PEC devices can encompass a large spectrum of device types [1], and whilst the theoretical maximum efficiency for each level of integration may be the same for a given conceptual design (i.e. number of junctions, optical and electrical configuration of those junctions) [2], the ease of engineering a feasible device may differ significantly [3]. In this work we investigate the performance of a thermally integrated but light absorption decoupled photo-electrochemical device.

A lab scale prototype (30 W scale) using concentrated light (~470 times concentrated) has previously experimentally demonstrated the advantages of the direct electronic coupling and spatial integration of the electrochemical splitting of water to the photo-voltaic cell, whilst utilising waste heat extracted from the solar irradiance to improve the kinetics of the electrochemical reaction [4]. In this work, the scale up of a similarly integrated device is dynamically simulated in order to gain a greater understanding into the operability and real world performance. The simulated system under study here, is based on the efficient real pilot plant scale (kW scale) demonstration which has been constructed on the EPFL campus. It is composed of a 7 m diameter solar parabolic dish concentrating onto the integrated solar hydrogen device, with the necessary liquid/gas handling periphery systems (e.g. pumping, separation, compression and storage). The hydrogen is produced and stored at 20-30 bar.

The operation, control and optimization of such a novel integrated system is non-trivial, as the integration which permits such high efficiency adds significant complexity to the process engineering. In this study, dynamic process modelling is used to assess the response of the system to daily, seasonal and yearly variations in solar irradiance and ambient temperature. Conversely, the demand for fuel, heat and electricity on campus will also temporally fluctuate and control strategies are found in order to maximise the efficiency or the agreement between production and demand. Time-dependent environmental conditions and realistic component performance data has been employed in order to get meaningful results that can direct the control strategies of the real life concentrated solar to hydrogen pilot plant. Additionally, the capacity to which controlling the flow rate can stabilise both the hydrogen production and performance degradation, as previously reported [5], has been assessed for the scaled system. Finally, the simulated performance of the EPFL scaled co-generation device is compared to similar competing technologies and the future perspective of this type of technology is discussed.