Transparent plastic solar cells fitted into windows

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.

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.

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.