Lifespan should be 20 years, possibly more. Non Battery system. Inverter is the piece that would go out. Panels will degrade over time.
Solar City update: After upgrading the structure in my attice, Solar City engineers still complain and won't add more panels to the older part of my house. O'well. I'm still working with them to give me the "details" of what is wrong. The lady told me over the phone, but I was driving and couldn't write it down.
Output: now that the sunny and longer days are here, I'm seeing some output! Highest yet is 14.75 kWh for the day. Today's was 13.52kWh. It's generating about half of what we use each day.
Overall I'm paying Solar City $20 month and it's saving $20 off the Xcel bill. Just wish I could get more panels and generate more than my usage each day.