Put all the other factors aside, the author at least ignored quite a few critical variables: 1. Decaying of the panels. I'm wondering if the panels can retain

Put all the other factors aside, the author at least ignored quite a few critical variables: 1. Decaying of the panels. I'm wondering if the panels can retain 50% of designed output after 7 years. 2. Maintenance. If the inverter go busted in 7 years, hopefully the warranty would be still valid by then. Also, the extra load panels put on roof was never factored when the house was built, it's not uncommon to see issues caused by that. 3. Variance of feed-in tariff. So if the tariff wasn't locked in, I'm pretty sure there would be surprises on how fast it can drop.