Green Tech

Solar company Konarka has developed a transparent solar cell that it hopes will be built onto electricity-generating windows.

The Lowell, Mass.-based company on Tuesday said it has reached an agreement with Arch Aluminum & Glass to use Konarka's plastic solar cells in building materials, including windows.

A transparent solar cell Konarka hopes will be fitted into power-generating windows.

(Credit: Konarka)

Under its Arch Active Solar Glass development, the company has built prototypes of windows with the solar cells between two panes of glass. The photovoltaic cells can be tinted different colors.

"It is energy-efficient and transparent with superior vertical performance and a subtle red, blue or green aesthetic. With these features, BIPV (building-integrated photovoltaics) will no longer need to be confined to spandrel or overhead applications," Arch CEO Leon Silverstein said in a statement.

Konarka makes organic solar cells made from flexible plastic. Last fall, it opened a factory in Massachusetts to manufacture the cells which come off assembly lines as spools fitted with wires to carry electricity.

The advantage of these flexible cells is that they can be used for a wide range of applications, such as power-generating military tents, portable chargers for electronics, and sensors.

Photos: Building on flexible solar cells

But these organic photovoltaics aren't very efficient at converting sunlight to electricity and won't last as long as a rooftop solar panel, which is typically under warranty for 25 years. Konarka said late last year that it achieved 6 percent efficiency in its labs but that's not yet available in its products. A high-efficiency silicon solar cell, the most common cell material, can be over 20 percent.

Konarka's factory is turning out red solar cells but has started making the transparent cells in limited runs for prototypes and development, according to a representative.

Although Konarka has raised over $100 million and has signed a number of partnerships, there are many people who are skeptical that the company can be profitable.

"The real key will be to see if they can make building-integrated products that can stand the weather for 20-plus years," clean-tech venture capitalist Rob Day from @Ventures told Greentech Media in December last year.

Konarka also faces growing competition in the building-integrated photovoltaics field. Thin-film solar manufacturers, including Heliovot, also make flexible cells that can be fitted onto glass or building structures such as awnings but are more efficient. Nanosolar's cells made from CIGS (copper indium gallium selenide), for example, are in the 9 percent to 10 percent range.

NEW YORK--Solar company Konarka wants to bring plastics to life with the sun.

Konarka has developed technology to create rolls of plastic that can convert light to electricity--a design that will result in solar power being embedded in everything from flashing Coke bottles to wireless sensors, the company claims.

Earlier this month, Konarka said that it has demonstrated the use of inkjet printing to manufacture its solar cells. And at a recent investor conference here, chairman and founder Howard Berke described Konarka's longer-term plans to embed small solar plastic cells in hundreds of products.

In the second half of this year, Berke said, Konarka will make its first shipments to customers and will announce the location of a factory.

Konarka's roll-to-roll manufacturing creates solar cells on plastic.

(Credit: Martin LaMonica/CNET Networks)

Initially the company intends to make portable solar chargers for gadgets as well as self-powered sensors, lights, and smart cards. Farther down the road, it plans to make solar windows and power-generating cloth.

In four years, Berke said, the company intends to have products for the building-integrated photovoltaics (PV) market with "bifacial cells," for placement on windows, that can convert electricity from both sides.

It is also working on a project, sponsored by the Department of Defense, to make fibers that can be woven into clothing, he said.

"You'll be able to wear, carry, integrate PV," said Berke. "Wherever plastics occur, you'll have PV."

But some solar industry watchers have become skeptical about whether this technology will ever live up to its promise. Konarka, founded in 2001, has raised several rounds of capital and taken government grants but still doesn't have a commercial product.

Plastic solar cells have the advantage of being flexible, unlike traditional silicon, but they're not nearly as efficient as rooftop panels.

Konarka's cells, which are made with a roll-to-roll manufacturing process, convert about 5 percent of the light that hits them into electricity, whereas typically solar panels with silicon cells are 16 percent to 20 percent efficient.

But its organic photovoltaic cells can convert low light, can be tuned for specific wavelengths, and can work even when the light hits at a low angle, Berke said.

"We see this as next-generation thin-film PV technology and not competing with silicon," he said.