news / 2016-07-18

Liquid salt storage for high-temperature heat

The TESIS facility is housed in the CeraStorE research building (source: DLR-CC-BY 3.0)

A key component for the future energy supply system is provided by high-temperature heat storage systems. In power plants, these enable a more flexible drive system and make it easier to store process heat in industrial production. Molten salts, for example, are used as the heat transfer media in these storage systems. Scientists from the German Aerospace Center (DLR) have developed a new storage unit for temperatures up to 560 °C. The construction of the test facility started in summer 2016.

At DLR’s TESIS test facility in Cologne, the scientists are using liquid nitrate and nitrite salt mixtures as heat transfer media. These are suitable for high temperatures between 180 and 560 °C. Heat at such a temperature level can be used in both power plant technology and industrial production. In general, liquid heat transfer media offer the advantage that the heat can be fed into and out of storage systems at high power and the media can be transported easily via pipes.

Benefits of molten salts

System diagram for the TESIS test facility (source: DLR-CC-BY 3.0)

The molten salt is nontoxic, nonflammable and unpressurized. Salt storage tanks can store up to 200 kWh/m3 with a temperature change of 250 Kelvin, and are cost-effective compared with other electricity storage systems. Their operating behaviour remains stable over many thousand charge cycles. DLR’s research activities are aimed at further reducing the costs and optimising efficiency. Components are qualified, the process technology is optimised and the concept further developed on the test facility.

 

The existing salt storage tanks were equipped with two tanks. However, the new storage system uses a single-tank concept. Three quarters of this tank is filled with natural stone. Relative to the volume, this has a similar heat capacity as the salt mixtures but costs only one tenth. A temperature stratification layer is formed inside the tank. Compared with systems currently available on the market, the new single-tank storage unit can reduce the capital costs by up to 40% depending on the boundary conditions.

 

The German Federal Ministry for Economic Affairs and Energy has funded the research project. It forms part of the CeraStorE interdisciplinary research facility.

Projects currently being funded

Links

> Salzbasierter Latentwärmespeicher „SALSA“
Project of the research initiative ForschungEnergiespeicher.