Renewable energy is derived
from natural processes that are replenished constantly. In its various
forms, it derives directly from the sun, or from heat generated deep
within the earth. Included in the definition is electricity and heat
generated from solar, wind, ocean, hydropower, biomass, geothermal
resources, and biofuels and hydrogen derived from renewable resources.
The five renewable sources
used most often are:
Biomass —
We have used biomass
energy, or "bioenergy"—the energy from plants and plant-derived
materials ,since people began burning wood to cook food and keep warm.
Wood is still the largest biomass energy resource today, but other
sources of biomass can also be used. These include food crops, grassy
and woody plants, residues from agriculture or forestry, oil-rich
algae, and the organic component of municipal and industrial wastes.
Even the fumes from landfills (which are methane, a natural gas) can
be used as a biomass energy source.
Benefits of Using
Biomass
Biomass can be used for fuels, power production, and products that
would otherwise be made from fossil fuels. In such scenarios, biomass
can provide an array of benefits. For example:
•The use of biomass
energy has the potential to greatly reduce greenhouse gas emissions.
Burning biomass releases about the same amount of carbon dioxide as
burning fossil fuels. However, fossil fuels release carbon dioxide
captured by photosynthesis millions of years ago—an essentially "new"
greenhouse gas. Biomass, on the other hand, releases carbon dioxide
that is largely balanced by the carbon dioxide captured in its own
growth (depending how much energy was used to grow, harvest, and
process the fuel).
•The use of biomass can
reduce dependence on oil because biofuels are the only renewable
liquid transportation fuels available.
• The main biomass
feedstocks for power are paper mill residue, lumber mill scrap, and
municipal waste. For biomass fuels, the most common feedstocks used
today are corn grain (for ethanol) and soybeans (for biodiesel). In
the near future—and with NREL-developed technology—agricultural
residues such as corn stover (the stalks, leaves, and husks of the
plant) and wheat straw will also be used. Long-term plans include
growing and using dedicated energy crops, such as fast-growing trees
and grasses, and algae. These feedstocks can grow sustainably on land
that will not support intensive food crops.
Water
(hydropower)
Hydropower
is one of the oldest sources of energy. It was used thousands of years
ago to turn a paddle wheel for purposes such as grinding grain.Because
the source of hydroelectric power 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.
Geothermal
Many technologies have
been developed to take advantage of geothermal energy—the heat from
the earth. This heat can be drawn from several sources: hot water or
steam reservoirs deep in the earth that are accessed by drilling;
geothermal reservoirs located near the earth's surface, mostly located
in western states, Alaska, and Hawaii; and the shallow ground near the
Earth's surface that maintains a relatively constant temperature of
50°-60° F.
This variety of
geothermal resources allows them to be used on both large and small
scales. A utility can use the hot water and steam from reservoirs to
drive generators and produce electricity for its customers. Other
applications apply the heat produced from geothermal directly to
various uses in buildings, roads, agriculture, and industrial plants.
Still others use the heat directly from the ground to provide heating
and cooling in homes and other buildings.
Other geothermal
resources exist miles beneath the earth's surface in the hot rock and
magma there. In the future, these resources may also be useful as
sources of heat and energy.
Wind
We have been harnessing
the wind's energy for hundreds of years. From old Holland to farms in
the United States, windmills have been used for pumping water or
grinding grain. Today, the windmill's modern equivalent—a wind
turbine—can use the wind's energy to generate electricity.
How It Works
Wind turbines, like windmills, are mounted on a tower to capture the
most energy. At 100 feet (30 meters) or more aboveground, they can
take advantage of the faster and less turbulent wind. Turbines catch
the wind's energy with their propeller-like blades. Usually, two or
three blades are mounted on a shaft to form a rotor.
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
then pulls the blade toward it, causing the rotor to turn. 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
Solar
Solar is the Latin word
for sun—a powerful source of energy that can be used to heat, cool,
and light our homes and businesses. That's because more energy from
the sun falls on the earth in one hour than is used by everyone in the
world in one year. A variety of technologies convert sunlight to
usable energy for buildings. The most commonly used solar technologies
for homes and businesses are solar water heating, passive solar design
for space heating and cooling, and solar photovoltaics for
electricity.
Businesses and industry
also use these technologies to diversify their energy sources, improve
efficiency, and save money. Solar photovoltaic and concentrating solar
power technologies are also being used by developers and utilities to
produce electricity on a massive scale to power cities and small
towns.
credit: NOAA, U.S.
DOE, American Wind Energy Association, Bureau of Land Management, Sandia
National Labooratory, The British Wind Energy Association, The World Wind Energy
Association (WWEA), The University of Illinois
