An interesting technology long used in industrial/commercial settings that is coming to the home. "Combined heat and generation" units can replace your home furnace. A natural gas-powered generator produces electricity, and the waste heat is then piped through the home for heating purposes. Although the unit costs approximately $13,000, the cost savings in electricity can be substantial and helps to offset the higher initial cost. Excess electricity can be sold back to the utility company.

In cold climates where blizzards and ice storms can knock out the electric grid for days and weeks, a system like this would be a great benefit--well, assuming that natural gas was still being delivered. I would think that the technology could be adapted to use propane. Claimed efficiency is 90%! Wow, that's excellent! In comparison, the typical internal combustion engine is only, what, something like 30% efficient? The rest of the energy is wasted as heat.

Anyway, I read about this technology in this C/Net article.