Hybrid power plant for energy storage and peak shaving by liquefied oxygen and natural gas

The increasing penetration of renewable energy sources in the electricity generation scenario forces to face new challenges to achieve an effective management of the power system both in technical and economic terms. Traditional energy storage solutions, like electrochemical cells and pumped hydro energy storage appear critical in terms of economic sustainability and site-dependency. The use of compressed air as energy storage has been investigated since the 20th century, but, in its first configuration, it was affected by site constraints as pumped hydro plants do. Liquid air energy storage has the chance to overcome those limits, but the experimental studies have far reached low efficiency. However, by rising the highest cycle temperature with the addiction of fossil fuel energy, these results can be largely improved. The paper deals with the thermodynamic analysis of a hybrid system including energy storage and production based on a liquid air energy storage plant where only oxygen is liquefied, while liquefied natural gas is used as fuel. In the production phase, liquefied oxygen and natural gas react in an oxy-combustion chamber where a large amount of water is added to keep the temperature at an acceptable level by evaporation. The system does not require an external water supply since all the water needed is produced by the cycle itself, allowing the plant to be placed also in remote areas with poor water resources. At the beginning of the cycle, both the reagents are liquid at very low temperature (below - 150 degrees C) and they need heat to be gasified; a large amount of this heat can be recovered from the combustion products, which, being cooled at suitable pressure, release liquid carbon dioxide which can thus be easily separated. Optimized arrangements, compared to the performances of the best available hybrid peak plants, even with sufficiently conservative hypotheses, reach high equivalent round trip efficiencies, even higher than 90%.