This is the best renewable system I know of. Biodigesters take vegan kitchen scraps and turn them into liquid fertilizer and methane gas that 20 million Chinese families (and some American schools) use for cooking fuel and/or to power generators. For videos about Dr. T.H. Culhane and biodigesters at the University of Florida, visit:
https://www.youtube.com/watch?v=0Ld7rr9poaE
https://www.youtube.com/watch?v=TKpjP0jw2GY
https://www.youtube.com/watch?v=S76WeYESkQ4
https://www.youtube.com/watch?v=xBkK8vANe-4