., and S. M. Marco, "Introduction to Heat Transfer," 3d ed
McGraw-Hill Book Company, New York, 1958.


T


K OF *C (kJ/kg OC)(k/ ) (km*se)


ggp cp

(W/m **C) Pr (m-' **C-')


999.8 1.79 X 10-'
999.8 1.55
999.2 1.31
998.6 1.12
997.4 9.8 X 10-*
995.8 8.6
994.9 7.65
993.0 6.82
990.6 6.16
988.8 S.62
985.7 5.13
983.3 4.71
980.3 4.3
977.3 4.01 -
973.7 3.72
970.2 3.47
966.7 3.27
963.2 3.06
955.1 2.67
946.7 2.44
937.2 2.19
928.1 1.98
918.0 1.86
890.4 1.57
859.4 1.36
825.7 1.20
785.2 1.07


273 32 0
277.4 40 4.44
283 50 10
288.6 60 15.56
294.1 70 21.11
299.7 80 26.67
302.2 90 32.22
310.8 100 37.78
316.3 110 43.33
322.9 120 48.89
327.4 130 54.44
333.0 140 60
338.6 150 65.55
342.1 160 71.11
349.7 170 76.67
355.2 180 82.22
360.8 190 87.78
366.3 200 93.33
377.4 220 104.4
388.6 240 115.6
399.7 260 126.7
410.8 280 137.8
421.9 300 148.9
449.7 350 176.7
477.4 400 204.4
505.2 450 232.2
533.0 500 260


4.225
4.208
4.195
4.186
4.179
4.179
4.174
4.174
4.174
4.174
4.179
4.179
4.183
4.186
4.191
4.195
4.199
4.204
4.216
4.229
4.250
4.271
4.296
4.371
4.467
4.585
4.731


0.566
0.575
0.585
0.595
0.604
0.614
0.623
0.630
0.637
0.644
0.649
0.654
0.659
0.665
0.668
0.673
0.675
0.678
0.684
0.685
0.685
0.685
0.684
0.677
0.665
0.646
0.616


13.25
11.35 1.91 x 10P
9.40 6.34 X10'
7.88 1.08 X 1010
6.78 1.46 X10"0
5.85 1.91 X 10"0
5.12 2.48 X10'o
4.53 3.3 X 10'o
4.04 4.19 X10"0
3.64 4.89 X10"0
3.30 5.66 x10"D
3.01 6.48 X 10'0
2.73 7.62 X 10"0
2.53 8.84 X 10o
2.33 9.85 X10'o
2.16 1.09 X10"
2.03
1.90
1.66
1.51
1.36
1.24
1.17
1.02
1.00
0.85
0.83











SOLAR THERMAL ELECTRIC SYSTEMS



Solar thermal electric systems include the following:

* Central receiver ("power tower") systems (CRS) which are
composed of a field of heliostats (mirrors) which are
controlled to reflect incoming direct solar rays to a
common absorber (receiver) elevated above the field by a
central tower. The energy, in the form of heat, is
transferred from the absorber to a working fluid (steam,
air, helium, sodium potassium eutectic or salts), which in
turn is the source of heat for a thermodynamic cycle
(Rankine, Brayton, or combined Rankine/Brayton) to convert
the heat into electricity.

o Line concentrators which are fields of distributed (discrete)
parabolic concentrating collectors which focus direct insolation
upon a line with single axis tracking and an open or cavity
receiver or absorber. The heat is transported from the array
via the absorber pipeline and is transferred to the working
fluid of a Rankine power cycle.

* Point concentrators which are fields of distributed (discrete)
paraboloidal concentrating collectors which focus direct sun
rays at a point, with dual axis tracking and a cavity receiver
(absorber). The heat is transported from the array in one
concept via steam, oils, or chemical mixtures to a central
Rankine power conversion system. An alternate concept is to
use individual power converters (Brayton or Stirling engines)
for each collector module, to produce electricity, and then
transport electric current to the power conditioning facility,
then to the busbar.

Flat plate collector systems could also be used but they are
uneconomical when used to produce electricity. There are essentially three
thermodynamic cycles that can be used separately or in combination for
energy conversion: Rankine, Brayton, and Stirling.









DISTRIBUTED COLLECTOR SYSTEMS (DCS)


1. COOLIDGE

An experimental solar irrigation project sponsored by the U.S. DOE
and run by the University of Arizona has been in operation since 1980.
It provides electricity to pump water from three 91 m deep wells at
Coolidge, Arizona to irrigate cotton crops. The power plant uses 2140
m2 of parabolic trough concentrating collectors to focus sunlight on
receiver tubes within which circulates the primary circuit heat
transfer fluid: Caloria HT-43, a synthetic oil stable at high
temperatures. The primary fluid vapourizes a low-boiling point
secondary fluid (toluene) that drives a Rankine-cycle turbine that
generates electricity.

