The big advantage of a rotary is that it is small and light (the MX-30's is of just 83occ), which in turn makes it very smooth. And as an electrical generator it really comes into its own – the principle is just the same as hydro-electric, nuclear, even wind turbines. The battery in the MX-30 R-EV is at just 188 kilos much smaller and lighter again than that in the standard all-electric version, and as such it offers a maximum range of just 53 miles. But the ability to automatically recharge adds another potential 350 miles removes any range anxiety a potential owner might have.