It’s unclear just what percentage of Supercharger power at Harris Ranch is being generated via diesel, as even apps devoted to tracking what kind of energy is delivered to Superchargers have no idea. But understand, generators play a vital role in backup power, or when extra power is needed to meet demand. Power outages are happening more often so standby, industrial generators are going to be more and more common in businesses, even at an EV supercharger location.
Experts at Tesla and other energy organizations have said that the superchargers operate much like your home, drawing electricity from the grid and only having an estimate of where the power came from--- thus our breakdown above for the US.
Bottom line, Tesla gets power for the superchargers the same way everybody gets power for their home or devices. When it’s busy, they will turn on a diesel generator to add extra energy to handle the demand. If there’s a power outage, the diesel generator will fire up to provide power as well, just like at a hospital, data center or any other business that can’t afford to sit idle-- in the dark.