I believe high efficiency conversion of small temperature differences to energy would be a breakthrough technology.
Geothermal power is the first that springs to mind.
Although, the closer that you can get to that ideal, the better!
The real breakthrough would be a machine that can harvest power without a temperature gradient/delta, something that could take the vibration of molecules and convert it directly to electricity. Something like this...
https://www.youtube.com/watch?v=KiLTEjm8zLw
https://phys.org/news/2020-10-physicists-circuit-limitless-p...
"The idea of harvesting energy from graphene is controversial because it refutes physicist Richard Feynman's well-known assertion that the thermal motion of atoms, known as Brownian motion, cannot do work. Thibado's team found that at room temperature the thermal motion of graphene does in fact induce an alternating current (AC) in a circuit, an achievement thought to be impossible."
The crucial question here is: Can this alternating current do work?
But that heat isn’t free. It has to be produced somewhere. You must “consume” the heat to produce electricity.
If you tried to generate power in the way you postulated, you would ignore the 300% number and instead look at the conversion rate between the energy it takes to produce that heat and the energy output.
(I believe this to be accurate, but I am speaking far beyond my expertise and invite correction if I have erred.)
The real issue is such a thing at scale would functionally be a storm generator: you'd be pulling warmer air in the upper troposphere down to ground level, chilling it, and then releasing it.
Think of it as mining the air/water for heat energy and turning it to electricity. No one said energy is being made from nothing. This is not being touted as a solution to climate change.
To rephrase the idea, is the following equation possible:
heat pump running costs <= heat extracted x electricity generation efficiency
At a single human scale there is near infinite air/water heat energy to run through the device. But could you do it efficiently enough?
This is the closest thing I could find on short notice: https://www.pv-magazine.com/2021/08/19/the-worlds-hottest-he...
They're not, they're actually around 30-60% efficient like most other heat engines. It's just the thing they do is move heat so people characterise the 'output'/ work as efficiency when in reality the relevant factor is something like output / output_of_reverse_carnot_cycle.
A 100% efficient heat pump would produce exactly as much electricity putting the heat back where it started as it used in the first place.
No.
A heat pump moves heat from one pool to another and adds whatever input energy required to move the heat to the whole system.
When you have two pools at different temperatures you can harvest energy from that difference but only as much as is there because harvesting the energy involves bringing the two pools closer in temperature.
There is nothing you can do to cheat this, whatever you do will bring the two pools closer together. If you bring in outside energy you will always be able to harvest less than you brought in.