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RedoxStorE

Thermochemical storage based on redox reactions for CSP applications - from the material to the process

Thermochemical energy storage for solar power plants uses the solar heat produced during on-sun operation to heat a material and power an endothermic chemical reaction (charging); should this reaction be completely reversible, this part of the thermal energy can be recovered completely by the reverse reaction taking place during off-sun operation (discharging). Main advantages of such technology are

• the higher energy density compared to sensible-only heat storage,
• possibility of storing/releasing the energy at constant temperature and
• the minimal thermal loss for the heat stored in the chemical reaction,
• with the linked advantage of possible long term storage.

In the project RedoxStorE, three DLR Institutes join their expertise to create a pilot thermochemical storage system based on moving reactive particles. The Institute for material research (WF-SFK) analysed and developed a suitable material based on Mn,Fe oxide and shaped it into granules. Also pellets, foams or honeycomb structures were analysed and compared to the granules. The institute of solar research (SF-SOL) proposed the use of a continuously operating rotary kiln, to drive the endothermic reaction, thus storing the solar energy inside the material. In this step, particles are fed inside a rotating cavity, open at one end to allow the entrance of concentrated solar radiation. While flowing through the cavity the particles absorb the incident energy, heat up and undergo the endothermic reaction. The institute of technical thermodynamic (TT-TPT) focus on the off-sun reactor, where the heat is extracted from the particles. This reactor is composed by a vertical cylinder, in which particles are slowly flowing down, controlled by a feeding system, while the cold gas flows couter-current to the particles, absorbing the heat released by the exothermic reaction and potentially being direct to a power turbine. After experimental tests of the granular material inside both reactors, some scale up guide-lines will be given to carry out a techno-economic analysis (made from the solar research institute SF-PFS) and define the potential of the complete process.

Rotary reactor for thermochemical storage of solar energy in the DLR solar furnace