If there's one biofuel that's truly an endless supply, it would have to be human poop. A waste treatment plant located in Orange County, California is producing hydrogen created from sewage. The Orange County Sanitation District claims it can make hydrogen cheaply by processing solid waste and feeding it to microbes that turn it into methane.

This will then be used to power fuel cells in the Hyundai Tuscon, which will be made available for leasing later this spring in a limited area around Los Angeles. The fuel will be pumped to local stations, making it possible for Hyundai to put its car on the streets. Right now, there are only about 10 hydrogen fuel pumps in the entire state, and most are supplied with hydrogen that’s made from natural gas.