ScienceDaily (Oct. 21, 2009) — Researchers at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) released a new study on the installed costs of solar photovoltaic (PV) power systems in the U.S., showing that the average cost of these systems declined by more than 30 percent from 1998 to 2008. Within the last year of this period, costs fell by more than 4 percent.
http://www.sciencedaily.com/releases/2009/10/091021144249.htm