Experimental investigation of a dual axis tracking linear Fresnel lens system installed in a small-scale greenhouse

The present study investigates the performance of a concentrated solar power system (CSP) which allows the balancing of solar irradiation that passes into the interior space and the irradiation that converges onto a collector. The system consisted of two Fresnel lenses with a total area of 4 m² which were mounted in individual aluminum frames to which a collector was connected at each end with hinged swing arms. To maximize the efficiency of the CSP system, a dual axis tracking system kept the lens and collector precisely aligned with the sun throughout the day and seasons. High accurate and reliable tracking was achieved by feedback from a 3-axis inclinometer. Measurements show that both transversal and longitudinal tracking errors were less than 0.5°, a factor two below the acceptance angles of the system. Results show that the maximum thermal efficiency was 40% when the temperature difference between ambient air and collector fluid was -15°C at a flow rate of 1.2 L min^‑1. This efficiency dropped to 10% at temperature differences between ambient air and fluid of 30°C at a flow rate of 0.6 L min^‑1. During the tests, the average direct normal irradiance was 470-780 W m^‑2. The next step is to improve the insulation of the collector. Then, the performance is expected to approach that of conventional evacuated tube collectors, but with the added benefit of the multiple functionality of this system.