Both of my nephews are working for a solar installation company called
Astrum (they are hiring!) and they have various financing packages, including a zero down installation, and you pay over time an amount that is about half of what you are currently paying for electricity.
There are several other companies out there doing the same thing; here in the USA and in England, too. Essentially, they lease your roof space, and you get the electricity for a very low rate. They pay for installation, and they get the carbon credit, because they can reduce the electricity they need to generate with carbon fueled plants.