Renewable Energy
Renewable energy sources can be replenished in a short period of time.
The five renewable sources used most often include hydropower (water),
solar, wind, geothermal, and biomass.
Biomass
Solar
Water
Geothermal
Wind
 
Renewable energy's impact on the world's energy picture is significant.
Many milestones have occurred during the history of using renewable
sources to generate electricity - but the overall use of these fuels
declined by almost 9 % from their 1996 peak to less than 7 quads (6.823
quads) in 2000.
The use of renewable energy is not new. Five generations (125 years)
ago, wood supplied up to 90 % of our energy needs. Due to the convenience
and low prices of fossil fuels, wood use has fallen. Now, the biomass
which would normally present a disposal problem is converted into electricity
(e.g., manufacturing wastes, rice hulls, and black liquor from paper
production).
Historically, low fossil fuel prices, especially for natural gas, have
made growth difficult for renewable fuels. The deregulation and restructuring
of the electric power industry could have a major impact on renewable
energy consumption. Demands for cheaper power in the short term would
likely decrease demand for renewable energy, while preferences for renewable's
included in some versions of proposed electricity restructuring legislation
would breathe new life into this industry.
Use of renewable's in the United States is not currently expected to
approach that of the major fuels, and due to their limitations (e.g.,
their intermittent nature - cloudy days have no solar gain, quiet days
mean no wind blows to drive wind turbines, dams are primarily for flood
control, so hydroelectricity production varies as dams' water levels
change), renewable's may never provide "the" answer to all
energy problems. Around the world, renewable energy is proving to be
of great value.
BIOMASS -- Energy from Wood, Garbage,
and Agricultural Waste
 Biomass
is organic material which has stored sunlight in the form of chemical
energy. Biomass fuels include wood, wood waste, straw, manure, sugar
cane, and many other byproducts from a variety of agricultural processes.
When burned, the chemical energy is released as heat. If you have a
fireplace, the wood you burn in it is a biomass fuel. What we now call
biomass was the chief source of heating homes and other buildings for
thousands of years. In fact, biomass continues to be a major source
of energy in much of the developing world.
Sugar cane, a good example of a biomass crop, is grown in many Southern
states and in the Caribbean. The chief commercial product, sugar, is
extracted from the cane by removing the juice; the remainder of the
plant, called "bagasse", still contains the chemical energy
of the sun. As with any biomass, bagasse produces heat when burned.
Ethanol, another biomass fuel, is an alcohol distilled
mostly from corn. For the last twenty years, it has been blended with
gasoline for use in cars in the USA. Using ethanol in gasoline means
we don't burn quite as much fossil fuel in our cars.
People in the USA are trying to develop ways to burn more
biomass and less coal and other fossil fuels. When burned, biomass does
release carbon dioxide, a greenhouse gas. But when biomass crops are
grown, an equivalent amount of carbon dioxide is consumed through photosynthesis.
Numerous biomass electric power plants, as well as steam producing plants
for industrial purposes (especially in the wood and paper products industry)
are located throughout the country.
The real environmental benefit of biomass will come when we can use
large amounts of biomass to generate electricity, thereby reducing consumption
of fossil fuels. This is a photograph of biomass fuel, probably wood
chips, being stored and dried for later use in a boiler.
Farmers are experimenting with "woody crops" (mostly small
poplar trees and switchgrass) to see if they can grow them cheaply and
abundantly.
Solar Energy -- Energy
from the Sun
The sun has produced energy for billions of years. Solar
energy is the solar radiation that reaches the earth.
Solar energy can be converted directly or indirectly into other forms
of energy, such as heat and electricity. The major drawbacks (problems,
or issues to overcome) of solar energy are: (1) the intermittent and
variable manner in which it arrives at the earth's surface and, (2)
the large area required to collect it at a useful rate.
Solar energy is used for heating water for domestic use, space heating
of buildings, drying agricultural products, and generating electrical
energy.
