Solar energy storage via a closed-loop chemical heat pipe

The performance of a solar chemical heat pipe was studied using CO2 reforming of methane as the vehicle for storage and transport of solar energy. The endothermic reforming reaction was carried out with a reactor packed with a supported rhodium catalyst and heated by the concentrated solar flux from the Schaeffer solar furnace at the Weizmann Institute (Rehovot, Israel). The maximum absorbed power was 8.5 kW. The reforming was run under variable insolation conditions, including partly cloudy days. The flux input was regulated by opening the doors of the concentrator building. The product gas temperature followed a predetermined set point that automatically controlled the flow of reactants to ensure constant composition of the reformer products. The exothermic methanation reaction was run in a multistage methanator filled with the same Rh catalyst and fed with the products from the reformer. High conversions were achieved for both reactions. In the closed-loop mode, the products from thereformer and from the methanator were compressed into separate storage tanks. The two reactions were run consecutively, and the whole process was repeated for over 60 cycles. The overall performance of the closed loop was satisfactory; scale-up work is in progress.