Write note on Energy storage. (7) Ans: Energy storage: - Large-scale storage of energy, which can be quickly converted to electrical form, can help fast changing loads. The options available are pumped storage, compressed air storage, heat storage, hydrogen storage and batteries. Pumped storage: - In areas where sufficient hydrogenation is not available, peak load may be handled by means of pumped storage. This consists of upper and lower reservoirs and reversible turbine-generator sets, which can also be used as motor –pump sets. The upper reservoir has enough storage for full load generations. Compressed air storage: - Compressed air can be stored in natural underground caverns or old mines. The energy stored equals the volume of air multiplied by pressure. At times of need, this air can be mixed with gas fuel to run a gas turbine. Heat storage:- Water with good specific and latent heat has been used. In generating stations, boilers can be kept ready on full steam for the turbine to pick up fast rising load. Boiler steam, when not in use can heat feed water for boilers in the station.Secondary batteries: - These have possible use in local fluctuating loads, electric vehicles and back up for wind and solar power. There are a number of batteries like lead acid cell, nickel cadmium cell and sodium sulphur cell.