An international group of researchers, coordinated by the Institute of Solar Research of the German Aerospace Center e.V. (DLR; Cologne, Germany;, is developing a sulfur-based storage system for solar power. Large-scale chemical storage of solar power and its overnight use as a fuel are to be achieved by means of a closed sulfur-sulfuric acid cycle. The four-year, €4.7-million Pegasus project is being funded under the E.U.’s Horizon 2020 Framework Program. The partners are DLR, the Karlsruhe Institute of Technology (KIT; Germany) the Center for Research and Technology CERTH (Greece), Brightsource Industries Israel Ltd., Processi Innovativi S.r.l. (Italy) and Baltic Ceramics S.A. (Poland).
using sulfur to store solar energy
In the process under development (diagram), elemental sulfur is burned as fuel for a power plant, producing electricity and SO2 gas. The SO2 is mixed with water and converted to fresh sulfur and dilute sulfuric acid in a disproportionation reactor. Both products (S and H2SO4) can be easily stored using conventional technology. To complete the cycle, the H2SO4 is concentrated and decomposed using heat produced by a concentrated solar-thermal tower. The technology will be tested under real conditions at the Jülich Solar Power Tower Facility (STJ) in Germany.
The partners will demonstrate the feasibility of the overall process. A detailed flowsheet will be drafted and the optimized integrated process scaled to the 5-MW thermal-power level shall be analyzed. Prototypes of the key components, such as the solar absorber, sulfuric acid evaporator, sulfur trioxide decomposer, and sulfur burner will be developed and tested. In addition, the materials required for heat absorption, transfer and storage and for the catalysts of the chemical reactions will be tested for efficiency and long-term stability.

By Gerald Ondrey