Within the borders of Cambridge, Massachusetts, are 17,000 rooftops, or 17,000 individual surfaces on which it might make sense one day to install photovoltaic cells. Of course, these roofs are not all equally fit for solar power. Some of them have weird chimneys or sloping architecture or tree shade. Some buildings are oriented in the wrong direction (for the sun’s purposes, at least), or they’re boxed in by even taller structures that block out natural daylight.

... "When an owner uses the map, they get a very good evaluation of how good the solar potential of their roof is,” says Christoph Reinhart, an MIT associate professor working on the project. Modern Development Studio’s web platform can even translate that solar potential into a financial cost, a payback period, a carbon emissions reduction and equivalent calculations for how many trees you’d have to plant or fewer miles you’d have to drive to achieve the same effect. “But we’d like to now say, what does it mean for the city?” Reinhart asks. “Where should we support putting photovoltaics on roofs?”