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A photochromic (PC) device comprising an electrochromic film (WO 3 ) together with a photoactive film (usually, dye sensitized TiO 2 ) coated on glass and a redox electrolyte (e.g., iodide/triiodide together with lithium salt) reduces the optical transmission under solar illumination and bleaches, again, in dark or at low intensity of light. This work reports, for first time, on an application of sputter coated TiO 2 and WO 3 films for this type of PC devices. The applicability of TiO 2 and WO 3 films in PC device is individually investigated in dye solar cells and electrochromic cells, respectively. A dye solar cell with 180 nm TiO 2 was shown to be sufficient for the charge generation for electrochromic coloration of the WO 3 . The compatibility of WO 3 and redox electrolyte was studied in electrochromic devices by considering their redox potentials. The bleaching of the PC device has to be adjusted by the so called “loss current”. To address this, a thin catalytic layer of platinum (Pt) is deposited in between the photoactive and electrochromic layers. The optimized PC device exhibits a visual (solar) transmission modulation from 74 (63) down to 30% (20%) in 40 min under 1.5 A.M. illumination, and the bleaching is regained in 45 min in dark.

In this paper we propose a method to predict hot spot temperatures in crystalline silicon photovoltaic modules operating under critical shading conditions prior to module fabrication. We developed a unique tool to evaluate the damage risk potential for an individual solar cell. We show that shading conditions leading to the most critical hot spot temperature do not necessarily coincide with the shading conditions for the maximum total power dissipation in the shaded cell. In fact, for an adequate prediction of temperature fields and the worst case shading scenario, spatially resolved information of the power dissipation on cell level and a thermal simulation of the module system are indispensable. Our approach is divided into three steps, starting with an electric network simulation of cell operating points for different shading scenarios. For these operating points we perform spatially resolved lock-in thermography measurements of the power dissipation on cell level. On that basis we compute three-dimensional temperature fields inside the module with a finite-element analysis for different realistic module operating conditions. The model is validated with experimental data on a module of industrial cells.

International audience; Photovoltaic-thermal collectors (or PV-T collector) are hybrid collectors where PV modules are integrated as an absorber of a thermal collector in order to convert solar energy into electricity and usable heat at the same time. In most of the cases, the hybrid collectors are made by the superposition of a PV module on the thermal absorber of a solar collector. In this paper, the approach is different and is to analyze thermal and optical properties related to both PV and solar thermal functions in order to identify an optimum combination leading to a maximum overall efficiency. Indeed, although these two functions do not exploit the same range of radiation wavelengths, thermal and PV functions are not so complementary due to photo-conversion thermal dependency. In this context, an alternative PV cell lamination has been developed with increased optical and thermal performance. The improvements were evaluated around 2 mA/cm2 in terms of current density in comparison to a standard module encapsulation. Based on this technique, a real size PV-T module has been built and tested at Fraunhofer solar test facilities. The results show a global efficiency of the PV-T collector above 87% (79% thermal efficiency plus 8.7% electrical efficiency, based on the absorber area).