While battery storage dominates discussions around storage, there are storage systems other than electrochemical. Thermal and mechanical storage systems are the two other prominent storage solutions.
Prominent among mechanical storage solutions is pumped hydro storage in which electricity during non-peak periods is used to pump water up to a reservoir and the water runs down during peak periods to turn a turbine and generate electricity. Prominent among thermal energy storage for large scale applications is storing heat in phase change materials (such as molten salt). In these systems, heat - or electricity converted to heat - melts the salt, and when the energy is needed, the salt is allowed to convert into a solid, when it releases the heat back again for use as heat or to run a turbine to generate power.
Pumped hydro systems have some large capacity implementations worldwide. The Bath County Pump Station in the United States for instance is a massive 3000 MW of pumped storage hydroelectric power plant. A few CSP power plants use reasonably large phase change materials based thermal storage capacities.
While pumped storage is a fairly well established mechanical storage technology, technologies such as compressed air storage, flywheel based storage are less so in the context of large scale renewable energy storage. Thermal storage solutions that use phase change materials are still undergoing evolution for large scale use for power or heat storage. One PCM-based thermal storage segment where significant innovations are happening is in the use of water/ice as a phase change material - many buildings worldwide are experimenting with using electricity to convert water into ice during non-peak power periods and using the ice to provide cooling during peak hours.
Other than simple heat storage systems (a residential hot water tank, for example) and pumped hydro storage, use of other mechanical and thermal storage systems for large scale heat or power storage so far has been quite selective, and have been mainly experimented and implemented in developed economies.
For the 2020-2030 period, innovations in this domain can be expected in ice-based PCM storage, utility scale storage using thermal or mechanical systems, liquid energy storage, hybrid storage systems, compressed air, CO2-based thermal storage and flywheel storage. Also expect increasing use of digital technologies to integrate these storage solutions and optimize them with the rest of energy and power ecosystems.
Pumped hydro storage has an impressive total global installed throughput capacity of over 181 GW, and a total installed storage capacity of over 1.6 TWh.
Thermal energy storage had a total global capacity of 234 gigawatt hour (GWh) of installed capacity in 2019 and this could increase to over 800 GWh by 2030.
Pumped storage and thermal energy storage together could thus account for about 2.5 TWh of energy storage capacity by 2030.
Such significant storage capacities can play a critical support role in enabling the optimal utilization corresponding renewable & sustainable energy sources (hydro power, solar thermal, waste heat, surplus solar or wind power etc.) and thus become a critical enabler for large scale decarbonization.
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Thermal & Mechanical Storage Decarbonization Avenue