In the 1830s, the British astronomer John Herschel used a solar collector
box to cook food during an expedition to Africa. Now, people are trying
to use the sun's energy for lots of things.
Electric utilities are are trying photovoltaics, a process by which
solar energy is converted directly to electricity. Electricity can be
produced directly from solar energy using photovoltaic devices or indirectly
from steam generators using solar thermal collectors to heat a working
fluid.
There were 14 solar thermal electric units operating in the US at the
end of 2001, with more on the way. Most of these are in California,
though Nevada, Arizona, Texas, and Virginia have them, too.
PHOTOVOLTAIC ENERGY
Photovoltaic energy is the conversion of sunlight into electricity
through a photovoltaic (PV's) cell, commonly called a solar cell. A
photovoltaic cell is a non mechanical device usually made from silicon
alloys.
Sunlight is composed of photons, or particles of solar energy. These
photons contain various amounts of energy corresponding to the different
wavelengths of the solar spectrum. When photons strike a photovoltaic
cell, they may be reflected, pass right through, or be absorbed. Only
the absorbed photons provide energy to generate electricity. When enough
sunlight (energy) is absorbed by the material (a semiconductor), electrons
are dislodged from the material's atoms. Special treatment of the material
surface during manufacturing makes the front surface of the cell more
receptive to free electrons, so the electrons naturally migrate to the
surface.
When the electrons leave their position, holes are formed. When many
electrons, each carrying a negative charge, travel toward the front
surface of the cell, the resulting imbalance of charge between the cell's
front and back surfaces creates a voltage potential like the negative
and positive terminals of a battery. When the two surfaces are connected
through an external load, electricity flows.
The photovoltaic cell is the basic building block of a PV system. Individual
cells can vary in size from about 1 cm (1/2 inch) to about 10 cm (4
inches) across. However, one cell only produces 1 or 2 watts, which
isn't enough power for most applications. To increase power output,
cells are electrically connected into a packaged weather-tight module.
Modules can be further connected to form an array. The term array refers
to the entire generating plant, whether it is made up of one or several
thousand modules. As many modules as needed can be connected to form
the array size (power output) needed.
The performance of a photovoltaic array is dependent upon sunlight.
Climate conditions (e.g., clouds, fog) have a significant effect on
the amount of solar energy received by a PV array and, in turn, its
performance. Most "current technology" photovoltaic modules
are about 10 percent efficient in converting sunlight to electricity
with further research being conducted to raise this efficiency to 15
percent.
The pv cell was discovered in 1954 by Bell Telephone researchers examining
the sensitivity of a properly prepared silicon wafer to sunlight. Beginning
in the late 1950s, pvs were used to power U.S. space satellites. The
success of PV's in space generated commercial applications for pv technology.
The simplest photovoltaic systems power many of the small calculators
and wrist watches used everyday. More complicated systems provide electricity
to pump water, power communications equipment, and even provide electricity
to our homes.
Photovoltaic conversion is useful for several reasons. Conversion from
sunlight to electricity is direct, so that bulky mechanical generator
systems are unnecessary. The modular characteristic of photovoltaic
energy allows arrays to be installed quickly and in any size required
or allowed.
Also, the environmental impact of a photovoltaic system is minimal,
requiring no water for system cooling and generating no by-products.
Photovoltaic cells, like batteries, generate direct current (DC) which
is generally used for small loads (electronic equipment). When DC from
photovoltaic cells is used for commercial applications or sold to electric
utilities using the electric grid, it must be converted to alternating
current (AC) using inverters, solid state devices that convert DC power
to AC. Historically, pvs have been used at remote sites to provide electricity.
However, a market for distributed generation from PV's may be developing
with the unbundling of transmission and distribution costs due to electric
deregulation. The siting of numerous small-scale generators in electric
distribution feeders could improve the economics and reliability of
the distribution system.
SOLAR THERMAL HEAT
The major applications of solar thermal energy at present are heating
swimming pools, heating water for domestic use, and space heating of
buildings. For these purposes, the general practice is to use flat-plate
solar-energy collectors with a fixed orientation (position).
