Green Glossary

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Annual Consumption – Annual consumption refers to the amount of electricity used in one year and is typically measured in kilowatt-hours (kWh). This information is available on your electricity bill or by contacting your energy provider.

Anthropogenic – Caused by man or resulting from human activities. Used in the context of greenhouse gas emissions produced as a result of human activities.

Atmosphere – The gaseous envelope surrounding the Earth. The dry atmosphere consists almost entirely of nitrogen (78.1% volume mixing ratio) and oxygen (20.9% volume mixing ratio), together with a number of trace gases, such as argon (0.93% volume mixing ratio), helium, radiatively active greenhouse gases such as carbon dioxide (0.035% volume mixing ratio), and ozone. In addition the atmosphere contains water vapor, whose amount is highly variable but typically 1% volume mixing ratio. The atmosphere also contains clouds and aerosols.

Atmospheric Lifetime – The lifetime of a greenhouse gas refers to the approximate amount of time it would take for the anthropogenic increment to an atmospheric pollutant concentration to return to its natural level (assuming emissions cease) as a result of either being converted to another chemical compound or being taken out of the atmosphere via a sink. This time depends on the pollutant's sources and sinks as well as its reactivity. The lifetime of a pollutant is often considered in conjunction with the mixing of pollutants in the atmosphere; a long lifetime will allow the pollutant to mix throughout the atmosphere. Average lifetimes can vary from about a week (e.g., sulfate aerosols) to more than a century (e.g., chlorofluorocarbons [CFCs], carbon dioxide).

Carbon Dioxide – Carbon dioxide (CO2) is an atmospheric gas that is a major component of the carbon cycle. Although produced through natural processes, carbon dioxide is also released through human activities, such as the combustion of fossil fuels to produce electricity. Carbon dioxide is the predominate gas contributing to the greenhouse effect, and as such is known to contribute to climate change.

Carbon Intensity – The amount of carbon by weight emitted per unit of energy consumed. A common measure of carbon intensity is weight of carbon per British thermal unit (Btu) of energy. When there is only one fossil fuel under consideration, the carbon intensity and the emissions coefficient are identical. When there are several fuels, carbon intensity is based on their combined emissions coefficients weighted by their energy consumption levels.1

Certification and Verification – Refers to the certification and verification of green power products. See the Certified and Verified Products section of this Web site for more information.

Climate – Climate in a narrow sense is usually defined as the "average weather," or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands of years. The classical period is three decades, as defined by the World Meteorological Organization (WMO). These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.

Combined Heat and Power – Combined heat and power (CHP), also known as cogeneration, is an efficient, clean, and reliable approach to generating power and thermal energy from a single fuel source. CHP is not a specific technology but an application of technologies to meet an energy user's needs. CHP systems achieve typical effective electric efficiencies of 50 to 80 percent — a dramatic improvement over the average efficiency of separate heat and power. Since CHP is highly efficient, it reduces traditional air pollutants and carbon dioxide, the leading greenhouse gas associated with climate change. Visit EPA's Combined Heat and Power Partnership Web site for additional information

Commodity Electricity – Is physical electricity in the absence of the technological, environmental, social, and economic benefits associated with a specific generation source. These benefits are transferable over geographic distance through a tradable instrument called a renewable energy certificate (REC) and can be re-associated with the physical electricity at the point of use.

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 any particular community. Rates were set, and consumers had little choice but to pay that rate. In recent years, however, many states have restructured their electricity industry and are now allowing consumers to choose from among competing electricity suppliers.

In these states with 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 – Power that is produced from non-renewable fuels, such as coal, oil, natural gas, and nuclear. Conventional fuels are finite resources that cannot be replenished once they are extracted and used.

Distributed Generation – 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, an increasing number of customers will be able to choose from a range of electricity suppliers who market different types of power products, including green power. In states without restructured electricity markets, local utilities may offer green pricing programs that enable customers to elect to have their utility generate a portion of their power from renewable sources. 

Emissions – The release of a substance (usually a gas when referring to the subject of climate change) into the atmosphere.

Energy Efficiency – Refers to products or systems using less energy to do the same or better job than conventional products or systems. Energy efficiency saves energy, saves money on utility bills, and helps protect the environment by reducing the demand for electricity. When buying or replacing products or appliances for your home, look for the ENERGY STAR® label — the national symbol for energy efficiency. 

Executive Order 13423: Strengthening Federal Environmental, Energy and Transportation Management –Executive Order 13423 calls for Federal agencies sets goals in the areas of energy efficiency, acquisition, renewable energy, toxics reductions, recycling, sustainable buildings, electronics stewardship, fleets, and water conservation.

