Sterling engine generator
 

Anyone ever built one that uses the temp differential between the outside air and the relatively stable temps about 30" under ground?

I'm talking about a really big one that could function on temp differentials as little as 10* or so.

Another option would be, during the day, to focus solar rays on it using a fresnel lens to increase the temp difference, but MY personal idea here is to keep it operating day and night, summer and winter, powering a low-output generator.

Any ideas?

So, run it on the temp difference between underground & the surface at night, & then kick in the afterburners in the day when the sun comes out? I like it!!

That's basically the idea. The temp is relatively stable at 30" below the soil depth, and it's even moreso here because the water line is less than 3" below deck at one particular point.

The air temp, however, is basically never stable at 50* for any length of time here... it's almost always above (way) or below (somewhat).

Since the engine can work (I think) with either a positive or negative differential, I imagine (based on that) that it will work even if the air temp is below the ground temp, so the "changeover" period being as short as it is, could be overcome with a temp switch on the generator and a large flywheel to keep the motor spinning with no little resistance until it can produce power again (say, at a 5* temp difference).

Of course, to produce any power from such a small temp difference, it's going to have to be a physically massive version of the sterling motor (comparatively), but I've seen designs (for school projects and such) that produce as little as 1w at a temp differential of as little as .5*C (4*F).

I read-up a little on the sterling engine a few years ago (regarding a hare-brained ecomodding idea, actually), but don't really remember too much about it. Seems they are really inefficient without the "optimiser", or whatever they called the compound stage, or whatever...

Wouldn't it be wild if the below-ground temperature differential could be used to power the sterling engine, then the output of the sterling engine be used for a ground-coupled heat pump, again benefitting from the stable below ground temps for HVAC dutyfor a building?

The ecomodder idea was to somehow utilise the waste heat from a car with a sterling engine, hooked to ???? dunno - a generator - the wheels - something.

It has been done years ago with about a quarter of an acre of stainless steel pipe, it is the collector that has to be bigger with low temp differential. Parabolics would be simpler, molten salt storage and if you like a solar fridge for cold storage and a sterling engine. heat pump is another name, commercial sized ones are made to scavenge waste heat from industry to make power. zeolite and water seems promising too, peltier units, more ways to skin the cat. Not for lack of solutions are we in this bind...