Large-scale solar hydrogen production through water splitting using a powder photocatalyst is considered one of the most promising methods of producing sustainable fuels in the future. In 2018, this research group demonstrated that water-splitting photocatalytic panel reactor can be scaled up to 1 meter squared in size without compromising the solar water splitting activity of the photocatalyst. However, large-scale separation and collection of solar hydrogen beyond the laboratory scale had never been realized. It was necessary to review the design of the photocatalytic panel reactor and develop a system to safely separate the gas mixture of hydrogen and oxygen in an outdoor environment.