The installed cost of solar photovoltaic (PV) power systems in the United States fell substantially in 2010 and into the first half of 2011, according to a report released on September 15 by DOE's Lawrence Berkeley National Laboratory (LBNL). The average installed cost of residential and commercial PV systems completed in 2010 fell by roughly 17 percent from 2009, and by an additional 11 percent within the first six months of 2011.