By David Roberts, Vox.

Much has been made of the rapid rise of renewable energy in the US, but the policy workhorse behind it does not get nearly enough attention or credit.

I'm talking about the renewable portfolio standard (RPS): state laws that mandate a certain minimum amount of renewable energy in the electricity mix, rising over time.

Some 29 states and DC now have RPSs in place.

These standards were mostly passed in the late 1990s and 2000s, when (not coincidentally) Democrats had more power in state governments.