Where space heating is the main consideration, the highest efficiency
with a fixed flat-plate collector is obtained if it faces approximately
south and slopes at an angle to the horizon equal to the latitude plus
about 15 degrees.
Solar collectors fall into two general categories: non concentrating
and concentrating.
In the non concentrating type, the collector area (i.e. the area that
intercepts the solar radiation) is the same as the absorber area (i.e.,
the area absorbing the radiation).
In concentrating collectors, the area intercepting the solar radiation
is greater, sometimes hundreds of times greater, than the absorber area.
Where temperatures below about 200o F are sufficient, such as for space
heating, flat-plate collectors of the non concentrating type are generally
used.
There are many flat-plate collector designs but generally all consist
of (1) a flat-plate absorber, which intercepts and absorbs the solar
energy, (2) a transparent cover(s) that allows solar energy to pass
through but reduces heat loss from the absorber, (3) a heat-transport
fluid (air or water) flowing through tubes to remove heat from the absorber,
and (4) a heat insulating backing.
Solar space heating systems can be classified as passive or active.
In passive heating systems, the air is circulated past a solar heat
surface(s) and through the building by convection (i.e. less dense warm
air tends to rise while more dense cooler air moves downward) without
the use of mechanical equipment. In active heating systems, fans and
pumps are used to circulate the air or the heat absorbing fluid.
SOLAR THERMAL POWER PLANTS
Solar thermal power plants use the sun's rays to heat a fluid, from
which heat transfer systems may be used to produce steam. The steam,
in turn, is converted into mechanical energy in a turbine and into electricity
from a conventional generator coupled to the turbine. Solar thermal
power generation is essentially the same as conventional technologies
except that in conventional technologies the energy source is from the
stored energy in fossil fuels released by combustion. Solar thermal
technologies use concentrator systems due to the high temperatures needed
for the working fluid. The three types of solar-thermal power systems
in use or under development are: parabolic trough, solar dish, and solar
power tower.
PARABOLIC TROUGH
The parabolic trough is the most advanced of the concentrator systems.
This technology is used in the largest grid connected solar-thermal
power plants in the world. One such complex in the U.S. uses parabolic
troughs. The Kramer Junction companies operate and maintain five 30-megawatt
Solar Electric Generating Systems (SEGS). These SEGS comprise 150 to
354 megawatts of installed parabolic trough solar thermal electric generating
capacity located in California's Mojave desert. The combined California
facilities produce more than 90% of the world's commercially available
solar thermal electric power.
A parabolic trough collector has a linear parabolic-shaped reflector
that focuses the sun's radiation on a linear receiver located at the
focus of the parabola. The collector tracks the sun along one axis from
east to west during the day to ensure that the sun is continuously focused
on the receiver. Because of its parabolic shape, a trough can focus
the sun at 30 to 100 times its normal intensity (concentration ratio)
on a receiver pipe located along the focal line of the trough, achieving
operating temperatures over 400 degrees Celsius.
A collector field consists of a large field of single-axis tracking
parabolic trough collectors. The solar field is modular in nature and
is composed of many parallel rows of solar collectors aligned on a north-south
horizontal axis. A working (heat transfer) fluid is heated as it circulates
through the receivers and returns to a series of heat exchangers at
a central location where the fluid is used to generate high-pressure
superheated steam. The steam is then fed to a conventional steam turbine/generator
to produce electricity. After the working fluid passes through the heat
exchangers, the cooled fluid is recirculated through the solar field.
The plant is usually designed to operate at full rated power using solar
energy alone, given sufficient solar energy. However, all plants are
hybrid solar/fossil plants that have a fossil-fired capability that
can be used to supplement the solar output during periods of low solar
energy. The Luz plant is a natural gas hybrid.
