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Old 09-25-17, 08:40 PM   #14
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Quote:
Originally Posted by ecomodded View Post
Has to be / must be a way to turn that heat into mechanical energy to run a generator
The Stirling cycle is the first thing that comes to mind, but in the traditional models, it would require too much of a ▲T gradient for this type of heat source.

Perhaps more applicable to the "slow burn" of compost heat is a large, slow apparatus.

Allow the mound to expand air in a chamber which pushes a small piston to pump water into a tower, or to a drum/tank on a hill. When the piston reaches the end of it's pump stroke the heating chamber is exhausted by the returning piston driven back by weight of the inlet water column. Next, a small volume of cool air is drawn back in to expand again as it is heated.

Essentially this is a simple piston pump (air-over hydraulic) which stores mechanical potential in a water tower. Just dump some of that stored water over a water-wheel to turn a generator when power is needed.

That method disconnects the short high-demand delivery of power from the slow and steady supply. Hydraulic storage of this type is fairly efficient, and if the thermal air-expansion system (a diaphragm, bellows or piston assembly) is buried in the mound and free of pressure-leaks, it should be relatively efficient and long lived too.

This kind of system could be made from common plumbing parts and other hardware-store items. A crankshaft is not necessary if a savvy designer uses linear piston valves, etc. Of course, a natural source of water must be close at hand and some form of elevation change (a hill, a tower, a roof-top vessel) must be nearby too.
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