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Stand on a busy street corner in any large, modern city and you’re likely to be surrounded by skyscrapers. While the idea of covering the tops of those buildings in solar PV panels is appealing, the actual opportunity for rooftop solar is limited. There’s not a lot of rooftop area to begin with, certainly not enough to supply even a fraction of the building’s energy requirements. And what rooftop there is is often occupied by HVAC systems, antennas, elevator equipment, and even recreation areas, all of which take up space and cast shade.
But now, look a little further down, just over the edge of the roof. What do you see? Acres of flat glass windows, presently underutilized. SolarWindow offers a way of turning all that vertical real-estate into a power generating system.
SolarWindow is both a company and a product.
The company, SolarWindow Technologies, Inc., has been built by a team of highly skilled scientists and entrepreneurs to develop and commercialize their breakthrough organic photovoltaic (OPV) coating technology.
The product, SolarWindow, is a polymer that can be applied as a liquid coating to transparent materials like glass. The coating turns ordinary double-pane windows into highly efficient and versatile solar panels, SolarWindows.
SolarWindow differs from conventional PV modules in several key factors.
While conventional photovoltaics – mono and polycrystalline silicon and inorganic thin film – depend on capturing as much light as possible, SolarWindow’s organic structure is designed to allow much of the visible light spectrum to pass through.
It’s this degree of transparency that gives SolarWindow one of its greatest advantages: It doesn’t have to be confined to opaque modules mounted on a building’s rooftop. Instead, it can be installed on the sides of a building, replacing conventional office windows.
Made from earth-abundant elements, primarily hydrogen and carbon, SolarWindow’s organic photovoltaic technology is cheaper and easier to manufacture than conventional modules made of inorganic materials like silicon, cadmium-telluride, and copper-indium-gallium-selenide. The polymer comprising SolarWindow’s photovoltaic coating can be dissolved in liquid and applied to a glass sheet in a relatively easy process, compared to the high-temperature and high-vacuum techniques commonly required for other solar coatings.
Since the SolarWindow can generate electricity from even incidental light, both natural and artificial, there’s no need to limit the placement of panels – or in this case, windows – to one side or area of the building, such as a south-facing location in the northern hemisphere. All sides of a building can be covered.
These factors, combined with SolarWindow’s high efficiency, lead to a rapid return on investment. SolarWindow President and CEO, John A. Conklin, explains, “When we model SolarWindow for a 50-story building, there’s roughly 6 acres of glass that allows us to take a passive window product and turn it into an active electricity generator. We’re looking at less than 1 year financial payback.”
As an example, a 50-story office building in the Arizona sun could produce about 1.5 gigawatt hours of energy versus about 0.12 gigawatt hours of energy for conventional rooftop PV on that same building. For a comparable building in New York City, with lower solar radiation levels, the figures would still be impressive, about 1.1 GW·h of energy for SolarWindow versus 0.09 GW·h for conventional rooftop PV. (The SolarWindow web site provides detailed financial and energy production estimates.)
SolarWindow is aiming for a pre-commercial launch of 2017, at which time a commercial prototype should be available. Actual production would come later. Conklin explains that “orders for glass are typically a year or two out. So, for example, in one of the conversations we’ve had with a strategic partner, they’re looking at glass today for windows in buildings in 2018.”
It’s been predicted that by 2050 about 86% of the developed world will be urbanized. That trend – limited real-estate combined with population growth – necessitates taller buildings, both residential and commercial. Given that the windows in a typical office building have a life expectancy of about 25 years, we can see the market potential for SolarWindow.
Conklin notes, “We’re looking at 9 out of 10 buildings replacing their windows in the very near future. There’s basically about an 8.3 billion square meter world flat glass forecast. In simpler terms that’s about 89 billion square feet of glass.”
Now, combine this projection with the near world-wide objective to mitigate climate change by reducing greenhouse gas emissions, using more renewable energy. “Given the demands for clean renewable energy,” Conklin says, “I believe SolarWindow is at a very strategic place for deployment of a clean disruptive technology that provides tall skyscrapers with the ability to produce renewable energy.”
Conklin concludes, “I don’t see renewable forms of energy going away. We rely on it now and we’re going to have to rely on it much more in the future.”
That will become even easier when every window is a solar energy generator.