  Energy storage becomes crucial for energy systems with an increasing share of
renewable energy sources. Artificial photosynthesis, in particular photovoltaic
water splitting, provides both sustainable energy generation and energy storage
in the form of hydrogen. However, only a few concepts for scalable devices were
reported in the literature. Here, we introduce a new concept which, by design,
is scalable and compatible with every thin-film photovoltaic technology. The
concept allows for independent geometrical optimization of the photovoltaic and
the electrochemical part. The scalability is achieved by continuous mirroring
of a base unit. We demonstrate a fully integrated, wireless device with a
stable and bias-free operation for 40 hours. The concept was scaled to an area
of 64 cm2 comprising 13 base units and exhibited a solar-to-hydrogen efficiency
of 3.9%. The concept and its successful realization is an important
contribution towards the large scale application of artificial photosynthesis.
