The skinny on photovoltaics using fabric and where to find it
By Amelia Amon
Buckminster Fuller famously asked a group of architects “How much does your building weigh?” His query to us now might be, “How much energy is embedded in your photovoltaic installation?” Flexible amorphous PV panels, nano-tech films and solar fabrics on lightweight tensile structures could be the ultimate in what Fuller called “ephemeralization” — described as technological advancement to do “more and more with less and less until eventually you can do everything with nothing.”1
These innovative, if still experimental, materials are not optimized for the utility-scale installations that currently dominate the solar market. In general, they are less efficient per square foot, require more space, and may not be as rugged and durable as crystalline technology. How will flexible PV function in whole-systems energy ecologies? Two aspects are examined:
1. Comparing current manufacturing capabilities and challenges for established technologies along with the potential for next generation photosynthetic films and silicon foils.
2. Innovative ways that designers, architects and engineers are incorporating solar into shade structures, canopies, awnings and portable enclosures for temporary events and disaster relief.
To create a new energy system based on clean renewable energy technologies, we’ll need to minimize the embodied energy it takes to produce and distribute electricity. Solar energy, manufactured and installed with the least amount of fabrication materials, in the areas where it is most needed, will be integral to our energy infrastructure — and ambiance. This paper presents an overview of the state-of-the-art in solar energy integration, ephemeralization and aesthetics.
Manufacturing flexible photovoltaics: Current market
Though most flexible solar panels are either amorphous silicon or organic solar, not all amorphous solar is flexible. Clear glass is often used as the substrate for amorphous PV, allowing a variable amount of light translucency for building integrated photovoltaics (BIPV). Glass panels are ideal for buildings, which provide more than sufficient structure for standard applications, but for mobile, temporary or applications without existing infrastructure (such as parking lots), glass is heavy, fragile and costly to replace. The amount of aluminum and/or steel required to hold it in place, bearing up to wind and snow loads, can add many years to the embodied energy payback period (the length of time it takes for the solar panels to produce the amount of energy used in the manufacture of the entire system; including frames, stanchions, bases, electrical, transmission and storage equipment).
The industry standard for flexible PV is roll-to-roll manufacturing, in which sunlight-absorbing material is deposited on a roll of substrate. A laser-scribing process isolates individual solar cells. Full panels are formed from the isolated cells through laser welding interconnects that are printed onto the surface of the material. Panels are encapsulated with protective surface layers and laminated onto various backing materials. In general, the roll-to-roll production line is composed of vacuum deposition, printing, laser scribing and welding machines.
PowerFilm Inc. (www.powerfilmsolar.com), originally known as Iowa Thin Films, has been manufacturing and selling flexible solar panels since the early 1990s. Based in Ames, Iowa, PowerFilm was founded in 1988 by Dr. Frank Jeffrey and Dr. Derrick Grimmer, both former research physicists from 3M. The flexible solar panels are produced on plastic substrates as thin as 1 mil (0.025mm) through a proprietary roll-to-roll manufacturing process. Standard rolls are 330mm wide and can be up to 732m long. The amorphous silicon used is cadmium free. PowerFilm’s silicon is extracted from silane gas, so it is not subject to silicon wafer supply constraints.
Flexible PowerFilm solar can be encapsulated in a variety of laminate materials for diverse applications and usage environments, such as moisture, heat, UV exposure, laminate durability and cost. Backing materials include metal, membrane and architectural fabric. Powerfilm’s solar efficiency is somewhat determined by the module design configuration, but generally figured to be in the 5% range.
United Solar Ovanic (www.uni-solar.com) uses a roll-to-roll process to produce a triple junction stacked solar cells on a stainless steel substrate. A subsidiary of Energy Conversion Devices, founders Stanford R. Ovshinsky and his wife, Dr. Iris M. Ovshinsky, pioneered amorphous solar in Michigan in the early 1960s. Uni-Solar was founded in 1990, increasing production capacity from 500 kW to 25 MW per year. At .4mm thickness, Uni-solar panels have limited flexibility, and are generally specified for standing-seam metal roofs or commercial membrane surfaces. The standard width is 394mm and up to 2500m long, but standard lengths are 2849mm for 68Wp, 5007mm for 124Wp, 5486mm for 136Wp or 144Wp.
