Introduction
Thermal energy storage (TES) refers to technologies that provide long-term storage of heat or cold for later use. Unlike conventional batteries, TES systems stock thermal energy by utilizing heat transfer between a storage medium and a heat sink or source. TES promises to deliver energy stability, address intermittency issues associated with renewable sources like solar and wind, and reduce peak demand on generation systems.
Need and Applications of Thermal Energy Storage
There are several factors driving the need for widespread implementation of TES technologies. One key factor is the intermittent nature of renewable sources like solar and wind which produce energy only when the sun shines or wind blows. TES allows excess thermal energy generated from such resources to be stored for later use when the source may not be available. Secondly, TES helps address demand-supply mismatch problems as heat can be stored during off-peak generation periods and supplied when demand peaks. This helps shave peak loads on the electric grid and reduce transmission congestion. TES also finds applications in buildings for space cooling and heating by buffering energy from HVAC systems. Other notable uses include industrial process heating/cooling and production of chilled water for air conditioning.
TES Materials and Methods
A variety of materials and technologies are used for TES depending on the temperature range and period of storage required. Sensible heat storage systems store energy by altering the temperature of a solid or liquid storage medium like water, molten salts, rocks or phase change materials. Latent heat storage utilizes the heat released or absorbed during phase transition of substances like paraffin wax or water for storage. Thermochemical storage relies on reversible endothermic chemical reactions to store energy in chemical bonds. Other methods include cryogenic storage using liquefied air or hydrogen and temperature gradient exchange using metallic foams. Each approach has its technical and economic viability depending on the application.
Commercial Applications of TES
Several commercial TES systems are currently operational worldwide to support solar thermal power plants and process heating applications. Andasol, located in Spain, was one of the first commercial plants to use molten salt storage achieving over 7 hours of full-load energy generation after sunset. Solar One and Solar Two projects in USA demonstrated 10 hours molten salt storage coupled with solar power towers. Industrial process heating levers TES vastly for processes requiring steam or heat treatment. Buildings have begun integrating TES in form of borehole thermal energy storage to provide summer cooling and winter heating. Moving forward, cost reductions through economies of scale and material innovations will make TES increasingly viable across sectors.
R&D Focus and Future Potential
Significant research continues to emerge new storage materials, designs targeting specific heat applications and system optimization. PCMs ranging from biobased oils to graphene-enhanced composites are being examined for high density storage. Thermochemical storage employing reversible hydrolysis/dehydration of salt hydrates shows promise at high temperatures. Researchers are also modeling hybrid thermal-electric systems leveraging complementary storage abilities. Government incentives and industry partnerships are supportingseveral large-scale pilot projects worldwide. If technology and installation costs keep declining, TES could emerge as a mainstream approach to store tens of gigawatt-hours of thermal energy in the future. Integrated with solar, waste heat and smart grids, it may play a transformative role in global energy management.
Conclusion
In conclusion, thermal energy storage is an important technology that helps maximize renewable energy generation, address intermittency issues and reduce grid loads from peak demand. It enables shifting of thermal loads in time by decoupling energy generation from use through versatile heat storage approaches. With further innovation and cost reductions, diverse TES solutions could soon help transition energy systems towards greater sustainability, flexibility and resilience worldwide. Looking ahead, hybrid multi-applications of TES will undoubtedly maximize its overall techno-economic and environmental benefits.
