Thermal Performance Assessment of the World’s First Solar Thermal Fresnel Lens Collector Field

Fresnel lenses are used in a wide range of solar energy applications, primarily due to their reduced material usage, low cost, and high optical efficiency. This study presents an investigation of the world’s first full-scale Fresnel lens solar collector field. The collector field consists of 144 two-axis tracking solar collectors manufactured by the Danish company Heliac and supplies heat to the local district heating network in Lendemarke, Denmark. The thermal performance of the solar collector field was determined using the quasi-dynamic test method. It was found that the peak efficiency was 11% lower compared to a brand-new collector and that heat losses from the collectors made up half of the total heat losses of the solar field. The reduction in the peak efficiency was primarily caused by soiling as the collectors were exposed to outdoor conditions for one year without cleaning. Furthermore, the system’s annual performance was determined using a simulation model developed in TRNSYS and validated by comparison to measurement data. For 2020, the heat generation was 373 kWh/m² (relative to aperture area) when operating with an outlet temperature of 90 °C and inlet temperature of 50 °C. Additionally, a sensitivity analysis of the annual heat generation was performed, varying the ground cover ratio, mean collector temperature, and soiling level. The sensitivity analysis showed that the heat generation was relatively insensitive to changes in the mean collector temperature, demonstrating that the collectors are suitable for generating heat above 100 °C, unlike flat-plate collectors.