Solar cells have been around since the 1950s. But now there is a race to develop transparent solar cell that can cover windows of buildings and still capture the sun's light for electricity.

Different kinds of light from the sun

There are three kinds of light that reach our planet from the sun. They are ultraviolet light, or UV, visible light, and infrared light. Together they make up what is called the solar spectrum.

Troy Townsend is a solar cell researcher at St. Mary's College of Maryland.

He says working with the transparent solar technology for windows means you cut the efficiency in half. That is because you are letting visible light—light you can see—pass through the solar cells instead of capturing and using that light to make electricity.

That leaves only light from the ultraviolet and infrared parts of the light spectrum to make electricity.

He spoke to VOA via Skype.

"One of the major challenges with transparent solar cells is developing a system that would allow you to absorb the maximum amount of UV and the maximum amount of infrared."

Because glass absorbs UV light, Townsend says the efficiency will drop even more, if the solar cell is on the inside of the window. But if the cell is put on the outside of the window, it could capture the light before it goes through the glass.

That would require the cell to be protected from the elements of heat, moisture, and cold. Townsend says the trick would be to find a clear material that would cover the cell—and still let the light come through.

Developing Photovoltaic Cells for Windows

Several colleges and private laboratories are working to develop photovoltaic compounds that could be applied to windows. They would be transparent, which means, you can see through them. So they would be able to collect the sun's energy without blocking the view through the window.

SolarWindows Technologies in Maryland says it has developed an efficient transparent solar cell. John Conklin is head of the company.

"We have actually taken a technology, organic photovoltaics, and innovated it into transparent technology, applied it to window glass and turned a passive window into an active electricity generating window."

Conklin says a solar window can be totally transparent. Or it could be tinted, or colored, which makes it more efficient.

"We can make the color darker or lighter, or blend the colors to go with the blue-green, a green-grey, a brown, depending on what the architect, the building owner or the building developers is looking at."

Conklin says his company is working with the U.S. Department of Energy to test and develop the technology. And he plans to have a commercial-ready product by the end of 2017. If he is successful, Conklin says his electricity-making window could pay for itself in one year.

According to a 2012 survey, there are 5.6 million commercial buildings in the U.S. They have more than 8 billion square meters of windows. Even if only a part of that glass could collect power from the sun, it could greatly lower the need for polluting fossil fuels.

I'm Anne Ball.

George Putic reported on this story for VOANews. Anne Ball reported and adapted this story for Learning English. Hai Do was the editor.