Our solar system has been running about a month now. It is comprised of 11 PV panels, each with its own inverter. These inverters are made by Enphase Energy and have monitoring capability built-in.
To monitor production, Enphase has a data gathering box called the Envoy. The Envoy goes out on the powerline network and queries the production data from each of the registered modules. The Envoy then uploads the data to Enphase's website for monitoring capability. With this data, we can graph the output of each panel, check on total output of the system, and show how much lifetime power has been generated.
It is interesting to see and fun to watch how much power is being generated at any one time. Unfortunately, with the record amount of snow in December, our output has been much smaller than the potential output. When the snow covers the panels, it takes a couple of days for the snow to melt off so the panels can start generating significant power again. But with 17" of snow in 1 day... and significant snow every weekend, and 2 inches here and there... our output is low. You can take a look at the graphs and charts on our dedicated monitoring website.