Why Energy Storage
The increasing amount of fluctuating renewable energy being made available to the electricity market in Germany requires the use of bulk energy storage in addition to the expansion of the national grid to ensure grid stability and energy during non renewable production phases. The natural gas storage industry can make a decisive contribution. The new concept, to efficiently store large amounts of renewable energy, is based on the "CAES - compressed air energy storage"- method. This technology currently achieves an efficiency of up to 45%. The biggest hurdle towards higher efficiency of this method is the heat that is generated during storage and withdrawal. By using the erneo technology, a thermodynamic efficiency of over 70% can be achieved.
The current state of the art is primarily aimed at storing the heat that is generated during compression and feeding it back to the gas stream during withdrawal or discharge. The temperature changes that occur during this process (compression of air in a cavern to approx. 150 bar and subsequent expansion from storage), are approximately 500°C. This enormous heat differential is the biggest challenge in the technical implementation of the conventional method of CAES.
In the procedure presented here, the process is run so that huge heat differentials are avoided and thus circumvents the biggest hurdle in the use of bulk energy storage using gas pressure storage systems. The erneo process runs in a closed circuit between two caverns, which are used for the compression and expansion of the gas, for example, between 100 and 250 bar pressure levels. The temperature changes occurring during this compression ratio are greatly reduced to a range of between 10-30°C for the same amount of stored bulk energy. These changes in temperature and pressure in the caverns and wells are within the same range as used within the gas industry and approved by national authorities for natural gas storage.
The erneo procedure is described here in detail and example calculations are presented for a high output of 100 MW and a low power (5-15 MW) for a day-long storage period. erneo developed the software for the simulation of the process where the thermodynamic processes in the caverns are calculated as well as for example pressure and temperature changes and the occurrence of water in the surface and sub-surface components. Using the erneo process heat storage takes place at lower temperatures which do not exceed 100°C. This allows water to be used as a storage medium. Due to the extra supply of heat and its storage, the efficiency and the process can be increased and the process can be run at a constant power output. Natural gas or other gases can be used as a working medium.