Fossil Fuels – Fossil fuels are the nation's principal source of electricity. Fossil fuels come in three major forms: coal, oil, and natural gas. Because fossil fuels are a finite resource and cannot be replenished once they are extracted and burned, they are not considered renewable.

Generation – The act of transforming energy into electricity.

Global Climate Change – Climate change refers to any significant change in measures of climate (such as temperature, precipitation, or wind) lasting for an extended period (decades or longer). Climate change may result from:

• Natural factors, such as changes in the sun's intensity or slow changes in the Earth's orbit around the sun
• Natural processes within the climate system (e.g. ,changes in ocean circulation)
• Human activities that change the atmosphere's composition (e.g., through burning fossil fuels) and the land surface (e.g., deforestation, reforestation, urbanization, desertification)

Global Warming Potential (GWP) – Global Warming Potential (GWP) is defined as the cumulative radiative forcing effects of a gas over a specified time horizon resulting from the emission of a unit mass of gas relative to a reference gas. The GWP-weighted emissions of direct greenhouse gases in the U.S. Inventory are presented in terms of equivalent emissions of carbon dioxide (CO2), using units of teragrams of carbon dioxide equivalents (Tg CO2 Eq.).

Conversion: Tg = 10^9 kg = 10^6 metric tons = 1 million metric tons

The molecular weight of carbon is 12, and the molecular weight of oxygen is 16; therefore, the molecular weight of CO2is 44 (i.e., 12+[16 x 2]), as compared to 12 for carbon alone. Thus, carbon comprises 12/44ths of carbon dioxide by weight.

Greenhouse Gases (GHGs) – Gases in the Earth's atmosphere that produce the greenhouse effect. Changes in the concentration of certain greenhouse gases, due to human activity such as fossil fuel burning, increase the risk of global climate change. Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, halogenated fluorocarbons, ozone, perfluorinated carbons, and hydro fluorocarbons.

Green Power – Renewable energy resources such as solar, wind, geothermal, biogas, biomass, and low-impact hydro generate green power. A green power resource produces electricity with no fossil-fuel based GHG emissions, has a superior environmental profile to conventional power generation, and must have been built after the beginning of the voluntary market (1/1/1997).

Green Power Marketers – Due to increased customer awareness of the environmental implications associated with conventional power generation, a growing number of utilities and other types of energy service providers have begun offering green power products. The term "green power marketers" usually refers to energy providers operating in states that permit retail competition in the electricity markets. In states that do not allow this retail competition, many utilities have begun offering green power options under what are typically referred to as green pricing programs. 

Green Power Product – Green power electricity products are supplied from renewable energy resources that provide the highest environmental benefit. Green power sold by regulated utilities is called green pricing, and when sold in competitive electric markets, green power is called green marketing.

Green Pricing – Some power companies are now providing an optional service, called green pricing, which allows customers to pay a small premium in exchange for electricity generated from green power resources. The premium covers the increased costs incurred by the power provider (i.e., the electric utility) when adding green power to its power generation mix. 

Green Power Purchasing – Green power can be purchased nationwide from several sources. Green power marketers offer green power products to consumers in deregulated markets, such as New Jersey, Pennsylvania, and New England. In states that do not allow retail competition in the electricity markets, many utilities offer green power products through green pricing programs. In addition, all customers nationwide have the opportunity to buy green power and stimulate the development of renewable generation sources through renewable energy certificates. Finally, customers can choose to install on-site generation, such as solar photovoltaics.

Hydroelectric Power (Large) – The process of generating electricity by harnessing the power of moving water is called hydroelectricity. Hydroelectric power (hydropower) is generated by forcing water that is flowing downstream, often from behind a dam, through a hydraulic turbine that is connected to a generator. The water exits the turbine and is returned to the stream or riverbed. Much of the hydroelectricity in the United States is generated at large facilities and in the Pacific Northwest, where it meets about two-thirds of the electricity demand. In the United States, hydroelectricity contributes about 10 percent of the total electricity supply.

Hydro (Small-scale) – In addition to very large hydroelectric plants in the West, the United States also has many smaller hydroelectric facilities. Like large plants, small-scale hydroelectric systems capture the energy in naturally flowing water and convert it to electricity. Although the potential for small hydroelectric systems depends on the availability of suitable water flow, these systems can provide cheap, clean, reliable electricity where the resource exists.

Kilowatt-hour – A kilowatt-hour (kWh) is a standard metric unit of measurement for electricity.

