For the data center not having a backup diesel generator would be a bit risky, at least until such time they can have battery back power that can last for say a whole day or more.
Agree. Hopefully it could at least be biodiesel.
I'll give the exception that construction crews will use fossil fuels and there may be heavy grid use as the Solar PV and Wind get installed and come on line but...
Since Tesla is bringing in power from two directions from two seperate electric companies and have thier own onsite power generation from solar and wind with battery backup I'd have to call any gas or diesel generator a tertiary or quaternary backup.
Dual Primary = Grid Power
Dual Secondary = Wind + Solar PV
Sole Tertiary = Battery (lots of Powerpacks)
Sole Quaternary = fossil fuel generators
and then I'd assume by the time the build out is complete they would try to move Grid Power down to the Tertiary Role and move the others up eventually giving us
Triple Primary = Wind + Solar PV + Geothermal
Sole Secondary = Battery (lots of Powerpacks)
Dual Tertiary = Grid Power
Sole Quaternary = fossil fuel generators
You could argue about which goes on what level (should the batteries and grid power share secondary status in the end? Should there be a Sole Primary with the other renewable bumped down to secondary status? Should Battery move up into and make a Triple Primary?).
But however you bundle or separate those power sources I can't imagine them ever using fossil fuels as a backup except for a near Zombie Apocalypse style outage. It'd have to be dark in the daytime (ash clouds, biblical rain, or something) and be still (no wind for significant periods) longer than thier battery backup design can handle AND the power from TWO different electrical grids would have to be unavailable.
The site should never be without power, you just might have to reduce or stop production using the highest power equipment to keep within the supply limitations.