So... (In the video) The, presumably, photovoltaic (electricity out) powers water pumps, how? Logic would seem to dictate electric motors.
There is something like 25% efficiency - World record being about 40% using
very expensive panels, impractical. More realistically probably 15% for commercial photovaltaic panels.
Solar generated heat to power a Stirling engine would, in theory, be vastly better, efficiency and cost-wise.
Interesting concept, using water pumped into air tanks to generate pressurized water to run turbines.
I don't think a conventional "free piston" Stirling (no connecting rods) would be capable of powering a mechanical water pump directly though. That would be a contradiction in terms, I think, probably.
Aside from all that. My point about "waste heat" from compressing air was that the heat of compression could be a direct energy resource in itself to power, or assist in powering, the Stirling engine being used to compress the air in the first place. So-called "bootstrapping".
I was thinking primarily in terms of transportation. Could such a water based pressure system be practical for a motor vehicle?
Many households with a private well, have similar air pressure tanks to temporarily store energy, so the pump does not have to run as frequently and smooth out the flow. Otherwise the pump goes on and off excessively.
I'm thinking that compressing air with water would not really eliminate the heat of compression. The water, having a very high heat capacity simply absorbs the heat. Where does that heat/energy go from there? The "up to" 81% efficiency seems dubious.
Storing the pressure tanks underground provides insulation and/or thermal mass, though the compressed air (in the video) is apparently, eventually stored above ground where it would be subject to heating and/or cooling, or both, depending on ambient temperature.
Just rambling, thinking out loud. A lot of food for thought.
My main point was that the heat of compression could be used as a resource, providing some of the heat to run the Stirling engine, rather than this heat being something to avoid or "overcome", how could it be used to advantage? Likewise in regard to the cold Exhaust produced in operating an air motor.
Compressed air systems generate a temperature differential, in essentially the same way as a vapor-compression heat pump. Compressing air generates heat. Decompressing air through an air motor or turbine produces very cold exhaust air.
Some system or arrangement should be able to make use of such a temperature differential generated by the compressed air system.
A Stirling/Compressed air power system would appear to be an ideal combination.
A system that included a large/heavy thermal mass, such as tanks of water, would probably not be practical in a system intended for personal autonomous transportation. Some mass public transport system perhaps.