Contribution of Renewable Energy to the U.S. Energy Supply

Before the 1900s, the United States relied almost entirely on renewable energy resources. These included biomass (such as wood for heat in homes and industry and vegetation for feeding draft animals), water mills for grinding grain, and wind for pumping water and marine transportation. By the 1920s, however, coal and oil had largely displaced these energy sources in nearly all sectors of the economy, although wood for home heating and hydroelectric power generation remained in wide use. Today, our economy is still dominated by the use of fossil fuels. According to data collected by the U.S. Energy Information Administration (EIA), approximately 86% of the energy consumed in the United States in 2001 came from coal, oil, and natural gas. Renewable energy resources (hydroelectric, fuels from biomass, geothermal, wind, and solar) supplied about 6%, and 8% in the form of electricity came from nuclear power plants. Production of renewable energy in 2001 decreased overall relative to previous years mainly because low amounts of precipitation in the western states led to lower hydropower production. Over the prior 10 years, the average annual contribution of renewable energy to total U.S. energy consumption was 7.3%.

Renewable resources supply energy for heating and cooling buildings and electricity generation, heat for industrial processes, and fuels for transportation. Nearly all this renewable energy is produced from resources in the United States (a small amount is imported). These energy resources reduce the use of fossil fuels and resulting air pollution, and contribute to our nation's energy independence and economic and political security. The U.S. renewable energy industry exports a significant amount of their products, which helps to offset our nation's trade imbalance. The table below presents data from the EIA reports referenced below.

U.S. Energy Consumption and Electricity Generation, 2001

Note: values are rounded.
* A quad is quadrillion British Thermal Units (Btu), and is the equivalent of about 180 million barrels of crude oil.
** Bill. kWh = a billion kilowatt-hours; One kilowatt-hour (kWh) is the equivalent of running a 100 Watt light bulb for 10 hours.

Of the total U.S. energy consumption in 2001, about 72 quads were produced in the United States, and about 30 quads were imported (mainly petroleum, but also some natural gas, coal, and electricity produced from various sources). About 4 quads of coal, oil, natural gas, other petroleum products, and hydroelectricity were exported.

Of the total supplied from renewable resources, 42% was from conventional hydroelectric power, 50% was from biomass/biofuels, 5.5% was from geothermal, 1% was from solar energy, and about 1% was from wind energy.

The following is a discussion each of the major types of renewable energy resources and their relative contributions to the energy supply.

Hydropower

Hydropower uses flowing water to produce mechanical energy, which is then used to produce electricity. There was about 79,400 megawatts (MW; a MW is one million watts) of generating capacity at hydropower dams in the United States in 2001. Most of this capacity is at large dams built by the U.S. government and electric utilities. There are many small (less than 1 MW) facilities operating around the country. The total output of hydroelectric plants varies from year to year because of variations in precipitation. There are many dams in the United States that could potentially be developed for hydropower production.

Biomass

Biomass includes wood, municipal and manufacturing process waste, agricultural crops and residues, and human and livestock manure. It is used to heat homes and buildings, produce heat and electricity for industries and utilities, and fuel for motor vehicles. In 2001, 2.87 quads of energy were produced from biomass. This included: 2.17 quads from wood, wood-derived waste, municipal solid waste, manufacturing waste, refuse-derived fuel, and methane recovered from landfills and sewage treatment facilities; 0.45 quads of wood and wood derived waste for heating homes and commercial buildings, and 0.147 quads from liquid biofuels (such as ethanol) used for transportation fuels.

Wood biomass includes wood chips from forestry operations, residues from lumber, pulp/paper, and furniture mills, and cordwood for home heating. The largest single source of energy from wood is pulping liquor, or "black liquor," a residue of pulp, paper, and paperboard production. These industries use black liquor and other residues to cogenerate process heat and electricity to supply over 50% of their energy requirements. The lumber and wood products industry uses residues such as sawdust and bark for a significant part of total energy requirements.

