Novel non-concentrating solar collector for intermediate-temperature energy capture

• Novel type of non-concentrating solar collector has been designed and fabricated.
• Solar collector achieves 268.5 °C at stagnation for 1000 W/m2 irradiance (1 sun).
• Collector achieves above 250 °C for liquid flow rates up to 0.68 L/(h m2) at 1 sun.
• For temperature gain of 214 °C compared to ambient, collector efficiency is 49%.
• Low-flow rate, high-temperature operation is promising for new solar applications.

Tremendous research efforts have been conducted studying the capturing and conversion of solar energy. Solar thermal power systems offer a compelling opportunity for renewable energy utilization with high efficiencies and excellent cost-effectiveness. The goal of this work was to design a non-concentrating collector, capable of reaching stagnation temperatures above 250 °C and fluid outlet temperatures under flow above 200 °C at 1000 W/m2 solar irradiance. The study provides a detailed description of the methods and materials for construction of non-concentrating, high-temperature, evacuated solar collectors, the output fluid temperature depending on the input flow rate of working fluid in a low-flow rate, high-temperature regime, and an analytical description of the heat transfer between the collector and the working fluid. Temperature gains compared to ambient far above 200 °C were possible under solar irradiance of 1000 W/m2 with collector efficiencies of 30% and more. For a temperature gain of 227 °C (fluid outlet temperature 253 °C), the collector efficiency was 30%, and for a temperature gain of 214 °C (fluid outlet temperature 240 °C), the collector efficiency was 49%. This result opens up many new uses for non-concentrating solar collectors in fields such as power generation, fuel reforming, and catalysis.

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