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Physics, Astronomy & Cosmology / Re: Can a heat pump system generate electricity from temperatures over 0 Kelvin?
« on: 29/05/2018 14:27:55 »
I was thinking about this too - if we have a 400% efficient way of heating something, surely we can make a power generator?
Sadly as mentioned in other posts thermodynamics rules this out. The same thing that means your heat pump can be 400% efficient also means that your Stirling engine (or whatever you use to generate electricity from the heat) can only be 1/400% = 25% efficient. Multiply the two together and you'll get 1 (or less than one in the real world). ie you'll lose more energy than you put in.
Basically the hotter the input to your electric generator, the more efficient it is. But the hotter the output of the heat pump, the less efficient it is. The two will always cancel out.
If this could work, you could e.g. use the electricity output to make a flywheel go faster and faster. Eventually you'll cool the world and the universe down to 0K and concentrate all the energy of the universe in the flywheel (you've reversed the big bang!). The 2nd law of thermodynamics says that energy always spreads out, and this is the opposite, so it's impossible, no matter how you tweak your heat pumps or generators.
Sadly as mentioned in other posts thermodynamics rules this out. The same thing that means your heat pump can be 400% efficient also means that your Stirling engine (or whatever you use to generate electricity from the heat) can only be 1/400% = 25% efficient. Multiply the two together and you'll get 1 (or less than one in the real world). ie you'll lose more energy than you put in.
Basically the hotter the input to your electric generator, the more efficient it is. But the hotter the output of the heat pump, the less efficient it is. The two will always cancel out.
If this could work, you could e.g. use the electricity output to make a flywheel go faster and faster. Eventually you'll cool the world and the universe down to 0K and concentrate all the energy of the universe in the flywheel (you've reversed the big bang!). The 2nd law of thermodynamics says that energy always spreads out, and this is the opposite, so it's impossible, no matter how you tweak your heat pumps or generators.