Electricity from biomass is mainly generated from wood, wood derived waste, and municipal solid waste (MSW). There are currently hundreds of biomass-fired power plants in the United States, of which only about a dozen are owned by electric utilities. Most power generation from biomass is by independent, or non-utility, power producers, such as pulp and paper mills, which use the most of the power at the plant site. A small, but growing amount of wood is co-fired with coal in power plants. Most biomass power plants range from 10 to 25 MW in generation capacity. There are a few 40 to 50 MW capacity plants in operation. The size of biomass power plants is principally constrained by fuel supply/cost considerations. It is generally not cost effective to transport biomass more than 50 miles (97 kilometers) for power generation.

There are 102 municipal solid waste-to-energy (WTE) facilities in the United States, with the capacity to consume (burn) around 100,000 tons of waste per day, or about 15 percent of the country's municipal solid waste (MSW). These facilities have a combined electricity generation capacity of about 2,800 MW. There are also about 350 MSW landfills that recover "biogas" (composed of methane, carbon dioxide, and other gases that forms as waste decomposes) and use it for various purposes. About 150 use landfill methane to generate electricity. The rest burn it for heating buildings or greenhouses or to evaporate liquids that leach from the landfills. At least one landfill processes the methane for use as a vehicle fuel. There are also numerous municipal sewage treatment facilities that recover biogas, which they use to heat the anaerobic digesters (which produce the biogas) and for electricity production.

The EIA estimates that in 2001 the total electric power generation capacity from all biomass resources was about 10,000 MW and that approximately 60 billion kWh were produced.

The use of wood in the form of cordwood, wood chips, and wood waste (sawdust) derived fuel pellets for space and water heating in buildings during 2001 is estimated at 0.45 quads. The majority was consumed by the more than two million households using wood as a main heating fuel and many millions more using wood as a supplemental fuel.

The use of liquid biofuels for transportation has increased significantly over the past few years, largely due to the legislative mandates of the Clean Air Act and National Energy Policy Act. Most liquid biofuels are made from ethanol (grain alcohol), and nearly all the fuel ethanol in the United States is produced from corn. Research is underway to produce ethanol from other crops and non-food materials such as agricultural residues and MSW, including wastepaper. There is a small, but growing consumption of "biodiesel," a fuel made from grain oils and animal fats for use in diesel engines.

Most of the fuel ethanol that is produced is used as an oxygenate to reduce vehicle air pollution and as a gasoline "extender" in "gasohol," which is also known as E-10, a 10% ethanol - 90% gasoline fuel, or in ethanol-gasoline blends lower than E-10. A small amount of pure or "neat" ethanol, or blended fuels such as E-85 or E-95, are consumed. In 2001, total consumption of fuel ethanol was 0.147 quads, or approximately 2 billion gallons (7.6 billion liters). On an energy content basis, this was the equivalent of about 1.3 billion gallons (4.9 billion liters) of gasoline.

Geothermal Systems

Geothermal energy was the third most-used type of renewable energy in 2001. There are two broad types of geothermal energy systems. The first use geothermal energy sources (hot water or steam that is created deep beneath the surface of the earth) in power plants to produce electricity. These sources of heat are extracted by drilling into the earth, or are used at places where they come to the surface, such as hot springs and geysers. There is about 2,830 MW of electricity generating capacity at about 70 geothermal power plants in California (which has most of them), Nevada and Hawaii. In 2001, geothermal power plants generated approximately 13.8 billion kWh of electricity. From year to year, small amounts are imported.

A second application of geothermal energy is to use geothermal resources to directly heat buildings, greenhouses, aquaculture facilities, pools at resorts and spas, and in industrial processes. For example several commercial buildings in Elko, Nevada and San Bernardino, California, use geothermal hot water for district heating. In Klamath Falls, Oregon it is used to de-ice a steep section of roadway. There are over 100 "hot springs" or spa resorts in the United States.

