I've been with Arcadia for over 1 year. My local utility provider is locked in to contracts mandating coal powered electricity with little alternative. I emailed Arcadia a question about offsetting my consumption and received a response within the hour:
"We are purchasing wind energy in the form of renewable energy credits. Let me explain.
In order to say that you're using renewable energy, you must purchase both physical electrons as well the corresponding Renewable Energy Certificates (RECs). Those two things together are what make up renewable energy. If you were to sign up with us, your utility would be providing the physical electrons, and we would be providing the RECs.
When you buy RECs (or when we buy them on your behalf), you are taking ownership of wind energy that's being fed onto the grid. Once energy reaches the grid, it mixes together with the energy from coal plants, hydroelectric plants, solar farms, etc. Utility companies then pull indistinguishable electrons off the grid and deliver them to homes and businesses. It is impossible to determine where the electrons came from - all consumers can do is ensure that wind energy is being fed onto the grid to match their personal consumption.
Wind farms rely on the revenue from RECs in order to offer their energy at a price that is competitive against fossil fuels. Anybody who says they're using renewable energy - even big companies like Google - are purchasing both physical electrons from the grid and RECs.
By purchasing RECs, you're increasing the demand for clean energy - which expands access and availability, helps the environment, and reduces our reliance on fossil fuels - without having to install and maintain your own equipment."
I do think their advertising is misleading, however, as in my case - I am still using and supporting dirty fossil fuels so it isn't exactly giving up one for another.