Short answers, pulled from the story.
A renewable portfolio standard is a regulation that requires increased production of energy from renewable sources such as wind, solar, biomass, and geothermal power. It is also known as the Renewable Electricity Standard at the U.S. federal level and as the Renewables Obligation in the United Kingdom.
California Senate Bill 350, passed in October 2015, requires retail sellers and publicly owned utilities to procure 50 percent of their electricity from eligible renewable energy resources by 2030.
Certified renewable energy generators earn a certificate for every unit of electricity they produce and sell that certificate along with the electricity to supply companies. Supply companies then pass the certificates to a regulatory body to demonstrate compliance with their obligation.
RPS-type mechanisms have been adopted in the United Kingdom, Italy, Poland, Sweden, Belgium, and Chile, as well as in 29 of the 50 U.S. states and the District of Columbia.
The UK's Renewables Obligation required 11.1 percent of electricity from renewable sources in 2010/11, or 4.0 percent in Northern Ireland. It started at 3 percent in the 2002/03 period and was set to rise to 15.4 percent by 2015/16, with the scheme running until 2037.
The Lawrence Berkeley National Laboratory credits RPS requirements with 60 percent of the total increase in American renewable electricity generation since 2000. It also reports that RPS programs' share of annual American renewables builds fell from 71 percent in 2013 to 46 percent in 2015.