Driving the length of Britain is an expensive endurance test that isn’t overly kind to the environment, but this week I helped do it for free, minus the emissions.A standard Renault 4, the kind of car parked on any suburban street, has covered the circa 870 miles from Land's End to John o'Groats without taking a single unit from the grid or burning a drop of petrol. Every electron came from the sun. The same journey in a petrol car works out at £120.48 in fuel (around $160 / AU$230), or £240 there and back (about $320 / AU$460), while...