A comparison of PV/electrolyser and photoelectrolytic technologies for use in solar to hydrogen energy storage systems

Abstract

The approach of using hydrogen for an energy store to offset seasonal variations in solar energy is one very much at the periphery of current renewable energy system design. Nonetheless, its inherent advantages for long term storage in stand alone power systems warrant further detailed investigation. This paper provides a comparative overview of the very disparate technologies within two generic approaches to achieving this goal. These are: photovoltaic (PV) powered electrolysis of water and direct photoelectrolytic (PE) generation of hydrogen from water. Comparison of these is difficult, however, the paper compares devices of similar material system and structure within each generic scheme. PV/electrolysis is the more mature technology but there is still a wide range of potential 'solar to hydrogen' efficiencies. A figure of about 9% is estimated for comparison, with justification given. The comparative figure for PE is more difficult to judge because of even more disparate approaches to specific problems of sufficient photovoltage and stability, but an approximate comparative figure of 5% is estimated. Thus making PV/electrolysis more appropriate at present. Nonetheless, inherent advantages of simplicity of system design and potential robustness mean that PE may become more appropriate as the technology develops.

Solar Hydrogen Reaching Maturity

“…Since electrolyzers operate at a voltage around 1.9 V [19], a DC-DC converter is needed to match PV output voltage and the voltage of the electrolyzer at its design point. The best choice for the electrolyzer is a Polymer Electrolyte Membrane (PEM) electrolyzer, since this type can more easily handle fluctuating input currents [20].…”

“…Moreover, because PV efficiency decreases with temperature and electrolyzer efficiency is highest at elevated temperatures, both can be put in different locations to address these requirements [19,22]. On the other hand, Rau et al [20] reason that a PEM electrolyzer directly attached to the back of a PV module would cool down the module, so enhancing its efficiency.…”

System Modelling for Hybrid Solar Hydrogen Generation and Solar Heating Configurations for Domestic Application

“…However, there is no complete model suitable for system design. In particular, the existing models do not capture the dynamic nature of a PEC unit when incorporated into an energy system, taking into account, for instance, variations in solar radiation, the temperature of the water in the PEC unit itself [6][7][8][9]. A model should take into account the differences due to the location of the unit and hourly, daily, and seasonal variations in solar radiation.…”

Design of Compact Photoelectrochemical Cells for Water Splitting

“…Coupling these units causes energy losses. Both technologies have their merits and the reader is referred to literature for a more detailed scientific comparison (Rongé et al, 2014a;Conibeer and Richards, 2007;Jacobsson et al, 2014).…”