How do sub-bandgap reflectors affect the performance of PV modules?

TL;DR

Sub-bandgap reflectors can modestly increase PV module energy yield by reducing temperature and potentially extending lifespan, with benefits varying by location and reflector quality.

Contribution

This study quantifies the impact of ideal and non-ideal sub-bandgap reflectors on PV performance and longevity across different locations.

Findings

Ideal SBR increases annual energy yield by 1.0-2.4%.

Reducing temperature may decrease degradation and extend PV lifetime.

Cumulative 30-year energy gain ranges from 2.2% to 4.0% with ideal SBR.

Abstract

Sub-bandgap reflectors (SBR) can reduce the temperature of photovoltaic (PV) modules by reflecting the near-infrared region of the solar spectrum with photon energies smaller than the electronic bandgap of the solar cell absorber material. We consider an ideal SBR, which reflects 100 % of non-harvestable low-energy photons but does not alter the reflectivity of the PV module for usable high-energy photons, and estimate how reducing the module temperature with the SBR affects the annual and the cumulative energy yield of silicon PV modules for six locations in North America and Europe. An ideal SBR would increase the annual energy yield between 1.0 % and 1.5 % for open-rack mounted modules and between 1.6 % and 2.4 % for close-roof mounted PV modules. Whether a non-ideal SBR provides a benefit in actual deployments strongly depends on the location and the optical properties of the coating. Beyond effects on the instantaneous power conversion efficiency and hence the annual energy yield, reducing the temperature by a SBR might also reduce the degradation and increase the overall lifetime of the PV module. By describing degradation using a simple Arrhenius approach using typical activation energies between 0.4 eV and 0.8 eV, we find that an ideal SBR increases the cumulative energy yield over 30 years between 2.2 % and 4.0 % for an open-rack mounted PV module in Princeton, New Jersey, USA.