In 29 states and the District of Columbia, renewable portfolio standard (RPS) policies require that utilities or load-serving entities include a certain percentage of renewable energy within their power generation mix; the percentages required and eligibility requirements vary among the states. Eligible renewable energy may either be purchased by load-serving entities to meet their RPS requirements, or may be bought by consumers or businesses wanting to buy renewable energy on a voluntary basis. However, green power certification programs and state RPS policy rules generally ensure that there is no double counting between the two markets (., that the same kilowatt-hour.
