Researchers from the Eindhoven University of Technology (TU/e) in the Netherlands have developed a series of measurement protocols for assessing the performance of luminescent solar concentrators (LSCs) with the aim of helping this technology reach commercial maturity.
The LSCs can be used as photonic devices in the production of fine chemicals in photomicroreactors, in dynamic “smart” windows to control light entering room spaces, for distribution of color-tuned light for enhancing plant growth in greenhouses, and they can also be utilized for improving the efficiency of photovoltaic panels.
The LSCs consist of luminescent materials that are also known as luminophores, which are groups of molecules that emit light when illuminated. These materials, which can be coated on the surface of a polymer or glass plate, or used as a dopant of the polymer or glass plate acting as a lightguide, are able to capture direct and indirect sunlight at one wavelength and re-emit it at a longer wavelength.
Integration with PV
If applied to PV, luminophores are able to capture high-energy photons that the photovoltaic panels cannot absorb and re-emit them as photons of lower energies. “The downshifted photons have energies that can be efficiently exploited by a mounted PV cell coupled to one or more edges or faces of the lightguide, thus harvesting the spectrally converted and optically concentrated photoluminescence photo transported there via total internal reflection,” the academics explained.
The LSCs can be integrated with finished PV modules with no need of modifying their electronic structure. “In addition, their aesthetic potential, color and shape tunability, combined with their ability to enhance PV response to diffuse light, may provide new opportunities for innovative product design concepts deployable in a variety of market segments as diverse as architecture, agriculture, transportation and other infrastructures,” the Dutch group explained, adding that the perfect match of the technology would be with building-integrated photovoltaics (BIPV).
The integration of LSCs and PV devices, however, remains difficult to analyze, as experiments that are being conducted worldwide are not presented in a uniform manner and all descriptions related to luminophores, lightguide materials, panel size, surface and edge modifications differ significantly. “Research groups working on LSCs tend to fall into two main camps in how they view LSCs, inevitably leading to the use of inconsistent metrics for their characterisation: LSCs are regarded either as a particular class of PV devices or as purely photonic systems,” the researchers said.
The lack of a universal standard for comparing the performance of these devices is what is currently keeping this technology in “relative obscurity,” according to the researcher, and the protocols that are now being applied, which are the same used for the PV technology, are inappropriate for LSCs. “It’s great that LSCs improve the efficiency of PVs, but this has led to a problem with standards,” the academics stated. “Progress has been slowed by the lack of standard reporting methods for LSCs, meaning it has been impossible to compare data collected for the past 40 years.”
The TU/e team believes that all standard measurements on LSCs should be carried out using an absorbing background or a mounting preventing reflections of unabsorbed light or luminophore-emitted light from re-entering the devices. Furthermore, the size and shape of the LSC should be described and the thickness of the lightguide should be thoroughly reported. Moreover, a clear indication of the manufacturer and type of light source, detector and integrating sphere used should be provided. A detailed checklist of the key metrics, measurements and experimental parameters should also be added.
“Currently, LSCs lack proper identity, and that’s not good for the technology,” said research co-author Michael Debije. “The field of LSCs has been around for 40 years, but has failed to gain industrial momentum.”
The proposed standards are presented in the study Laboratory protocols for measuring and reporting the performance of luminescent solar concentrators, published in Energy & Environmental Science.
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