Electrical power is fed into local electric-utility lines, from
which power is drawn as needed to pump about 5300 litres per minute
from the three wells, each of which requires about 50 KW. Maximum
power output is rated as 175 KW of which approximately 25 KW is for
power plant pumps and motors. Figure 1 shows schematically the
elements of the system. The Acurex collectors raise the temperature
of the Caloria HT-43 oil to around 290"0. The oil is then circulated
through a 30,000 gallon (114 m3) thermal storage tank. A
disadvantage with this Particular thermodynamicc cyc le is that the
pressure in the condenser is below atmospheric, thus raising the
possibility of air leaking into the system. Toluene forms explosive
mixtures with air at low concentrations.


Turbine


Figure 1. Diagram of Coolidge Pumping System








2. ALMERIA

As another example of a DCS system we look at the Small Solar
Power Systems Project (SSPS) initiated by the International Energy
Agency (IEA). Supported and funded by eight European countries and the
U.S., the SSPS is part of the IEA Research and Development program
which is aimed at applying and demonstrating those new or improved
energy technologies that offer significant potential for contributing
to future energy needs.

The principal objective of the SSPS project is to examine in some
detail the feasibility of using solar radiation to generate electric
power for possible application either in established grids or in
communities whose geographical situation renders conventional
electrical supply techniques difficult and costly. Evaluation is to be
performed with respect to two dissimilar engineering approaches. A
solar farm or DCS using parabolic trough collectors is to be located
adjacent to a central receiver system (CRS) using a field of
heliostats.

The technical and oeprational objectives are to compare both
technological concepts, based on the same design philosophy and
operated under the same environmental conditions. The SSPS-DCS plant,
which has a rated output of 500 KWe, utilizes the pilot-system
experience of Acurex in building irrigation plants in New Mexico and
Arizona, as well as of the German company M.A.N. in operating similar
systems in Spain, Mexico, (and Australja. The plant has two collector
fields of approximately equal size (see Table 1). One field is made up
of 10 loops of 60 collectors manufactured by Acurex; the other field
consists of 14 loops of 6 collector modules developed by M.A.N. Both
of these collector designs are line-focusing parabolic trough types.

The Acurex collector is arranged to track the sun in a single-axis
mode, the rotational axis being oriented in the east-west direction.
The M.A.N. collector modules employ two-axis tracking for orientation
in azimuth and elevation. Application of the two design concepts in
the same location offers the opportunity to compare life-cycle costs
versus annual energy output under realistic conditions.

The heat transfer and power conversion systems of the DCS have
been designed with three heat transfer loops.

1) The first loop takes low temperature oil, Caloria
HT-43 at 225"C, from the bottom of a thermal storage
tank, circulates it through the collector fields, and
returns it at a temperature of 295"C to the top of the
storage tank.

2) In a second loop, a boiler takes the hot oil from the
storage tank, discharges the thermal energy to the
steam loop, and returns the oil to the thermal storage
tank.

3. The third loop circulates water through the boiler and
then expands the generated steam through a turbine
generating electricity. The low-enthalpy steam is
condensed and pumped back to the boiler.
Figure 2 shows a simplified diagram of the DCS process
flow.



































































F~. 2 Simlplified schematic diagram of DCS process flow


COLLECTORSTORAGE SYSTEM
FIELDS


Table 1. SSPS Distributed Collector System- Performance Data


__


Design day 80, 12:00 (equinox noon)
point: solar insolation
Collector ACUREX collector, model 3001
fields: 60 groups in 10 loops
MAN collector,
model 3/32, "HELIOMAN'
84 modules in 14 Ioops
total aperture area
concentration ratio
land-use-factor (ACUREX/MAN)
heat transfer medium
collector inlet temperature
collector outlet temperature
Thermal one-tank-thermocline,
storage: storage medium
capacity equivalent to
hot/cold temperature


0,92 kW/m2
2674 m2


2688 m"

5362 mn
ca. 40
0,27/0,32
thermal-oil (HT-43:
2250C
2950C

thermal-oil (HT-43)
0,8 MWhe
2950C/2250C
2950C
2250C
2850C
25 bar
4933 kW
2580 kW
577 kW
500 kW
22,4%
19,4%
10,1%


Steam
generator:


Power
(at design
point):


HT-43 inlet temperature
HT-43 outlet temperature
steam outlet temperature
Steam pressure
solar insolation
thermal
gross electric
net electric


Efficiencies thermal/gross electric
(at design thermal/net electric
point): insolation/net electric


SPOWER CONVERSION
SYSTEM













iet~p~m~--~-
"';
r~as~P~~.r




: -I'


Ep gre 3. The parabolic-trough single-axis tracking collector by Acurex.


The two-axis tracking concentrator by M.A.N., in stow position with faces down.


