The focus of the CPVMod research project is the development of innovative, high-performance concentrator photovoltaics (CPV) modules. The advantage of CPV modules is the concentration of sunlight onto highly efficient solar cells that are only a few square millimeters in size, thus saving semiconductor material. In addition, the modules achieve conversion efficiencies of more than 30%. The modules developed as part of the CPVMod project are to be produced using cost-effective and robust manufacturing technologies. These manufacturing technologies are intended to enable reliable module production also in the vicinity of future CPV installation sites with a high regional value-added share. The technology is particularly suitable for areas in the Earth's sun belt with a high proportion of direct sunlight.
In the subproject "CPV Module in Modular Design: Module Design and Module Performance", the module design is being evaluated and further developed by Fraunhofer ISE in cooperation with the project partners AZUR SPACE and ORAFOL. Besides a high electrical efficiency, the focus of the module design is on the production technology to be used based on simple methods for quality assurance. A further project aim is the examination of the components and the module for long-term stability and the evaluation of the module output power under external conditions.
Figure 1 shows two AZUR C3PV modules. Both modules each deliver more than 400W of electrical output power with efficiencies of over 30%. The modules consist of arrays of Fresnel lenses and Enhanced Fresnel Assemblies (EFA) mounted on a metal unit. The metal unit serves as an efficient heat distributor and thus, as a passive cooling unit of the solar cells. Due to the focusing of the sunlight by the Fresnel lenses, not only electrical energy but also non-negligible amounts of heat are generated in the solar cells. This heat must be redistributed sufficiently in the CPV module to prevent electrical losses due to increased temperature. The heat differences within the CPV modules could be determined in CPVMod using thermal finite element simulations (FEM). Figure 2 shows the heat distribution within the CPV module. As expected, the highest temperatures occur in the solar cells however on a level usual for CPV modules.
In order to be able to evaluate these temperature differences, thermo-mechanical FEM simulations have been carried out in the next step. So far, neither significant mechanical loads in the module nor critical displacement of the solar cell position could be determined. Therefore, a sufficient redistribution of the heat quantity in the module is guaranteed.
Furthermore, manufacturing tolerances in the module construction process have been quantitatively evaluated in the project. An important factor is the positioning of the Fresnel lens in relation to the solar cell. In order to evaluate this variable, individual lens-cell units have been characterized electrically using a special test construction on a solar simulator (Figure 3). The result of this characterization is shown in Figure 4 as a standardized output power versus a displacement of the lens in relation to the solar cell. It could be shown that the module design is very tolerant to lateral displacement. Even with a displacement of more than ±0.3mm in the x-direction, the relative power loss is less than 3%. These evaluations help our industry partners to further improve the reliability and manufacturing technology for CPV modules.