Experimental studies of the technical feasibility of a lamination process for PVT-direct modules

The PVT-direct module covers the technical connection of solar PV technology and solarthermal systems. The structure is similar to conventional PV modules apart from the backsheet which is replaced by an aluminum backside plate. Along with compressor, gas cooler for heat rejection and expansion valve the PVT-direct module acts as an evaporator in a heat-pump cycle. The module is characterized by a direct CO2 evaporation in small microchannels which are brazed on the aluminum backside plate. The combination of both photovoltaic and thermal components in one module leads to high demands in terms of the choice of materials and the production process itself. In this context, further investigations on the technical feasibility of a lamination process for solar PVT-direct modules are necessary in order to guarantee an intended market maturity.
The development of a suitable lamination process and its parameters form the major part of this work. The lamination schedule depends on the performance and structure of the used encapsulating material as well as the laminator itself. The lamination process is adjusted through experimental studies until satisfactory results are achieved. It can be characterized by the maximum lamination temperature and the total process time along with the heating/cooling ramp.
The additional aluminum backside plate including headers and microchannels can have a significant impact on the PVT-direct module during lamination process. Therefore, measurement methods which indicate the state of the module after the lamination are required. On the one hand, the quality of the adhesion between the different parts of the module is an important factor for long-term resistance of the system. The cross linking of the encapsulating material and of the adhesion layer is verified by DSC-Measuring. On the other hand - due to a changed design of the PVT direct module and mechanical stress distribution during the lamination process - the mechanical condition of the cells inside of the laminate is checked. This can be evaluated by Electroluminescence-Measuring in order to ensure the absence of cracks and fraction of the PV-cells.
Current tasks involve the distortion of the laminated modules due to different thermal expansion coefficients of glass and aluminum as well as the occurrence of blisters in the laminate. These issues and the lamination of a module in standard measures will be addressed in the ongoing process of the project.