The RSPB has had a green energy scheme with Scottish and Southern Energy since 2000. It was one of the first, one of the best and one of the most successful green energy schemes around. But, the scheme closes on 31 March this year. I have moved my custom to another green energy provider.
I seem to remember that much of their initial boost to 'green energy' was from increased efficiency from existing hydro-electric schemes without drowning any new valleys - which is about as green as you can get.