Another type of geothermal energy is to use the temperature of the earth at depths down to 15 feet (5 meters), or of ground water, to operate heat pumps for space heating and cooling, and water heating in homes and buildings. These systems are often called "geothermal," or "ground-" or "water-source" heat pumps. There are about 500,000 geothermal heat pumps in the United States, and the number of installations is increasing by around 37,000 per year.

Solar Energy Systems

Solar energy systems use solar radiation for heating buildings and water; for producing high temperature steam for industrial process heat and to generate electricity; or to convert solar energy directly into electricity. The EIA estimates that in 2001 the total amount of energy supplied by these systems was 0.064 quads, and that nearly 500 million kWh of electricity were produced by solar power generating systems. The actual amounts are difficult to determine because the exact number of working solar systems is unknown, and the amount of solar radiation converted to useable energy varies at every installation. The three basic categories of solar systems are discussed below.

Solar Thermal Systems for Heating Buildings

Passive and active solar thermal energy systems make a valuable contribution to heating homes and businesses throughout the nation. Between 1975 and 1985, the use of solar energy in homes and businesses grew dramatically, largely because of Federal tax credits for the purchase of solar energy systems. In 1975, U.S. manufacturers shipped approximately 3.74 million square feet (ft2) [0.35 million square meters (m2)] of low and medium temperature solar collectors for installation in the United States. In 1985, the year the tax credits expired, an estimated 19 million ft2 (1.77 million m2) of collectors were shipped. In 1986, low and medium temperature collector shipments dropped to about 4.64 million ft2 (0.43 million m2).

In 2001, low and medium temperature solar thermal collector shipments for installation in the United States (mainly for pool heating, followed by domestic water heating) were about 10.4 million ft2 (0.97 m2). Assuming an average daily solar insolation of 1,500 Btu per ft2 (378 kilocalories per 0.09 m2) and an average system efficiency of 50%, and that all the systems were in operation for at least 60 percent of the days in the year (or 237 days), then these systems can supply about 1.84 trillion Btu of heat annually. The total amount of low and medium temperature solar collector area shipped between 1979 and 2001, excluding exports, was about 252 million ft2 (23.4 million m2).

There are also hundreds of thousands of homes and thousands of commercial and institutional buildings in the United States that incorporate passive solar features for thermal comfort and lighting. The contribution of these design elements to the energy requirements of these buildings is difficult to estimate.

Solar Thermal-Electric Power Plants

Heat from solar energy is also used to produce electricity. The Solar Electric Generating Systems (SEGS), located in the Mojave Desert at Harper Lake and Kramer Junction, California, are the largest solar power plants in the world. The SEGS consist of five operating hybrid solar thermal parabolic trough/natural gas turbine power plants. These power plants have a combined generation capacity of 354 MW (peak). The U.S. Department of Energy (DOE) and 12 electric utilities retrofitted the 10 MW Solar One Power Tower, a solar thermal central receiver pilot plant near Barstow, California. Solar One produced 35 billion kWh from 1984 to 1988. Solar Two began full power production in early 1996, and completed its testing in 1999. The plant has since stopped operation. While in operation, the plant generated 8.5 billion kWh. The DOE has also supported the development of parabolic dish-stirling engine systems up to 25 kilowatts capacity for utility and remote power applications.

Photovoltaic Systems

Photovoltaic systems (PV) are based on solar electric cells, which convert solar radiation directly to electricity. Individual solar cells are configured into modules of varying electricity-producing capacity. Modules are rated on their electricity generating capacity in peak Watts (Wp) at 1,000 watts per m2 (10.76 watts/ft 2) of solar radiation. PV applications range from powering watches and calculators to large installations with thousands of peak kilowatts generating capacity (KWp) for utility power. The largest number of systems are installed where utility power line extension or the use of fossil fuel generators are expensive or unfeasible, such as: remote communication facilities; rural homes, farms, and ranches; marine and railroad signaling devices; and highway sign, billboard, and parking lot lighting. The number of systems connected to electricity distribution and transmission systems is increasing. These types of systems range in size from systems of less than one to several kilowatts on houses, to systems over 100 kilowatts on large buildings or in large, "central station" arrays. The largest single "system" is being built by Tucson Electric Power near Springerville, Arizona. It now as a rated capacity of 2.4 MW from 22,276 PV panels spread out over 28 acres.

