The module is based on the principle of splitting water molecules using the high photovoltage generated by multi-cell units. These cells, in turn, are electronically and thermally connected to electrolysis cells.
Solar power is used directly in hydrogen production
The centerpiece of the photovoltaics/electrolysis module is concentrating photovoltaics (CPV): An array of Fresnel lenses focuses direct sunlight onto III-V solar cells with an open-circuit voltage of over 4 volts, explained Dr. Juan Francisco Martínez Sánchez, project manager for the new development at Fraunhofer ISE.
III-V solar cells are considered the most efficient solar cells in the world. Currently, they are used primarily in space, but could also be used in CPV modules on Earth for electricity generation. A Fresnel lens is a special type of optical lens that, due to its structure, has less volume and mass than conventional lenses.
The solar cells are connected directly to the cathode and anode of two PEM(proton exchange membrane) electrolysis cells connected in series within the photovoltaic/electrolysis module. Dr. Tom Smolinka, head of the Membrane Electrolysis Department at Fraunhofer ISE, added that the electricity from the solar cells is thus used directly for hydrogen production without any detours.
Tests in Freiburg Demonstrate the Technology's Potential
In field tests, a prototype of the photovoltaic/electrolysis module converted up to 31.3 percent of solar energy into chemical energy, based on the calorific value of hydrogen. The lens area was 64 square centimeters. The outdoor tests were conducted over 13 summer days in Freiburg on a two-axis solar tracker.
Clearsun Energy, a spin-off, is seeking investors
"The development is still in its early stages," said Dr. Frank Dimroth, head of the III-V Photovoltaics and Concentrator Technology Department at Fraunhofer ISE. To further develop the concept, the team is now seeking investors for the planned spin-off, Clearsun Energy.
Clearsun Energy joined the AHEAD program in 2022. AHEAD is a Fraunhofer technology transfer program that guides and provides financial support to deep-tech founders from the initial business idea through the development of a business model to market entry. In 2025, the Werner Siemens Foundation invested 14 million euros in further cell and module development at Fraunhofer ISE.
Starting in 2028, Clearsun Energy aims to achieve an annual production capacity of more than 300 MW for CPV cells. By 2030, the company plans to scale up production of Micro-CPV modules to over 1 GW per year.
