New reactors for efficient thermochemical energy storage

Supply from renewable sources can be inconsistent in the short term when the wind dies down, the waters become calm and the clouds hide the Sun. Development of energy- and cost-efficient storage will enable power systems to store excess energy beyond immediate requirements and retrieve it when needed.

Concentrated solar power (CSP) is particularly well suited to accommodating intermittent demand as it can be combined with large-scale thermal energy storage. Such technology is appealing because it is safe and produces no greenhouse gas emissions. Although simple in concept, storing heat at high temperatures cost efficiently and for long periods has not been easy to accomplish.

Researchers within the project TCSPOWER (Thermochemical energy storage for concentrated solar power plants) successfully validated thermochemical energy storage reactor/heat exchanger solutions in CSP plants, overcoming major challenges related to high temperatures. The validation of the reactor concept was performed in a pilot-scale system of about 100 kWh capacity.

The team approached the task with reversible thermochemical reactions – endothermic in one direction to take in the heat for storage and exothermic in reverse to free heat for the power block. The materials used were metal oxide-based: manganese oxide and calcium oxide. The redox reaction of manganese oxide took place at 700 °C and was intended for an open operation since the reaction partner Oxygen can be exchanged with the ambient. On the other side, calcium oxide reacts reversibly with water vapor in a temperature range of 400-600 °C and was considered to be integrated in steam power plants.

The innovative reactor concept is designed to reach a required power level but is at the same time independent from the required capacity. Therefore, the capacity can be easily increased by adding additional cheap tanks to store the required amount of the reaction material. To move the reactive solids through the reaction zone, researchers granulated the reactive powder in the case of the manganese oxide. To enhance the flow of the calcium oxide they added nanostructure additives to the powder.

This efficient and cost-effective thermal energy storage solution allows taking advantage of the long-term and loss-free storage possibility that comes with thermochemical energy storage. Combined with CSP generation this technology will ensure more stable energy supply since it offers full dispatchability for long storage periods. Further refinements to the reactor will advance the technology towards the commercialisation phase. TCSPOWER technology should accelerate uptake of renewable energy resources and their intermittency will no longer pose a problem.