Shipments of PV modules have increased steadily since 1982, the first year that data was collected by the EIA. In 1982, a total of 6.99 MWp of generating capacity were shipped for installation in the United States. In 2001, shipments within the United States totaled 36.3 MWp. (About 10.2 MWp were imported and about 61.4 MWp were exported.) This was an 83% increase over shipments in 2000. The total capacity of PV cells and modules shipped for use in the USA since 1982 is at about 207 MWp. Assuming that 70 percent of these systems are in "the sun," in operating order, and producing at 100 percent of their nominal Wp ratings (however unlikely), and an average daily solar insolation for the entire country of 4.5 kWh (per square meter per day), then these systems could have potentially produced around 238 million kWh (of direct current electricity) in 2001. The availability of financial incentives for PV systems in California and a few other states has increased grid-connected systems on homes and large systems on commercial buildings.

Wind Energy Systems

Water-pumping windmills and small wind electric generators were at one time widely used throughout the western United States. The rural electrification programs of the 1930s and 1940s largely replaced the need for these systems. Starting in the late 70's and early 80's there was a resurgence in wind energy use. There are now thousands of turbines operating in the United States. The EIA estimates that in 2001 there was at least 4,100 MW of installed generating capacity (a 71 percent increase in installed capacity over 2000) and about 5.8 billion kWh of wind generated electricity produced. The majority of wind turbines are owned and operated by independent power producers that sell the electricity to utilities.

While California leads the nation with the most installed wind power capacity at about 1,800 MW, wind power projects are being developed all around the country. States with installed capacity over 100 MW are Texas with 1,100, Iowa with 423, Minnesota with 336, Washington with 228, Oregon with 218, Wyoming with 141, and Kansas with 114. (Source: American Wind Energy Association, 1/21/03). There are also thousands of small wind turbines with capacities of up to 10 kilowatt (KW) in use throughout the United States, for which reliable data on their output is unavailable.

Wind power production has nearly tripled in the past decade largely as a result of the availability, since 1994, of a federal tax credit of 1.5 cents per kiloWatt-hour (adjusted annually for inflation), the development of the so-called "green power" market, and the institution of renewable portfolio standards in several states (see discussion in The Future of Renewable Energy below).

Advances in wind turbine technology have brought the cost of wind energy down to $0.05/kWh and less in areas with favorable winds. The operating life of wind turbines is now 20 years, compared to 1-5 years before 1975. The average turbine capacity has also increased from less than 20 KW before 1975. Now most utility-scale turbines being installed are rated at least 650 KW. Turbines as large as 2 MW capacity are also available, with 6 MW turbines under development.

The Future for Renewable Energy

It is difficult to accurately forecast energy use because of the many technical, economic, and political factors that affect what types and how much energy is produced and consumed. The EIA expects continued growth in renewable energy use for the next 25 years, though the relative contribution will remain about the same. The rate of growth will depend on:

• Overall economic growth and resulting energy demand in the United States and the rest of the world
  
  
• Availability and price of fossil fuels, mainly oil and natural gas the political commitment of governments to address the issue of climate change from global warming attributed to fossil fuel combustion
  
  
• Changes in the U.S. electric utility industry that are underway in many states and which are proposed on a national level, and how the use of renewable energy resources are encouraged in individual states and nationally, such as the development of the "green power" market, the establishment of "renewable portfolio standards," and access to power transmission grids for new renewable energy projects
  
  
• Technical advances and cost reductions in renewable energy technologies, as well as fossil fuel and nuclear generation technologies
  
  
• Support for renewable energy by citizens (by buying renewable energy equipment or "green" renewable power) and the government (by continuing to support research and development of renewable energy technologies and providing financial incentives and support for renewable energy production).

