Impact case study database

Conventional solar panels, based on silicon technology sandwiched between glass coverings, are now widely deployed and are one of the cheapest renewable energy sources worldwide. However, the manufacturing processes are complex and require ultra-clean manufacturing environments. Solar panel modules can be mounted on top of a roof or wall structure, however there are emerging opportunities for solar technologies to be integrated into the building fabric. So-called ‘building-integrated photovoltaics’ (BIPV) as an alternative to traditional silicon panels, offer the opportunity for the whole roof of a building to generate power. It also offers an opportunity to make the material more lightweight and flexible to allow for curved surfaces. An additional challenge for silicon PV is that the high capital costs of manufacturing plants and very high-energy consumption is centring the manufacturing in Asia and thus is not supporting local manufacturing supply chains.

Direct integration of the photovoltaic material with steel roofing is an attractive opportunity, given the current production of 100,000,000m² of coated steel for buildings that is manufactured by Tata Steel in the UK annually. Approximately 60% of this output is used in the UK, providing a significant opportunity to produce more sustainable energy at scale.

Since 2007 SU materials scientists [G1], Worsley’s team, tackled these issues to develop an inexpensive, ambient printable photovoltaic device that could be integrated directly into the fabric of the building at large scale. This work was initially funded by the EPSRC “Metal substrate mounted flexible dye sensitised semiconductor solar cells” project, which became one of the forerunners to the SPECIFIC Innovation and Knowledge Centre (IKC) [G2, G3]. SPECIFIC now covers work on PV manufacturing and electrical storage, thermal generation and storage, and building integration and design in support of the transition to solar powered buildings.

Initial research published in 2011 [R1] led to the development of a prototype metal-mounted dye-sensitized solar cell in collaboration with Tata Steel, and this work highlighted the potential for building-integrated PV on sheet steel roofing materials. A number of key technical breakthroughs were made in lightweight flexible metal mounted PV at Swansea during this pre-commercial, early adoption period, which underpinned the initial technology demonstration of the BIPV concept on steel products supported by collaborative research grants alongside the IKC core team.

In 2011, Watson’s research team at Swansea produced the world’s first dye-sensitized solar cell deposited directly onto a steel substrate, a critical enabler to large-scale roll-to-roll manufacture [G1, R1]. In particular, the work probed the influence of direct integration of the PV device stack through multi-layer deposition onto a pre-painted construction substrate. The method was based around chemically isolating the underlying substrate using a dual high temperature-stable organic coating combined with an electrically conductive metal layer. Though the work illustrated the issues of substrate expansion during long-term high-temperature processing, it paved the way for the development of post-processed layers rather than direct deposition.

A major bottleneck in the manufacture of low-cost solution-processable PV is the time required to manufacture the device which prior to our research was known to be 30 minutes. The Swansea team has developed alternative heating and curing methods using near-infrared radiation and photonic techniques that can achieve the same result in just 12.5 seconds [G2, G4]. When these technologies are applied to the dye-sensitized solar cell, such as those developed in [R1], the manufacturing time is reduced from many hours to under 2 minutes. This means that the manufacturing process shifts from being a costly batch process to a higher volume, cheaper and continuous process. In 2014, Carnie and Charbonneau sought to understand the influences of short process times on the performance of PV devices and found that rapid processing could be undertaken without detriment to material behaviour or performance [R2, P1]. Despite the dye-sensitized technology forming only the pre-commercial prototype, the work provided a benchmark for the evolution from slow and expensive batch processes to continuous fabrication.

To enable the translation of conventional glass-mounted, solution-deposited solar cells onto a flexible but opaque surface such as steel, a transparent top electrode is required. Under normal circumstances, this would be applied via a low volume, costly vacuum process. In 2015 [G3, G4], the team developed a, low-cost and transparent laminate electrode, requiring only finger pressure for application, that not only performs comparably to vacuum-evaporated metallic contacts but also provides mechanical adhesion that the evaporated material does not [R3], [P2, P3]. This product was developed for solution-processed PV technology and acted as the forerunner for the incumbent commercially-deployed CIGS (Copper, Indium, Gallium, Selenium) product.

In 2015 members of the Tata Steel research team at Shotton established BIPVCo as a spinout in partnership with Swansea Innovations (the university commercialisation team). The team helped BIPVCo with both the legal structuring for the creation of the separate entity, negotiations, and support to gain private sector investment. The SPECIFIC IKC team worked closely to help scope and design the manufacturing unit, establish local lab testing facilities, and support key aspects of the work on adhesion and lifetime prediction required to integrate photovoltaic (CIGS) foils into premium steel coated roofing products co-developed with Tata. Once established the Tata team took on permanent roles with BIPVCo to drive it forward leaving their positions in Tata but continuing to operate on the Shotton site.

In order to develop greater understanding of in-service performance and provide evidence that the commercial product can be deployed successfully in demanding environments, the research team at SPECIFIC, analysed the performance of the first trial production BIPVCo mounted product applied to an Active Classroom building located at SU’s Bay Campus [G3, G5], [R4]. Using data collected during a twelve-month period on SU’s Active Classroom (a purpose-built showcase for several solar-based technologies), the research showed that, in the oceanic climate of SU, which is defined by a narrow annual temperature range and a high level of precipitation, there is significant fluctuation in PV performance of the BIPVCo product throughout the year. This evolved into an understanding of the link between the Active Classroom battery system and the point at which the PV power output drops to the base load of the building when the battery is full. The work fed data back to BIPVCo and illustrated the product stability and performance variation over the twelve-month period. Recommendations on how to link the product with smart control algorithms to optimise future PV-battery systems were made.

Durrant and Watson has also established a weathering and stability capability at SU [G3, G6] which allows extensive monitoring of PV devices both at lab-scale (in the development phase) and in-service on our fully monitored active buildings [R5]. These capabilities support product development by enabling standardised test conditions to be run on both developmental prototypes and complete products. This work builds on our historical experience in monitoring the stability of organic coatings and enables more accurate projections of product lifetimes from laboratory experiments. The BIPVCo materials are also part of the international exposure testing programme with Tata group and five Indian Institutes of Technology in the SUNRISE programme [G7].