My idea is to have different ways to store energy in Create.

Flywheel energy storage where you spin something up using power and then you can do the opposite to get power out later on.

Water pressure battery where you pump water up into a chamber with energy, then let it fall down again through a drain block to get power out.

Solid weight battery where you lift something heavy up and then let it down to generate energy.

Those are just some examples.

They could be set up to kick in whenever power below a set threshold stops generating or when the system is overstressed.

Some methods of power storage would be more or less efficient than others, but some release energy much quicker than others and so could be used as basically a capacitor for when short bursts of power are needed such as big occasional crafts or bulk smelting many items for a minute.

Very common suggestion.

While this is a common suggestion, I think the Flywheel idea in particular is brilliant- they were used (and even in some cases, still are used, I think) to store and release energy, and it would give another use to the Flywheel itself! It would also be neat to apply this to the furnace generator too, allowing the Flywheel to keep moving things a bit after the furnace stops generating.

This would also work really cool with the stress and RPM systems too, so instead of all/nothing power storage of most mods, as the Flywheel loses energy to friction it would slow down, slowing the RPM of anything pulling mechanical energy from it until eventually it stops.

If it has to be harder to store power, the system could require occasional re-lubrication with some kind of fluid to keep the flywheel storage efficient, perhaps using deployers to occasionally re-lubricate them (or just manually doing so).