Is there any option to store AC voltage?
Does they have any option to store excess energy?


"Excess energy" is typically stored in pumped-water hydroelectric reservoirs. This is used for 99% of world bulk storage capacity and may be up to 87% efficient. Ref

Balancing (and smoothing) supply and demand is one of the reasons for large-scale (national) power-grids.

Being able to rapidly increase or decrease supply is one of the reasons for using gas-powered and hydroelectric generators instead of wind/solar/tidal powered generators.


  Is there any option to store AC voltage?


That's a kinda strange way to think of things. You could write the AC voltage down on a piece of paper and store that. :-)

As you said, the storable output of power plants is energy, not voltage. Outside cryogenic research labs, this is done by converting the energy to some non-electrical form.



On a household scale, off-grid. I believe you'd typically store excess generator output (solar, wind) as chemical energy in a large, heavy and expensive bank of lead-acid batteries, or maybe as thermal energy (heat) in a large body of water. Obviously you'd have to rectify any AC to DC in the former case.

If your household is on-grid and has it's own (non-fossil fueled) generating capacity, you'd typically "store" your surplus in the grid. This can be financially super-efficient as some nations pay you more to deposit your energy than they charge you to withdraw it.