SOLAR DISH
A solar dish/engine system utilizes concentrating solar collectors
that track the sun on two axes, concentrating the energy at the focal
point of the dish because it is always pointed at the sun. The solar
dish's concentration ratio is much higher that the solar trough, typically
over 2,000, with a working fluid temperature over 750oC. The power-generating
equipment used with a solar dish can be mounted at the focal point of
the dish, making it well suited for remote operations or, as with the
solar trough, the energy may be collected from a number of installations
and converted to electricity at a central point. The engine in a solar
dish/engine system converts heat to mechanical power by compressing
the working fluid when it is cold, heating the compressed working fluid,
and then expanding the fluid through a turbine or with a piston to produce
work. The engine is coupled to an electric generator to convert the
mechanical power to electric power.
SOLAR POWER TOWER
A solar power tower or central receiver generates electricity from
sunlight by focusing concentrated solar energy on a tower-mounted heat
exchanger (receiver). This system uses hundreds to thousands of flat
sun-tracking mirrors called heliostats to reflect and concentrate the
sun's energy onto a central receiver tower. The energy can be concentrated
as much as 1,500 times that of the energy coming in from the sun. Energy
losses from thermal-energy transport are minimized as solar energy is
being directly transferred by reflection from the heliostats to a single
receiver, rather than being moved through a transfer medium to one central
location, as with parabolic troughs. Power towers must be large to be
economical. This is a promising technology for large-scale grid-connected
power plants. Though power towers are in the early stages of development
compared with parabolic trough technology, a number of test facilities
have been constructed around the world.
Solar One, near Barstow, California which operated from 1982 to 1988,
at about 10 megawatts, was the world's largest power tower plant. In
Solar One, water was converted to steam in the receiver and used directly
to power a steam turbine. The heliostat field consisted of approximately
1,800 heliostats. The storage system stored heat from solar-produced
steam in a tank filled with rocks and sand using oil as the heat-transfer
fluid. A consortium comprising the U.S. Department of Energy and a number
of electric utilities, led by Southern California Edison, redesigned
Solar One to a more advanced molten-salt technology, which started operation
in 1996, Solar Two.
Hydropower -- Energy from Moving Water
Of the renewable energy sources that generate electricity, hydropower
is the most often used. It accounted for 7.2 percent of U.S. generation
and 76 percent of renewable generation in 2000. It is one of the oldest
sources of energy and was used thousands of years ago to turn a paddle
wheel for purposes such as grinding grain. Our nation’s first
industrial use of hydropower to generate  electricity
occurred in 1880, when 16 brush-arc lamps were powered using a water
turbine at the Wolverine Chair Factory in Grand Rapids, Michigan. The
first U.S. hydroelectric power plant opened on the Fox River near Appleton,
Wisconsin, on September 30, 1882. Until that time, coal was the only
fuel used to produce electricity. Because the source of hydropower is
water, hydroelectric power plants must be located on a water source.
Therefore, it wasn’t until the technology to transmit electricity
over long distances was developed that hydropower became widely used.
Mechanical energy is derived by directing, harnessing, or channeling
moving water. The amount of available energy in moving water is determined
by its flow or fall. Swiftly flowing water in a big river, like the
Columbia River along the border between Oregon and Washington, carries
a great deal of energy in its flow. So, too, with water descending rapidly
from a very high point, like Niagara Falls in New York. In either instance,
the water flows through a pipe, or penstock, then pushes against and
turns blades in a turbine to spin a generator to produce electricity.
In a run-of-the-river system, the force of the current applies the needed
pressure, while in a storage system, water is accumulated in reservoirs
created by dams, then released when the demand for electricity is high.
Meanwhile, the reservoirs or lakes are used for boating
and fishing, and often the rivers beyond the dams provide opportunities
for whitewater rafting and kayaking. Hoover Dam, a hydroelectric facility
completed in 1936 on the Colorado River between Arizona and Nevada,
created Lake Mead, a 110-mile-long national recreational area that offers
water sports and fishing in a desert setting.
