The PURPA, passed in 1978, requires that all utilities in the United States must buy electricity from qualified independent power producers (IPPs) at the avoided cost of electricity generated by the utilities.
7. 1978年通过的《公共事业规章政策法》要求美国所有公用事业必须以各单位发电可避免成本，向合格的独立电力公司购电。