Re: Grid vs. Off-Grid
I don't know (not in the business)--but my guess is 5-15 years on average for the electronics. Electrolytic Caps and fans are typical weak points. Thermal cycling and high temperatures are another big killer...
I used to qualify computer disk drives back in the 1980's--and two weeks in a thermal chamber cycling every 4 hours between min/max operational temperatures would kill 80% of the vendors (at the time)--mostly popping components off the board and breaking solder joints. Good drives/mfg.--I never got them to fail thermally.
Regarding temperatures--The Engineering Rule of Thumb is for every 10C increase in temperature, you cut the life by 1/2... 30C increase is 1/2*1/2*1/2=1/8th the life. Also works the other way, cooling by 10C would double life.
Keeping your equipment+batteries cool and in stable temperatures is 1/2 the battle.
Xantrex (and others probably) have a 10 year warranty on the GT Inverters (used to be 5 years).
Wiring (in conduit) should last the life of the building. I don't know how long UV rated/stable wire is "supposed to last" in sunlight. My home's utility drop is UV rated and all twisted in a bundle--so I would hope it would last the life of the installation.
Solar panels, that are not damaged or mfg. faults--should last 25-40 years (crystalline silicon panels are supposed to only have ~80% output after 20-25 years--Solar Guppy has posted before that "good panels" seem to output 100% of their power even decade(s) later).
Also--long panel life means that you may need a new roof with 40+ year rated roof covering. You don't want to install the panels on an old roof.
20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.