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Report RSE 18002425

Simulation of the performance of InGaP solar cells for luminescent concentrators



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G. Timo´ (RSE SpA) , A. Minuto (RSE SpA), S. Rizzi (RSE SpA)

GESTDOMANDA 2017 - Demand Side Management

The improvement achievable in luminescent windows applications, using InGap instead of Silicon cells, are reported. This solution is very promising for Builiding integrated PV, which may provide important benefits in terms of electrical demand profiles.

In the field of renewable energy, the low-concentration photovoltaic (PV) technology, in particular,concerning the so-called luminescent concentrators, is becoming an increasingly attractive solution forthe integration of PV technology in buildings, increasing the share of local self-production andimproving load profiles for the electrical system. These PV modules consist of semi-transparentpolymethylmethacrylate (PMMA) slab, containing special nano-particles (dyes) that have the ability toabsorb part of the sunlight and to re-emit it in a narrow wavelength range, thus giving a typical colour tothe slab.

Unlike simple coloured panels that are inserted into buildings with exquisitely aesthetic role,the luminescent concentrators combine the architectural function with the energetic one. To reach thisobjective, photovoltaic cells are installed at the edges of the luminescent concentrator, converting intoelectrical energy the light that impacts on the slab surface. In order to optimize the performance of theluminescent concentrator, the dye must be adequately coupled with the solar cell material, i.e. the solarcells have to be made of materials with “energy gap” values (i.e. with absorption energy thresholdvalues) as close as possible to the energy value at which the dye light emission reaches its maximum. Sofar, this coupling has not been optimal, since the luminescent concentrators, operating at a lowconcentration, have required the utilization of low-cost solar cells, such as the silicon ones, whoseenergy gap value deviates significantly from the average energy value of the photons emitted by thedyes.

More recently, the development of new materials and manufacturing processes for photovoltaicdevices have paved the route for the use of III-V compounds, previously reserved only for the highconcentration applications, also for the luminescent concentrators, with the perspective to set up a PVtechnology with high conversion efficiency at low cost. RSE has then started a study to assess theadvantage of using InGaP-based solar cells in luminescent concentrators, owing to the better couplingbetween the energy gap of the semiconductor material and the emission spectrum of the dyes used in theluminescent concentrators.

The main objective of the activity has been to evaluate the potential increaseof the module performance by replacing the "traditional" silicon-based cells with InGaP ones, by testingdifferent luminescent slabs, supplied by an industry with which RSE has signed a collaborationagreement. Initially, in order to obtain a simulation as much realistic as possible, outdoor tests have beencarried out with the aim of experimentally determine the light spectrum emitted at the edges of theluminescent slab; subsequently, a software program has been developed in order to calculate thephotovoltaic conversion efficiency of InGaP cells when placed at the edges of these slabs. A conversionefficiency as high as 44.7% has been achieved with InGaP cell, which is four time higher than theefficiency value obtained with silicon solar cells. It follows that the production of energy could increasefrom 3 to 4 times, adopting this solution.

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