• One kilowatt-hour (kW) is equal to 1,000 watt-hours (Wh).
• A watt-hour is the amount of energy delivered at a rate of one watt (W) for a period of one hour.
• One watt is the amount of power rate of one joule of work per second of time.
• Example: A 100 watt light bulb in use for 10 hours uses 1000 watt-hours, or 1 kilowatt of electricity. (100 watts x 10 hours = 1000 watt-hours = 1 kWh)

Megawatt-hour – A megawatt-hour (MWh) is equal to 1,000 kWh.

Methane (CH4) – A hydrocarbon that is a greenhouse gas with a global warming potential most recently estimated at 23 times that of carbon dioxide (CO2). Methane is produced through anaerobic (without oxygen) decomposition of waste in landfills, animal digestion, decomposition of animal wastes, production and distribution of natural gas and petroleum, coal production, and incomplete fossil fuel combustion. The global warming potential (GWP) is from the Intergovernmental Panel on Climate Change's (IPCC's) Third Assessment Report (TAR).

Metric Ton – Common international measurement for the quantity of greenhouse gas emissions. A metric ton is equal to 2205 lbs or 1.1 short tons.

Net Metering – A method of crediting customers for electricity that the customer generates on site in excess of their own electricity consumption. Customers with their own generation offset the electricity they would have purchased from their utility. If such customers generate more than they use in a billing period, their electric meter turns backwards to indicate their net excess generation. Depending on 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" Renewables – The voluntary green power market came into existence in the late 1990's. January 1, 1997 is considered a definitive point in time when green power facilities could be adequately identified as having been developed to serve the green power marketplace. Green power facilities placed into service after January 1, 1997 are said to produce "new" renewable energy. The "new" criterion addresses the additionality requirement for the voluntary market.

Nitrogen Oxides (NOX) – Gases consisting of one molecule of nitrogen and varying numbers of oxygen molecules. Nitrogen oxides are produced in the emissions of vehicle exhausts and from power stations. In the atmosphere, nitrogen oxides can contribute to formation of photochemical ozone (smog), can impair visibility, and have health consequences; they are thus considered pollutants.

On-site Renewable Generation – Electricity generated by renewable resources using a system or device located at the site where the power is used. On-site generation is a form of distributed energy generation. For more information about distributed energy technologies that are renewable and non-renewable. 

Renewable Energy – The term renewable energy generally refers to electricity supplied from renewable energy sources, such as wind and solar power, geothermal, hydro power, and various forms of biomass. These energy sources are considered renewable sources because their fuel sources are continuously replenished.

Renewable Energy Resources – See Green Power Market section of this Web site.

Renewable Energy Certificates (RECs) – Also known as green tags, green energy certificates, or tradable renewable certificates. RECs represent the technology and environmental attributes of electricity generated from renewable sources. RECs are usually sold in 1 megawatt-hour (MWh) units. A certificate can be sold separately from the underlying generic electricity with which it is associated. Once the REC is sold separately from the underlying electricity, the electricity is no longer considered renewable. RECs provide buyers flexibility to offset a percentage of their annual electricity use when green power products may not be available locally.

Renewable Portfolio Standard – The requirement that an electric power provider generate or purchase a specified percentage of the power it supplies/sells from renewable energy resources, and thereby guarantee a market for electricity generated from renewable energy resources.

Retail Competition – In states with retail competition, consumers have the opportunity to choose their energy provider and purchase products based on the price or on the source of power supplied to their home or business.

Short Ton – Common measurement for a ton in the United States. A short ton is equal to 2,000 lbs or 0.907 metric tons. See metric ton.

Sulfur Dioxide – High concentrations of sulfur dioxide affect breathing and may aggravate existing respiratory and cardiovascular disease. Sensitive populations include asthmatics, individuals with bronchitis or emphysema, children, and the elderly. Sulfur dioxide is also a primary contributor to acid rain, which causes acidification of lakes and streams and can damage trees, crops, historic buildings, and statues. In addition, sulfur compounds in the air contribute to visibility impairment in large parts of the country. This is especially noticeable in national parks. Sulfur dioxide is released primarily from burning fuels that contain sulfur (such as coal, oil, and diesel fuel). Stationary sources such as coal- and oil-fired power plants, steel mills, refineries, pulp and paper mills, and nonferrous smelters are the largest releasers.

Utility – A utility is a municipal or private business that provides electricity to the public and is subject to governmental regulation.

Vintage – A term that refers to the year that purchased green power was generated. 

Source: Energy Information Administration's Energy Glossary