i found this post hoping someone was thinking of a turnkey system that would work off ground (or well) water. not yet, is the answer. I was also worried about the “size” of the thermal reservoir and open loop vs closed loop. no idea what the answer is. as for the beach … here you go

http://hawaii.gov/dbedt/info/energy/renewable/otec

cheers

for example, allow heat to flow from ground water to air. tap that flow to produce electricity. use that electricity to run heat pump from ground water to heat your house.

the problem with such a scheme is the delta T between ground water and outside air may not be very large, and so the elec generation is not very efficient.

If you want the heat pump to heat the house AND run a sterling engine you would need to add extra electrical energy to the heat pump. Even this extra electrical energy you would be unable to recover fully through the sterling engine.

Even if you got the sterling engine for free you would reduce the effectivness of the whole system by connecting it. A sterling engine has nothing sensible to do alone with a heat pump. It is only attempting to reverse, what the heat pump just did. You would save more on the elctricity bill by turning down the heat pump a bit and disconnect the sterling engine. You are attempting to invent the eternity machine. It is againt fundemantal laws of physics. It cannot ever be.

I cannot explain it. I have to realise that. I really tried – sorry!

MicroCHP power generators run by burning gas. This is a Stirling engine that converts heat into electricity. If we were to replace the gas heat source with hot water and if you attached a Stirling engine that could convert 20% or higher then you would be producing a surplus. There are Stirling engines that have efficiencies as high as 30%.

The important part to remember, is that the goal isn’t to generate lots of electricity, but to heat your house with the ‘waste’ heat that is left over. We’re not trying to get rid of that heat, we want to use it to heat a house.

You’re right that for Stirling engines, the high temperature differentials will increase their efficiency. The source of the heat going in isn’t cold air or cold water, it’s very hot water produced by the heat pump.

You have to remember that such a furnace will be running more often when it is colder outside. So you couldn’t produce energy year round unless you didn’t mind heating your house during summer (or say heating your pool).

I’m not making this stuff up, you can find these details out here:
http://en.wikipedia.org/wiki/Sterling_engine
http://en.wikipedia.org/wiki/Heat_pump

Off course I do not dispute that with a heat pump you can heat a lot more for the same electricity becaue you cool the ground and use that thermal energy to heat the house. The factor for this is the COP. If it is 3, you get 3 watts of heat for every watt of electricity you spend on the heat pump. The COP varies with the working conditions of the heat pump. The smaller the temperatur diference between the cold liquid from the ground and the hot liquid or air leaving the heat pump, the better COP you get. Fot the sterling engine it is the other way around. The bigger the temperature difference the better the efficiency, so what is good for the heatpump is bad for the sterling engine.

The manufacturers are giving specs for their equipment under reasonably favourable working conditions. You cannot take the specified COP of a heat pumpe and calculate it up against the specified efficiency of the sterling engine.

Thermal energy likes to move from warm to cold. The sterling engine takes advantage of this desire and turn some of this thermal energy into electrical energy and the whole mix gets colder than it would have been without the sterling engine because the sterling engine took som energy. The heat pump is doing the opposite. It goes against the desire to mix into one common temperature. Instead it increases the diference in temprature. This, in contrary to the other process, costs electrical energy to run the heat pump and the average temperature af the whole thing becomes higher, because the heat pump added some electrical energy.

The sterling engine is essentially reversing the process of the heat pump and it can never take more energy out of it, than what was put into it without cooling the house down and heating up the ground.

Laws of thermodynamics will not allow you to “harvest” heat from a colder place and put it into a warmer one with a net gain of energy. This would be necesarry if the sterling engine should deliver at plus in electrical energy by reversing this same process again.

I can never work. It is difficult for me to explain. I hope you will understand what I mean.

Of course, you could spend a lot more than $30K for both by the time you pay for installation, but I don’t think my estimate for the equipment is that far off. Plus, who knows if it would work? I’m just suggesting the possibility that it might.