Evolutionary algorithm for optimization of nonimaging Fresnel lens geometry

Hybrid high-concentration photovoltaic system designed for different weather conditions

In this study, we propose a novel high-concentration photovoltaic (HCPV) cell by considering both the light leakage characteristics of the Fresnel-lens-based solar cell modules and the performance issues arising from cloud shading in practical use. We use our self-constructed systems to conduct field measurements for up to half a year under various environmental conditions. According to the acquired results, it was surprising to know that in the area other than the focusing area, the so-called light leakage region, there always bears illuminance of about 20,000-40,000 lx whether it is a sunny day or a cloudy day with different cloud conditions. Such an interesting result is caused by the light scattering of the clouds and the inherent leakage characteristic of a Fresnel lens. To prove this important finding, we simulated the illuminance of the Fresnel lens structure used in the measurement with apertures of different sizes to determine the detected area. In the laboratory, the diffuse plates were used to mimic the situation of varying cloud layer thicknesses. The trend of calculated and measured results fitted well with the field measurements. Also, the experimental and simulation results show that the round angle and draft facet of the Fresnel lens were responsible for light leakage. This finding prompted us to propose a hybrid high-concentration solar module in which more cost-effective polycrystalline silicon solar cells are placed around the high-efficiency wafer of HCPV to capture the dissipated light leakage and convert it into usable electricity.

Optimizing two-level hierarchical particles for thin-film solar cells

For the thin-film solar cells embedded with nanostructures at their rear dielectric layer, the shape and location of the nanostructures are crucial for higher conversion efficiency. A novel two-level hierarchical nanostructure (a sphere evenly covered with half truncated smaller spheres) can facilitate stronger intensity and wider scattering angles due to the coexistence of the merits of the nanospheres in two scales. We show in this article that the evolutionary algorithm allows for obtaining the optimal parameters of this two-scale nanostructure in terms of the maximization of the short circuit current density. In comparison with the thin-film solar cells with convex and flat metal back, whose parameters are optimized singly, the short circuit current density is improved by 7.48% and 10.23%, respectively. The exploration of such a two-level hierarchical nanostructure within an optimization framework signifies a new domain of study and allows to better identify the role of sophisticated shape in light trapping in the absorbing film, which is believed to be the main reason for the enhancement of short circuit current density.

Performance of see-through prism CPV module for window integrated photovoltaics

We have examined the performance of a see-through photovoltaics module that uses a low-concentration prism concentrator by undertaking ray-tracing analysis and an on-site experiment. The incident angle dependency of the prism concentrator makes it possible to concentrate direct solar radiation onto solar cells and transmit diffuse solar radiation. Fewer solar cells can then be used without sacrificing the conversion efficiency or lighting performance. The module generates approximately 1.15 more electricity than a conventional module while operating with 63% less solar cell area. We also introduce a design method for the concentrator geometry that adjusts the incident angle dependency for different latitude and tilt angles.

Design of wavelength selective concentrator for micro PV/TPV systems using evolutionary algorithm

This paper describes the results of exploring photonic structures that behave as wavelength selective concentrators (WSCs) of solar/thermal radiation. An evolutionary algorithm was combined with the finite-difference time-domain method (EA-FDTD) to determine the optimum photonic structure that can concentrate a designated wavelength range of beam solar radiation and diffusive thermal radiation in such a manner that the range matches the photosensitivity of micro photovoltaic and thermophotovoltaic cells. Our EA-FDTD method successfully generated a photonic structure capable of performing wavelength selective concentration close to the theoretical limit. Our WSC design concept can be successfully extended to three-dimensional structures to further enhance efficiency.