Existing storage is, by a very large margin, pumped hydro. Current hydro storage is mostly shared with hydro generation reservoirs, all of which encompass a watershed. New pumped hydro often uses just an elevated depression, dammed box canyon, or even a diked level spot -- no watershed needed -- and can bank sea water.
Storage as anhydrous ammonia or liquified hydrogen is attractive because tankage is cheap and transportable, and it can be burned in existing turbines or sold to other utilities or to industry as feedstock, fertilizer, or fuel. International shipping is has begun converting to ammonia fuel.
Storage as liquified nitrogen is similarly attractive. The production equipment is very mature tech. LN2 is boiled in ambient air to drive a turbine.
Underground compressed air is attractive because it is simple and cheap. Extraction is via turbines, optionally spiked with fuel.
Underground hydrogen is common because it is simple and slots into existing NG infrastructure.
Various underwater methods -- compressed air, evacuated-cavity, buoyancy -- are very cheap if the mechanical parts remain onshore.
Battery chemistries competing with lithium use cheaper, often heavier, sometimes less inflammable materials. Iron, molten metal, sodium-ion, "flow".
In all cases, the determiner of competitiveness is economics. It is far from clear which aspects will dominate, and which will end up cheapest in them. Batteries cost per max MWh stored. Some cost per max MW in or out, with cheap tankage. Some are very cheap to construct and add onto. Some produce saleable surplus. Round-trip efficiency is all over the map, and in some is improving fast. Round-trip efficiency doesn't matter like it did when top-line generation was costly.
One thing we know is that Energy Vault, a $2B market-cap property, will not be in the mix.
Storage as anhydrous ammonia or liquified hydrogen is attractive because tankage is cheap and transportable, and it can be burned in existing turbines or sold to other utilities or to industry as feedstock, fertilizer, or fuel. International shipping is has begun converting to ammonia fuel.
Storage as liquified nitrogen is similarly attractive. The production equipment is very mature tech. LN2 is boiled in ambient air to drive a turbine.
Underground compressed air is attractive because it is simple and cheap. Extraction is via turbines, optionally spiked with fuel.
Underground hydrogen is common because it is simple and slots into existing NG infrastructure.
Various underwater methods -- compressed air, evacuated-cavity, buoyancy -- are very cheap if the mechanical parts remain onshore.
Battery chemistries competing with lithium use cheaper, often heavier, sometimes less inflammable materials. Iron, molten metal, sodium-ion, "flow".
In all cases, the determiner of competitiveness is economics. It is far from clear which aspects will dominate, and which will end up cheapest in them. Batteries cost per max MWh stored. Some cost per max MW in or out, with cheap tankage. Some are very cheap to construct and add onto. Some produce saleable surplus. Round-trip efficiency is all over the map, and in some is improving fast. Round-trip efficiency doesn't matter like it did when top-line generation was costly.
One thing we know is that Energy Vault, a $2B market-cap property, will not be in the mix.