By: Julie Knight The Willis Tower, which once went by the much more famous title of Sears Tower, has 1,451 feet worth of windows that, until now, were actually somewhat of an energy drain. As part of a pilot program, a portion of the south side of the 56 floors has been fitted with Pythagoras Solar transparent solar-powered windows. The company sites that these photovoltaic glass units (PVGU) provide a triple benefit,—-energy efficiency, energy generation and they look nice too! Not only does the unit act as a sunshade to keep cooling costs down, but it also harnesses about as much solar power as a normal roof-mounted photovoltaic surface. And, if the program is successful, enough solar windows might be added to Willis Tower to amount to a 10-acre solar plant and provide nearly two megawatts of solar power. This green project which began in November 2011; and, the Tower will be utilized as a massive solar electric plant through the installation of a pilot solar electric glass project. The use of mass-scale solar power window installations will directly improve the energy efficiency and the energy generation potential of Willis Tower’s exterior envelope. This will help preserve day lighting and at the same time reduce heat gain, producing the same levels of energy as a regular solar panel. The building integrated photovoltaic (BIPV) solution could expand to over 2 megawatt of solar power generation, making the iconic Willis Tower a massive urban vertical solar farm! There are also plans of replacing the current black anodized aluminum and bronze tinted windows to a silvery mirror glass in order to reduce the air conditioning costs as a lighter color would result in less heat absorption. The project will result in unparalleled energy savings and reduced CO2 emissions to the tallest building in the Western Hemisphere. This will reduce the base building electricity use by up to 80 percent, which includes a combination of energy savings and co-generation (simultaneously generate both electricity and useful heat). The energy savings equal 68 million kilowatt hours annually or 150,000 barrels of oil every year. In definable terms that is $9,656,000.00 per year in savings!