[dredmorbius]

An alternative to storage is dispatchable demand. This would require high-load activities or uses which can be rapidly cycled.

Storage batteries, pumped storage, and CAES are examples of this, though simple raw thermal banking (hot water heating, typically) is an excellent way to suck up excess Joules or GWh.

1 GWh is roughly the energy required to heat a pool of water 1 hectare * 1 m by 86 degrees Celsius. This scales to multiple GWh by increasing area, depth, or both. Conversion to steam is also possible, though that requires more engineering (pressure is A Thing). Substrates such as molten salt have a lower heat capacity per unit mass, but can be heated to far greater temperatures.

Storage at the scale of entire US generating capacity for multiple weeks using molten salt thermal storage, even accounting for Carnot cycle efficiency losses (about 20-50% depending on specifics, 30% is a good ballpark) is actually a tractable-scale concept. Existing petroleum storage facilities are roughly comperable in size, though molten salt would require somewhat more robust facilities and insulation.

Whilst it doesn't have the net efficiencies of pumped hydro (exceeding 90% round-trip storage efficiency), pumped hydro lacks sufficient developable sites, and has significant environmental impacts.