One provision of PURPA is the requirement for increased use of energy cogeneration. The law forced electric utilities to buy power from other more efficient producers, such as cogeneration plants, if that cost was less than the utility's own "avoided cost" rate to the consumer; the avoided cost rate was the additional costs that the electric utility would incur if it generated the required power itself, or if available, could purchase its demand requirements from another source. At the time generally, where demand was growing, this "avoided cost" was considered to be the construction and fossil fuel costs incurred in the operation of another thermal power plant.