Electricity storage by means of compressed air with compression heat recovery – SEARCH

Respecting European objectives in terms of reducing greenhouse gases entails the fast development of electricity generation from renewable energy sources and nuclear energy. The fluctuating and intermittent character of renewable energy sources and the high modulation costs of nuclear power stations make it necessary for control to be improved over the energy flow rates between the supply and the demand of electricity: the commissioning of flexible, high-performance storage facilities would seem to be an appropriate response to this issue. Two types of energy mass-storage installations are currently capable of storing and releasing electricity at powers above 100 MW during several hours: pumping stations and compressed air energy storages (CAES). However, neither of them is able to meet the requirements for storing electricity brought about by respecting European objectives and the development of renewable energy sources and nuclear energy: sites where pumping stations plants might be built are rare in Europe. As for CAES installations, their electrical efficiency is weak (under 50% for first-generation of CAES plants) and they emit large amounts of CO2 - they do not recover the heat generated by the compressors and therefore require preheating of the air at the turbine’s entrance. As a result, one of the solutions consists in developing third-generation CAES installations, known as AA-CAES for Advanced Adiabatic Compressed Air Energy Storage. This type of storage’s main characteristic is that it recovers the compression heat in a “heat regenerator”, which enables electric efficiencies up to 70% and avoids CO2 emissions. The AA-CAES also has other advantages: It can be built in most parts of the territory; there are no specific safety problems; it offers voltage ranges between 50 MW and several hundred megawatts during several hours - therefore it provides excellent adaptation to local constraints of the transport networks, etc. In France, the development of some 20 AA-CAES facilities, with a unit power of 200 MW and an operational life of at least 30 years, could be considered as a realistic hypothesis. This would make it possible to store and generate close to 2% of the country’s electricity generation (equivalent to 15% of total wind electricity), to rationalize the management of trapped energy generated from renewable energy sources, to reduce CO2 emissions by around 6 millions metric tons per year, to secure sensitive electric zones and, finally, to optimize the utilization curves of nuclear power stations. Nevertheless, AA-CAES technology entails massive heat storage (up to the thermal GW), at high temperatures (350°C to 550°C), high pressures (150 to 200 bars) in a regenerator enduring daily cyclic charges, in a lined rock cavern (LRC) - being the most appropriate technology for high pressure leak-free pneumatic storage. However, no storage project fulfilling all of these criteria has yet been realized. The consortium, which already has solid knowledge on the subject thanks to its long time cooperation, therefore offers to overcome the various scientific and technological challenges that have been identified, in order to be in a position to carry out a life-size demonstration unit as soon as possible.