I currently get my electricity from an electric company. I would like to get a windmill installed on my roof to supplement my electricity needs. I want to be able to use the windmill to get as much free electricity as I can, and I would like to continue to keep getting the rest of the electricity I need from the electric company. I live in a townhouse. After I get a windmill installed on my roof, how do I make it so that I can get electricity from my windmill as a supplement to the electricity I get from the electric company?