Sydney: A researcher is tapping windows in high-rise buildings to produce energy cheaply and more efficiently with transparent solar cells, a study reveals. Mark Bissett, who just completed his doctorate from the Flinders' School of Chemical and Physical Sciences, used transparent carbon nanotubes, which can be 'sprayed' onto windows, to utilise sunlight. These nanotubes are more efficient and cheaper than their energy-sapping silicon counterparts, used in solar cells. Besides, the technology mimics photosynthesis, the process whereby plants obtain energy from the sun, according to a university statement. "Solar power is actually the most expensive type of renewable energy - in fact the silicon solar cells we see on peoples' roofs are very expensive to produce and they also use a lot of electricity to purify," Bissett said. "The overall efficiency of silicon solar cells are about 10 percent and even when they're operating at optimal efficiency it could take eight to 15 years to make back the energy that it took to produce them in the first place because they're produced using fossil fuels," he 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, Bissett said they still had many financial and environmental advantages. "It's basically like tinting the windows except they're able to produce electricity, and considering office buildings don't have a lot of roof space for solar panels it makes sense to utilise the many windows they do have instead," said Bisset.