https://i.stuff.co.nz/environment/climate-news/300306177/department-of-conservation-caught-charging-plugin-hybrid-electric-vehicle-with-diesel-power

edit - explanation from blinkibill

"This is a bit silly. They didn’t install the generator just for the car - the system runs the entire electricity grid for the island and the car plugs into that grid.

Rakiura isn’t on the national grid."