Manufacturing flexible photovoltaics: Organic solar and nano-technology
There has been a great deal of interest and millions of dollars of investment in organic solar (OSCs or OPV). Those closest to immediate availability are based on a photoelectrochemical process. Known as Grätzel cells, this technology was originally invented by Michael Grätzel and Brian O’Regan in 1991.2 Nanotechnology is used to deposit or “print” a photo-active material to convert solar energy into electricity. This “active” layer is extremely thin — only a few tenths of a micrometer thick, i.e. less than 1/1000 of a silicon cell, so potentially extremely cost effective.
High-tech companies and university research teams are actively competing to improve the manufacturability, efficiency and durability of these cells. The 3 to 5% efficiency range is often cited, which is significantly lower than crystalline or amorphous silicon. Several technologies may improve these results. The capability of organic solar cells to produce electricity at lower light levels and indirect sunlight may compensate for its lower full sun efficiency.
Konarka (www.konarka.com), a Lowell, Mass., company spun off from research done at the University of Massachusetts, has raised nearly $60 million in funding for research and manufacture of its patented Power Plastic®. At only 2–10 mils thick, Konarka’s Power Plastic solar cells are very flexible, semi-transparent and can be printed in a variety of colors and patterns.
Konarka has a development agreement with SKYShades, a supplier of shade and tension membrane structures based in Orlando, Fla. and Brisbane, Australia. Together, they are developing prototypes for active solar shade structures. They expect to be shipping product to established development partners by mid 2009, with general market availability later this year. It is estimated that the cost will be one third that of “traditional” solar.
Konarka is also developing Power Fiber, a method of weaving photovoltaic material directly into fabric. In this case, the layering of the photo-active material, the transparent electrode and the substrate is done on tubular strands of fiber. As it is still in development, it is unclear what the potential efficiency will be, but the applications are myriad.
Plextronics Inc. (www.plextronics.com), in Pittsburgh, Pa., was founded in 2002 as a spinoff from Carnegie Mellon University. Its organic solar cells are based on conductive polymer technology developed by Dr. Richard McCullough. Currently, their Plexcore® PV holds one of the highest verifiable efficiency rating at 5.4%. Plextronics opened a small-scale manufacturing facility to print demonstration modules using solar inks with commercially scalable manufacturing techniques in January 2009.
There are numerous other commercial ventures in organic solar, spun off from university research. Solarmer Energy Inc. (www.solarmer.com) is developing plastic solar cells for portable electronic devices that will incorporate technology invented at the University of Chicago. Other “players” include Wake Forest University’s Center for Nanotechnology and Molecular Materials, University of Michigan, The University of Alberta and the National Research Council’s National Institute (NINT) for Nanotechnology.
Manufacturing flexible photovoltaics: Solar foils
Silicon Genesis (www.sigen.com) of San Jose, Calif., announced its new ultrathin solar-cell foil at PHOTON’s 7th Solar Silicon Conference in Munich, Germany in March 2009. The foil combines the advantages of low silicon material utilization of thin-film PV with the high efficiency potential of mono c-Si PV. The company has previous expertise in minimizing the amount of “kerf,” silicon crystalline that is lost when cutting silicon bricks into thin wafers or through breakage in transport and handling. This new material is called “20-20,” because it is 20 microns thick and could go up to 20% efficiency, if it is made into a double–sided cell. Silicon Genesis is currently seeking partners to produce panels or shade structures that incorporate this material. SiGen’s “PolyMax™ kerf-free foils” have the potential to be the first robust and highly flexible mono-crystalline silicon cells.
Innovative design strategies
The promise of lightweight, flexible solar materials offers great opportunities for designers, architects and innovators. Eliminating the need for bulky frames and costly permanent fasteners, these new materials allow for the exuberant gesture. With increased awareness of the dangers of excessive sun exposure, particularly to children, there will be a growing need for shade structures — that can now produce energy. Parking lot solar shades can protect customers from the elements, direct night-lighting downward for “dark-sky” compliance, advertise and promote awareness, and offer electrical access for plug-in hybrids. A 2006 study by Richard Perez and his team at Atmospheric Sciences Research Center at the University at Albany, revealed that New York State could produce 15 to 20% of its energy needs by covering retail parking lots.3
FTL Solar One of the design innovators in this field was originally part of FTL Design Engineering Studio, which designed and developed the solar tent for the Under the Sun exhibit at the Smithsonian Museum of Design at the Cooper-Hewitt, NYC in 1998 (see fig 1). Todd Dolland and his team design and develop solar tensile structures for a wide range of markets.
