Almost every power plants produce Alternating current. It is not necessary that entire energy that they produced are consumed in real time. Does they have any option to store excess energy?
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.
The most effective way to store an AC energy is to rectify it and charge Li-Ion accumulators and then to convert it back to AC by electronic inverters.
The high efficiency is because of the high efficiency of the Li-Ion cells and the high efficiency of the switching mode inverters.
Unfortunately, this method has many other disadvantages. The main of them is that the Li-Ion accumulators are too expensive for the needed capacity.