By Katherine Tweed, GreenTech Media.

The renewable portfolio standards that many states have enacted are responsible for 60 percent of the growth in non-hydro renewable energy generation, according to a new study from Lawrence Berkeley National Laboratory.

Most of the additional capacity to meet RPS requirements has come from wind, but in recent years, solar energy is gaining traction. Renewable portfolio standards call for a certain percentage of power generation to come from renewable resources, although what qualifies as renewable and which power generators have to meet the obligations varies by state.