Renewable Energy Glossary of Terms
[This glossary is a compilation of terms from the EPA Web site as well as the Guide to Purchasing Green Power, published by The Center for Resource-Solutions.]
Annual consumption. Annual consumption refers to the amount of electricity used by a consumer in one year and is typically measured in kilowatt-hours (kWh). This information can be acquired from your electricity bill or by contacting your energy provider.
Carbon dioxide. The burning of fossil fuels releases carbon that has been stored underground for millions of years into the atmosphere. During the combustion process, the carbon in these fossil fuels is transformed into carbon dioxide, the predominant gas contributing to the greenhouse effect. Increases in the emissions of carbon dioxide and other gases, such as methane, due to the burning of fossil fuels and other human endeavors, accelerate heat-trapping processes in the atmosphere, gradually raising average temperatures worldwide. Carbon dioxide is absorbed and released at nearly equal rates by natural processes on the earth, an equilibrium that is disrupted when large amounts of carbon dioxide are released into the atmosphere by human activities, such as the burning of fossil fuels.
Combined heat and power (CHP). Combined heat and power (CHP) is an electricity generation technology, also known as cogeneration, that recovers waste heat from the electric generation process to produce simultaneously other forms of useful energy, such as usable heat or steam. On average, two-thirds of the input energy used to make electricity is lost as waste heat. In contrast, CHP systems are capable of converting more than 70 percent of the fuel into usable energy.
Commodity electricity. Commodity electricity is generic electricity not associated with a particular power generation source.
Competitive markets. Until recently, most consumers received generation, transmission, and distribution services from one local utility company. As a regulated monopoly, the utility was given an exclusive franchise to provide electricity to consumers in a particular community. Rates were set, and consumers had little choice but to pay the rate for their area. In recent years, however, many states have restructured their electricity industry and are now allowing consumers to choose from among competing electricity suppliers. In states permitting retail competition, sellers of electricity obtain power by contracting with various generation sources and setting their own price. Consumers in these states have the opportunity to choose their energy provider and purchase products based on the price or type of power supplied to their home or business. Some consumers are exercising this choice and switching to accredited "green power" resources. In states that have not restructured their electricity markets, consumers interested in purchasing renewable energy now have the option to participate in green-pricing programs offered by their local utility.
Conventional power. Conventional power is power produced from nonrenewable fuels such as coal, oil, natural gas, and nuclear fuels. These fuels are a finite resource that cannot be replenished once they have been extracted and used.
Distributed generation. Distributed generation refers to small, modular, decentralized, grid-connected, or off-grid energy systems located in or near the place where energy is used.
Electricity supplier. As states restructure their electricity markets, more and more customers will be able to choose from a range of energy suppliers that market different types of power products, including green power from renewable energy. Restructured local utilities offer electricity products generated exclusively from renewable resources or, more frequently, electricity produced from a combination of fossil and renewable resources. In states without restructured electricity markets, local utilities may offer green-pricing programs, in which customers may elect to have their utility generate a portion of their power from renewable sources.
Energy efficiency. Energy efficiency refers to products or systems using less energy to do the same or a better job than conventional products or systems can. Energy efficiency saves energy, saves money on utility bills, and helps protect the environment by reducing the amount of electricity (and associated environmental impacts) that needs to be generated.
Fossil fuels. Fossil fuels are the United States' principal source of electricity. The popularity of these fuels is due largely to their low cost. Fossil fuels come in three main forms: coal, oil, and natural gas. All three were formed many hundreds of millions of years ago before the time of the dinosaurs, hence the name fossil fuels. Because fossil fuels are a finite resource and cannot be replenished once they have been extracted and burned, they are not considered renewable.
Global climate change. For most of human history, changes in the earth's climate resulted from natural causes that took place over thousands of years. But today, human activities are beginning to affect our climate in serious and immediate ways by rapidly adding greenhouse gases to the atmosphere. These gases trap heat close to the earth that would otherwise escape into space, intensifying a natural phenomenon called the greenhouse effect. Over the next century, scientists project that global temperatures will rise two to six degrees Fahrenheit as a result of rising concentrations of greenhouse gases. Scientists also believe that this rate of global warming will be unprecedented compared with that of the past 10,000 years. Global warming could result in a rise in sea levels, changes in patterns of precipitation, more variable weather, and many other consequences. These changes threaten our health, agriculture, water resources, forests, wildlife, and coastal areas. For more information on the science and impacts of global climate change, visit the EPA's Global Warming Web site (www.epa.gov/globalwarming).
