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 27.4deg and a concentration ratio between 1.5 and 1.75 over this entire cone angle. Furthermore, due to its small size (90mm x 72.6mm x 80mm), the design is portable. Selective surfaces, black chrome and TiNOX, 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.

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