“Performance of Water Compensated Compressed Air Energy Storage System”,

In a growing energy scenario, electric utility companies have to take into account new managing strategies. The increasing seasonal gap in energy demand, the penetration of stochastic sources (wind and sun) and of combined heat and power plants are making more and more difficult to schedule power production. Energy storage can balance supply and demand over different time scales, with technical and economical benefits. The two options for large size plants are pumped storage hydro and Compressed Air Energy Storage (CAES). In the present paper, a CAES plant both with and without water compensation, is considered. The time window is an entire year as there is a remarkable difference between the seasons. Indeed in winter and summer the price fluctuation amplitude can be profitably exploited while between seasons are less suitable in a storage perspective because of the relative flatness of the daily price pattern. The adopted strategy is based on two price thresholds: below the former, a single charging step is carried out at night, above the latter, one or more steps of electricity production are carried out at peak hours. Finally, amid the thresholds, the plant works as a mere gas turbine or is shut off. Of course the mere GT working is available only if turbo compressor and expander are consistent and this affects the performance of each machine during charge or discharge phases. The shape of the daily price pattern strongly impacts on the cash flow. The proposed model is applied to the present Italian scenario as the energy market, taxes and services are concerned. The water compensated plant attains a storage density nearly twice higher than without compensation.