The purpose of this study is the proof that non-concentrating solar-thermal collectors can supply the thermal energy needed to power endothermic chemical reactions such as steam reforming of alcoholic (bio-) fuels. Traditional steam reformers require the combustion of up to 50% of the primary fuel to enable the endothermic reforming reaction. Our goal is to use a selective solar absorber coating on top of a collector-reactor surrounded by vacuum insulation. For methanol reforming, a reaction temperature of 220–250°C is required for effective methanol-to-hydrogen conversion. A multilayer absorber coating (TiNOX) is used, as well as a turbomolecular pump to reach ultra-high. The collector-reactor is made of copper tubes and plates and a Cu/ZnO/Al2O3 catalyst is integrated in a porous ceramic structure towards the end of the reactor tube. The device is tested under 1000 W/m2 solar irradiation (using an ABB class solar simulator, air mass 1.5).
Numerical and experimental results show that convective and conductive heat losses are eliminated at vacuum pressures of <10−4 Torr. By reducing radiative losses through chemical polishing of the non-absorbing surfaces, the methanol-water mixture can be effectively heated to 240–250°C and converted to hydrogen-rich gas mixture. For liquid methanol-water inlet flow rates up to 1 ml/min per m2 of solar collector area can be converted to hydrogen with a methanol conversion rate above 90%.
This study will present the design and fabrication of the solar collector-reactor, its testing and optimization, and its integration into an entire hydrogen-fed Polymer Electrolyte Membrane fuel cell system.