FIB ,













CENTRAL RECEIVER SYSTEMS

Eight central receiver system experiments and pilot plants are now in
operation or under construction throughout the world, each with the output
power of one megawatt or more of thermal energy. Two of these systems are
now operating in the United States and France, and six more--located in the
United States, France, Italy, Japan, and Spain--are under construction.
All told, they represent an investment of at least $250 million.

One of the first relatively large systems, a 1 MWt solar furnace con-
structed by the French at Odeillo in the Pyreness Mountains, was converted
in the late 1970's to generate electricity for demonstration purposes. In
this application, the thermal power was removed from the receiver by means
of a hot-oil heat-transfer loop to thermal storage, or directly to an oil-
to-steam heat exchanger to operate a steam turbine coupled to an electric
generator.

As a solar furnace, the Odeillo plant develops temperatures up to
3,O000C without the need for direct flame-firing of test specimens or use
of heat-exchanger enclosures. Sixty-three heliostat mirrors, controlled by
computers, reflect the sun's radiation onto a parabolic mirror which in
turn concentrates the radiation on the fixed-focus area.

The Central Receiver Test Facility (CRTF) installed in 1977 at Sandia
National Laboratories in New Mexico is a test bed for components and sub-
systems for the Barstow, Cdlifornia, pilot electric plant. Its sophisti-
cated tower contains three test bays served by an elevator. The field
consists of 222 heliostats which can focus five megawatts of thermal power
into a test bay.

The 10MWe Barstow steam plant now under construction will be connected
to Southern California Edison utility grid, and is expected to serve the
needs of a community of 6,000. Its storage system will be designed to
provide 7MWe for four hours.

A two-megawatt electric plant is under construction at Targasonne,
near Odeillo. Two towers will allow the testing of one receiver subsys'tem
while another subsystem is being installed or modified. Molten salt will
be used as the heat-transfer fluid and also as, the thermal-storage
material.

A third Spanish plant, a 1MWe facility to be built at the Almeria
site, is receiving assistance from the United States in the use of newly-
developed design methodologies and computer programs. All three plants
are expected to be operational by 1982.

Under Japan's Project Sunshine program, two pilot plants with
different design approaches are under construction at Nio, Kagawa
Prefecture, on Shikoku, one of Japan's major southern island. Capable of
producing 1,000 kWe each, the two plants are now operational.

Figure 5 shows the basic components of a central receiver system.














FIGURE 5,
CENTRAL RECEIVER SO LAR THERMAL POWER SYSTEMn



AUXILIARY POWER


I SUBSYSTEM RECEIVER SUBSYSTEM EETI OE
TRANSMISSION
RECEIVER NETWORK



TOWER I POWER
REGULATION

STEAM ,TURBINE(S) aon


Source: ERDA, Central Receiver Solar Thermal Power System Phase 1, 10 MWe Pilot Plant, Washington, D. C.,
1976.











1. ALM1ERIA

The SPSS CRS plant has a rated output of 500 kWe. Solar radiation is
concentrated about 450 times by a heliostat field with approximately 4000 m2
of reflective surface. The Martin Marietta fi rst-generation hel iostats
track the sun both in asimuth and elevation, with a maximum pointing error
of about 2 mrad whenever the wind speed is less than 13 km/h. The field is
designed to survive wind speeds of up to 144 km/h, seismic activities of
0.6 m/s2, and the impact of 20 mm hail at 20 m/s. Additional performance
data is indicated below in Table 2.








Table 2. SSPS Central Receiver System- Performance Data


I


Design day 80, 12:00 (equinox noon)
point: solar insolation
Heliostat total reflective surface area
field: concentration ratio
land-useifactor
Cavity heat transfer medium
receiver: aperture size
active heat transfer surface
inlet temperature
outlet temperature
Thermal two-tank-system, storage medium
storage: capacity equivalent to
hot storage temperature
cold storage temperature


0,92 kW/mz
4000 m2
450
0,22
Sodium
9 m2
16,9 m2
2700C
5300C
Sodium
1,0 MWhe
5300C
2750C
5250C
2750C
510"0
100 bar
3675 kW
2283 kW
600 kW
517 kW
26,3%
22,6%
14,1%


Steam
generator:


Power
(at design
point):

Efficiencies
(at design
point):


sodium inlet temperature
Sodium outlet temperature
steam outlet temperature
steam pressure
solar insolation
thermal
gross electric
net electric
thermal/gross electric
thermal/net electric
insolationinet electric





Transfer of thermal energy in the sodium cooled system is performed at
high temperature (5300C) and low pressure (4 bar). The incoming energy
(2.7 MWt at the design point) which produces peak fluxes on the tube bundle
of the receiver of 0.63 MW/m'2, is passed through a storage system to the
boiler. The third loop generates steam and delivers it to the turbines at
510*C and 100 bar.

