What Is Green Power?
What Are Renewable Energy Resources?
Renewable energy resources are continuously replenished, and include
wind, solar, geothermal, low impact (or small) hydropower, biomass and
biogas. All of these resources reduce the environmental impact associated
with traditional power generation.
Currently, less than 2% of the nation’s energy supply is generated from
non-hydro renewable resources. The majority of our nation’s electricity is
generated from fossil fuels.
Current Fuel Mix for U.S. Electricity Generation
(Source: Data from U.S. EPA, eGRID, 2000.)
Renewable Energy Sources
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Wind
energy is produced using wind turbines that capture the
energy created by the blowing wind. Spinning wind turbine blades
connect to an electric generator, which in turn produces electricity.
Since the early 1980s, wind turbines have been steadily increasing
their electrical output while also decreasing their costs. The average
large-scale wind turbine now generates 1.5 MW of electricity, enough
to power over 450 homes for one year, more than 15 times the capacity
of wind turbines installed two decades ago. Wind power costs were
often higher than 30 cents per kilowatt-hour in the early 1980s, but
today they are often less than 5 cents per kilowatt-hour. As a result
of these advances, wind energy is one of the fastest growing and most
widely used renewable energy sources. Installed wind energy capacity
currently exceeds 6,300 MW, and more than 1,500 MW of wind power
serves the voluntary green power markets. Since 2000, nationwide
installed wind turbine capacity in the United States has more than
doubled.
Solar
power is produced using solar cells, also known as
photovoltaics. Photovoltaic cells can turn light (“photo”) energy into
electricity (“voltaics”). Like batteries, solar cells generate direct
current (DC) which is then converted to alternating current (AC) using
inverters. Solar cells can be used to generate electricity on-site at
facilities, and they are often mounted on rooftops.
Geothermal
energy is heat from underneath the Earth’s surface that can
be harnessed as steam, and the steam can be used to spin an electrical
generator to produce electricity. Most of the nation’s geothermal
electrical resources are located in the western part of the United
States.
Low-impact
(small) hydropower is created when the flow of water spins a
turbine in a setting that has reduced environmental impacts. Eligible
facilities meet criteria such as minimum impact on river flows, water
quality, fish passage, and watershed protection. In the absence of
information on these environmental criteria, a minimum generating
capacity (30MW) determines eligibility. Eligible hydropower facilities
often operate in a “run of the river” mode, in which little or no
water is stored behind a dam.
Biomass
is organic material that releases energy as heat when burned. Examples
of biomass fuels include wood, wood waste, straw, manure, and
agricultural crops. Most biomass power plants burn biomass fuels
directly to produce steam. This steam is usually captured by a
turbine, and a generator then converts it into electricity.
Biogas
(or methane) is produced when organic material (biomass) decays. This
gas can be captured at landfills and wastewater treatment plants and
then burned to generate electricity. Biogas can be used in a fuel cell
to generate electricity. Fuel cells are not renewable energy unless
they use a renewable fuel.