Researchers at the AGH University of Krakow in Poland and its Eko-Energia AGH student group have published a study about their approach to lightweight bifacial vehicle integrated PV (VIPV) modules, featuring front and rear-side glass fiber-reinforced composite (GFRC) layers, on the SSRN open access platform for early stage research.
“The modules we have developed employ glass fiber-reinforced sheets/mats on both the front and rear sides of the modules. This makes the modules bifacial, resulting in slightly higher energy output for a given area,” Pradeep Padhamnath, Assistant Professor, AGH University of Krakow, and research leader, told pv magazine.
The biggest challenge in fabricating the modules was designing the appropriate layer of materials providing the optimum combination of optical transparency, strength, and flexibility. “Although, in the paper, we have shown only five stacks, we tested more than 20 different layer combinations based on the simulation results,” said Padhamnath.
The optical characteristics of the prepared laminates were measured using a UV-VIS spectrometer and simulated current-voltage characteristics were tested with a light lab PV simulator. The team noted that it was able to calculate the final optical properties, but the mechanical properties could be tested only experimentally. “The layers that performed the best optically often had insufficient mechanical properties,” explained Padhamnath.
The five proof-of-concept modules were made with interdigitated back-contact (IBC) solar cells and a variety of front and back-layer GRCF weights to find the best combination for weight, cost, solar transmissivity and mechanical strength constraints.
The scientists sandwiched two IBC cells between layers of GFRC sheets with the resin drawn under vacuum and cured at room temperature. The modules were prepared without using a stringer or laminator. The layer of GRCF mat on the front, and another layer of twill-weave fiberglass reinforced composite fabric (TW-GRCF) on the rear, ranged in weight from 50g/m2 to 150 g/m2 and on the rear from 150 g/m2 to 450 g/m2. A standard PV glass that was 3.2 mm thick and 7200 g/m2 was used as a reference. All prototypes had the same encapsulation film.
The stack with the 50g/m2 GRCF at the front and 250 g/m2 TW-GRCF at the rear was selected for further testing. The group noted that further development of a gentler peeling process, or automation of the peeling process could enable the use of the lighter weight GRFC material.
Another aspect of the study examined end-connector materials, comparing the performance of aluminum (Al), copper (Cu) and nickel (Ni) connectors. The team’s electroluminescence (EL) and current-voltage output (IV) measurements revealed the Ni alloy enabled the lowest relative degradation. Cracks were observed in Al modules but were not observed in modules with Cu or Ni connectors, the group said.
Further details of the work were shared in “Development of low-cost light weight c-Si photovoltaic modules for applications in VIPV,” published on SSRN.
“The next step is scaling up and making large modules to be integrated into the vehicle. The Eko Energia team is building the vehicle's body from scratch at their fabrication facility at the university. We have the design and concept of integrating modules into the vehicle's body/surface during its fabrication,” said Padhamnath.
The module degradation tests were performed at the Solar Energy Research Institute of Singapore (SERIS) at the National University of Singapore (NUS).
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