PV for glass and steel11 / 2011, Research & Development | By: Sara Ver-Bruggen
Organic PV: Several developers of novel solar cells are teaming up with suppliers of building façade and envelope materials to turn buildings into renewable electricity generators. But why are these industrial players working with developers of solar cells that fall so far below acceptable efficiencies?
The mood at this year’s EU PVSEC was acutely sensitive as to what the next 12 months or so hold in store. But while the conventional photovoltaics industry prepares for a period of belt-tightening, other industries, specifically those that supply the global construction market, are turning to novel PV technologies as opportunities to add value to their product lines and enhance their future competitiveness.
Markets for building-integrated photovoltaics (BIPV) are significant. The glass and steel industries produce billions of square meters of products for construction markets every year, of which even a small percentage is worth pursuing by third-generation PV. This partly explains why an increasing number of glass, coated steel and other building façade component suppliers are working with developers of solar cell technologies wherever there is potential to closely integrate PV and building components.
Lars Pfeiffer of ThyssenKrupp Steel Europe says, “How conventional PV panels are produced is nothing like the manufacturing involved in processing building components, but when we start to look closely at how organic and polymer PV (OPV) are made, there are some similarities between coating and processing steel and solar cells.” Third-generation PV covers a wide range of materials engineered with semi-conducting properties at the molecular level. They include, but are not limited to, small organic molecule semiconductors, large molecule organic polymer semiconductors, metal nanoparticles, quantum dots and silicon nanostructures. Most R&D efforts are focused on OPV and dye solar cells (DSC). DSCs are based on nanoparticles of titanium dioxide covered with a molecular dye that absorbs light.
Third-generation photovoltaics are compatible with low-temperature processing. Clean room environments required for crystalline silicon (first-generation PV) and thin-film PV (second-generation) manufacturing are not required for third-generation PV fabrication. This expands production possibilities considerably. Some developers, like Oxford Photovoltaics in the UK, are working on screen-printing DSCs onto glass, whereas Heliatek in Dresden, Germany, is focused on vacuum processing OPV onto plastic with high-volume roll-to-roll equipment. Third-generation PV films and coatings, due to their potentially high light-absorption properties can be made nanometers thick, achieving modules with high-transparency levels, ideal for integration into windows and glazing. The use of low-cost, high-throughput printing and coating techniques means less energy is consumed during their manufacture, and capital investment in equipment is lower than that required for silicon-based devices and other thin-film technologies.
Moving out of silicon’s shadow
In spite of this, the situation in the current PV industry, which has developed around crystalline silicon which today accounts for 80 percent of the market, means all alternatives are measured against the performance of silicon modules. The International Electrotechnical Commission (IEC), the Institute of Electrical and Electronics Engineers (IEEE), ASTM International (American Society for Testing and Materials) and Underwriters Laboratories Inc. (UL) all publish standards for PV products and all are based around crystalline silicon. Standards for newer and third-generation PV technologies do not exist yet, but efforts have been focused on the efficiency and stability of OPV devices. To add to the challenge, many third-generation PV technologies are being developed for BIPV applications, so effective standards for rating performance characteristics will need to acknowledge the performance criteria placed on the building components they are integrated with. This is important because it means other industries will set the performance criteria for BIPV technologies. “The results of tests such as light soaking on OPV cells produced by Heliatek last year indicate the stability of the cells and their potential suitability for BIPV applications,” says Martin Pfeiffer, the start-up’s Chief Technology Officer.
Partners that Heliatek is working with to develop BIPV applications supply the building-glass and façade industries. Compared with other PV technologies, the key properties that make OPV suitable for certain BIPV applications include their light-weight, semi-transparency and outstanding low light performance,” says Chief Executive Officer Thibaud Le Séguillon. He adds, “We are working with a glass company on a potential application where OPV can be used also to produce a tinted glass as well as provide an energy-harvesting functionality.” As Le Séguillon points out, third-generation PV also outperform silicon in certain conditions, especially in low light and under cloudy skies and shade, which means they are suitable for sides of buildings, where silicon PV modules would generate less if illumination was too low. Like their thin-film cousins, third-generation PV also exhibit excellent mechanical robustness, which results in higher efficiencies in higher temperatures. Standards developed for third-generation PV would be able to take all of these characteristics into account, establishing a more diverse PV industry with different products suited for very diverse applications and environments. Konarka is contributing to BIPV standards development including the Fraunhofer Multi-element project, ISOS 1, 2 and 3 and IEC.
Increasingly, developers of third-generation PV are working with industrial partners, proving that the lower power conversion efficiencies of third-generation PV need not be a disadvantage for BIPV applications. Large buildings such as commercial offices, skyscrapers, industrial sheds and factories and plants have a lot of surface area. Depending on the building itself, PV modules that can be supplied with tinted glazing or a metal roof or façade do not need to operate at such high efficiencies. According to Swedish start-up NLAB, which is installing a pilot production line for making DSC glass modules, if its panels have an efficiency of five percent, they can generate 50 watts of electricity per square meter, so that a one square meter glass façade is enough to power one square meter of office space. Heliatek expects its first modules made from OPV on PET substrates to emerge from its pilot vacuum roll-coating equipment to reach efficiencies of between five and six percent.
