Theoretical analysis of a novel, portable, CPC-based solar thermal collector for methanol reforming

In this paper we propose a new solar thermal collector which is suitable for providing heat for endothermic chemical reactions. The particular reaction that is considered is hydrogen production by menthol reforming. The design presented here is based on CPC (compound parabolic concentrator) technology, which can operate without complicated (and costly) tracking systems. It consists of a small, double-sided selective surface receiver in a vacuum envelope comprised of CPC reflectors and a glass aperture cover. Heat absorbed by the receiver is transferred to the working fluid inside micro tubes where the chemical reaction is occurring. This design, to the best of our knowledge, represents the first time that a vacuum package (which creates thermal concentration) has been combined with a CPC-based optical concentrator for thermo-chemical applications. This collector design can convert over 78% of incident solar radiation into heat with a concentration ratio of 1.75, allowing for a high solar-to-fuel efficiency in chemical reactions. This study establishes both the optical and thermal models needed to predict the performance of this type of collector. The results show that the collector stagnates at very high temperatures (up to 600°C), and can provide solar heat in the form of a small collector for a variety of portable applications – e.g. methanol reforming that requires temperatures of around 250°C.