There was a gentleman who offered to make me a partner in a startup business venture a long time ago - he was rigging Ford Pinto engines to run on natural gas and adapting them to a generator. He would set them up on a stand in your backyard, and encase them for noise.
The heat from the engine went into your swimming pool, spa and/or house. The electricity went to run your house, but excess energy was sold back to the utility.
It was called "Cogeneration," because the excess jiuce was a side effect of using the engine to heat pool spa and house.
It wouldn't work without the pool: there was simply too much heat produced by the little engine - it would keep just about any home at sauna temperatures. But he was convinced that these units would make enough extra juice to pay for themselves and offset some of the natural gas used to run them. Plus you could run the pool and spa both at 104 if you wanted to.
Anybody know of anyone doing this? I passed on the opportunity and always wondered if I missed anything.