[allenz]

Google's report from 2013, cited from their blog, says that they resell electricity at a "slight net loss".[1]

I didn't compare to buying RECs. The point is that Google is 100% renewable voluntarily. While RECs may be worth some tax credits, it's obviously a net cost or else Facebook would also be 100% renewable.

That said, I'm fairly confident that Google's approach is more costly than just buying RECs because demand for RECs is not very high. Google doesn't buy RECs directly because they want stronger guarantees of additionality:

"Buying a few years’ worth of RECs from a renewable project does not provide the stable and sizable cash stream that a renewable project developer needs to get financing to build new green power projects. In a PPA [power purchasing agreement], Google is agreeing to buy all the power from a project for many years. Google has, in effect, totally accepted the power price risk that the project owner would otherwise face—instead of taking the risk of selling into the power market on a short-term basis, Google is providing the seller with a guaranteed revenue stream for 20 years. This is something the developer can literally take to the bank. If we were to buy only the RECs, this would represent a fraction of the value of a typical power project,5 and would still leave the renewable developer to face the market risks of future energy prices, making it much harder for them to obtain financing for projects.

[1] http://static.googleusercontent.com/external_content/untrust...