The project, which is being undertaken by Pythagoras Solar, a clean-energy start-up, involves solar electric glass.
It is part of a the five-year, $350 million initiative announced two years ago to do a complete “green” makeover of the 110-story skyscraper which, with the aid of wind turbines, solar panels, roof gardens and efficiency technologies, will reduce the building’s electricity use by 80 percent and save 24 million gallons of water a year.
For its part, Pythagoras Solar power will install solar electric glass on the building's southern-facing windows – those that get the highest sun exposure – to create a 2 MW solar farm that will reduce the tower’s reliance on the power grid.
The company calls its pane design high-density photovoltaic glass units (HD-PVGUs).
The technology contains a thin layer of monocrystalline silicon, sandwiched between glass, which acts as a cell. An internal plastic prism directs angled (direct) sunlight onto the cell, while allowing diffuse daylight and horizontal (less intense) sunlight through.
The result is windows that still provide breath-taking views of he city, only without the glare or daytime heating. Meanwhile the panels produce electricity that Pythagoras Solar claims is on par with rooftop panels.
The Willis Tower installation alone is expected to produce as much power as a 10-acre ground installation would, while also reconciling solar power with one of its thorniest challenges: How to implement an array of meaningful size within an urban setting.
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