Taiwanese researchers have developed a system with a 2 × 2 Fresnel lens array and a solar panel made of III-V materials and polycrystalline solar cells with low light leakage.
The scientists said that HCPV systems combined with a Fresnel lens can absorb sunlight even in cloudy weather conditions, and that these devices, however, suffer from light leakage.
“Fresnel lenses are designed to significantly reduce lens weight to meet the requirements of a solar tracking system,” they noted. “However, unlike conventional lenses, uneven and discontinuous lens surfaces that are divided into multiple segments can inevitably cause significant light leakage due to manufacturing defects such as radii of curvature and draft angles of fabricated Fresnel lenses.”
The researchers assumed the use of a Fresnel lens with a width of 129 mm and a thickness of 1.81 mm. They considered a focus area of 1.1 mm × 1.1 mm, an in-focus power ratio of 63%, and a light leakage ratio outside the focus area of 37%. They also measured the light energy in the light leakage region of Fresnel lenses of different constructions in monochromatic light radiation and used diffusive plates with varying penetration rates to mimic the outdoor conditions of cloud layers of different thicknesses.
Based on the results of this simulation, the team was able to design a HCPV system capable of providing good performance even under cloudy skies. It contains a set of 2×2 Fresnel lenses in a box with two rotary gauges that can be manually adjusted to face the sun directly at any time. The PV unit relies on a high-efficiency solar panel based on III-V materials at the focal point and polycrystalline solar cells placed around it.
“Light leakage from the Fresnel lens structure and scattered sunlight passing through clouds can be directed to a polycrystalline silicon-based solar panel for power generation,” the researchers said. “When the sky is clear, the light is concentrated on the efficient solar cell, so the efficiency of electricity production is high. In a heavy cloud, sunlight cannot be concentrated into an efficient solar cell, so traditional HCPV cannot efficiently generate electricity, but this structure can still generate electricity with polycrystalline solar panels.
Through simulation, the Taiwanese group was able to verify that the Fresnel lens can achieve an illuminance of about 20,000 to 40,000 lx in the light leakage area, whether it is a sunny day or a cloudy day with different cloud thicknesses.
The research group presented the HCPV system in the study “Hybrid high-concentration photovoltaic system design for different weather”, which was published recently Scientific reports.
The team includes researchers from National Taiwan Central University and National Yang Ming Chiao Tung University.
“The proposed new solar power system is useful for achieving optimal solar energy production under different cloudy skies,” they concluded.