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| Journal Article | FZJ-2025-02257 |
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2025
Elsevier
New York, NY [u.a.]
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Please use a persistent id in citations: doi:10.1016/j.ijhydene.2025.04.166 doi:10.34734/FZJ-2025-02257
Abstract: Coupling of photovoltaics (PV) with electrochemical (EC) water splitting is an established concept for storage of excess PV energy via production of green hydrogen. However, intermittent PV output presents a challenge for the stability and lifetime of EC devices in both direct coupled and power electronic assisted systems. The use of batteries is a viable way of smoothing out PV output fluctuations, which is beneficial for EC stability and ultimately lifetime. In our studies of direct coupled PV-EC-battery (PV-EC-B) systems, we have demonstrated self-sustaining operation of the device without control electronics. In addition to the expected storage function, the batteries stabilize the power coupling and improve the solar-to-hydrogen (STH) efficiency of the system despite their own power losses. This synergistic effect originates from the distribution of the daily PV energy over longer periods of EC operation i.e. the reduction of the EC input power and the related kinetic losses. This STH efficiency gain is addressed from two orthogonal viewpoints. First, we investigate how high the synergistic STH gain can be in the optimized system composed of high-efficiency PV and EC components operating close to the system efficiency limit. We show that in a basic day-night operating cycle, an optimally coupled PV-EC system with STH efficiency of 23.0 % can reach STH efficiency of 25.4 % once battery is included. The STH efficiency increase achieved in the PV-EC-B system is 2.4 % abs. higher than the STH efficiency in the reference PV-EC system and 1.9 % abs. higher than the theoretical STH limit of the reference system determined by the EC polarization curve. The second aspect is related to the downscaling of an electrolyzer facilitated by the reduced EC power in the system with battery. We show that the battery allows a reduction of the electrolyzer capacity in the PV-EC-B system by about a factor of two, while operating at the same efficiency as the reference PV-EC system. These results are crucial for the future design, techno-economic and life cycle analysis of advanced PV-powered water splitting.
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