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Quick theoretical question


Active Member
Doesn't efficiency depend upon how we define it? For example, I want to make a heater. Instead of using a resistive element, I attached a peltier to an infinite thermal source (let's say the crust of the earth). I put in 100W, but I get 200W (or some quantity >100W) of heat energy out of it on the 'hot' side of the pelt.

It's by no means 'free energy', but, practically and not in a physics sense, I am getting something for nothing, yes?


Obviously not, you're getting the heat from the earth. To save energy rather than doing the raw heating/cooling by brute force with an air condition some modern heating systems sink a large heat transfer coil a decent distance under the house where the ground temperature stays nearly constant all year long. The tubing goes into a compressor and acts as a heat pump pulling heat out of or putting it into the ground near the house. The ground itself maintains equilibrum with the surrounding area because of the sheer thermal mass of the ground. The energy used in the compressor is only a fraction of what is needed if a traditional heating or cooling source is used. I think they more predominatly used in areas with temperate climates beacuse the average ground temperature is important in effciency.


New Member
What you discribe is the prinsiple of a heat pump that takes the energie sorce form ground water

a heat pump is a reversed aircon in principle and takes the heat out of the water or air and put it in the hot water side in the mashine for further use

you have machines that require 5 KWH electrical energy but generate about 25 KW of thermal energy in the same hour

It's not a wonder machine it's only suking energy form a other form in an efficient way but there are still convertion losses



Active Member
Man, you guys totally missed the 'practically and not a physics sense'. I was simply making a point that practically speaking the additional heat energy is 'free' in a cost sense. I made A's in physics all the way through quantum mechanics and analytical chem, so I understand all manner of conservation laws.

You guys did confirm a bias I perceived on this forum: many are too quick to say 'still obeys laws of physics' and not pay attention to the practical matters of the situation. If someone were to come around and say 'hey let's burn gasoline in internal combustion engines' you guys would shoot it down for still being significantly less than 99.9% efficient, even though for the last 100 years it's been a kickass method of automotive locomotion. In that case I am getting something for nothing because the chemical energy was stored in the petrol long, long ago.
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Well-Known Member
Most Helpful Member
I think the phrase 'free energy' is what make people immediately think that the energy conservation laws are being broken.

I understand what you are saying and I agree, its the efficient release of stored energy. It could be coal or any of the fossil fuels.

It could be argued that wind turbines tap into the kinetic energy stored in the wind is 'free energy'.

For example in Iceland they use hot water produced by geothermal energy to centrally heat their buildings.

I think someone should come up with better definitions of 'free energy' and 'released energy'.
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Well-Known Member
If I may add my 2 bob's worth here :rolleyes:. The laws of physic's states theres no 'free lunch' with energy, For any given given power there will be a loss any anyone that states different is a crock :p. The term 'free energy' can be pointed towards 'renewable energy'. Take solar, wind, hydro - all have an input capital cost to setup and a payback time to recoup any captial outlay. After that payback time you could call anymore power gained as 'free renewable energy' I'll give a good example here, the total capital outlay for my shed array was just over $5,000. Since then i've done over $8,000 worth of work and any extra power goes into heating the hotwater for the house.:D

So in real terms do I have 'free energy' NO I DON'T what I have is 'free renewable energy'.

The end of the day you only get out what you put in and the intial outlay will determine when the switch over takes place.

Cheers Bryan :D

5 years off the Grid on Xmas day

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