Average installed costs for PV systems in the US declined from $10.80 per watt in 1998 to $7.50 a watt in 2009 (in real 2009 dollars), according to DOE's Lawrence Berkeley National Lab study, "Tracking the Sun III: The Installed Cost of Photovoltaics in the United States from 1998-2009."
The results are based on data from 78,000 residential and non-residential PV systems totaling 874 MW and representing 70% of grid-connected PV in the US.
Preliminary data also suggest a significant decline in 2010. The cost of systems installed through the California Solar Initiative program declined by $1 a watt in the first ten months of 2010 and by $1.20 a watt in New Jersey during the first six months of 2010.
The trend varied based on system size. For example, from 2008-2009, the average cost for 5-10 kW and 10-100 kW declined by $0.4/W and $0.3/W, respectively, but was flat for systems under 5 kW and 100-500 kW, and rose by $0.3/W for systems under 500 kW.
Small PV of 2 kW averaged $9.9/W, while those greater than 1,000 kW averaged $7.0/W (or about 29% less). Two multi-megawatt utility-scale PV systems installed in 2009 had much lower costs ($2.5/W and $5.1/W), showing the benefits of scale in bringing solar PV costs down.
Costs were lowest for systems with mid-range module efficiencies in 2009. For systems under 10 kW, for example, systems with module efficiencies of 15-16% had an average installed cost of $7.40/W, compared to $8.20/W for systems with efficiencies of 12% and $8.30/W for systems with module efficiencies over 18%.
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