As you may know, residents (and businesses) can take a 30-percent federal tax credit when purchasing solar PV systems. You also may know, however, that reading about tax rules is about as much fun as watching silicon degrade, molecule by molecule. Luckily, the freshly amended investment tax credit (ITC) is fairly straight forward. It provides a tax credit worth up to 30 percent of total system costs, with no dollar amount cap. But what, exactly, is a tax credit? And how is it different from a tax deduction?