A thermal energy storage (TES) device is a system that stores energy in the form of heat for later use. The concept of thermal storage is not novel and has been applied in the steel making industry for a long time. TES can be used to store energy, in the form of heat, in industrial process and space heating / cooling applications without the need to convert it back to electricity.

TES devices typically consist of an insulated container or tank that is filled with a storage material that can absorb and release heat energy. The material used for the storage medium can be a solid, liquid or gas.

During the charging phase, the TES device absorbs thermal energy from a source such as the electricity grid, waste energy from industrial or solar collectors. The stored energy can then be used when needed during the discharge phase to provide heating or cooling, or to generate electricity.

Solar generation is typically high during the day and wind more commonly at night. Due to its inherent intermittency, renewable energy availability can cause higher price fluctuations in local electricity markets. Energy storage devices allow us to buy energy when prices are low and use them when we’d otherwise have to purchase at a high price. This is increasingly important as we bring more renewable energy onto the grid, and price fluctuations increase. In order to use effectively and economically expand clean generation to allow for 24/7 usage, we desperately need storage.

We throw away a very valuable resource. Without grid-scale storage, generators are forced to curtail their resources when they are producing more power than the grid can handle. By curtailing, we are literally throwing away “free” energy and significantly reducing returns on renewable capital investments.

Lithium-ion batteries are considerably more expensive than TES systems. TES systems rely on inexpensive raw materials and can scale for large industrial use better than lithium-ion. Additionally, TES devices have a lower environmental impact than lithium-ion batteries, which require the mining and processing of rare earth metals. Using Li-ion in the industry also has its limitations as electric boilers can only go up to ~800°C, a significant portion of industrial heat requirement is above this threshold.

Thermal energy systems often exist in parallel with existing fossil fuel systems due to their nascency. The TES system provides heat, typically in the form of steam, in the same way that a traditional boiler would. As trust in technology improves, TES systems could replace traditional boilers entirely.

The TES system provides heat within a broad range of temperatures that can reach up to 1000°C. Heat can be stored at high temperatures then brought down to industrial process specific temperatures.

A variety of companies across the globe have begun designing and now piloting thermal storage devices. By our count there are over ~35 companies making large TES solutions.