FTL Solar’s PowerPark I is a 12m wide, extendable solar shelter designed to shade two rows of cars. One unit of the modular system is comprised of four 6m by 6m PowerMods. The 12m by 12m area is cantilevered out from a single column to cover eight parking spaces and produce 1,100 watts of power. Structures are designed to be technology-neutral, so the flexible photovoltaics can be replaced due to wear, tear or technology improvements. While minimizing the required support structure, FTL Solar’s PowerPark suspends PowerFilm PV modules laminated to a durable, structural fabric in a compelling form that evokes waves on the sea. It shows exciting potential to transform unsightly parking lots into rippling fields of energy harvest.
The military has tremendous interest in deployable solar structures or tents. As shown from above at a U.S. Army Trade Show, this off-grid application is lightweight, compact and quick to install.
xDesign at the Environmental Health Clinic The Environmental Health Clinic at New York University is a clinic and lab with the understanding that our health is dependent on external local environments, rather than solely on the internal biology and genetic predispositions of an individual. Natalie Jeremijenko, NYU professor, engineer and artist is the founder of xDesign and has initiated several tensile solar design projects with collaborative groups. Based on a structural system by Foiltec (www.foiltec.de), xDesign has created an innovative structural system that incorporates Texlon foil pillows into a structural system that uses 50 to 90% less material than a standard roofing system. Adding solar power production to the light-filtering and insulating qualities of the roofing materials adds to the environmentally friendly aspects of this system.
Jeremijenko’s Green Light System, another project in a similar vein, uses photovoltaic window awnings to power super-efficient LED lights specially tuned to grow indoor plants to improve indoor air quality. This is a collaborative project with Will Kavish, designer/fabricator and Amelia Amon, solar designer (this author). Highly visible solar awnings become a proclamation of the residents’ green values, as well as blocking sunlight to reduce summer heat gain. By using battery storage, each solar awning can provide sufficient energy to run the fixture, due to the low wattage of the LED lights.
Soft House “Soft House,” exhibited at the Vitra Design Museum in Essen, Germany, is a theoretical but visually pleasing project designed by architect Sheila Kennedy of Kennedy & Violich Archiutecture Ltd., Boston, Mass. The concept is a structure that harvests energy through solar-energy-collecting textiles hung in the home like curtains.
The project grew out of Kennedy’s MIT architecture course, Soft Space: Sustainable Strategies for Textile Construction. Kennedy is following up by developing a solar light for developing countries
Summary and conclusions
Flexible solar fabrics are the future. They show tremendous potential for producing energy with minimal use of materials and the capacity to be beautifully integrated into the built environment
Roll-to-roll printed solar cells also promise to reduce the amount of time required to pay back the quantity of energy embodied in fabrication for several reasons:
1. Reduction of capital equipment costs make ramp-up less expensive by using traditional printing processes and equipment
2. It minimizes raw material usage, particularly the expensive, exotic and potentially-toxic metals and highly processed silicon most solar panels use.
3. Reduce manufacturing waste by using very accurate nano techniques, eliminating cutting waste and breakage (in the case of mono-crystalline) and disposition waste (in the case of standard amorphous silicon).
Though overall power-production efficiency levels are significantly lower, by absorbing a broader light spectrum flexible modules show potential to work without optimal sunlight. This is an advantage for integrating solar into urban areas and onto complex forms. Like the complex ecologies of the natural world, the energy systems of the future will intertwine a variety of technologies, distributing energy the way the Internet distributes information. Attractive, lightweight, rugged solar offers designers, architects, engineers and innovators the opportunity to produce energy exactly where it is needed, at the point of use. Applying solar to our existing infrastructure minimizes transmission losses, increases energy security and conserves natural habitats for other species. The intriguing benefit of tensile solar applications is that it can also make our cities, towns, retail malls, campuses and suburbs more beautiful and livable as well.