Greenhouse effect. The greenhouse effect is produced as greenhouse gases allow incoming solar radiation to pass through the earth's atmosphere, while preventing part of the outgoing infrared radiation from the earth's surface and lower atmosphere from escaping into outer space. This process occurs naturally and has kept the earth's temperature about 59 degrees Fahrenheit warmer than it would otherwise be. Current life on the earth could not be sustained without the natural greenhouse effect.
Greenhouse gases (GHG). Gases in the earth's atmosphere produce the greenhouse effect. Changes in the concentration of certain greenhouse gases, due to human activities such as the burning of fossil fuels, increase the risk of global climate change. Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, halogenated fluorocarbons, ozone, perfluorinate carbons, and hydrofluorocarbons.
Green power. Electricity that is generated from renewable energy sources is often marketed as "green power," a term that implies a smaller environmental impact from electricity generation. The resources that qualify as green power vary depending on the state or organization.
Green power marketers. Energy suppliers operating in states that permit retail competition in the electricity markets are usually referred to as green power marketers. This term can also include utilities that offer green power options under what are typically referred to as green-pricing programs.
Green power products. Green power products refer to electricity generated exclusively from renewable resources or from a combination of fossil and renewable resources.
Green pricing. Green pricing is an optional service offered by regulated utilities to allow customers to support a greater level of utility investment in renewable energy by paying a premium on their electric bill. Usually green pricing is offered in areas that do not allow retail competition.
Interval meter. An interval meter is an electricity meter that measures a facility's energy usage in short increments (typically 15 minutes). These meters are useful for determining electricity demand patterns and participating in real-time pricing programs.
Kilowatt-hour (kWh). A kilowatt-hour is the basic unit for measuring the generation and consumption of electrical energy. A megawatt-hour (MWh) of electricity is equal to 1,000 kilowatt-hours. A kilowatt and a megawatt are units of generation capacity.
Low-impact hydropower. Low-impact hydropower is hydroelectric power generated with fewer environmental impacts, by meeting criteria such as minimum river flows, water quality, fish passage, and watershed protection. These hydropower facilities often operate in a "run of the river" mode, in which little or no water is stored in a reservoir.
Net metering. Net metering is a method of crediting customers for electricity that they generate on-site. Customers generating their own electricity offset what they would have purchased from their utility. If they generate more than they use in a billing period, their electric meter turns backward to indicate their net excess generation. Depending on the individual state or utility rules, the net excess generation may be credited to their account (in many cases at the retail price), carried over to a future billing period, or ignored.
New renewable generation. New renewable generation facilities are those built in the recent past or will be built to meet the growing market demand for green power. For Green-e certification, new generation must have come online since the late 1990s (depending on the region; see the Green-e Web site for more details).
On-site renewable generation. On-site renewable generation refers to electricity generated by renewable resources using a system or device located at the site where the power is used.
Peak demand. Peak demand is the maximum power consumption for a facility, measured over a short time period such as 15 minutes or an hour.
Power marketer. A power marketer is an entity that buys and sells power generated by others. A green power marketer is an electricity supplier that offers a green power product.
Renewable electricity. Renewable electricity is power generated from renewable resources and delivered through the power grid to end users.
Renewable energy certificate (REC). A renewable energy certificate (REC), also known as a green tag or tradable renewable certificate, represents the environmental, social, and other positive attributes of power generated by renewable resources. For example, RECs may represent the emissions avoided by renewable power generation compared with those of conventional sources. RECs can be purchased separately from electricity service.
Renewable energy resources. Renewable energy sources, such as wind, solar, geothermal, hydropower, and various forms of biomass, are continuously replenished on the earth. Some definitions also include municipal solid waste as a renewable resource.
Renewable portfolio standard (RPS). A renewable portfolio standard (RPS) is a regulatory mandate or target stating that a minimum percentage or amount of each electricity supplier's resource portfolio must come from renewable energy.
