Actually it happened last week, but today is the first day since then that we've had uninterrupted sunshine, and boy, are we crankin'. Because of all the trees, even the sunniest part of the roof only gets sun for part of the day, but even today, in early March, the system will offset the whole day's worth of electricity usage. Woo-hoo!
The website to which we are now connected has a piece which describes in imaginary concrete terms what impact the panels have each day: You planted a tree today. Or: You took x cars off the road today. Which is silly and technically false, but fun.
It wasn't cheap, but rebates and discounts took 40% off of the initial cost of buying and installing the system. Our current usage is so low that it will still take twenty years to pay for itself (maybe less, assuming the boys use more electricity as they grow older), but dollars, in the end, are less important than cool new technology--I mean, saving the earth--right?