Thermal Regimes of Fresnel Lenses and Cells in “All-Glass” HCPV Modules

Abstract

We report on research carried out at the Ioffe Physical Technical Institute in the field of operational conditions of the high-concentration photovoltaic (HCPV) module components. The subject of investigations are thermal regimes of the primary Fresnel lenses and multijunction solar cells. Two main issues governing the design of a solar concentrator module with III-V triple-junction solar cells (SCs) are considered: the effective concentration of radiation using Fresnel lenses, and effective heat removal from SCs. By theoretical and experimental simulating these processes, the design parameters of modules' elements have been found. A test batch of sub-modules (HCPV modules based on individual Fresnel lenses) has been fabricated and tested. The influence of different operation temperatures on the optical efficiency of Fresnel lenses and conversion efficiency of solar cells have been estimated.

Tuning the current ratio of a CPV system to maximize the energy harvesting in a particular location

“…If SMR increases, that is, the incident spectrum shifts to blue, the current photogenerated by the middle subcell decreases lowering the system efficiency ( fig.1). If the ambient temperature decreases, the refractive index of the silicone increases, the lens becomes more converging, and the amount of red light over the 3J solar cell increases [4][5][6][7]. It would be desirable that those two phenomena would happen simultaneously so some kind of compensation would take place leading to an increase of the module tolerance.…”

“…In second place, the ambient temperature influences the behavior not only of the solar cell but also on the concentrating optics. In particular silicon-on-glass (SoG) Fresnel lenses have been reported to be highly sensitive to temperature [4][5][6][7].…”

Assessment of the optical efficiency of a primary lens to be used in a CPV system

“…In addition, we must check that the heating of the sensor under concentrated light does not modify its spectral response. The temperature of the lens also needs to be controlled since, for certain materials, this parameter has a strong influence on the lens performance (Rumyantsev et al, 2010;Hornung et al, 2010;Askins et al, 2011). Nevertheless, the main drawback that disallows the outdoor measurement is the fact that the Sun may not be available when needed.…”

Methodology of quantifying curvature of Fresnel lenses and its effect on CPV module performance

“…However, deformations at the inner surface of the lens are not measurable with the checkerboard method. For SoG, the most critical deformations are caused by the difference in the coefficient of thermal expansion (CTE) between the silicone and the glass, which produces lens facet deformation [7][8][9][10] that is not observable with the checkerboard method. Nevertheless, there is a significant bending effect in large SoG lenses, due to the weight of the glass or differential pressures in real operation, that is measurable with the proposed method.…”