Collaboration produces efficient solar power generated hydrogen

The research group, including Assistant Professor Yasuyuki Ota and Professor Kensuke Nishioka from the University of Miyazaki, and Professor Masakazu Sugiyama of the University of Tokyo, connected the new high efficiency concentrator photovoltaic cells installed in the University of Miyazaki's outdoor testing area to water electrolysis equipment. They used polymer electrolyte membranes and to electrical conversion equipment (DC/DC converters), especially designed by Fujitsu Laboratories to efficiently convert the electricity obtained from the solar cells. 

The result was the successful production of hydrogen throughout the day in actual sunlight, efficiently and stably. The average energy conversion rate of sunlight to hydrogen throughout the day was 18.8%, establishing a practical system. 

The electrical conversion equipment Fujitsu Laboratories developed for this system enables high energy conversion efficiency (90%) from the solar cells to the electrolysis equipment. This is achieved by controlling the voltage and electric current supplied to the electrolysis equipment, in accordance with the varying temperature and amount of solar radiation that changes with the time of day, to consistently generate the maximum output from the solar cell. 

Concentrator photovoltaic cells require optics-based designs for components such as lenses, and advanced tracking technology to ensure the lenses accurately face in the sun's direction, so it is not easy to improve power generation efficiency in actual outdoor environments. 

For this trial, the concentrator photovoltaic modules (manufactured by Sumitomo Electric Industries) were mounted on a high accuracy sun tracking mount at the University of Miyazaki, and were able to achieve an average power generation efficiency (in converting solar energy to electrical energy) of 27.2% throughout the day in actual outdoor sunlight conditions. 

Going forward, the power generation efficiency of concentrator photovoltaic modules under actual operating conditions is expected to improve to 35%, and assuming an energy transfer efficiency of 80% from electricity to hydrogen in water electrolysis, it is anticipated that the energy conversion efficiency from sunlight to hydrogen will reach 25%.

Furthermore, it is easy to extend the hydrogen production equipment used in this trial to large-scale solar power generation systems, making it an important technology in the scaling up of hydrogen production that will be needed in the future. 

Moreover, the hydrogen was produced using the sunlight falling on Miyazaki prefecture. This is a form of energy production that utilises Miyazaki Prefecture's solar resources, and by storing and utilising hydrogen produced in this way, local production and consumption of energy can be expected in Miyazaki. Reductions in production costs are critical to the widespread use of hydrogen energy. 

Currently, concentrator photovoltaic cells are more expensive than ordinary photovoltaic panels, but outside of Japan, in areas of abundant sunlight with strong solar radiation, it has been possible to reduce energy production costs with greater generation efficiency. If gigawatt-level deployments necessary for hydrogen production move forward outside Japan, the price of concentrator photovoltaics may fall to a level equivalent with silicon photovoltaics. 

Combined with electrolysis equipment, the costs for which are falling due to technological advancements and mass production, these developments may reduce hydrogen production costs below Japan's Ministry of Economy, Trade, and Industry's target of up to 20 yen per cubic normal meter. The newly developed electrical conversion equipment eliminated restrictions on system configuration between the solar photovoltaic power system and the electrolysis equipment, accelerating the scaling-up of solar-based hydrogen production. 

In order to further promote the spread of solar power generation systems and hydrogen production using electrical energy obtained from those systems, not only are further improvements in efficiency and reductions in cost necessary, but there is also a need for improvements in system resilience in the face of changes in input power. 

The research group hopes to contribute to the further spread of hydrogen sourced from renewable energy by advancing research and development so as to improve resilience based on further field trials.