Loong, this is from the Altestore.com:
"Generally speaking, solar electric systems take from 12 to 20 years to pay for themselves depending on your location and what your local utility charges for electricity...That said, more and more states have very aggressive rebate programs and tax credits for both individuals and businesses to reduce the initial cost of the system."
My recent bill for 561 kWh is $48.61. I saved $15 by being in the low income energy support program at 26% saved.
I would save 30% at under 400 kWh a month. I expect to get there once Dan leaves - this is an amount for two people, one of whom (dan) has a heavier electrical use style than i do.