TECHNICAL INVESTIGATION OF A PHOTOVOLTAIC MODULE WITH INTEGRATED IMPROVED PHASE CHANGE MATERIAL Ewald Japs, Gerrit Sonnenrein 1 , Julia Steube 2 , Jadran Vrabec 1 , Eugeny Kenig 2 , Stefan Krauter University of Paderborn Department of Electrical Energy Technology – Sustainable Energy Concepts, Pohlweg 55, D-33098 Paderborn, Germany, Tel. +49 5251 602303, Fax. +49 05251 603235, e-mail Ewald.Japs@upb.de, Stefan.Krauter@upb.de 1 Department of Thermodynamics and Energy Technology, Warburger Straße 100, D-33098 Paderborn, Germany, Tel. +49 5251 604139, Fax. +49 05251 603522, e-mail Gerrit.Sonnenrein@upb.de, Jadran.Vrabec@upb.de 2 Department of Fluid Process Engineering, Pohlweg 55, D-33098 Paderborn, Germany, Tel. +49 5251 602161, Fax. +49 05251 602183, e-mail Julia.Steube@upb.de, Eugeny.Kenig@upb.de ABSTRACT: High operating temperatures inside a crystalline silicon photovoltaic cell causes a significant negative effect to its energy conversion efficiency. A reduction of this temperature would not only lead to a gain in energy yield of a PV module but also would has a positive effect to its degradation rate and lifetime. One effective approach seems to absorb the heat flow via phase change materials (PCM). Unfortunately, due to its low thermal conductivity and the mass required to provide a sufficient heat storage capacity, its application for PV modules has been very limited. This investigation includes an assessment of a new PCM compound, featuring an increased thermal conductivity, but with a lower heat storage capacity. For this reason, a single crystalline silicon PV module has been equipped with a conventional, commercially available PCM and another one with the new PCM compound. Both PV-PCM modules and a bare reference PV module have been compared at real summer outdoor conditions in the PV-Outdoor-Laboratory of the University of Paderborn. Keywords: PV module, PV materials, phase change material 1 INTRODUCTION Based on the fact that crystalline silicon PV modules are showing performance losses at increasing operating temperatures (at about -0.45%/K), the development of an adequate technical and cost-effective cooling measure is essential for progress in PV performance [1]. Numerous approaches to realize active or passive cooling measures for PV modules have already been investigated, but none of them reached a relevant market penetration [2], [3], [4]. Thereby, the main challenge is to realize a cooling measure, which is functional, applicable and cost-effective at the same time. Particularly for PV applied in buildings a maintenance-free, passive cooling measure would have a high applicability [5]. Moreover, a passive cooling measure without any necessary of additional infrastructure and energy requirements during operation would have a much higher chance for applicability. One effective approach seems to absorb the heat flow via phase change materials (PCM). However, these materials have some drawbacks. A couple of studies regarding PV equipped with PCM describe its low thermal conductivity as one of the main disadvantages. The materials with the highest thermal conductivity examined within PV literature features a thermal conductivity value of 1.09 W/m·K [6] [7]. In this technical investigation, a new paraffin based compound with a thermal conductivity of 2.4 W/m·K has been studied. This high thermal conductivity has been achieved by addition of a new compound to a PCM. The new resulting PCM compound material shows a reduced heat storage capacity caused by a decreased share of effective phase change material. However, a higher thermal conductivity value compared to a regular low value has a higher chance for a better performance and applicability. Therefore, one PV module has been equipped with this new PCM compound and another PV module has been equipped with the same PCM compound but without the increased thermal conductivity property. These PV-PCM modules and one unequipped identical PV module have been measured and compared simultaneously at outdoor summer conditions 2013 in Paderborn, Germany. 2 PRELIMINARIES 2.1 Characterizing the PCMs applied The applied PCMs have been encapsulated hermetically in bags consisting of an aluminum-polymer compound. Each bag contains about 500 g of PCM. Due to the high inaccuracy of the latent heat value specified in the PCM data sheet of about ±7.5%, additional measurements of this property have been carried out. Figure 1: Heat flow absorption capabilities as a function of temperature (thermographs) of both PCMs compared in the investigation. Two thermographs have been obtained by differential scanning calorimetry measurements, as shown in Fig. 1. Hence the values for the latent heat of PCM and PCM+ (improved phase change material) have been calculated by determining the area under each curve, marked with dashed line fillings in Fig. 1. Resulting values have been below the aforementioned inaccuracy value and are shown in Table 1. 28th European Photovoltaic Solar Energy Conference and Exhibition 500