Developing Modular Interconnections for Disassemblable PV Modules

Abstract

The remarkable expansion of the PV industry can be attributed to cost reductions and technological advancements, resulting in solar energy becoming an appealing and sustainable option. However, there is a growing concern regarding the environmental impact of disposing decommissioned solar panels. To address this issue, Biosphere Solar, a startup based in Delft, is actively engaged in developing recyclable and repairable solar panels, embracing a circular and sustainable approach. Their ongoing research is centered on solar modules made without EVA lamination, with the goal of facilitating easier disassembly. A crucial aspect of achieving disassembly of solar cells involves exploring modular interconnections that allow for the disconnection of interconnections between solar cells.

Although modular interconnections are already employed in batteries, electrical switches, and communication systems, their potential application in connecting solar cells has not been extensively explored. This thesis explores various interconnection approaches aimed at facilitating modular interconnections within PV modules constructed using interdigitated-back-contact (IBC) solar cells, following the structure established by Biosphere Solar for PV modules. The objective is to allow for the replacement of damaged solar cells without adversely affecting neighboring functional cells. Four distinct concepts were investigated, each utilizing the dog-bone contact wire to connect IBC solar cells in series. These concepts include a desolderable interconnection using a single dog-bone wire soldered with SnBi (a low melting temperature solder alloy), desoldering between the contact regions of two dog-bones connected through the fusion of tin coatings at overlapping areas, interconnection mechanisms based on contact pressure within a polymer-based cell-bed, and a contact pressure interconnection mechanism based on magnetic force. Both contact pressure interconnection mechanisms involve two dog-bones to create a series connection between a pair of solar cells.

After evaluating the technical feasibility of the aforementioned concepts, prototypes were developed, each incorporating the specified approaches. Furthermore, two reference prototypes were fabricated to establish benchmarks for comparison. Both prototypes employ conventional interconnections with a single dog-bone and SnAgCu solder alloy. The difference lies in the module build-up: one follows the Biosphere Solar approach (without EVA), while the other adheres to the traditional module build-up (with EVA and lamination). For the sake of simplicity, the reference prototype constructed using the Biosphere Solar approach and utilizing the SnAgCu solder alloy is referred to as the ’SnAgCu’ prototype, while the one built using EVA lamination is referred to as the ’EVA’ prototype.

I-V measurements revealed that the prototypes with single dog-bone based interconnection soldered using the SnBi solder alloy and two dog-bones with molten joint connections achieved the highest efficiencies (21.51% and 21.17%, respectively) compared to the other prototypes based on concepts explored for creating modular interconnections. The improved cell-bed design, which has a screw-based mechanism, showed an increase in efficiency (20.68%) compared to the slider-based mechanism (18.46%). The prototype with magnetic force-based interconnections achieved an efficiency of 19.94%. The two reference prototypes had efficiencies of 21.58% (SnAgCu) and 21.98% (EVA).

All prototypes, except for the one utilizing the slider-based interconnection in the cell-bed, underwent thermal cycle tests. Toward the conclusion of the thermal cycle testing, the prototypes featuring desolderable interconnection mechanisms (a single dog-bone soldered using the SnBi solder alloy and two dog-bones with soldered contact regions) exhibited the highest efficiencies compared to the other prototypes developed to explore potential concepts for modular interconnections.