Sneaky Solar

SRS Energy

SUNROOF SRS Energy makes solar roofing tiles designed to blend in with Southern California's traditional clay versions.

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Topics Covered

solar cells, building-material, BIPV, photovoltaics, copper indium gallium diselenide (CIGS), alternative energy,, sustainability

DuPont, Konarka
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Powerful Coatings DuPont's new encapsulants for thin-film photovoltaics protect delicate solar cells from the elements (left), and Konarka’s semitransparent solar polymer—shown here in front of a flower—could turn windows into energy-collecting devices (right).

The next big leap in solar materials will be hard to see. Solar energy firms and building-material suppliers are working together to integrate solar cells into building materials, and one measure of success for these products is how well they blend into the overall building aesthetic.

For now, the market for these building-integrated photovoltaics, or BIPV, is small, and the materials they use are still quite visible. But increasing demand, material innovations, and government incentives could power the industry to wrap buildings in an invisible solar cloak.

The solar industry defines BIPV as solar installations that also serve as functional building materials, such as roofing, shading systems, or window glazing. Adding photovoltaics to building materials themselves, rather than installing costly "after market" panels, can help cut the cost of solar energy, advocates say.

Buildings clad in nearly invisible solar cells are mostly visions of the future, and BIPV claims just a tiny share of the overall market for solar cells. Even promoters of the technology refer to it as "embryonic." In Europe, where the technology has had the best reception, installed BIPV capacity reached 40 MW in 2008, less than 3% of the continent's overall solar market. That sliver was worth just over $300 million, according to Akhil Sivanandan, an analyst at the market research firm Frost & Sullivan.

Frost & Sullivan research also shows that the market for BIPV is fragmented, with no one company controlling more than 10% of it. Most large solar-panel manufacturers, such as Suntech Power, Kyocera, and United Solar Ovonic, are looking to building materials to help them expand into new areas. Adding to the diversity are a host of smaller firms with second- and third-generation technology and the materials companies that supply them.

But firms are jumping into BIPV because it is expanding rapidly. Sivanandan pro­jects an average growth rate of 18% per year through 2014, when revenues from BIPV installations will reach about $780 million.

Analysts say growth for BIPV this year could have been higher than 18%, but it was interrupted by the economic downturn. Tight credit and lack of construction spending have delayed production and product development by 18 months to two years.

About 80% of BIPV installations today are traditional crystalline silicon panels, usually made into flat, glass-topped roofing structures or used on custom-designed sun shades. Newer thin-film solar technologies promise to reduce the mass and avoid the brittleness of traditional silicon wafers. Makers of thin-film materials like copper indium gallium diselenide (CIGS) are targeting BIPV, and the more familiar amorphous silicon is also in the running. Third-generation organic polymer materials could offer the thinnest, and least visible, solar coverage.

Firms with new technologies will benefit most when the economy—and construction—picks up again, according to NanoMarkets, a market research firm that covers thin-film technologies. Principal analyst Lawrence Gasman says thin-film photovoltaics are easier to adapt for building applications and that flexibility will push the svelte cells into first place by 2015.

CIGS thin-film technology stands out for its ability to blend in. Dow Building Solutions has included CIGS cells developed by Tucson, Ariz.-based Global Solar Energy in its plans for a new, flexible solar roof shingle. "CIGS has proven to be the most efficient, cost-effective thin-film technology for BIPV applications," says Bob Cleere­man, Dow's senior director of solar and structural technology. The company says its shingles will be available beginning in mid-2010, although it has not disclosed the exact materials that will be used.

Global Solar started developing CIGS cells in 1996 with funding from the U.S. military. Its goal then was to put solar cells on soldiers as part of the Future Warrior program. But now, "BIPV is our mission in life," says Tim Teich, vice president of sales and marketing. Although CIGS can be used like traditional solar cells, "the best feature of the product is that it is lightweight, flexible, and configurable. The shingle looks like a regular three-tab shingle you buy at Home Depot," Teich adds.

The other benefit of CIGS is that it boasts a higher efficiency than other thin-film technologies. Dow picked Global Solar in part because the cell's 10% real-world sunlight conversion efficiency meets requirements under the Department of Energy's Solar America Initiative. In 2007, Dow received a $20 million cost-sharing grant from DOE to develop BIPV products. During lab testing at DOE's National Renewable Energy Laboratory, CIGS cells achieved an efficiency of 20%.

But CIGS has a long way to go to reach its potential and compete with the 20% efficiency achieved with traditional crystalline silicon cells, NanoMarkets' Gasman says. "The problem with CIGS and all thin-film photovoltaics is that they underperform in cost efficiency compared with crystalline silicon." To really take off, he adds, CIGS will require large investments to boost real-world efficiency.

Flexible BIPV also needs to achieve the 25-year life span required of most building materials, according to Teich. He says the company is looking to chemical firms like Dow to develop flexible polymers that will protect the sensitive CIGS cells from the elements, especially moisture.

In May, DuPont announced two new ionomer photovoltaic encapsulants for thin-film roofing tiles. Steve Cluff, business director for DuPont Photovoltaic Encapsulants, agrees that a next advance should be to make even more flexible polymers; but that, he acknowledges, will be difficult to achieve. "When you go to something flexible, you have to use an organic-type material, which is normally not impervious to moisture," he says.

Amorphous silicon is also popping up on rooftops. SRS Energy, based in Philadelphia, manufactures Solé Power Tiles designed to blend with the clay roofing versions that are popular in Southern California. The solar material in the tiles is made by United Solar Ovonic, a subsidiary of Energy Conversion Devices.

To expand the possibilities beyond the roof, thin-film solar firm Konarka Technologies has partnered with Arch Aluminum & Glass to put a semitransparent coating of organic solar film on window glass. Dan Williams, Konarka's vice president of product development, claims that a prototype of the solar glass lets in about 80% of sunlight, making the coating similar to standard energy-saving coatings.

Despite the "cool" factor of the new technology, Frost & Sullivan's Sivanandan insists that BIPV still has to make sense economically. BIPV is similar to other types of renewable energy, he explains: It is most successful wherever a combination of high energy costs and government incentives cancel out the up-front expense.

One of those places is Germany, which leads Europe in installed residential BIPV capacity because of loan programs and so-called feed-in tariffs, which allow owners to sell excess energy back to the electric grid at attractive rates. Now, France and Italy offer similar incentives.

Federal stimulus spending is likely to ramp up U.S. demand for residential BIPV starting in early 2010. Already, BIPV is sprouting in California, which, in addition to being sunny, has expensive electricity and offers generous subsidies for solar power.

When the current economic crisis passes, Gasman says, builders and their clients will be left with the inevitable problem of higher energy costs. "When the numbers really begin to add up, it pushes people to be innovative," he says. "The sun will never start charging for its service."

Chemical & Engineering News

ISSN 0009-2347

Copyright © 2011 American Chemical Society