There are other advantages too. Marc Thomas, President of DyeTec, a DSC glass venture between materials supplier and technology enabler Dyesol and Pilkington Glass North America (part of NSG), says, “The implication of BIPV was recognized quickly by the partners in DyeTec. Cost is already burned into the building, as the PV element is part of the material. In this application, you remove the cost of the glass processing for a conventional PV module and the cost of installation because you have to do it anyway.” ThyssenKrupp Steel Europe sees potential for taking Konarka’s OPV modules, produced like a plastic film on roll, and applying these to its steel façades.
Konarka led a press conference at the EU PVSEC to announce its new partnerships. The company’s co-founder Howard Berke is back in charge, steering the company out of a period of what could be described as the wilderness years, where it looked like bags for charging iPods threatened to be the commercial zenith of Konarka’s Power Plastic. As well as a new executive team, which includes James Buntaine who was previously CTO of Eastman Kodak’s organic LED (OLED) business, Konarka has new industrial collaborators. These include ThyssenKrupp Steel Europe, Bischoff Glastechnik, which has supplied glazing for prestigious buildings such as the Reichstag (German Parliament) in Berlin, Lapp Group, supplier of cables and connectors, and Fraunhofer Institute for Wind Energy and Energy System Technology, IWES. At the press conference Berke’s enthusiasm was palpable as he jumped up time and again to hand out sheets of film printed with organic solar cells to the audience, drawing upon the aesthetic qualities of the samples; solar modules as thin, flexible, near transparent plastic sheets for easy integration, in red, green and dark blue hues.
ThyssenKrupp Steel Europe is drawing up a joint development agreement (JDA) with Konarka, so ThyssenKrupp’s Lars Pfeiffer cannot go into much detail about the two companies’ collaboration. But the company says, “In 2012, pilots are planned with the view of commercialization occurring within a three-year time frame. The collaboration is focused on façade integration.” The Color/Construction unit of ThyssenKrupp Steel Europe is a leading supplier of steel construction elements. During the production of construction elements, steel strip is coil coated with films, paint or plastic coatings, in various combinations to provide protection and enhance the metal’s durability. These continuous coating lines could potentially be used to apply the OPV surface.
In its first phase the partnership will see Konarka deliver ThyssenKrupp its solar cell film, or foils, which will be cut and laminated onto the color coated steel element. The OPV film will be adhered to the steel element at the factory ready for delivery to the construction site.
Longer term there is the potential to produce the cells as part of the steel color coating process. Some details of this are being ironed out in the JDA.
Earlier this year ThyssenKrupp Steel introduced with Juwi Group construction elements featuring roof-parallel PV modules. The PV systems consist of solar modules installed on special, roof-parallel substructures. The substructure is matched to the roofing elements supplied by ThyssenKrupp Steel Europe. The systems are suitable for both single-skin roofs and roofs made of sandwich panels, which provide heat insulation.
The collaboration with Konarka will address façade elements, where aesthetic qualities of Konarka’s Power Plastic, such as the different colors, can be exploited. ThyssenKrupp’s façade products range considerably, depending on application and properties applied to the steel by coating and foil processes, from 20 euros to up to 200 euros per square meter.
Dyesol and Tata Steel, a leading supplier of color-coated steel in Europe, have been running an incubator facility for the past few years at Tata’s site in Shotton, Wales, to develop a roll-to-roll line that can produce cells on coated steel for making metal roofing on warehouses and industrial sheds, a market which is estimated by Dyesol to be worth over 100 billion pounds (GBP). The PV Accelerator, which is staffed by a team drawn from both Tata and Australia-headquartered Dyesol, is aiming to commercialize its BIPV steel roofing by 2015.
Over in the U.S., DyeTec recently installed pilot equipment at its facility in Toledo, Ohio. DyeTec’s BIPV program is funded by the Ohio Third Frontier Fund. In addition to shipping-specialized DSC equipment to DyeTec, Dyesol has also sent staff to Toledo so that DyeTec can begin developing large-size prototype DSC glass panels. The modules DyeTec will produce will be made of transparent conductive oxide (TCO) glass made by Pilkington and will be targeted at downstream suppliers in the glazing and façade market to produce DSC-TCO glass products for BIPV, BAPV and automotive integrated PV (AIPV) applications.
Despite the interest third-generation PV technologies are generating for BIPV applications, this is a technology that is only on the verge of finding its feet outside of the lab. The conventional PV industry is not going to pave the way for the commercial use of third-generation PV, but routes to market are being explored by OPV and DSC developers working with suppliers of components to the construction industry. The next few years will see these partnerships focus on exploiting compatibilities and synergies between third-generation PV production and coating, laminating and other industrial methods for processing building components. In this time, frame conditions for demand will emerge. Today, a handful of countries have introduced BIPV feed-in tariffs, but the real challenge is to make BIPV technologies commercially viable without subsidies. This will occur as we learn more about how much energy buildings consume, the cost of paying for this energy and how, supported by fit-for-purpose standards, BIPV can be a cost-effective solution.