11.3 Compressed air tanks
One way to store energy is to compress air. At times when energy is cheap or while using renewable sources, we compress air and store it in tanks. The scheme of such a system of compression and production of electric energy with the use of energy accumulated in gas tanks is shown in the film "CAES - Compressed Air Energy Storage - IMAGES Project – animation".
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The system introduces gas through a filter, low-pressure and high-pressure compressors into large volume natural tanks such as an underground salt chamber or smaller volume artificial tanks. A cooler lowers the gas temperature to reduce thermal stresses in the system. The processes of filling both the natural tank and the artificial one are shown in the following frames of the video. The energy stored in this way can be used at any time, e.g., during energy peaks when electricity prices are highest or in emergency situations to produce electricity. The compressed gas is released through a recuperator and preheating chambers, which drive high-pressure turbines and then low-pressure turbines. Coaxially with the turbines, a generator is placed to generate electricity, which is transmitted to the grid. A schematic of the electricity production process is shown in the final frames of the film, where compressed air is drawn from an underground salt chamber.
The production is analogous if we draw compressed gas from artificial reservoirs. Just filling the tanks in times of cheap energy and then switching to produce it when energy prices are high makes economic sense. The process becomes even more profitable if the system is fed by a photovoltaic power plant whose peaks in production do not coincide with the peaks in grid consumption. A second even more relevant aspect is energy security. Similar to pumped-storage power plants, compressed-air systems are an important means of securing the continuity of the electricity supply in case of failure of other sources.
An example of a compressed air system is shown in the film "RWE Power: ADELE - Adiabatic compressed-air energy storage (CAES) for electricity supply".
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