Solar powerSolar-technology developers want to put the walls and windows of your workplace to work for them. While most solar panels on buildings today perch atop the roofs of homes and businesses, these developers of so-called "building integrated" solar products see dollar signs in the millions of square feet of vertical real estate on high rises and other commercial buildings.

One such company is San Mateo, Calif.-based Pythagoras Solar, which this week announced plans to launch a solar window -- or, more properly, a "photovoltaic glass unit" -- to produce electricity while helping keep buildings cool in hot weather and still allowing plenty of daylight in. The unit includes a solar cell and a prism, which reflects light onto the cell to boost its electricity production, sandwiched between two panes of glass.

Pythagoras plans to launch the product, its first, in the third quarter of this year. It's targeting commercial buildings, and says the unit will be available for windows, skylights and building facades.

A Powerful Prism

The prism is what sets Pythagoras's technology apart from some of the other solar cell-embedded glass designs. While a solar cell absorbs sunlight and generates power on its own, the prism concentrates the sunlight so that more of it hits the cell. The idea is that the prism, made of cheap plastic, enables Pythagoras to use a smaller cell to achieve the power output of a larger one, thereby cutting manufacturing costs.

"The feedback we get is that in order for a product to get to mainstream, it not only has to replace conventional materials, but it has to simultaneously deliver on energy-efficiency generation and electricity generation in order to make the economics work," says Vice President of Business Development and Marketing Udi Paret.

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Pythagoras' cell-cum-prism design can convert 14 percent of the sunlight that hits the cell into electricity, he says. That efficiency is higher than some of the similar offerings on the market today, which deliver less than 10 percent efficiency. In addition, because the prism captures some of the light for electricity, the building will stay cool, reducing the need for air conditioning, he adds.

Pythagoras already has customers using its glass unit in field trials in the United States, Israel and China, says Paret, who declined to disclose names. The 3-year-old startup expects to see its solar glass in larger projects -- projects involving hundreds of thousands of square feet of glass -- starting in 2011, he says.

Competition and Cost

Of course, Pythagoras isn't alone in its goal of integrating solar power with buildings. A growing number of companies are working to introduce solar materials to replace the roofs, walls and windows of skyscrapers and homes, which make up a potentially huge market for the solar industry.

Suntech Power, in China, and Scheuten, in the Netherlands, have designed similar products that they say can provide shading and insulation, as well as solar power. Dow Chemical plans to introduce solar roofing shingles sometime this year. And Konarka Technologies, in Lowell, Mass., which is developing solar cells in the form of thin films, has partnered with building materials company Arch Aluminum & Glass in Florida.

But so far, it has proven challenging to come up with products that are easy to install, long-lasting and cost-effective. First of all, these solar materials are likely to cost more than their non-electric counterparts.

"The No. 1 challenge is cost," says Robert Raymer, technical director of the California Building Industry Association. "With the downturn of the market, it's far more difficult for home buyers to get loans to qualify these days. If you are putting in a system of 3 to 4 kilowatts, then that's $25,000 to $35,000. That's a lot."

The higher prices also will likely raise concerns about additional maintenance costs for building owners, considering that windows with electrical components are likely to be more expensive to replace than conventional windows. The best solar cells on the market today last a few decades, but a building -- and its windows -- typically lasts far longer. Finally, solar cells need wiring and other equipment to ferry the electricity into the grid.

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