residential 2 kW photovoltaic system in Seattle:
estimate save 2600 kilowatt hours per year
electricity cost: .08 per kilowatt hour
savings $208 per year
installation cost: maybe 2 to 6 dollars per watt
a larger system costs less per-watt
estimate $10,000
208/10,000=.02
source for example: //www.nrel.gov/docs/fy04osti/35297.pdf
Seattle City light rates
National Renewable Energy laboratory
price trends