My system got commissioned today. It is winter, so while I was there I looked at the production rates. At the peak of the day, it was making more than 8,000 watts, which is pretty nice. I was hoping for more, as it is a 12,750 watt system. However, as I mentioned, to avoid wind loading problems, the panels were mounted flat to the roof, and this (over the year) costs about 10%.

The difference between STC and PTC on the panels is part of the deal. What is that? Solar panels are rated with standard conditions, or STC. This is where the panels are supposed to be 245 watts. But the real world performance is PTC, which for these panels, is about 217 watts. So rather than 12,750 watts, the real world is closer to 11,300 watts. Knock another 10% off that, and I should see a little over 10,000 watts on a nice summer day, not considering inverter losses and such, which might cost another 5%. So if I see 10,000 watts in the summer and 8,000 watts in the winter (at the peak of the day) I think I’ll be happy.

Next week they will be installing the web monitoring equipment, and when they do I will post some graphs of what the system is doing, and see if I can extrapolate a year’s production.