I've come across this concept before. I think it might have been another post on the same site where they talk about direct mechanical use of hydro-power which

I've come across this concept before. I think it might have been another post on the same site where they talk about direct mechanical use of hydro-power which made me look further into it. I wonder what the efficiency of using direct hydro / wind power to power an air compressor (say rejecting the excess heat to preheat the hot water supply) and releasing the compressed air for air conditioning.