You've probably heard of an internal combustion engine, like what power cars and airplanes. Well there's such a thing as an external combustion engine - a steam engine. A steam engine just needs some source of high pressure steam, the source of heat you find to boil the necessary water is almost a separate problem. You could use a wood fire, a coal fire, an oil fire, a natural gas fire. I've seen a small steam engine that runs on a tea candle. Heat from a geothermal vent, concentrated sunlight, or nuclear power.

How about a diesel engine? Large oceangoing vessels with 2-stroke diesel engines the size of a duplex put out a lot of waste heat, plenty enough to boil water and run a steam turbine engine. The diesel engine provides main propulsion, the steam engine powered by its exhaust provides electricity. Ships with such a system can shut down their aux engines while underway saving tons of fuel per voyage.