The German signed cavity-type receiver has a vertical octagonal
aperture of 9.7 m.Sodium flows in six horizontal parallel tubes which
wind back and forth from the bottom to the top of the cavity. Sodium enters
the inlet header at 2700C at the bottom of the panel and leaves the outlet
header at 5300C near the top. The receiver is mounted on top of a 43 m high
steel tower with a concrete foundation.

A cold sodium vessel and a hot sodium vessel,each having a volume of
70 m3, provide storage for the CRS. Sodium enters the hot storage vessel
from the receiver at 5300C, is pumped to the helical-tube steam generator,
then is returned to the cold sodium vessel at 2750C. The power conversion
unit is a steam-driven five-piston motor coupled to a three-phase generator.
The operating conditions of this unit are indicated below.


Thermal input (steam)
Inlet pressure
Inlet temperature
Back pressure (
Speed
Motor


2200 kWt
100 102 bar
500 520"0
0.3 bar
1000 rpm
845 Hp
600 kWe
562 kWe
27.3 %
25.5 %


Gross output
Net output
Efficiency (!
Efficiency (


gross/thermal)
net/thermal)


HELIOSTAT
FIELD SYSTEMl


SODIUM HEAT-TRANSFER
SYSTEM


POWER CONVERSION
SYSTEM


Fig 6. Simplified schematic diagram of CRS process flow





' rrr' -~~'--
'' '

-i
~.... '~O~e~~Cr3


The 43-meter-high receiver tower
as seen from the ground, with a
view of the back of the sodium
receiver.


T~i~t







84














































The cavity-type sodium receiver of the CRS~ is shown mounted on the receiver
tower. In this photograph, the receiver doors are closed, showing a single
heliostat image.





Closeup of the CRS heliostat field shows the Martin Marietta first-generation-
type heliostats, some of which are in the stowed position with the reflecting
surface facing downward (foreground).


r-
r rI i: '' '
~P









2. BARSTOW

Construction of a CRS pilot plant capable of generating 10 MWe is in
the process of being completed near Barstow, California. This project is
the first of its kind in the U.S. and will be a pilot operation for judging
the feasibility of central receiver systems.

Seven major systems are involved in total plant operation: the collec-
tor, receiver, thermal storage, master control, plant support, beam charac-
terization, and electric power generating systems. (The first six of these
make up the solar facility.) The heliostats of the collector system reflect
solar energy onto the receiver mounted on a 90.8 m (298 ft) tower. In the
receiver, water is boiled and converted to high-pressure steam (5160C and
10.3 MPa; 960*F and 1465 psia), which is then converted to electrical energy
by the turbine/generator. Any steam from the receiver in excess of the
energy required (35.7 MWt) for the generation of 10 MWe net power to the
utility grid is diverted to thermal storage for use when output from the
receiver is under that needed for rated electrical power.

When the turbine operates directly on steam from the receiver, the
pilot plant's rated output is 10 MWe plus 1.8 MWe parasitic loads (internal
plant loads). When operating from the thermal storage system alone (274oC
and 2.7 MPa; 5250F and 385 psia), the net electrical output is 7 MWe.
Overall efficiency of the system ranges from 13.5%n (full insolation day) to
11.1 % (full energy storage operation).

Collector S~ystem

The collector field, consisting of 1818 Martin Marietta suntrackng
heliostats, asatalreflecting area of 72,538 m 7170f2 n
is divided into four quadrants. Each heliostat is made of 12 slightly con-
cave mirror panels totaling 40 m2 (430 ft2) of mirrored surface that
focus the sun's rays on the receiver. The mirror assembly is mounted on a
geared drive unit for azimuth and elevation control.

There are a total of 1240 heliostats in the two northern quadrants and
578 heliostats in the two southern quadrants. In the southern quadrants,
the heliostats are focused on each of the 6 preheat panels under optimum
conditions. In the northern quadrants, the heliostats are focused on each
of the 18 boiler panels so that the heat is distributed over the length of
the panels.

The collector control subsystem consists of a micro-processor in each
heliostat, a heliostat field controller for groups up to 32 heliostats, and
a central computer called the heliostat array controller. The annual and
diurnal sun position information for pointing each heliostat are stored
within this control subsystem. The heliostats can be controlled indivi-
dually or in groups in either manual or automatic modes. The heliostat
array controller is located in the plant control room and is functionally
tied into the master control system. The plant operator can control the
collector field through either the heliostat array controller or the master
control system.











The heliostats are designed to operate in winds up to 36 mph and will
be stowed in a mirror-down position in higher winds. Design specifications
include survivability in a stowed position in winds up to 90 mph. Several
heliostats have satisfactorily passed tests in which wind-induced structural
loads were simulated.

Receiver Systen

The receiver system consists of a single-pass to superheat boiler with
external tubing, a tower, pumps, piping, wiring, and controls necessary to
provide the required amount of steam to the turbine. Steam demand can be
varied from the control room by the operator, or the receiver system can
react to a demand from the electric power generating system up to the
receiver's rated output.

