100% electric? Isn't that going to be an expensive car then? Would you trust a complete stranger with an expensive car without full knowledge of whether or not they can pay the (probably hefty) excess on the insurance?
I hear that it works well in the USA, especially in airports with little else there. I have seen the keys on the hook saying "please bring back full" and a donation box. It didn't seem that you needed to pay anything - but a donation was customary.
If I were you I'd buy an old cheap car that is mechanically sound, and most importantly cheap to insure commercially. Say bring back full or pay £40 (or whatever a full tank normally costs) and boom. But you'll find that it is a bit of hassle...