BIPVT – Thin Building Integrated Photovoltaic-Thermal Collector
Duration /
2016
Funding /
ETH SEED
A/S Team /
I. Hischier, J. Hofer, A. Schlueter
Selected Publications /
1 / I. Hischier, J. Hofer, L. Gunz, H. Nordborg, A. Schlueter. "Ultra-thin and lightweight photovoltaic/thermal collections for building integration," in: Energy Procedia (Amsterdam: Elsevier, 2017) 122, 409-414. DOI Research Collection
Integrating solar thermal collectors and photovoltaic (PV) modules into the building envelope plays a key role for the contemporary goal of constructing net-zero and plus-energy buildings. To maximize the energy harvest from the limited amount of surfaces suitable for solar application, PV-thermal (PVT) hybrid collectors have been proposed. These co-generating devices use the incident solar radiation more efficiently by cooling the solar cells with a stream of air or water which, at the same time, improves the electricity yield and provides heat for domestic hot water generation and space heating. Currently, the number of commercially available PVT systems is still very limited. Existing PVT collectors are heavy, require complicated installations limiting their applicability, and are more expensive than using both a conventional PV panel and a thermal collector to achieve the same performance.
The goal of the BIPVT project was to integrate solar collectors with thin-film solar cells in a novel PVT solar collector. The combination of these two emerging, high-potential technologies resulted in a new type of lightweight, highly efficient PVT collector with significant savings in cost and material use. Ultimately, a bendable collector design was envisioned which could be tailored to curved surfaces, opening up new and versatile application possibilities for building integration well beyond the capabilities of today’s conventional systems.
CIGS solar cells exhibit a very high absorption for the entire solar spectrum and a relatively high temperature dependence of power production, which make them particularly promising for integration into a hybrid PV solar thermal collector system. Thin film solar cells based on CIGS reach efficiencies exceeding 20% and perform better than crystalline silicon cells in low-light and shading conditions. Moreover, the flexibility and low weight of the modules makes it particularly suited for BIPVT application. Thin-film CIGS modules can be produced at low cost and are environmentally less critical than other PV technologies as less primary energy and no cadmium is required during production.
Aluminum roll-bond solar thermal collectors achieve higher performance at lower cost compared to standard flat plate solar collectors. Roll-bond absorbers directly integrate liquid channels in the absorber plate and the fabrication process allows customizing channel design to achieve optimal heat transfer and homogeneous temperature distribution, which is important for minimization of mismatch losses in the PV modules.
Schematic detail of a BIPVT collector
Following a conjugate heat transfer (CFD) simulation of a BIPVT collector, different lamination and bonding processes, material structures, channel geometries and PV cell arrangements were investigated. The results were integrated into a system simulation to identify optimal operating conditions of the collector and ensure an integrated system design.
A lab scale PVT module was assembled and experimentally characterized to validate the previously developed numerical model. The characterization included measurements of the thermal and electrical performance for different module designs and operating conditions.
Left: Unglazed PVT collector prototype made of a flexible CIGS solar module glued onto aluminum microchannel thermal collector. / Right: Image and schematic representation of experimental setup used to evaluate the PVT prototype concepts under outdoor conditions.