The receiver is designed to produce 5160C (9600F) steam at 10.3 MPa
(1465 psia) at a flow rate of 112,140 1b/h. The receiver has 24 panels (6
preheat and 18 boiler), each approximately 0.9 m (3 ft) wide and 13.7 m
(45 ft) long. The panels are arranged in a cylindrical configuration with a
total surface area of 330 m2 (3252 ft2). Each panel consists of seventy
Incoloy 800 tubes through which water is pumped and boiled. The external
surface temperature of the receiver tubes at rated output will be approxi-
mately 6210C (1150aF). Each receiver tube is 0.69 cm (0.27 in.) inside
diameter and 1.27 cm (0.5 in.) outside diameter. These boiler tubes are
made with thick walls and special metal in, order to withstand the effects of
diurnal cycling, which can cause premature metal fatigue. In contrast to a
solar boiler, conventional boilers are kept heated even when steam and/or
electrical demand is low. In a solar receiver, the heat source disappears
when the sun is obscured or not shining, and the boiler cools. When insola-
tion returns, the boiler is reheated.

Within each panel, all tubes are welded to the adjacent tubes for their
full length on the outside surface only. The receiver panel exterior is
painted with a special black paint ("Pyromark") to increase thermal energy
absorption. The interior surface of the receiver panels is insulated.

The tower, holding the receiver 90.8 m (298 ft) above the desert floor,
has a 7.6 m (25 ft) deep footing and a 1500 ton concrete base. The tower is
equipped with a temporary crane for installation of the receiver panels.
The wide area of the tower beneath the receiver houses air-conditioned rooms
where the receiver computer controls and some of the beam characterization
system are located.

Thermal Storage System

The thermal storage system provides for storage of thermal energy to
extend the plant's electrical power generating capability into nighttime or
during periods of cloud cover. It also provides steam for keeping selected
portions of the plant warm during non-operating hours and for starting up
the plant the following day. Sealing steam is required in the turbine
casing even when it is not running. Even though the primary source for this
turbine sealing steam is thermal storage, a small auxiliary electric boiler
is standing by in case the thermal storage system is depleted or not
operating.





View of the tower with the boiler re-
ceiver mounted at its apex. A man is
standing beneath and to the left of the
receiver behind the railing.


The storage tank is 13.7 m (45 ft) high, 19.8 m (65 ft) in diameter
(inner), and built on a special lightweight, insulating concrete for reduc-
ing heat loss to the ground. The walls are made of steel and 30.5 cm (1 ft)
of~h insula 'ion and the roof is aluminum plus 61 cm (2 ft) of insulation.
The 381 m(946,000 gal) capacity tank, filled with rock, sand and about
908 m3 (240,000 gal) of thermal oil (Caloria HT 43), acts as a heat stor-
age vessel or unit.

Desuperheated steam from the receiver is routed through dual heat
exchangers in which thermal storage oil is heated. The heated oil is pumped
back into the tank and thermal energy is transferred to the rock and sand.
When fully charged, the temperature of the thermal storage mixture (oil,
rock, and sand) will be approximately 3020C (5750F). When discharging, the
heated oil is pumped through another heat exchanger to boil water. Steam at
274"0 (525*F) and 2.7 MPa (385 psia) can be delivered to the turbine at a
rate of 105,000 1b/h. The rated electrical capacity of the plant operating
on thermal storage energy is 28 megawatt-hours (28 MWe-h) net output, i.e.,
7 MWe power for 4 hours. After discharging, sufficient thermal energy will
be available for heating, sealing steam, and restarting the plant the next
day.

As do other plant systems, the thermal storage system has its own con-
trols and also can be controlled both manually and automatically through the
master control system.





r.
.L7:
..,.~ ~~ .
ir- ?
... ,u ~~ 'i;r
-~
, ,..-. ~~
'
-'v ~.`r ...,.
'- - .-~-'cL ~L~,'.~ b:l -~LI~C
. .~.: ~L -
-r~L~T'i~ s'
.9~ .~L'~L~
"' 'c~- ii~t~
I~iJ


89
.-ie.


' ~.7is(~R1'4)
I


r~i~
''
' ~ .~.~
~n~..~ZL 04
~NI
i
T'' 'f*r .
"'LI..~n
i===
I-.- r
-= 1-
.
--
~~-1_-_-1
.~,S~s ---
r rr
,L ~LI I
r~-rTT= ~
Ir~r
~ r~ r
~-~ ~ , ~" ~
I -L =J ~ F ~---
L~P ~S~_IL LL--~-~

"-i~ t;i~-~c:


;;,: ;r,4`r~L7*' :: T:-;


_ I
':,:~ ~P) -'",

:
~tt--~
,

'~ "~~


a
li4.YL Li- t5~1?
..
- o --u t '~-
+: '
--L;. '`''
- -e
.2: -I ~
-I~.-"r~~r*-X ;
~7"'~F~1
. -~:~i~:~ ~4_f~:,~i~,~~* 5~
~Ls-
.,1
U
~ ~~r~,'-:
c.,.

