Once upon a time I read about a magnetohydrodynamic (MHD) generating plant that was built in the Soviet Union.
A MHD generator generates electricity directly from a flame. No engine, no boiler, no intermediate steps at all. Basically you have a couple of wire mesh grids in the path of a flame and you connect wires to these grids and you get electricity. Of course the grids are probably made of platinum or some other exotic substance, and the efficiency is not all that great, but you can't make a simpler machine.
I think a small generator like this would be a great power source for all sorts of remote locations, like our monitoring sites. It would also be great for campers and explorers, anyone who wants electricity where there isn't any other supply. Batteries, as demonstrated by our rooftop station this weekend, go bad.
I was thinking that one should be able to build a miniature MHD generator that would run on propane. Use it to generate electricity in remote locations to run radios. No batteries needed. As long as you have fuel, you have juice. Sell it to backpackers. Use it anyplace where you need a small amount of power, and you don't have, or don't want wires, and you don't want a big noisy generator set. I'm sure there would be a market for it if it could be built.
2 months ago