Electric cars have two major downsides. One is battery weight; the other is range.
Neither, of course, applies to an electric tractor.
Weight is an advantage for a tractor because the tractor gets extra traction. In fact, most diesel and gasoline tractors have weight added. Range isn't a problem for a tractor because it rarely travels very far away from the charging station.
Above is a video of Steve Heckeroth's Solar Electric Tractor model 12 as featured on Permies.com. We even get a quick tour of the solar part!