Almost two-thirds of the total U.S. hydroelectric capacity for electricity
generation is concentrated in nine States (Washington, California, Oregon,
New York, Tennessee, South Carolina, South Dakota, Arkansas and Nevada)
with approximately 22 percent in Washington, the location of the nation’s
largest hydroelectric facility -- the Grand Coulee Dam.
It is important to note that only a small percentage of all dams in
the United States produce electricity. Most dams were constructed solely
to provide irrigation and flood control.
Some people regard hydropower as the ideal fuel for electricity generation
because, unlike the nonrenewable fuels used to generate electricity,
it is almost free, there are no waste products, and hydropower does
not pollute the water or the air. However, it is criticized because
it does change the environment by affecting natural habitats. For instance,
in the Columbia River, salmon must swim upstream to their spawning grounds
to reproduce, but the series of dams gets in their way. Different approaches
to fixing this problem have been used, including the construction of
"fish ladders" which help the salmon "step up" the
dam to the spawning grounds upstream.
Geothermal Energy -- Energy from
the Earth's Core
On May 18, 1980, Mt. St. Helens , an active volcano in Washington,
erupted, providing a vivid display of the energy contained within the
Earth. Most volcanic activity occurs around the Pacific Ocean's rim,
the Ring of Fire. 
Volcanic energy cannot be harnessed (controlled and collected), but
in a few places heat from the earth, called geothermal energy, can be
collected. Usually, engineers try to collect this heat in the rare places
where the Earth's crust has trapped steam and hot water. Here, they
drill into the crust and allow the heat to escape, either as steam,
or as very hot water. Pipes carry the hot water to a plant, where some
of the steam is allowed to "flash," or separate from the water.
That steam then turns a turbine - generator to make electricity.
 Geothermal
energy was first used to produce electricity in Italy in 1903. At the
end of 1999, there were 204 generating units producing electricity from
geothermal energy in the USA. Most of these are located in California
and Nevada; Utah has two geothermal plants and Hawaii, formed by volcanic
eruptions, has one. Generation from geothermal sources is therefore
"site specific," meaning it's only possible in a few places
under unique geologic conditions. One such site in California, called
The Geysers, can produce almost as much electricity as all the other
geothermal sites combined.
Geothermal energy can be used as an efficient heat source in small
end-use applications such as greenhouses, but the consumers have to
be located close to the source of heat. The capital of Iceland, Reykjavik,
is heated mostly by geothermal energy.
 Geothermal
energy has a major environmental benefit because it offsets air pollution
that would have been produced if fossil fuels were the energy source.
Geothermal energy has a very minor impact on the soil - the few acres
used look like a small light-industry building complex. Since the slightly
cooler water is reinjected into the ground, there is only a minor impact,
except if there is a natural geyser field close by. For this reason,
tapping into the geothermal resources of Yellowstone National Park is
prohibited by Law.
Wind Energy -- Energy from Moving Air
What is wind?
Wind is air in motion. It is produced by the uneven heating of the
earth’s surface by the sun. Since the earth’s surface is
made of various land and water  formations,
it absorbs the sun’s radiation unevenly. When the sun is shining
during the day, the air over landmasses heats more quickly than the
air over water. The warm air over the land expands and rises, and the
heavier, cooler air over water moves in to take its place, creating
local winds. At night, the winds are reversed because the air cools
more rapidly over land than over water.
Similarly, the large atmospheric winds that circle the earth are created
because the surface air near the equator is warmed more by the sun than
the air over the North and South Poles. Wind is called a renewable energy
source because wind will continually be produced as long as the sun
shines on the earth. Today, wind energy is mainly used to generate electricity.
The History of Wind
Throughout history, people have harnessed the wind in many ways. Over
5,000 years ago, the ancient Egyptians used wind power to sail their
ships on the Nile River. Later, people built windmills to grind their
grain. The earliest known windmills were in Persia (Iran). These early
windmills looked like large paddle wheels.
