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What is it?

Concentrated solar is used to generate heat to drive a series of chemical reactions that produce hydrogen. The chemicals used in the process are reused within each cycle, creating a closed loop that consumes only water and produces hydrogen and oxygen. In this 'hybrid' system, multiple steps are required, and electrical input is required for one of the reaction steps.

Why is it important?

This multi-stage process has a lower required operating temperature than two-stage solar thermochemical water splitting. This is, however, at the cost of increased system complexity.


  • Inputs: Sunlight, electricity, water
  • By-products: Oxygen
  • Operating temperature: Varies from medium to high (Hybrid sulphur at least 750°C, copper chloride lower at 300-400°C)


  • Can make use of concentrated sunlight as heat source
  • Requires lower temperatures than 2-stage solar thermochemical water splitting


  • Has an electrolysis step which requires electricity input alongside heat
  • Heavy-metal processing required
  • Production of toxic or corrosive chemical intermediates

RD&D priorities

  • Investigate efficiency and durability of materials for thermochemical cycling
  • Develop efficient and durable reactor designs for thermochemical cycling
  • Improve reactor and electrolyser performance
  • Develop low-cost method for separation of O2 from SO2 prior to SO2 electrolysis
  • Scale-up SO2 electrolysis step from the 100-W to the hundreds of kW scale

Known active organisations

  • Flinders University
  • The University of Adelaide

Other opportunities like this

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