S ,* '-ar~ ~+5;.1

~~t
d


I ;i~i3 ''
; I ~-


June 1981


'
..
r.


1.-, ._ ----
SE;afi~
~c~~--
*"
.Pnl.'"p,


September 1981


.-~*
'zL~p~J~e~lf3i~s~;: _,;I
_~Y~"~,~',' _~-~p~--~~~F~~ku
~;~;:~X~c~:i~~""t"~ ~T;; b.ac~-,
r-
t
VI,
...~ LTECa~S;; *iil~U
ii.h4~~~ ~
r
,;tu'?r' F IIr
r -:~c~
~ -..--5
i-.
'~~~" '

r
_~__~
~r~ I
rr I'
r I.. , ,- = I'
r
-- r-
'' '-''
-.X7:'L~i*lr
-" ~1:. ~
.~~~5~~' '
R
: - Pu;~
i~ii~ Cc e
c
r: g r
Ir
~ -

'Ya' Yi4~~ Ir
2.
r
r
,
rL.b
,'~ 'k~: w~ I;`













The capital cost of the Barstow 10 MWe CRS plant is estimated at 141 M$.
Annual operating and maintenance costs are estimated as 3.7 M$. Construc-
tion took 5 years. These data permit us to make an estimation of the cost
of the electricity that will be produced by the plant.

The capital cost of 141 M$ does not include interest charges on the loan.
Construction costs are 141/5 = 28.2 M$/yr for 5 years. We assume interest
is charged at 15% annually. The total capital cost, including capital
charges, is therefore given by:

0.1b.1 M

The capital recovery factor (CRF) for this debt, based on 15% interest rate
and a 40 yr lifetime, would be:


CRF (0.15, 40) =0.15 =0.15056
1 (1 + 0.15)-40J

So the amount paid annually in capital charges is 190.14 x 0.15056 = 28.63
M$/yr.

Operation and maintenance coststare 3.7 M$/yr, so total annual costs may be
estimated as 32.33 M$/yr.

How much electricity will the plant produce? This is very difficult to
estimate at this stage in the development and demonstration of CRS plants.

Data for California suggest that the direct insolation is about 3200 kWh/m2
per year. Using this figure and the total heliostat area of 72,538 m2,
the gross insolation is about 232.12 x 106 kWh/yr.
The efficiency of the Almeria CRS plant is estimated as about 14% (insola-
tion kWh to net electric kWhe). So an approximate estimate of net electric
output for the Barstow 10 MWe plant would be:

0.14 x 232.12 X 106 = 32.5 x 106 kWhe/yr

Assuming that all routine maintenance is performed at night, so that the
daytime plant factor is 100%, the cost of electricity produced by the sys-
tem is approximately:

32.33 x 106 $/yr =095$kh
32.5 x 10b kWhe/yr


or very nearly $1 per kWhe.











BIOGAS

Biogas is produced by the anaerobic digestion of biomass material.
Animal wastes, when fermented by methane-forming bacteria in the absence of
air, will produce over a period of a month approximately 30 60 litres of
gas per kilogram of dung. The gas, which is predominantly methane, can be
used for heating, lighting, cooking, and for operating gasoline or diesel
engines.

There is now considerable interest in this simple technology. There
are reportedly 7 million biogas units in China (including the world's
largest biogas plant which generates 90 kW of electrical power), 90,000
units in India, 30,000 in Korea, 9,000 in Taiwan, over a thousand in Nepal,
and lesser numbers in Japan, Philippines, Vietnam, Indonesia, Thailand,
Pakistan, Bangladesh, and Sri Lanka, as well as throughout Afri'ca and
Central and South America.

The Digestion Process

In anaerobic digestion, organic waste is mixed with large populations
of microorganisms under conditions in which air is excluded. Under these
conditions, bacteria grow which are capable of converting the organic waste
to carbon dioxide (CO2) and methane (CH4). The anaerobic conversion to
methane yields relative little energy to the microorganisms themselves.
Thus, their rate of growth ib low and only a small portion of the degradable
waste is converted to new bacteria, most is converted to methane. Si nce
this gas is insoluble it escapes from the digester fluid where it can be
collected and used as fuel. As much as 80 90% of the degradable organic
portion of a waste can be stabilized in this manner, even in highly loaded
systems.

Anaerobic treatment of complex organic materials is normally considered
to be a two-stage process, as indicated in Figure 1.






COMLX ORGANIC C8
OGNICS p ACIDS C 0,
ACID MdETHANE
FORMATION FORMATION
FIRST STAGE SECOND STAGE
WASTE CONVERSION WASTE STABILIZATION
Figure i. The two stages of anaerobic methane digestion.