Centuries later, the people of Holland improved the basic design of
the windmill. They gave it propeller-type blades made of fabric sails
and invented ways for it to change direction so that it could continually
face the wind. Windmills helped Holland become one of the world’s
most industrialized countries by the 17th century.
American colonists used windmills to grind wheat and corn, pump water,
and cut wood. As late as the 1920s, Americans used small windmills to
generate electricity in rural areas without electric service. When power
lines began to transport electricity to rural areas in the 1930s, local
windmills were used less and less, though they can still be seen on
some Western ranches.
The oil shortages of the 1970s changed the energy picture for the country
and the world. It created an environment more open to alternative energy
sources, paving the way for the re-entry of the windmill into the American
landscape to generate electricity.
Windmill Mechanics
Windmills work because they slow down the speed of the wind. The wind
flows over the airfoil shaped blades causing lift, like the effect on
airplane wings, causing them to turn. The blades are connected to a
drive shaft that turns an electric generator to produce electricity.
Wind Machines Today
Today’s wind machines are much more technologically advanced
than those early windmills. They still use blades to collect the wind’s
kinetic energy, but the blades are made of fiberglass or other high-strength
materials.
Modern wind machines are still wrestling with the problem of what to
do when the wind isn’t blowing. Large turbines are connected to
the utility power network—some other type of generator picks up
the load when there is no wind. Small turbines are sometimes connected
to diesel/electric generators or sometimes have a battery to store the
extra energy they collect when the wind is blowing hard.
Types of Windmills
Two types of wind machines are commonly used today, the horizontal–axis
with blades like airplane propellers and the vertical–axis, which
looks like an egg-beater.
Horizontal-axis wind machines are more common because they use less
material per unit of electricity produced. About 95 percent of all wind
machines are horizontal-axis. A typical horizontal wind machine stands
as tall as a 20-story building and has three blades that span 200 feet
across. The largest wind machines in the world have blades longer than
a football field! Wind machines stand tall and wide to capture more
wind.
Vertical-axis wind machines make up just five percent of the wind machines
used today. The typical vertical wind machine stands 100 feet tall and
50 feet wide.
Each wind machine has its advantages and disadvantages. Horizontal-axis
machines need a way to keep the rotor facing the wind. This is done
with a tail on small machines. On large turbines, either the rotor is
located downwind of the tower to act like a weather vane, or a drive
motor is used. Vertical-axis machines can accept wind from any direction.
Both types of turbine rotors are turned by air flowing over their wing
shaped blades. Vertical-axis blades lose energy as they turn out of
the wind, while horizontal-axis blades work all the time. At many sites,
the wind increases higher above the ground, giving an advantage to tall
horizontal-axis turbines. The small tower and ground-mounted generators
on vertical-axis turbines make them cheaper and easier to maintain.
Wind Power Plants
Wind power plants, or wind farms as they are sometimes called, are
clusters of wind machines used to produce electricity. A wind farm usually
has dozens of wind machines scattered over a large area.
Unlike coal or nuclear plants, many wind plants are not owned by public
utility companies. Instead they are owned and operated by business people
who sell the electricity produced on the wind farm to electric utilities.
These private companies are known as Independent Power Producers.
Operating a wind power plant is not as simple as plunking down machines
on a grassy field. Wind plant owners must carefully plan where to locate
their machines. They must consider wind availability (how much the wind
blows), local weather conditions, proximity to electrical transmission
lines, and local zoning codes.
Wind plants also need a lot of land. One wind machine needs about two
acres of land to call its own. A wind power plant takes up hundreds
of acres. On the plus side, farmers can grow crops or graze cattle around
the machines once they have been installed.
After a plant has been built, there are still maintenance costs. In
some states, maintenance costs are offset by tax breaks given to power
plants that use renewable energy sources. The Public Utility Regulatory
Policies Act, or PURPA, also requires utility companies to purchase
electricity from independent power producers at rates that are fair
and non-discriminatory.
