A thing you can use which gets forgotten often in the conversation is “natural” / physical batteries, or better put stores of latent energy. Essentially, “push heavy thing up hill, make it come down later”.
I know little about it, but you can release the kinetic energy stored in heavy objects at higher altitudes basically whenever, using say a dynamo on the wheels of a wagon of heavy rocks you previously pushed uphill.
I mean, “economy” fundamentally is the allocation of limited resources, if something is limited at a point when it’s needed, then economical doesn’t sound like the wrong word to use? (I’m aware economical means cheap, BTW)