Skyscrapers could one day generate enough power to offset much of their energy consumption, thanks to a breakthrough by Australian researchers who have moved a step closer to creating solar-cell windows.

For his recently completed PhD, Mark Bissett, from Flinders University’s School of Chemical and Physical Sciences, has developed a solar cell using transparent carbon nanotubes that can be sprayed onto windows.

Carbon nanotubes are cheaper and more efficient than their energy-sapping, silicon-based solar cells, Dr Bissett said. The nanotubes can be applied to windows without blocking light, and are also flexible enough to be weaved into a range of materials.

But the technology is 10 years away from becoming a commercial reality, Dr Bissett said.

While the amount of power generated by solar windows would not be enough to completely offset the energy consumption of a standard office building, Dr Bissett said they still had many financial and environmental advantages.

“In a new building, or one where the windows are being replaced anyway, adding transparent solar cells to the glass would be a relatively small cost since the cost of the glass, frames and installation would be the same with or without the solar component,” Dr Bissett said.

A solar cell is created by taking two sheets of electrically conductive glass and sandwiching a layer of functionalised single-walled carbon nanotubes between the glass sheets, he said.

“When light shines on the cell, electrons are generated within the carbon nanotubes and these can be used to power electrical devices.”

At present, solar power is the most expensive type of renewable energy, Dr Bissett said. “The silicon solar cells we see on peoples’ roofs are very expensive to produce and they also use a lot of electricity to purify.”

But Andrew Blakers, Director of the Centre for Sustainable Energy Systems at Australian National University, said most commercial cells were now “16-18% [efficient]. The record is 25%, SunPower makes 23% cells in large volume.”

Silicon cells typically took two to three years to repay their energy investment, and the time frame was falling as the cells became thinner, he said.

The cost of solar cells had “declined by a factor of three since 2007,” Dr Blakers said. “[Solar-generated] electricity is now in the 10-15 cents per kilowatt-hour range for large systems and about 20 cents per kilowatt-hour for small systems - highly competitive with retail tariffs … and knocking on the door to competitiveness with wholesale electricity from new gas fired power stations, with gas at world parity prices.”