These 'boffins' are so focused on the design brief that they forget that you will need a petrol/diesel or electricity (coal fired power) powered compressor to pump up the tank when empty. Where is the green eco saving in that, maybe it comes with a foot pump. I remember back in the mid seventies when a bloke in a shed in a Sydney back yard developed an air powered conversion for his old Cortina. When it was publicised in the papers, the oil industry tried to buy him off and when he wouldn't sell, his shed and car mystriously burnt down. Funny how we are still stuck buying petrol.
