Is limestone the energy storage option of the future?

Powerful, cheap energy stores are vital for the energy shift to succeed. Now, a new energy storage option seems to be emerging in the form of slaked lime that displays many promising properties.


Imagine if energy stores could effectively be carved from limestone. Instead of using batteries, people with photovoltaic cells on their roofs could then store the electricity they have generated in the form of chemical energy in small limestone energy storage units kept in their cellars, meaning they can save costs.

Researchers at the German Aerospace Center (DLR) have proposed a plant that, in essence, does precisely that. It makes use of a principle that has been known for a long time: slaked lime (calcium hydroxide) obtained from limestone can be ‘burnt’ by heating to create burnt lime, or calcium oxide. This is used to store the energy supplied in chemical form, which can theoretically be stored indefinitely (provided the burnt lime is kept dry). It reacts with water in a strong exothermic reaction, returning to calcium hydroxide, meaning the stored energy is also discharged and can no longer be used. A new test facility in Cologne is being used to test both reactions in a controlled environment for energy storage purposes.

This approach has two key advantages: using cheap limestone as a storage medium promises to lower costs and represents a huge saving compared to the comparatively more expensive phase-change storage options, which provide the base load capacity for solar power stations. And unlike traditional thermal storage systems, which cool down sooner or later, despite the insulation, limestone storage systems can even store thermal energy seasonally.

However, as is often the case, there is a catch. The storage medium is a powder, which is a nightmare for mechanical engineers. Therefore, it could be a while still until the technology finds widespread adoption.

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Eckhard Störmer ist the point of contact for your questions concerning the future of energy.

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