PV–technologies such as crystalline– and thin film– silicon, perov- skites, and (Ag, Cu)InGaSe2 (A-CIGS) can be used to supply the energy to drive an electrolyzer [6,9–12] with theoretical STH efficiencies span- ning from about 25% from serial interconnected solar cells to 32% for tandem approaches when using un-concentrated solar illumination [13].