Optical Analysis of a New CPC-Based Solar Collector Designed for Hydrogen Production

Methanol reforming to produce hydrogen is an excellent way to provide fuel 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 new type of solar collector which has high overall efficiency. The advantage of the proposed design is that it can achieve high temperatures (up to 250°C) without tracking thus reducing capital and running costs. A CPC (compound parabolic concentrator) collector was designed with a half angle of 27.4 degrees and a concentration ratio between 1.5–1.75 over the entire cone angle. Furthermore, due to the small size of the designed type of collector, it would be easy to manually orient it so that the axis is aligned east-west, which would allow it to concentrate all day. The fabricated collector shown later in this paper has the advantage of being portable with a thickness of just 70mm. In this design, we use a vacuum layer between the receiver and the frame to minimize the convective heat loss and to allow for thermal concentration. Selective surfaces, such as TiNO_x, are employed in the receiver to absorb solar (short wavelength) radiation while minimizing emission of thermal (long wavelength) radiation. An optical analysis via ray tracing shows an optical efficiency of 80% to 85% in the range of half incident angle. Also, a prototype of the designed CPC collector is manufactured and shown in this paper.