Researchers at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) released a new study Tracking the Sun II: The Installed Cost of Photovoltaics in the U.S. from 1998-2008 on the installed costs of solar photovoltaic (PV) power systems in the U.S. According to the report, the average cost of these systems declined by more than 30 percent from 1998 to 2008, and fell by 4 percent in the last year. The most recent decline in costs is primarily the result of a decrease in PV module costs.