System for compressed gas energy storage

A method of storing, at a natural gas storage facility, electrical power from a power grid and later returning stored electrical power to the power grid, the method comprising:

• receiving natural gas from a natural gas pipeline system at a pipeline pressure;
• receiving electrical power from a power grid to power a compressor;
• compressing the natural gas from the pipeline pressure by the compressor to a reservoir pressure to produce high-pressure natural gas, in which compressing the natural gas further produces waste heat of compression;
• capturing the waste heat of compression with a second heat exchanger;
• heating thermal transfer fluid with the waste heat of compression;
• temporarily storing the thermal transfer fluid in a hot tank after heating the thermal transfer fluid with the waste heat of compression and before heating the removed natural gas with the first heat exchanger;
• temporarily storing the high-pressure natural gas in an underground, depleted gas reservoir;
• removing a portion of the high-pressure natural gas from the reservoir;
• heating the removed natural gas with a first heat exchanger;
• temporarily storing the thermal transfer fluid in a cold tank after heating the removed natural gas with the first heat exchanger and then returning the thermal transfer fluid to the second heat exchanger;
• expanding the heated natural gas through an expansion engine from the reservoir pressure to the pipeline pressure to produce reduced-pressure natural gas;
• driving, with the expansion engine and concurrent with the expansion, a generator that is co-located at the natural gas storage facility with the reservoir, the expansion engine, and the first heat exchanger;
• producing electrical power with the generator;
• transmitting the produced electrical power to the power grid;
• and
• returning the reduced-pressure natural gas to the natural gas pipeline system.