It is the difference between input temperature and output temperature. It is what all engines run on.
Take a copper wire, put one end in a fire and the other end in a snow bank and electricity will flow.
The problem with these above ideas are that we are using a low grade heat or cold source. And that is exponentially harder then using say, gasoline which burns very hot and ambient air temperature.
Agreed. Just hoping that someday someone will be able to take the concept and harness it on a smaller scale for a single home or homestead
The reality is that there is energy all around us.
We will have free energy devices as soon as we will stop turning them to war.
Until then, there are many sources of energy around us.