3 ms·

I suspect the maximum stored energy for the compressed air solution is significantly higher. Not only can you store the energy required to lift the water to th

by audunw 2y ago

I suspect the maximum stored energy for the compressed air solution is significantly higher. Not only can you store the energy required to lift the water to the surface, but after all the water is lifted you can keep compressing the air in the closed reservoir to store even more energy. If you only used water you could of course build an open reservoir with more storage capacity instead. But maybe these will be built in areas where that’s not feasible. It’d take much more space on the surface, and you need to deal with evaporation.

usrusr 2y ago
I do wonder, regarding the hydrostor approach, if the stored energy (theoretical best, excluding all losses) is 2x the amount that would be stored if it was just the water head (mass x height), with air displacement served by an open connection to the surface, or if there can be more to it: Constant volume CAES would store energy without any water lift involved, and with water mediated constant pressure CAES the lifted water is added to the amount of energy contained in the "air spring". But that's balanced at equal force in the force x surface area x underground reservoir level system. My bird's eye view understanding suggests that it would come down to 2x the amount of energy stored in either (minus losses, of course) due to the balance. Is that the maximum energy a water-column mediated constant pressure A-CAES could hold, per water displacement volume x head height, or am I missing something? That 2x would surely be an improvement over conventional mineshaft pumped hydro, but it would also define a somewhat sobering limit to the amount of theoretical best case capacity. Minor but perhaps very relevant detail: afaik, or rather as far as I don't know, hydrostore aims at a shaft depth equivalent to a pressure either right below of where pure CO2 would liquefy, or right above where that happens (no idea about the boiling points of N2, O2 and all those other main components of ambient air). I think the target depth is not quite that deep, as in carefully avoiding the "transliquid" range (as in transonic).

by audunw 2y ago

usrusr 2y ago

I do wonder, regarding the hydrostor approach, if the stored energy (theoretical best, excluding all losses) is 2x the amount that would be stored if it was just the water head (mass x height), with air displacement served by an open connection to the surface, or if there can be more to it: Constant volume CAES would store energy without any water lift involved, and with water mediated constant pressure CAES the lifted water is added to the amount of energy contained in the "air spring". But that's balanced at equal force in the force x surface area x underground reservoir level system. My bird's eye view understanding suggests that it would come down to 2x the amount of energy stored in either (minus losses, of course) due to the balance. Is that the maximum energy a water-column mediated constant pressure A-CAES could hold, per water displacement volume x head height, or am I missing something? That 2x would surely be an improvement over conventional mineshaft pumped hydro, but it would also define a somewhat sobering limit to the amount of theoretical best case capacity. Minor but perhaps very relevant detail: afaik, or rather as far as I don't know, hydrostore aims at a shaft depth equivalent to a pressure either right below of where pure CO2 would liquefy, or right above where that happens (no idea about the boiling points of N2, O2 and all those other main components of ambient air). I think the target depth is not quite that deep, as in carefully avoiding the "transliquid" range (as in transonic).