Assessing the value of hydrogen thermal energy storage and electric thermal energy storage in NEOM city

A large community such as NEOM City which is supposed to be powered only by wind and solar renewable energy requires a significant amount of energy storage. Given the limitations of the current energy storage technologies, from the total storable energy to the time this energy is stored, from the cost to the technology readiness level, it is important to provide assessments of continuing evolving alternative technologies. The cases of electric (external) thermal energy storage (eTES), and hydrogen thermal energy storage (hTES), are here considered. eTES is based on warming up a molten salt by using an electric resistance. The molten salt is then used to warm up a power cycle fluid for dispatchable energy production running a thermal power cycle. eTES suffers from round trip efficiency below 50 % but may handle a larger amount of energy at a lower cost compared to lithium-ion battery energy storage. eTES may benefit from integration with concentrated solar power with (internal) thermal energy storage. hTES is then based on green hydrogen production by electrolyzers, storage of the hydrogen in tanks, and combustion of the hydrogen to warm up a power cycle fluid for dispatchable energy production running a thermal power cycle. Of cost more difficult to estimate, also depending on the deployment of electrolyzers and round trip efficiencies below 50 %, hTES has the benefit to permit the storage of any amount of energy even over long time scales such as those needed to compensate for seasonal variability. Before electrolyzers provide the due amount of green hydrogen, the combustion power plant can be run with natural gas, delivering if not zero CO 2 emission, certainly the lowest life cycle CO 2 emission for dispatchable electricity at present. Finally, eTES and hTES can be coupled with each other, and also integrated with waste-to-energy (WTE) systems, for a more comprehensive and sustainable approach based on common thermal power cycles.