Cost is not the same thing as value.
How much degeneration is there in the first few months? Cheap panels typically lose 2%.
What is long term degeneration rate? Cheap panels can be two to three times as fast as top quality Panasonic or SunPower.
I hope it works out for you, but Solar City/Tesla incompetence stories abound.
The Q cell panels degrade at 0.54% per year, whereas a Panasonic panel I was looking at degrades 0.26% per year. So after 20 years, there will be a 5.6% difference in a Qcell panel system vs a Panasonic panel system.
I have a 6.8kW system. So a 5.6% difference over 20 years is a power output difference of 380W production. The panels are 340W each. Solution? Buy one more panel of the cheaper panel compared what you would have purchased with the more expensive but slower degrading panel. Financially the cheaper panel still comes out ahead, even accounting for faster degradation, because the price difference is just too large.
Also, the cheapest non-Tesla premium panels that I could find (Panasonic, LG, Sunpower panels) were about $3.4/W installed, vs $2/W Tesla panels installed. With a huge 40% difference in cost, there needs to be a very large difference in efficiency, degradation, and temperature coefficient to justify the higher cost of premium panels. The spec difference just isn't that big between the Q cell and Panasonic or Sunpower panels.
I'm also surprise that in the Tesla contract the Tesla panels are warranted for roof leakage for 10 years, system maintenance for 20 years, and system repairs are included for solar panels (at least 12 years) and inverter (at least 10 years). It's not as long as some of the other companies which offers 25 years for everything, but I question who would survive longer, Tesla a multi-billion dollar company (I know, not a guarantee for anything) or even the best among small local installers.
Tesla customer service does leave a lot to be desired though. Sigh, I have to keep reminding myself that the $9000 price difference in a 6.8kW system is worth the pain of having to deal with Tesla.