Can alternating current be stored?
Your question should read, "Can electrical energy be stored?", as 'power' is simply the rate of utilising energy. The answer is, in a sense, yes. Hydroelectric generation systems 'store' huge amounts of energy in reservoirs, which can then be converted into electrical energy upon demand. Some hydroelectric plants will actually pump water from a lower reservoir to an upper reservoir during periods of low demand so that the upper reservoir is refilled, ready to provide more energy on demand. Direct storage of very small amounts of energy can be achieved with capacitors, but the amount of energy stored is very low and not of much use other than for specific, low-energy, applications -certainly not enough for practical purposes. Finally, we could argue that batteries store electrical energy although, like hydroelectric dams, the energy is provided by the work done (in this case, by chemical reaction) by the battery rather than by 'storage'.