In the first stage, there is no methane production. Instead the com-
plex organic are changed in form by a group of bacteria commonly called
"acid-forming bacteria". Complex materials such as fats, proteins, and
carbohydrates are converted to more simple organic materials -- principally
fatty acids. Acid-forming bacteria bring about these initial transforma-
tions to obtain small amounts of energy for growth and reproduction. This
first phase is required to transform the organic matter to a form suitable
for the second stage of the process. This is the stage that produces the
methane.

During the second stage the organic acids are converted by a special
group of bacteria into carbon dioxide and methane. The methane-forming bac-
teria are strictly anaerobic and even small amounts of oxygen are harmful to
them. There are several types of these bacteria, and each type is charac-
terized by its ability to convert a relatively limited number of organic
compounds into methane. Consequently, for complete digestion of the complex
organic materials, several different types are required. The most important
variety which utilizes acetic and proprionic acid, grows quite slowly and
hence must be retained in the digester for four days or longer; its slow
rate of growth (and low rate of acid utilization) usually represents one of
the rate-limiting steps around which the anaerobic process must be designed.

The methane-forming bacteria have proved to be very difficult to iso-
late and study, and relatively little is known of their basic biochemistry.
Figure 2 indicates schematically the general biochemical anaerobic digestion
process.


INORGAINIC FRACTION INERT MATERIALS

RAW
NON-DIGESTIBLE LIGNIN TYPE
ORGANIC FRAC TION MATERIALS
WASTE ORGANIC
FRAIXION/ DIGESTI(BLE
& FRACTIONAC-
FORMING
BACTERIA

VOLATILE
ACIDS
SIMPLE




METHANE-PRODUCING BACTERIA




METHANE I CARBON WATER
DIOXIDE A ND
cH4; CO2 RSE

Figure 2, The biological breakdown of organic material in a methane
digester.












The amount of gas produced and its composition will depend on the
characteristics of the feed material and the conditions under which the
digester operates.

Animal manures, when slurried with water, are excellent feed materials
and under optimal conditions produce good quality gas. Tables 1 and 2
indicate the estimated gas production from the dung of cattle, pigs and
poultry. These figures (Table 1) imply biogas generation rates as follows:

Dairy cattle 30 litres gas/kg dung
Beef cattle 42 litres gas/kg dung
Swine 53 litres gas/kg dung
Poultry 116 litres gas/kg dung

Carbon Nitrogen Ratio

The ratio of carbon to nitrogen (C:N) in the digester feed critically
affects the operation of the digester and the composition of the gas. Gas
production can be increased by supplementing substrates that have a high
carbon content with substrates containing nitrogen, and vice versa. If the
C:N ratio is too high, the process is limited by the availability of nitro-
gen; if the C:N ratio is too low, ammonia may be produced in quantities
large enough to be toxic to the bacterial population. For optimum produc-
tion of methane the C:N ratio should be about 30:1. Tables 3 and 4 show C:N
ratios for many common animal and agricultural wastes. Further qualitative
information on the influence of the C:N ratio on digester performance is
shown in Table 5.

It should be noted that in order to evaluate the feasibility of using a
particular biomass material for biogas production, both the C:N ratio and
the biodegradability need to be known. The wide range of values reported in
the literature is an indication that a degree of caution is advisable in
designing digesters utilizing waste materials for which no direct experi-
mental or operating data are available.

pH Level

The bacterial population in anaerobic digesters is sensitive to pH
levels. The optimal pH range lies between 7.0 and 7.2 but gas production
will proceed satisfactorily between 6.6 and 7.6. When the pH falls below
6.6 there is an inhibitory effect on gas production. Acid conditions below
about 6 will suppress the methanogenic bacteria and shut down gas produc-
tion. Under normal operating conditions, however, the biochemical reactions
tend to automatically maintain the pH level in the proper range.

During the start up of the digester acidic conditions may sometimes
occur since the acid-forming bacteria at first multiply much more rapidly
than the methanogenic bacteria. To alleviate this problem artificial
means to raise the pH to about 7 may be required. Bicarbonate of soda is
reportedly an effective anti-acid agent. It should be mixed with the feed
slurry: about 10 grams of bicarbonate to 30 litres of slurry.


















