Community
OpenEnergyMonitor

Generate electricity from surplus hot water

Imagine that I have a surplus of solar hot water that can’t accumulate on my apartment and cant install solar electrical panels.
So i’m thinking on installing a thermoelectrical generator.
Any one has any kind of information on this ?

If i use it in reverse and circulate hot water on the pipe would it produce useful electrical energy?

The link gives no indication of the operating principle, but my guess is it works on the Peltier Effect. What you want is a device that uses the related Seebeck Effect.

And these are readily available, and are called thermocouples. There are very common as a temperature sensor. I have one to go with my multimeter.

The bad news is, you get very little voltage out, though the current can be enough to be useful. A unit with many in series (sometimes called a thermopile) is used in gas central heating boilers - it works as a flame failure device and holds the gas valve energised while the pilot flame is present and heating the thermopile. If the flame goes out, the valve de-energises preventing an escape of gas.

So without even doing the maths, my guess is it would be impractical to extract enough power to be useful, given that the water is very low grade heat as compared to a flame.

Further readings just discovered that even though Peltier Efect is generating a temperature differential with electrical power and that the inverse is called Seebeck Effect, devices are specific and optimized for each effect.
Worst is that with current technology Seebeck Effect is massively inefficient (8%).

Any other ideas?

The problem you have is the heat from the hot water is ‘low grade’ - there’s not a big temperature differential between that and ambient, so it’s difficult to do anything useful with the heat.

In a moment of frivolity, I did think of an atmospheric engine (invented by Thomas Newcomen, in 1712) in which you’d draw air heated by the water into a cylinder and then cool it with a cold water spray, hence suck a piston down. I don’t think the efficiency of that would break any records either.

Wasn’t that the engine Mr. Watt is famous for making his improvements on?

It is. From memory, he more than doubled the efficiency.

We’ve got a statue of him and colleagues Matthew Boulton & William Murdoch.

1 Like

Always dangerous. From this, the figure is 5 times:

A Stirling engine perhaps? But I have only ever seen one as a toy on a mug of tea!