Thermochemical Energy Storage: Storing Heat in Chemical Reactions

Energy storage is often associated with batteries and electricity. However, many industrial processes and buildings need energy in the form of heat.

Among thermal energy storage technologies, thermochemical energy storage (TCES) stands out due to its unique properties. It operates over a wide temperature range, making it suitable for integration with solar power and other heat sources. TCES systems store and release heat through reversible chemical reactions.

A well-known example is the calcium hydroxide / calcium oxide pair: Ca(OH)₂ (solid) ⇌ CaO (solid) + H₂O (gas)

During the charging step, calcium hydroxide (Ca(OH)₂) is heated and decomposes into calcium oxide (CaO) and water vapour (H₂O). This process absorbs heat and stores this energy in the form of chemical potential within the products (CaO, H₂O).

When heat is needed, H₂O is brought back into contact with CaO, and the two react to form Ca(OH)₂ again. This hydration reaction is exothermic and releases heat at a useful temperature, which can be used in a heating system or in a power cycle.

Because energy is stored in chemical form and not just as hot water, TCES reaches higher energy density and can store heat for longer periods. Storage can last from a few hours to several seasons with very low losses.

An additional advantage of the Ca(OH)₂/CaO system is its stable multicyclic performance. This makes the material more reliable for repeated storage and discharge operations. The reaction typically occurs at temperatures around 500 °C under a steam pressure of 1 atm. The operating temperature increases at higher steam pressures.

Although TCES with Ca(OH)₂ is still at an early development stage (TRL 3–4), laboratory studies show strong potential for future large-scale applications.

CymitQuimica supports this line of research by supplying metal oxides, salt hydrates, support materials and catalysts, and standards and analytical reagents to help develop and evaluate new TCES materials.