Dairy Beef
Cattle Cattle Swine Poultry

Manure production
(1b/day/1000 lb live weight) 85 58 50 59

Volatile solids
(lb dry solids/day/1000 lb
live weight) 8.7 5.9 5.9 12.8

Digestion efficiency of the
manure solids (%) 35 50 55 65

Bio-gas production
(ft3/1b VS added) 4.7 6.7 7.3 8.6
(ft3/1000 lb live weight/day) 40.8 39.5 43.1 110.9


(lb x 0.454 = kg: ft3/1b x 0.062 = m3/kg)


Amount of gas produced per Percentage
tonne of dried material in content of
Material cubic metres methane
General stable
manure from 260 -280 50-60
livestock
Pig manure 561
Horse manure 200 -300
Rice husks 615
Fresh ras630 70
Flax stalks or hemp 359 59
Straw 342 .59
Leaves from trees 210-294 58
Potato plant
leaves and vine 260 -280
etc.
Sunflo wer leaves 305
and stalks
Sludge 640 50
Waste water from
wine or spirit 300-600 58
making factories


Table A. Estimated manure and
wastes (i)


bio-gas production from animal


~sb~ PGas vield of some common fermentation materials.


(17)





















Table 3. Nitrogen Content and C/N Ratio" (2)

Total Nitrogen
Material (% dry weight) C/N Ratio

Animal wastes
Urine 16.0 0.8
Blood 12.0 3.5
Bone meal -3.5
Animal tankage -4.1b
Dry fish scraps -5.1b

Manure
Human feces 6.0 6.0-10.0
Human urine 18.0
Chicken 6.3 15.0
Sheep 3.8
Pig 3.8
Horse 2.3 25.0b
Cow 1.7 18.0b
Steer 1.35 25.3

Sludge
Milorganite -5.4b
Activated sludge 5.0 6.0
Fresh sewage -11.0b

Plant meals
Soybean -5.0
Cottonseed -5.0b
Peanut hull -36.0b

Plant wastes
Green garbage 3.0 18.0
Hay, young grass 4.0 12.0
Hay, alfalfa 2.8 17.0b
Hay, blue grass 2.5 19.0
Seaweed 1.9 19.0
Nonleguminous vegetables 2.5-4.0 11.0-19.0
Red clover 1.8 27.0
Straw, oat 1.1 48.0
Straw, wheat 0.5 150.0
Sawdust 0.1 200.0-500.0
White fir wood 0.06 767.0

Other wastes
Newspaper 0.05 812.0
Refuse 0.74 45.0

Notes: a. From "Anaerobic Digestion of Solid Wastes" (Klein) and Methane Digesters for
Fuel Gas and Fertilizer (Merrill and Fry).
b. Nitrogen is the percentage of total dry weight while carbon is calculated frorn either
the total carbon percentage of dry weight or the percentage of dry weight of
nonlignin carbon.



















Table 9. Approximate values for the carbon/nitrogen ratios of some
of the common materials used for biogas pits. (17)
Nitrogen as a Carbon/
Carbon as apercen- percentage of nitrogen
Material tage of total weight total weight ratio
% % %
r straw 46 0.53 87:1
Dry rice stalks 42 0.63 67: 1
Maize stalks 40 05 5: 1
Fallen leaves 41 1.00 41:1
Soya bean stalks 41 1.30 32: 1
Wild grass: i.e.
weeds etc. (in1404 271
China often narrow,
thin leaved)
Peanut vine stalks 11 0.59 19: 1
Fresh sheep manure 16 0.55 29: 1
Fresh cow/ox manure 7.3 0.29 25: 1
Fresh horse manure 10 0.42 24: 1
Fresh pig manure 7.3 0.60 13: 1
Fresh human manure 2.5 0.85 2.9: 1


Table 5 C/N Ratio and Composition of Bio-gas 95


Notes: a. Adapted from Methane Digester for Fuel Gas and Fearriie (Merrill and Fry).


Materilat


Gas
Methane CO, Hydrogen Nitrogen


C/N low (high nitrogen)
Blood
Urine
C/N high (low nitrogen)
Sawdust
Straw
Sugar and starch
potatoes
com
sugar beets
C/N balanced (near 30:1)
Manures
Garbage


little much little much


little much much little


much


some little little













Temperature Effects


The temperature of an aerobic digester strongly effects its perfor-
mance. The optimum temperature for mesophilic anaerobic digestion is about
350C. Gas production and digestion will proceed at lower temperatures but
the rate of digestion is reduced. An example of the relationship between
residence time, temperature, and gas production that was obtained in one
study is shown in Figure 4. As a rough approximation, for every + 50C
temperature change (mean daily ambient) from 250C, the daily gas production
will vary by about 20%. This applies to a temperature range between 100C
and 35"C. Below 10*C gas production drops off rapidly. As long as the
digester volume is not too small, there is sufficient thermal capacity to
smooth out diurnal variations in ambient temperature. The slurry tempera-
ture will be approximately equal to the mean 24 hour ambient temperature.
Small digesters (less than 1 cubic metre) can be expected to show stronger
temperature variations throughout the day.










~ 86'F (30C)
77*F (25*C)
I / 68*F (20C)
r- 59*F (15*C)
~e, 50*F (10*C)


time (days)


Figure -3. Bio-Gas Production as Related to the Temperature
of the Digester and the Time of Digestion (1)