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Flexible photovoltaics

April 1st, 2011 / By: / Markets, Sustainability

As the performance and durability of flexible photovoltaics increase, so do market possibilities.

At the World Expo 2010 Shanghai (“Better City—Better Life”), which ended on October 31, the Japan Pavilion presented a 100 by 50 by 24-meter dome with a roof made of steel-framed ETFE film: architecture with an organic image. Putting the emphasis on “eco,” one of the main features of the structure was its use of photovoltaic membrane. ETFE film panels with photovoltaic (PV) cells were placed in a checkerboard pattern on the roof; air is brought in between the two ETFE films to form a pillow, and amorphous silicon PV films are put inside of the ETFE film. The ETFE film pillows were then placed onto the steel frame.

Amorphous silicon PV film is thin, lightweight and flexible. The power generation is 37kW at the maximum, which covers approximately 5-10 percent of the electricity that the Japan pavilion uses. The ETFE film was made by the Asahi Glass Co. Ltd., Tokyo, and the PV cells by Fuji Electric Systems Co. Ltd., Tokyo; the pavilion roof was constructed by Taiyo Kogyo Corp., headquartered in Osaka. With another unique feature, the Eco Tube system that allowed in sunlight and wind and accumulated rainwater, the Japan Pavilion became an environmental experiment in architecture, searching for ways to lower environmental loads.

The sunlight that shines on our planet has enormous energy. The solar energy that reaches the the earth is about 1.37kW per meter squared; it is said that if we could convert 100 percent of solar energy into useable power, just one hour of irradiation would be needed to cover the annual energy consumption of the world.

Developing photovoltaics

Japan is heavily dependent on imports of almost all its energy resources, including oil and coal. Development and promotion of photovoltaics has been active since the 1970s, influenced by the government system and subsidy policies—PV is regarded as one of the most promising energy resources to develop. From a new system inaugurated in 2009, and with the popularity of the “green” movement, the production and sales of PV cells have been growing rapidly in Japan.

Various types of PV cells have been developed, most recently flexible and bendable PV styles. Many companies have been trying to merge this flexible PV and membrane material, to be used as sun shades and on roofs. But until recently, practical success has been slow in coming.

IFAI Japan conducted workshops on PV in September and November 2010, studying the thin organic PV film manufactured by Konarka Technologies Inc., Lowell, Mass. Right now, Konarka is the only company in the world that markets the organic PV (OPV), called Power Plastic®. The company has been successful making thin, flexible, rugged and lightweight organic PV films, using bulk heterojunction technology, that can be attached to a membrane. Konarka’s products are already on the market, being used on umbrellas, tents, roofs and shelters, as well as in bags and chargers for consumer electronic devices. The transparency and coloring availability of the film widen the list of possible applications. Shinji Kawahara, director of business development for Japan at Konarka Technologies Japan, says, “As to the per square meter price, the current cost of it is competitive to any other thin PV cells, and it has a good possibility of getting even lower in cost, with its mass-production system in the future.”

Kawahara admits that the conversion efficiency of 3 percent in the module base is not enough; the company is expecting module efficiency to reach 10 percent in 2015. Durability is also a significant factor for BIPV applications; it is now 3-5 years with flexible barrier films. The company is working on increasing the product’s life span to 10 years by 2015, with a better barrier film. OPV also works well under conditions of low light and high temperatures. Konarka has emphasized energy accumulation performance.

Ongoing industry discussion

Reflecting the great interest of the industry, the PV workshops attracted many IFAI Japan members, who joined in the discussion with a number of questions and comments.

Several Japanese companies are now successfully merging PV with membrane using the amorphous silicon PV film. The conversion efficiency is generally more than OPV at this time, but the cost of it is also generally higher. Shinji Nanami, manager of the advanced structures division of Taiyo Kogyo, the installer of the roof of the Japan Pavilion, says the thickness of the amorphous silicon PV film (FWAVE) is about 1 mm, and it is less than one-tenth the weight of conventional PV using glass. This meant that transportation and installation of the roof was easy and required fewer people. The film doesn’t break like glass might, and because it is flexible and lightweight, could be applied to ETFE.

Sometimes using PV films can spoil the appearance of a building, but used with ETFE, and considering the pavilion’s unique design, the roof well reflected the futuristic appeal of the Shanghai Expo. Nanami notes that the membrane material is designed to bear wind load, but the PV cells are not, making it a challenge to attach at times.

N.I. Teijin Shoji Co. Ltd., Osaka, is another company supplying amorphous PV with architectural membrane to the market, and exhibited it at IFAI Expo Asia in Singapore in March. Teijin is known in the industry for its commitment to environmental issues. According to Kenichi Noda with the company’s industrial fabrics department, “Our product has about 20 years of durability with the ETFE surface of the PV, as well as light weight and flexibility. And it can be applied to various places including external walls, and the PV can be attached to various fabrics. But it has room for improvement as well. We need to increase the conversion efficiency. At this time, ours is about 8 percent, while crystal system silicon PV is about 16 percent.”

Amorphous silicon PV modules block the sunlight, so if placed on the surface of an awning, for example, it will become darker under the awning. The appearance of the modules themselves must also be considered.

Empowering the panel

Chukoh Chemical Industries Ltd., a PTFE coated membrane material manufacturer headquartered in Tokyo, has developed a completely seamless photovoltaic integrated architectural membrane material, FGT-Solar. Ms. Hanako Ogawa, senior marketer in the development division of Chukoh Chemical, says, “Our PTFE coated glass-fiber architecture fabric, Skytop, has been used in more than 1000 projects at home and abroad so far. FGT-Solar adds value to our Skytop surface.”

Generally, FGT-Solar is offered as a panel with an aluminum frame, 800mm wide by 1900mm long, weighing 9.5kg per panel. A nonpanelized version of FGT-Solar is also available. “This is one of the unique features of FGT-Solar,” says Ogawa. “Originally, PTFE coated glass-fiber material required special fabrication techniques. However, FGT-Solar is pre-fabricated with an aluminum panel; it can be installed not only by professionals, but also by a local builder. Its light weight is the most efficient feature. It has only half the weight of the solid-PV panel, which can contribute to reduce installation costs; it is easy to install and replace also, thanks to the modularization.”

FGT-Solar partially covers the surface of the material; the generated power is expected to reduce daytime electricity costs. Flexible and lightweight, it will not break, so is much less likely to cause injury compared to conventional PV, which uses glass.

Applications include the walkways of public facilities, school buildings, and electric power generation from walls and surfaces, especially in remote areas; Chukoh would like the challenge of installing the panels for an off-grid area in the future. According to Ogawa, “We want to develop PV cells merged with architectural membrane for a large-scale structure. But, as the elongation of the membrane and the PV cell is different, and the membrane and PV are attached completely, it may be broken when the membrane stretches too much. So at this time this is only for the smaller size project.” Conversion efficiency and cost are also ongoing challenges.

Teijin’s Kenichi Noda says that with the amendment of energy-saving laws and the School New Deal to encourage PV installation in schools, the market for photovoltaics is expected to grow even more.

There are still many challenges to overcome, but conversion efficiency and other performance factors, lower costs and easier installation technology are rapidly advancing. Increasing the efficiency of PV with membrane will increase the possibilities for a more eco-friendly world, thanks to the specialty fabrics industries.

Ms. Kikuko Tagawa is executive director of IFAI Japan.

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