Average annual insolation at the top end is about 250W/sqm. If...

Average annual insolation at the top end is about 250W/sqm. If that shed was 10m x 10m = 100 sqm then we're looking at about 25kW average insolation. If 20% of that (solar panel efficiency) is converted to volts and amps, that is 5kW average over 24 hrs, or about 120kW hrs per day.
So enough to run the 75kW charger for about 1.5 hrs a day, or about 3 cars per day.

Good ol' fossil fuel for anything over and above that.

Diesel gennys run about 0.4l per kWhr, so need about 16 litres to get the 40kWhr or so per extra car.