Comparison of methods for discharging an isochoric compressed air tank in compressed air energy storage systems

Renewable energy sources are characterized by intermittent operation, which creates the need to store surplus energy and release it at the time of demand. Energy storage systems that keep energy in compressed air can be a solution to this problem. Therefore, it is necessary to identify the method of releasing compressed air and select the most efficient one. In the study conducted, two particular ways of controlling the expansion of air stored in the tank emerged: control through a cut-off function of air supplied into cylinder and through the use of pressure regulator. To indicate which solution is more cost-effective from an energy point of view, a series of simulations were carried out using the Matlab environment. Operation with the highest efficiency and with the highest sustainability was achieved using a PID (proportional-integral-derivative) controller and a function controlling the level of opening of the valve passing air to the expander. The method considering the presence of the buffer tank provided rotation stability in a much shorter system operation time, while the baseline scenario (which did not include any form of system control) was characterized by instability, short operation time and low efficiency.