While electricity produced from renewable energy is not new, it is being "repackaged" or marketed as "green power." Green power is electricity generated from renewable resources, but usually excludes power from large dams and waste-to-energy incinerators. This power is usually sold at a premium or higher price than electricity produced from fossil fuels, because it costs more to produce. There are over 300 electric utilities in 32 states now offering green power to their customers. Most of these programs sell power produced by wind and landfill gas to energy projects that were developed in the last 10 years.

A concept related to green power is the so-called renewable energy certificate or "green tag." A green tag is essentially equal to the extra cost of producing green power relative to electricity produced from fossil fuel (perhaps one to two cents per kWh). In a way it represents the value of avoiding air pollution or greenhouse gases from fossil fuel. A green power producer can sell green tags to anyone, and sell the actual green power produced at the price that other electricity is sold for. For example, a consumer in a state where green power is not available could purchase $100 worth of green tags from an organization or company that works with wind power producers in other states. The wind power is sold into the electricity grid at a price competitive or equal to the price of electricity from other sources in, so that the people who actually consume the electricity do not pay more for it. Thus the sale of the green tags helps to support wind power projects and provide consumers with "virtual" access to green power when they may not be able to purchase it directly. An expanding market for green tags will help support new renewable energy projects.

Renewable portfolio standards (or RPS) have been established in several states, and a national RPS has also been proposed. An RPS is a requirement that a specific amount or percentage of power generation come from renewable energy resources. The state governments in Arizona, California, Connecticut, Hawaii, Illinois, Iowa, Maine, Massachusetts, Minnesota, Nevada, New Jersey, New Mexico, Pennsylvania, Texas, and Wisconsin have established state RPS. Colorado, Florida and Minnesota have set an RPS for specific utilities. For example, the RPS in Texas led to the installation of most of the existing wind power capacity in that state. Individuals, companies, colleges, universities, and city, county, state, and federal government agencies are effectively setting their own RPS by installing renewable energy equipment on their property or buying green power.

Getting electricity from renewable energy projects to consumers is a very important factor that could affect the growth of renewable energy, especially wind power. While there are enormous wind energy resources around the country, many of the best wind resource areas are far from existing power lines or existing power lines are already at or near full capacity. So important issues that need to be addressed are who should pay for new power lines, how existing power line carrying capacity is shared, and how power line use is charged for.

There are many advantages of renewable energy that will help to maintain its place in our energy supply:

• There is a huge potential renewable energy resource—250 times total annual U.S. energy consumption.
  
  
• Advances in renewable energy technologies are reducing manufacturing costs and increasing system efficiency, thereby reducing the cost of energy.
  
  
• Negative environmental and health impacts of renewable energy use are much less than fossil fuels and nuclear power.
  
  
• Renewable energy technologies generate power at the point-of-use, allowing homeowners, businesses, and industry to produce their own power, or decrease the use of utility power.
  
  
• Solar water and space heating systems, solar electric systems, and geothermal heat pumps reduce peak power demands for electric utilities, and can avoid expensive distribution and transmission system upgrades to meet increasing electricity demand.
  
  
• There is strong support from the American public for renewable energy.

References

The above information was taken primarily from the following sources.

Annual Energy Outlook, Energy Information Administration, U.S. Department of Energy. A print version is available from U.S. Government Printing Office (see Source List below).

Annual Energy Review, Energy Information Administration, U.S. Department of Energy. A print version is available from U.S. Government Printing Office (see Source List below).

Database of State Incentives for Renewable Energy

GreenPower Network
U.S. Department of Energy

Renewable Energy Annual, Energy Information Administration, U.S. Department of Energy. Features the 1995 Renewable Energy Annual through the most current annual data available. Other renewable fuels publications are also featured.

For Additional Information

Information about renewable energy electricity generation facilities connected to electric transmission and distribution systems throughout the United States is contained in DOE's Renewable Electric Plant Information System (REPiS) database.

Source List

U.S. Government Printing Office (GPO)
Please contact the GPO for specific ordering information and shipping and handling charges that may apply.

This fact sheet was reviewed for accuracy in May 2003.

NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

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