Optical filters for spectral splitting photovoltaic-thermal collectors
File(s)
Author(s)
Masilo-Kumi, Joy
Type
Thesis
Abstract
Solar energy technologies, such as photovoltaic cells for electricity and solar thermal collectors for heat, have garnered significant research interest. Combining these technologies results in a hybrid photovoltaic-thermal (PVT) collector that simultaneously generates electricity and heat. Only low to medium-temperature heat (up to 80 °C) can be generated because high-temperature heat (above 80 °C) reduces the efficiency of the PV cells. To address this, optical filters are incorporated into the collector to achieve a thermally decoupled design that separates the PV cells from the thermal absorber.
The optical filters investigated include dielectric-metal-dielectric (DMD) films and metasurfaces. The DMDs used consist of titanium dioxide (TiO2) as the dielectric layer and silver (Ag) as the metallic layer. The metasurfaces consist of nanostructured material arrays, particularly nanodisks. These optical filters operate by splitting the solar spectrum into wavebands. The waveband transmitted or reflected to the PV cells matches PV cells’ spectral response, and the rest is directed to the thermal absorber. Incorporating optical filters results in a spectral splitting photovoltaic-thermal (SSPVT) collector. When coupled with concentrators such as mirrors or lenses, a spectral splitting concentrating photovoltaic-thermal (SSCPVT) collector is produced.
A parabolic trough SSCPVT collector with two fluid channels was used in this study. One is a PV cooling channel, and the other is for the thermal absorber. A coupled optical-electrical-thermal model of the SSCPVT collector was developed in COMSOL Multiphysics. The SSCPVT collector achieved an overall (electrical and thermal) efficiency of 55% without an optical filter. The simulated metasurface filter increased the overall efficiency to 63%, while the simulated DMD filter reached 68%. In comparison, the fabricated DMD filter only reached 60%. This discrepancy can be attributed to the fabricated filter’s lower transmittance compared to the simulated one, due to optical losses from defects such as surface roughness.
The optical filters investigated include dielectric-metal-dielectric (DMD) films and metasurfaces. The DMDs used consist of titanium dioxide (TiO2) as the dielectric layer and silver (Ag) as the metallic layer. The metasurfaces consist of nanostructured material arrays, particularly nanodisks. These optical filters operate by splitting the solar spectrum into wavebands. The waveband transmitted or reflected to the PV cells matches PV cells’ spectral response, and the rest is directed to the thermal absorber. Incorporating optical filters results in a spectral splitting photovoltaic-thermal (SSPVT) collector. When coupled with concentrators such as mirrors or lenses, a spectral splitting concentrating photovoltaic-thermal (SSCPVT) collector is produced.
A parabolic trough SSCPVT collector with two fluid channels was used in this study. One is a PV cooling channel, and the other is for the thermal absorber. A coupled optical-electrical-thermal model of the SSCPVT collector was developed in COMSOL Multiphysics. The SSCPVT collector achieved an overall (electrical and thermal) efficiency of 55% without an optical filter. The simulated metasurface filter increased the overall efficiency to 63%, while the simulated DMD filter reached 68%. In comparison, the fabricated DMD filter only reached 60%. This discrepancy can be attributed to the fabricated filter’s lower transmittance compared to the simulated one, due to optical losses from defects such as surface roughness.
Version
Open Access
Date Issued
2025-04-30
Date Awarded
2026-04-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Markides, Christos
Sponsor
Commonwealth Scholarship Commission
Publisher Department
Department of Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)