Flexible Thin Film Solar Photovoltaic Cells
Conventional solar PV panels were designed to be ground mounted and at best Building Applied based on the very nature of the crystalline silicon cells and their limitations / characteristics. As for building integrated photovoltaic functionality, form and function did not match. There was a clear need to rethink the form of solar PV and its embodiment in order to meet the needs and opportunities it presented for a true building integration and its attendant benefits. This is the vision of turning buildings in to power stations without making them look like one.
After 5 years of collaborative research and development with industry partners, academic institutions and venture capitalists, BIPVco was spun out to global investors as a business to integrate flexible thin film solar photovoltaic cells directly onto common roofing substrates and materials.
Throughout this period many cell technologies were investigated and discounted. Dye Sensitised cells, Organic, Crystalline Silicon and Perovskites were all deemed either unsuitable, not sufficiently developed technically or not yet commercially viable.
Second generation photovoltaic technology known as Copper Indium Gallium Selinide (CIGS) has long been viewed as a thin film technology with a very bright future, but until 3 years ago there was not any commercial scale manufacturing of the cell technology in a flexible format.
Throughout the R&D / pre competitive phase, the business case and the value proposition to the customer was always foremost in the mind of CEO Daniel Pillai and COO Paul Bates, the founders of BIPVco. “It’s no good coming up with an idea for a commercial product and its features and benefits if you can’t manufacture it to make the product at a sensible cost point in partnership with serious commercial / supply chain partners to offer a fully warranted solar PV functional roof / wall”
BIPVco’s modules use flexible CIGS technology that is integrated directly onto the roofing component using adhesive or direct lamination by heat and vacuum sealing. The process has been developed to be compatible for direct integration onto standing seam pre painted steel roofs and single ply membrane roofs. The peel and stick option is also available for aluminium standing seam roofs.
The approved building envelope substrates have to go through a rigorous accelerated torture testing and assessment process in order to assess their stability and durability over the warranted life of the PV functionality and beyond. Long-term warranties of durability and performance are only possible when the PV functionality is anchored to a robust and durable substrate that can be relied upon and backed up by the manufacturer.
Presently the closest to an integrated PV option for a roof is to use clear laminates or glass mounted crystalline silicon PV cells incorporated into an aluminium mounting structure, much like traditional on-roof crystalline solutions. However, this approach has little structural integrity and is not the most cost efficient way of combining solar in to the buildings fabric. Two sets of contractors will be required to install the roof and the solar PV using this approach, rather than using the one contractor to install a roofing system with the BIPVco factory attached solar cells pre integrated on to the roofing system.
Crystalline silicon PV cells also have a uniform industrial look that not only adds considerable extra weight to the building structure (approx. 15-20 kg/m2) but also impacts on the aesthetics of the building. They are easily broken and not very vandal nor theft proof.
The flexible thin film modules are not breakable and being integral to the roof less prone to theft.
To do away with the unsightly crystalline silicon PV cells one has to do away with the glass and aluminium frame. This means the photovoltaic cell itself will need to be robust enough to be attached directly to a roof and therefore will need to be flexible. Crystalline silicon PV cells are fragile and not flexible, hence require the glass to protect them from disintegration from external forces and internal thermo / mechanical movements. The aluminium frame is required to support the glass.
The initial target market is architecturally specified new build projects and roof re-cladding projects. As the market changes from being investment led, focused on return on investment (ROI), a more sustainable demand-led market is emerging. Given the scarcity of land and its need for agriculture etc. and the desire to consume the generated power at source within the building, the demand for building integrated photovoltaics with its aesthetic and structural benefits will increase.
The value propositions of flexible thin film solar photovoltaic cells are wrapped up in the value of the roof itself. “For a new building that requires solar PV generation, the traditional way is to have multiple contractors, one to commission the roof and another for the building applied photovoltaic system. In our solution the PV installation becomes part of the roofing installation itself, which presents the installer with many cost saving opportunities in both labour and material not to mention the benefits of reduced time and the associated reduction in cost of preliminaries ” says Daniel Pillai.
The flexible thin film solar photovoltaic cells are suitable for commercial, industrial and residential roofs. Other buildings, such as churches, stations, and stadiums, which are due for re-roofing could also benefit from the aesthetically sympathetic look of the product. The modules weigh under 3kg/sq metre compared with 1520kg/sq meter for a crystalline silicon PV module. Many existing buildings have little or no spare load carrying capacity and the additional loads from BAPVs render them unsuitable. This opens up their potential of thin film flexible products to be used on buildings with little spare load carrying capacity. The zero impact of wind loads and the absence of ballasting opens up a much wider roof top applications.
One of the first projects the flexible thin film PV used was a new university building at Swansea University, which was completed in September 2016. This building has 17KW of flexible thin film PV on a metal standing seam roof. One of the benefits of CIGS technology is its ability to generate energy under low light (cloudy days). In cloudy mid winter days, the above system was producing 7KW power. Multiple diodes of the smaller cells also provide additional protection from disproportionate loss of generation should shadows be cast or bird droppings obstruct light from reaching the cells.