Chicago’s iconic Willis Tower (formally the Sears Tower) is set to become a massive solar electric plant with the installation of a pilot solar electric glass project. The high-profile project on the south side of the 56th floor will replace the windows with a new type of photovoltaic glass developed by Pythagoras Solar which preserves daylighting and views while reducing heat gain and producing the same energy as a conventional solar panel. The project could grow to 2 MW in size — which is comparable to a 10 acre field of solar panels — turning North America’s tallest building into a huge urban vertical solar farm.

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The project is a collaboration between the tower’s owner and the manufacturer to prove the viability of the building integrated photovoltaic (BIPV) system, which will also save energy by reducing heat gain and cooling costs. The new windows, dubbed high power density photovoltaic glass units (PVGU), are a clever hybrid technology that lays typical monocrystalline silicon solar cell horizontally between two layers of glass to form an individual tile. An internal plastic reflective prism directs angled sunlight onto the solar cells but allows diffuse daylight and horizontal light through. Think of it as alouvered shadewhich allows for views but cuts out the harsh direct sun.

The manufacturer claims that the vertically integrated solar cells will produce the same amount of energy as normal rooftop-mounted solar panels. This is great news for cities that have precious little rooftop space and towering walls of glass. The product is also a potential breakthrough in energy efficiency in glass towers, where solar heat gain is the bane of energy-efficient design.