Michael Wara, environmental law professor at Stanford University, talks with correspondent Daniel Goldstein about what people should expect when they sign up to buy renewable energy.

Wara says the electrons that come out of your power socket are the same as those used by people who aren't paying for renewable power. He says what you're paying for is a renewable energy certificate, or REC. They pay for the so-called "green attributes" in addition to the power that everyone pays for. Those REC's don't necessarily pay for construction of more wind farms or solar panels.

He believes oversight is an issue. He says companies that sell RECs are trying, but questions whether the RECs are properly accounted for. He says the onus is on consumers to make sure they know what they're actually buying. But he alleges companies are often selling the same RECs twice - once to the consumer and once to a compliance buyer, or a utility that has to comply with a renewable portfolio standard.

Wara says consumers should make sure they know where the REC is coming from - such as a wind farm or a biomass plant - and if that source actually counts as renewable energy in their part of the country. He says they also need to make sure the REC has actually been retired and is not sold twice.

He says there's very little government oversight over the different kinds of RECs people buy and some industry resistance to creating it. Consumers often don't know what they're getting when they sign up to buy renewable power, and that's where more government oversight could help.

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