In order to say that you're using renewable energy, you must purchase both physical electrons as well as 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 and hydroelectric plants, solar farms, landfill gas, 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 sourced onto the grid on their behalf.
Wind farms rely on the revenue from RECs 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.