Thermal analysis of a micro solar thermal collector designed for methanol reforming

•A micro solar thermal collector with vacuum insulation is proposed.•Thermal performance of the collector has been both theoretically and experimentally analysed.•The collector can stagnate at 327 °C for an irradiance of 1000 W/m2.•The collector is suitable to drive endothermic reactions like methanol reforming.

A solar powered micro-reactor for hydrogen production is analysed in this study. A small, portable (∼4 W), compound parabolic concentrator (CPC)-based collector was designed and manufactured to provide heat for a methanol reforming (endothermic) chemical reaction. The designed collector consists of a small, flat, double-sided selective-surface receiver in a vacuum package. To our knowledge, the design represents the first time that a high vacuum package (<10−2 Pa) has been combined with a CPC for this purpose. Our previous optical and thermal models predicted that 78% of incident solar flux could be concentrated to the flat receiver with a concentration ratio of 1.75. In this paper, the collector’s performance was assessed for different volumetric flow rates (liquid flow rates at the inlet ranging from 0 to 350 μL/min) with and without a vacuum to validate the theoretical analysis of our previous work. Results showed that the experimental temperature measurements without a vacuum were well matched with the theoretical values. Additionally, it was shown that the temperature can be dramatically increased in a vacuum environment. In the vacuum experimental configuration, a stagnation temperature of 327 °C was found for an irradiance of 1000 W/m2. Temperature measurements for flow rates ranging from 0 to 100 μL/min also agreed with the theoretical model. Overall, this system represents a compact, portable solar collector which is capable of achieving high operational temperatures without tracking.