Today the energy sources used to create electricity differ in many ways, including in their environmental impacts. In the United States, conventional means of electricity generation use fossil or nuclear fuels--forms of power generation that impact human health and the environment through air emissions and other effects. Despite advances in pollution controls over the last 30 years, conventional power generation is still the nation's single largest source of industrial air pollution. Electricity markets are changing, however, offering cleaner ways of producing power and giving many consumers the ability to choose how their power is generated. One of these choices is power from renewable sources that is marketed as green power. Innovative organisations are encouraging the use of these new sources of green power and, at the same time, are reducing their own impact on the environment. In some parts of the United States, the deregulation of electricity has enabled consumers to choose the provider of their electric power and thus to buy green power from their chosen supplier. In regulated markets, too, hundreds of utilities now offer their customers the opportunity to purchase green power through green-pricing" programs. Even in areas where consumers cannot buy green power directly, renewable energy certificates (RECs) are available in every state to allow consumers to support green power. While no form of electric power generation is completely benign, electricity generated from renewable resources such as solar, wind, geothermal, small and low-impact hydro power, and biomass has proved to be environmentally preferable to electricity generated from conventional energy sources such as coal, oil, nuclear, and natural gas. The Guide to Purchasing Green Power focuses on electricity generated from renewable energy resources, both delivered through the grid and generated on-site. By buying green power instead of conventional power, consumers can reduce the environmental impact caused by their use of electricity and fossil fuel. For instance, on average, every kilowatt-hour (kWh) of renewable power avoids the emission of more than one pound of carbon dioxide. Because of the sheer quantities of energy involved, consumers of a large amount of electricity may have an enormous environmental impact. If the typical commercial facility switched to 100 percent renewable power or used RECs to offset emissions, this could amount to thousands of tons of emissions avoided each year. A wide range of organisations have purchased green power: federal, state, and local governments; universities; businesses; nonprofits; and individual consumers. By purchasing green power, these organisations are both helping the environment and meeting their own environmental goals. The many other benefits to buying green power range from financial benefits to public relations and even national security. As of the end of 2003, nearly 1,650 megawatts(MW) of new renewable generating capacity had been added to meet the United States' demand for green power. This capacity is enough to meet the annual electricity needs of more than 500,000 houses. Leading organisations are finding that green power is an effective part of a strategic energy management plan to achieve environmental, financial, and other goals. Successful energy management plans are often a "portfolio analysis" that considers options such as energy efficiency, load management, power purchases, on-site generation, and non-electric (thermal) energy needs. As with any investment portfolio, the best mix of these options depends on the particular situation. Because buying green power is still relatively uncommon in today's energy markets and because these markets offer a wide range of choices, this book provides leading-research for organisations that have decided to buy green power but want help in figuring out how to do it, as well as for organisations that are still considering the merits of buying green power.