DEPARTMENT OF PLANNING AND NATURAL RESOURCES
VIRGIN ISLANDS ENERGY OFFICE
45 ESTATE MARS HILL
FREDERIKSTED, VIRGIN ISLANDS 00840
TELEPHONE 340 773-1082 STX FAX 340 772-0063
340 774-3320 STT FAX 340 714-9531
Wind is the natural movement of air across the land or sea.
uneven heating and cooling of the earth's
surface and by the earth's rotation. Land
and water areas absorb and release different
amount of heat received from the sun. As
warm air rises, cooler air rushes in to take
its place, causing local winds. The rotation
of the earth changes the direction of the
flow of air. This produces prevailing
winds, including the Caribbean's trade winds
Wind is caused by
Local winds caused by uneven
heating of land and water
n Warm Air Rises
Cool Sea Breeze
,m "During the day, air over the ocean
r S"" a.. Is cooler than air over the land
. Surface features such as mountains
and valleys can change the direction and speed of prevailing winds. Wind energy
uses the energy in the wind for practical purposes like generating electricity,
charging batteries, pumping water, or grinding grain. Large, modern wind turbines
operate together in wind farms to
produce electricity for utilities.
Homeowners and remote villages to
help meet energy needs use small
Throughout history people have
harnessed the wind. Over 5,000 years
ago, the ancient Egyptians used wind
power to sail the their ships on the Nile
American colonists used windmills to
grind wheat and corn, pump water, and
cut wood. When power lines began to
transport electricity to rural areas in the
1930s, the electric windmills were used
less and less. Then in the early 1970s, oil
shortages created an environment eager
for alternative energy sources, paving the
way for the re-entry of the electric
windmill on the American landscape.
Converts the kinetic energy
of wind into electricity WIND ENERGY BASICS
"Catch" the wind
GENERATOR Wind turbines capture the wind's energy with two or
Produces eItcity three propeller-like blades, which are mounted on a rotor,
to generate electricity. The turbines sit high atop towers,
oTOWER taking advantage of the stronger and less turbulent wind
To raise blade s
high where wind
is sr, h r at 100 feet (30 meters) or more aboveground.
"' C twr."' A blade acts much like an airplane wing. When the wind
blows, a pocket of low-pressure air forms on the
\downwind side of the blade. The low-pressure air pocket
ELECTRONIC CONTROL SYSTEMc then pulls the blade toward it, causing the rotor to turn.
Hooked into computer to control machine
This is called lift. The force of the lift is actually much
stronger than the wind's force against the front side of the blade, which is called
drag. The combination of lift and drag causes the rotor to spin like a propeller, and
the turning shaft spins a generator to make electricity.
Wind turbines can be used as stand-alone applications, or they can be connected to
a utility power grid or even combined with a photovoltaic (solar cell) system.
Stand-alone turbines are typically used for water pumping or communications.
However, homeowners and farmers in windy areas can also use turbines to
generate electricity. For utility-scale sources of wind energy, a large number of
turbines are usually built close together to form a wind farm. Several electricity
providers today use wind farms to supply power to their customers.
WIND ENERGY TECHNOLOGIES
Modern wind turbines are divided into two major categories: horizontal axis
turbines and vertical axis turbines. Old-fashioned windmills are still seen in many
Horizontal Axis Turbines (HAWT)
Horizontal axis turbines are the most common turbine configuration used today.
They consist of a tall tower, atop which sits a fan-like rotor that faces into or away
from the wind, the generator, the controller, and other components. Most
horizontal axis turbines built today are two or three-bladed, although some have
fewer or more blades.
Vertical Axis Turbines (VAWT)
Vertical axis turbines fall into two major categories: Savonius and Darrieus.
Neither turbine type is in wide use today.
The Darrieus turbine was invented in France in the 1920s. Often
described as looking like an eggbeater, this vertical axis turbine
has vertical blades that rotate into and out of the wind. Using .
aerodynamic lift, these turbines can capture more energy than -
drag devices. The Giromill and cycloturbine are variants on the VERTICAL ASWIND MACHINE
.Darrieus "egg beater" type
Darrieus turbine. Dus p
First invented in Finland, the Savonius turbine is S-shaped if viewed from above.
This drag-type VAWT turns relatively slowly, but yields a high torque. It is useful
for grinding grain, pumping water, and many other tasks, but its slow rotational
speeds are not good for generating electricity.
The amount of energy produced by a wind machine depends upon the wind speed
and the size of the blades in the machine. In general, when the wind speed
doubles, the power produced increases eight times. Larger blades capture more
wind. As the diameter of the circle formed by the blades doubles, the power
increases four times.
ADVANTAGES AND DISADVANTAGES OF WIND ENERGY
Wind is a renewable energy resource. Wind patterns in the Caribbean provide
strong, steady trade winds in specific areas throughout most of the year.
Wind power can be used with battery storage or pumped hydro-energy storage
systems to provide a steady flow of energy.
Used as a "fuel," wind is free and non-polluting, producing no emissions or
Use of wind power as a source of electricity will help reduce the Territory's
complete dependence on fossil fuels.
Wind farms can be combined with agricultural activities such as cattle grazing.
Wind machines must be located where strong, dependable winds are available
most of the time.
Because winds do not blow strongly enough to produce power all the time, energy
from wind machines are considered "intermittent," that is, it comes and goes.
Therefore, electricity from wind machines must have a back-up supply from
Wind towers and turbine blades are subject to damage from high winds and
lightning. Rotating parts, which are located high off the ground, can be difficult
and expensive to repair.
The environmental drawback may be a wind farm's effect on native bird
populations, as well as its visual impact on the surrounding landscape. To some,
the blades are an eyesore; to others, they're a beautiful alternative to conventional
Wind Energy Program: www.eren.doe.gov/wind
The National Renewable Energy Laboratory's National Wind Technology Center:
Sandia National Laboratory: www.sandia.gov/wind/