UC Berkeley

The use of optically concentrating lenses integrated with wireless photoelectrochemical cells provides a mechanism to potentially reduce the energy input required to manufacture solar fuels-producing devices. In this work, a modeling approach is used to assess the annual fuel production from such integrated devices. The model captures optical, heat transfer, photoelectrochemical and climactic phenomena. The variation of design parameters such as cell dimensions, lens type, photovoltaic cell type, optical reflection management coatings and deployment location is investigated for a system that uses an optical concentration ratio of 10. The model then predicts the system’s operating temperature, operating current density and solar fuel production efficiency for every hour of the year in any location for which sufficient weather data is available.

It is found that the devices that perform most efficiently are sufficiently small to enable effective optical capture and minimize potential losses in the electrolyte. Small ion exchange membrane coverage fractions are sufficient to enable optimal light capture while exhibiting small ohmic drops in the photoelectrochemical cell. Careful management of antireflection coatings and protection layers is required to maximize optical transmission to the current-limiting junction in the device’s photovoltaic cell. Employing simple passive cooling to maintain sufficiently low cell temperatures during extreme, quiescent ambient conditions can be achieved in certain climates but not in others. Additional measures must be undertaken to prevent electrolyte freezing in colder climates. However, despite these challenges, annual weighted average solar to hydrogen efficiency of 11.2% can be realized in high insolation locations, and stably efficient operation is possible with proper cell design. Locations with very poor direct solar irradiation resources can still exhibit annual weighted average solar to hydrogen efficiencies in excess of 9%. Additionally, the model’s predictions of device temperature are found to be in agreement with results produced in COMSOL Multiphysics. These investigations therefore help to elucidate the potential research and development work needed for future development and deployment of this technology.