A third party will pay to put a system on your facility's roof. They will then sell that company solar energy at a discounted rate. The more power produced, the more you save. The accounting is the same. You have two electric bills (the utility always provides power that can't be offset by solar). This is an excellent option if the company has cash flow concerns, but you still want to reduce your energy spending. This can generally mean an annual energy cost savings in the 20% range.