TEXTILES.ORG
Decades of research narrows the search for affordable and efficient solar panels for tents.
By Todd Jensen & Sigrid Tornquist
For flexible solar panels to have a place in the world of tents they have to be lightweight, and they have to pull their weight; in other words, they have to benefit the bottom line. Fabric manufacturers and scientists have been working on developing flexible solar panels using thin film technology—the construction of an extremely thin layer of a substance on a substrate— since the 1970s, but it is only recently that tented applications for solar panels are becoming viable options for tent manufacturers.
Material options
The two most common elements used in manufacturing thin-film technologies are amorphous silicon and CIGS (copper indium gallium diselenide). The oldest and best developed thin-film technology uses amorphous silicon—silicon atoms that can be laid down on a substrate but do not have to be configured in a lattice pattern to act as a semiconductor. Naizil® S.p.A, Binago, Italy, manufactures photovoltaic panels using a proprietary thin-film coating technology developed in collaboration with Flexcell® at the Institute for Micro-Technology, University of Neuchatel, Switzerland.
“Naizil’s solar panel has been designed and developed specifically in order to utilize solar technology on all those applications where the traditional rigid mono or polycrystalline silicon modules cannot be used because of their rigidity and weight,” says Alberto Ziliotto, president of Naizil S.p.A. “The most important fields of application are identified in architectural structures, building facades and frame-supported structures, and are expanded in all those applications that require extreme flexibility, lightness and very low weight.”
A more recent development—thin-film photovoltaic (PV) modules based on the use of CIGS—is the primary technology used by Ascent Solar Technologies Inc., Thornton, Colo. These materials are what allow the product to be so lightweight—less than one pound per square foot of roof surface.
Ascent interacts extensively with FTL Solar LLC, New York, N.Y., to integrate its flexible solar modules with the latest structural tent innovations and lightweight fabrics. A tent covered with PV modules is not only a shelter from the elements but also its own power station. A major benefit of solar tents is the elimination of the need for generators in locations where a standard power source is not available.
“The best situations for this are the large party tents,” says Brian Blackman, public relations director for Ascent Solar. At present, the savings in electricity costs may not be enough to pay for the increased costs of a solar approach; however, certain clients can benefit by displaying an environmentally conscientious approach to their events.
Climate and the consistency of sunlight are factors that can determine which option may be best. “Compared to a crystalline silicon panel, an amorphous silicon panel of comparable size produces less power but performs better at lower light intensities, making it a good, low-cost choice for environments where interrupted sunlight is the norm,” according to www.green-planet-solar-energy.com, an online resource guide on solar energy. “The CIGS panel has better performance than the amorphous silicon in terms of maximum output, but worse low-light performance.”
An alternative to silicon-based solar technologies is OPV (organic photovoltaic technology). Konarka Technologies Inc., Lowell, Mass., uses a photo-reactive polymer material invented by Konarka co-founder and Nobel Prize in chemistry winner, Dr. Alan Heeger. Power Plastic® uses recyclable materials and is comprised of several thin layers: a photo-reactive printed layer, a transparent electrode layer, a plastic substrate and a protective packaging layer. Power Plastic is being applied to a range of shade structures for a variety of purposes, from stadium-sized tents to awnings and carports.
The solar tarpaulin
Solar tent tarpaulin coverings are an option for converting tented events to solar power without the expense and time necessary to affix the solar modules to the tent roof. ORGATENT, a subsidiary of RöDER Zelt-und Veranstaltungsservice GmbH, Büdingen, Germany, has joined forces with its partner TENTSO S.A., Nyon, Switzerland, developing tent tarpaulins with integrated solar modules. While there can be some financial benefit with reduced electric costs, the major advantage to the solar tarpaulin made by Röder may be its ability to send a message and project a green image—for instance, when a company from the power industry wants to display its renewable products or an automobile manufacturer presents its newest automotive technology involving biofuels, says Thomas Roman, sales manager at Röder.
Even though the technology is not affordable enough to generate great savings in energy costs with solar tents and tarpaulins, in certain situations they can be a valuable tool, such as in remote rural areas where no power source is available or power has been lost as a result of a natural disaster. The solar cells can run ventilation systems, lighting and other critical electrical functions, avoiding the need for both generators and the fuel to run them.
The current tarpaulin available from Röder can contain multiple solar panels. Each panel covers 3.24 square meters and costs about €300 (about $418). A panel can generate up to 170 watts per hour and has a 20-year guarantee.
Tax credits for the use of solar tents are another matter, and may not be practical at this time. “Taking advantage of tax credits will be handled differently in every country,” Roman says. “It may possibly work in the area of storage or hangar-type tents, where the large roof surfaces of the constructions stay for a longer period of time, so that the tents will be rated like other buildings that use solar technology. At the present time, however, the flexible cells do not have the same capacity as the solid glass ones so they are not likely to be used for a permanent building.”
A kilowatt saved …
Solar is an up-and-coming possibility for energy efficiency in tents, but there are other ways to save significant amounts of money on energy costs. Röder has developed tent construction materials that display significant energy conservation properties. The company manufactures tents with insulated roofs and walls that have air conditioning and heating requirements that are less than half those of standard materials. Röder is continuing to improve on this and plans to reduce the heating and cooling costs to 25 percent of what conventional tents consume. A prominent example is a heated warehouse the company built for a car manufacturer in northern China. The temperature requirement for this structure is no lower than 20 C (70 F) with outside temperatures that can fall to minus 30 C (minus 22 F). With Röder’s thermoroof system and insulated walls, the client was able to reduce diesel fuel needs by 400,000 liters in just one winter.
Raise the roof
Saint-Gobain Performance Plastics Corp. in Merrimack, N.H., has been using PTFE-coated fiberglass membrane SHEERFILL® on roofs for almost 30 years, with the original structure built in 1973 and still going strong. The company expects a 25-year life on the roofs. The versatility of this material lies in its greater translucency and the fact that because it is malleable, many different designs are possible.
Marcel Dery, global marketing manager for SHEERFILL, says that in the last four to five years a number of companies have tried to attach PV to fabrics, with PVC/polyester at one end of the roof fabric spectrum being used for temporary structures, such as tents. These materials are workable in the 250 F to 280 F range so they are not damaging to the PV. However, the PTFE used with SHEERFILL requires temperatures of 700 F, which can seriously damage PV. Within the past year, Saint-Gobain has filed patents on an attachment system that allows PV to be adhered to PTFE. One major benefit to the company’s method is that it will allow the PV to be removed if one breaks, or replaced when more efficient materials become available.
“The interest in these products is growing rapidly with the demand in Europe and Japan being much higher than in the U.S., although the U.S. is quickly catching up,” Dery says. The product is expected to be on the market in 2011.
The horizon
The future of solar tents will likely not lie solely in the advantages of a free and silent source of power, but in the combination of multiple technologies, such as high-efficiency insulating structures and PV-imbedded fabrics. At present, the energy efficiency of flexible PV is not yet up to the standards of permanent heavy glass panels, but recent advancements are bringing competitive flexible solar options to the table for tent manufacturers.
As more applications for thin film PV appear and the use of solar tents and tarpaulins increases, the wider acceptance of this technology will lead to greater opportunities for tent manufacturers, tent renters and their customers as concerns about energy efficiency, energy costs and availability continue to mount.