"Storage" can synthesize hydrocarbons, i.e. fuel, which can then be stored forever, until energy is needed.

This was already possible by the time of WWII, but now there are many methods in development for reducing carbon dioxide by electrolysis, and then use the product to synthesize longer hydrocarbons, which have higher efficiency than the older methods.

The round-trip efficiency of this will always be worse than for batteries, which remain a better option for short time storage, but synthesizing fuel will be a valid method for storing energy for the winter during the summer, and also for applications where batteries are unsuitable, like aircraft and spacecraft.

We can also do things like desalinate water and pump it uphill when solar is plentiful and prices are negative. No need to get hydrocarbons involved.

Creating fresh water and pumping it uphill to a reservoir that is uphill of a turbine would help solves two problems in Southern California.