The Institute for Solar Energy Research in Hamelin (ISFH) is working on two innovations for industrial silicon solar modules within the SUPERPV project. One innovation increases the light harvesting for bifacial photovoltaic (PV) modules and the other targets the integration of in-laminate bypass diodes into solar modules, which are processed with solar cell production equipment.
ISFH is a German research institute of the state of Lower Saxony and a non-profit limited liability company. Moreover, ISFH is an associated research institute of the Gottfried Wilhelm Leibniz Universität Hannover. Our field of work in photovoltaics includes fundamental material research as well as development of processes and tools needed for the fabrication of solar cells and modules. The main emphasis is the development of novel silicon solar cells and the corresponding module technology to achieve energy conversion efficiencies above 20% on the module level. Our superior goal is the reduction of the levelized costs of electricity (LCOE) of solar energy conversion, which is in line with the objectives of the SUPERPV project.
A reduction of the LCOE can be achieved by increasing the conversion efficiency of the solar module without increasing the production costs or deteriorating the long-term reliability of the module. In a typical bifacial glass-glass module, a large fraction of the light incident on the cell gaps is lost and not converted by the solar cells within the module. In the SUPERPV project, we apply white color within in the cell gaps on the rear glass by screen printing processes to enhance the light harvesting of the solar module. Due to the white color, the light incident on the cell gaps is internal reflected within the module, which increases the probability that it impinges one of the solar cells. In areas where there is no cell gap, the rear glass in not covered with white paint. This preserves the bifacial properties of the module and the solar cells can absorb light that hits the rear side of the module. Thus, employing commercially available glass printing processes allows to increase the performance of bifacial PV modules cost-effectively and thus, reducing the LCOE. We simulate the optimal geometry for the white pattern on the rear glass for the bifacial module with our in-house ray tracing software Daidalos (https://www.daidalos-cloud.de/). The software also allows the implementation of radiation time series to perform annual yield estimations for the innovative modules at locations with different climate.
Another possibility to improve the LCOE is to reduce the inactive area of the solar module and hence, increase the efficiency. Applying in-laminate bypass diodes enables to reduce the area and material consumption by the string-to-string interconnection. Additionally, the junction box can be designed such that it leads to less shading on the rear side. We developed a process to produce the in-laminate bypass diodes with solar cell production tools, which potentially can reduce the costs of these diodes for a PV cell and module manufacturer.
We test all modules within accelerated aging tests to ensure the long-term stability of the innovations. Finally, all module innovations are compared to reference bifacial modules at five demonstration sites with different climates to demonstrate their application and benefits in field experiments.