I realize I'm posting in an old thread but I want to give an update.
My wife and I decided to go ahead and install a solar electric system, even though our electricity usage is fairly low - she really likes to be as green as possible. We put up a 14 panel system, with a maximum generating capacity of 3KW (but the peak generated has been about 2.6KW). Right now, it's generating about 18KWh a day, when we have cloudless days. I've noticed a gradual increase in the amount generated as the days get longer. On a cloudy day that could fall to 8KWh and would probably go lower on a really cloudy, rainy day.
The surprise is that we're generating more electricity than we use. I've had days when our net usage is as much as -9KWh, but my average since March 11 (when things went live) is -4KWh per day. I need to build up a cushion because in August and September I know I'll use a lot more than I generate with the A/C on.
I'm on a "net metering plan" which means that I only settle up with the power company once per year, although I get a "bill" each month to let me know what my cost status is. If I was accumulating a big obligation (meaning I'd owe a lot of money) I can make monthly payments - but I don't have to pay until the end of the year. If we wind up with the power company owing us money, they will pay us or roll over the credit to the next year.
I have no idea how long it will take to pay for the system (I bought it outright) but I'm sure it will be somewhere around ten years. The system has a 20 year warrantee on it, but I expect it to last longer than that. Analyzing the return requires you to make estimates on what electricity will cost in the future. Putting in the system isolates me from future cost increases - and if I can generate more power (I guess the proper term is energy) than I use, I'll be rooting for large increase in the cost of power. Ah, capitalism, it all depends on what side of the equation you're on
Mike