Sixteen Percent Solar-to-Hydrogen Efficiency Using a Power-Matched Alkaline Electrolyzer and a High Concentrated Solar Cell: Effect of Operating Parameters

The effect of electrode area, electrolyte concentration, temperature, andlight intensity (up to 218 sun) on PV electrolysis of water is studied using a highconcentrated triple-junction (3-J) photovoltaic cell (PV) connected directly to analkaline membrane electrolyzer (EC). For a given current, the voltage requirement torun an electrolyzer increases with a decrease in electrode sizes (4.5, 2.0, 0.5, and 0.25cm2) due to high current densities. The high current density operation leads to highOhmic losses, most probably due to the concentration gradient and bubble formation.The EC operating parameters including the electrolyte concentration and temperaturereduce the voltage requirement by improving the thermodynamics, kinetics, andtransport properties of the overall electrolysis process. For a direct PV−EC coupling, themaximum power point of PV (Pmax) is matched using EC I−V (current−voltage) curvesmeasured for different electrode sizes. A shift in the EC I−V curves toward open-circuitvoltage (Voc) reduces the Pop (operating power) to hydrogen efficiencies due to theincreased voltage losses above the equilibrium water-splitting potential. The solar-to-hydrogen (STH) efficiencies remainedcomparable (∼16%) for all electrode sizes when the operating current (Iop) was similar to the short-circuit current (Isc ) irrespectiveof the operating voltage (Vop), electrolyzer temperature, and electrolyte concentration.