Analysis of a New Compound Parabolic Concentrator-Based Solar Collector Designed for Methanol Reforming

Methanol reforming is a well-known method of producing hydrogen for hydrogen-based fuel cells. Since methanol reforming is an endothermic process, requiring an energy input, it is possible to use this reaction as a way to store primary energy. In this paper, we propose that this reaction can be driven with a vacuum packaged, nonimaging solar collector which has high overall efficiency. The linear compound parabolic concentrator (CPC) collector was designed with a half angle of 27.4 deg and a concentration ratio between 1.5 and 1.75 over this entire cone angle. Furthermore, due to its small size (90 mm × 72.6 mm × 80 mm), the design is portable. Selective surfaces, black chrome and TiNO_X, are analyzed for the receiver to absorb solar (short wavelength) radiation while minimizing emission of thermal (long wavelength) radiation. Importantly, this design uses a vacuum layer between the receiver and the frame to minimize the convective heat loss. A ray-tracing optical analysis shows an optical efficiency of 75–80% over the entire half incident angle range. Stagnation tests show that under vacuum conditions, temperature up to 338 °C is achievable. Overall, the proposed design can achieve high temperatures (up to 250 °C) without tracking—which reduces overall cost, operational limitations, and enables a portable design.