There are a few companies currently offering to install solar PV on your roof at no cost to you if you have a large enough(~300m2) south facing one. They own the panels & maintain them & recoup the ~£800 per annum government subsidy for 25 years. All you get out of it is home use of the electricity generated (any revenue generated from any that is exported goes to the company) and the panels become yours after 25 years (efficiency may have diminished a bit by then, but generally solar PV is reliable for a very long time. Effectively you are renting out your roof space for a little free electricity (remember you may not be there to use it if you work away from home). Worth a thought if you can't afford to install your own or don't want the hassle of maintaining them.
More details here