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.