What powers Doc Brown’s DeLorean by 2015 in "Back to the Future Part II"?

We get our first look at the answer at the end of "Back to the Future" when Doc returns from 2015 and casually tosses banana peels, beer, and other household trash into his "Mr. Fusion Home Energy Reactor." This nifty little device converts garbage into power for the time machine's flux capacitor and time circuits, which means the future solved the energy and waste disposal problems at the same time. Mr. Fusion completely replaces the plutonium reactor, so Doc no longer has to dodge Libyan terrorists every time he wants to take a trip through time. The prop was built from a Krups coffee grinder and served as a parody of the popular Mr. Coffee line of appliances. However, Mr. Fusion only handles the electrical power needed for time travel, while the DeLorean still runs on regular gasoline for driving around. But that's a problem for "Back to the Future Part III."