Dive summary:

• Some roofs have huge potential for solar-energy production, but some just aren't suitable because they face the wrong way or perhaps are shaded by surrounding buildings.
• The Sustainable Design Lab at MIT and Modern Development Studio in Boston joined forces to devise a mapping tool that shows solar energy potential, and they tested it out on MIT's home turf in Cambridge, Mass.
• The program also generates figures for potential cost of solar installation, the payback period and how much the installation would reduce carbon emissions.

From the article:

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. ...