Wind Resources
Where is the best place to build a wind plant? There are many good
sites for wind plants in the United States including California, Alaska,
Hawaii, the Great Plains, and mountainous regions. Scientists say there
is enough wind in 37 states to produce electricity. An average wind
speed of 14 mph is needed to convert wind energy into electricity economically.
The average wind speed in the U.S. is 10 mph. Because of the availability
of consistent wind, some companies are considering installing wind machines
offshore. Scientists use an instrument called an anemometer to measure
how fast the wind is blowing. An anemometer looks like a modern-style
weather vane. It has three spokes with cups that spin on a revolving
wheel when the wind blows. It is hooked up to a meter that tells the
wind speed. A weather vane shows the direction of the wind, not the
speed.
As a rule, wind speed increases with altitude and over open areas with
no windbreaks. Good sites for wind plants are the tops of smooth, rounded
hills, open plains or shorelines, and mountain gaps that produce wind
funneling. The three biggest wind plants in California are located at
mountain gaps.
Wind speed varies throughout the country. It also varies from season
to season. In Tehachapi, California, the wind blows more from April
through October than it does in the winter. This is because of the extreme
heating of the Mojave Desert during the summer months. The hot air over
the desert rises, and the cooler, denser air above the Pacific Ocean
rushes through the Tehachapi mountain pass to take its place. In a state
like Montana, on the other hand, the wind blows more during the winter.
These seasonal variations are a good match for the electricity demands
of the regions. In California, people use more electricity during the
summer when air conditioners are used for cooling. Conversely, more
people use electricity in Montana during winter heating months.
Wind Production
How much energy can we get from the wind? There are two terms to describe
basic electricity production: efficiency and capacity factor.
Efficiency refers to how much useful energy (electricity, in this case)
we can get from an energy source. A 100 percent energy efficient machine
would change all the energy put into it into useful energy. It would
not waste any energy. There is no such thing as a 100 percent energy
efficient machine. Some energy is always lost or wasted when one form
of energy is converted to another. The lost energy is usually in the
form of heat, which dissipates into the air and cannot be used again
economically. How efficient are wind machines? Wind machines are just
as efficient as most other plants, such as coal plants. Wind machines
convert 30-40 percent of the wind’s kinetic energy into electricity.
A coal-fired power plant converts about 30-35 percent of the chemical
energy in coal into usable electricity.
Capacity refers to the capability of a power plant to produce electricity.
A power plant with a 100 percent capacity rating would run all day,
every day at full power. There would be no down time for repairs or
refueling, an impossible goal for any plant. Coal plants typically have
a 75 percent capacity rating since they can run day or night, during
any season of the year.
Wind power plants are different from power plants that burn fuel. Wind
plants depend on the availability of wind, as well as the speed of the
wind. Therefore, wind machines cannot operate 24 hours a day, 365 days
a year. A wind turbine at a typical wind farm operates 65-80 percent
of the time, but usually at less than full capacity, because the wind
speed is not at optimum levels. Therefore, its capacity factor is 30-35
percent. Economics also plays a large part in the capacity of wind machines.
Wind machines can be built that have much higher capacity factors, but
it is not economical to do so. The decision is based on electricity
output per dollar of investment.
One wind machine can produce 1.5 to 4.0 million kilowatt-hours (kWh)
of electricity a year. That is enough electricity for 150-400 homes
per year. In this country, wind machines produce 10 billion kWh of energy
a year. Wind energy provides about 0.1 percent of the nation’s
electricity, a very small amount. That is enough electricity to serve
a million households, as many as in a city the size of Chicago, Illinois.
California produces more electricity from the wind than any other state
followed by Texas, Minnesota and Iowa. Some 13,000 wind machines produce
more than one percent of California’s electricity. (This is about
half as much electricity as is produced by one nuclear power plant.)
In the next 15 years, wind machines could produce five percent of California’s
electricity.
