Complex sentence: Phase I will have a capacity of 300 MW, which will be sold to Pacific Gas & Electric Company, while Phase II will have a capacity of 250 MW, which will be sold to Southern California Edison.
Split into simpler sentences: Phase I will have a capacity of 300 MW, which will be sold to Pacific Gas & Electric Company. While Phase II will have a capacity of 250 MW, which will be sold to Southern California Edison.