Installed solar costs fell 17% in 2010 to $6.20 a watt on average for all “behind-the-meter” solar systems in the United States compared to 2009 in constant dollars, according to a September 2011 report by the Lawrence Berkeley National Laboratory.

The report said that “partial data” suggests the average cost fell another 11% in the first half of 2011 to $5.50 a watt. Costs for systems of 10 kilowatts or smaller in size ranged in 2010 from a low of $6.30 a watt in New Hampshire to $8.40 a watt in Utah. California and New Jersey, two states with the most amount of solar activity, were in the middle of this range.

Many rooftop solar systems are owned by third parties who sell electricity or lease the systems to building owners or homeowners and claim tax subsidies on the solar equipment that are then passed through to the customers in the form of a reduced electricity price or rent for use of the system. The report said that ownership by a third party added 30¢ a watt to the installed cost on average in 2010.

German homeowners paid significantly less for solar systems in 2010 than homeowners in the United States: smaller residential systems of 3 to 5 kilowatts in size cost $4.20 a watt on average, after installation, in Germany, compared to $6.90 a watt in the United States.

Keith Martin