Why is California out-producing every other state in developing wind
energy? More than any other reason, wind energy has taken off in this
state because of California’s state policies that support renewable
energy sources. Other states have just as good wind resources as California.
Ten years ago, the United States was the king of wind energy. The U.S.
produced 90 percent of the world’s wind-blown electricity. By
1996, that number had dropped to 30 percent. What happened to the wind
industry? Wind is the fastest growing energy technology in the world
today. In the last three years, wind capacity worldwide has more than
doubled. Experts expect the production from wind machines to triple
in the next few years. India and many European countries are planning
major new wind facilities. In the United States, however, wind capacity
grew very slowly in the 1990s. Many new wind projects were put on hold
because of electricity deregulation. Utilities were not sure how deregulation
would affect many new technologies. Would the government still encourage
utilities to invest in renewable energy projects? Would there be a market
for the energy produced? The answers to these questions are still not
known. Nevertheless, investment in wind energy is beginning to increase
because its cost has come down and the technology has improved. Wind
is now one of the most competitive sources for new generation.
Another hopeful sign for the wind industry is consumer demand for green
pricing. Many utilities around the country now allow customers to voluntarily
choose to pay more for electricity generated by renewable sources.
The wind industry is poised to make a comeback. New wind plants are
now operating or under construction in Washington, Oregon, Nevada, Montana,
Wyoming, Texas, Iowa, Kansas, and other states. The direction is changing
for wind energy in the U.S.
Wind Energy Economics
On the economic front, there is a lot of good news for wind energy.
First, a wind plant is far less expensive to construct than a conventional
energy plant. Wind plants can simply add wind machines as electricity
demand increases.
Second, the cost of producing electricity from the wind has dropped
dramatically in the last two decades. Electricity generated by the wind
cost 30 cents per kWh in 1975, but now costs less than five cents per
kWh. New turbines are lowering the cost even more.
Wind & the Environment
In the 1970s, oil shortages pushed the development of alternative energy
sources. In the 1990s, the push came from a renewed concern for the
environment in response to scientific studies indicating potential changes
to the global climate if the use of fossil fuels continues to increase.
Wind energy offers a viable, economical alternative to conventional
power plants in many areas of the country. Wind is a clean fuel; wind
farms produce no air or water pollution because no fuel is burned.
The most serious environmental drawbacks to wind machines may be their
negative effect on wild bird populations and the visual impact on the
landscape. To some, the glistening blades of windmills on the horizon
are an eyesore; to others, they’re a beautiful alternative to
conventional power plants.
Future of Wind
Wind Churner
With a blade that’s 144 feet in diameter, the Vestas V44-600
is the largest wind turbine in operation. Perched atop a 160-foot tower
west of Traverse City, Michigan, the turbine provides slightly less
than one percent of the Traverse City Light and Power Company’s
total output. But, that’s enough for about 200 residential customers.
These patrons, who get all their electricity from wind power, agreed
to pay about 20 percent more than other utility customers to support
the project. The turbine was built in Denmark. The blade tips pitch
to capture the most energy from the winds and the rotor and generator
speed can vary slightly to smooth out power fluctuations. In average
winds of 14 to 15 mph, the annual production from the wind turbine is
estimated at between 1.1 and 1.2 million kWh.
WARP
A different kind of system to convert wind energy into electricity
has been designed by an aeronautical engineer in Connecticut. Alfred
Weisbrich’s Wind Amplified Rotor Platform (WARP) has no blades;
instead, it looks like a stack of wheel rims. Each module has a pair
of turbines mounted to both of its concave surfaces. The concave surfaces
channel wind toward the turbines, amplifying wind speeds by 50 percent
or more. Weisbrich’s company, Eneco, plans to market the technology
to power offshore oil platforms and wireless telecommunications systems.
In the future, however, the Eneco design could be used by utilities
for major power generation. Huge WARP fields could be built with towers
hundreds of feet tall, each generating megawatts of electricity. Turbines
could even be integrated into buildings to provide power for the occupants.
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