Short answers, pulled from the story.
A renewable portfolio standard requires electricity supply companies to produce a defined fraction of their power from sources like wind, solar, biomass, and geothermal. Certified generators earn certificates for every unit of electricity they create and sell these documents alongside physical power to suppliers.
California Senate Bill 350 passed in October 2015 and requires retail sellers and publicly owned utilities to procure 50 percent of their electricity from eligible resources by 2030. This structure allows private markets to drive implementation while maintaining strict government oversight.
RPS-type mechanisms have been adopted across several countries including Italy, Poland, Sweden, Belgium, and Chile. Australia enacted the Renewable Energy (Electricity) Act 2000 to establish its framework while China adopted a renewable energy target in 2006 and modified it in 2009.
Since its introduction the Renewables Obligation has more than tripled the level of eligible renewable electricity generation. That figure rose from 1.8 percent of total UK supply to 7.0 percent in 2010 after being introduced in England and Wales in April 2002.
RPS requirements were responsible for 60 percent of the total increase in American renewable electricity generation since the year 2000 according to findings reported by the Lawrence Berkeley National Laboratory. Their share dropped from 71 percent of annual American renewables builds in 2013 to 46 percent just two years later in 2015.