The ANU found more than six   hundred thousand potential sites around the world  where closed loop pumped hydro systems could work,   00:07:29 at least from a geographical and topographical  point of view anyway, representing a potential   of about twenty-three million gigawatt hours of  energy storage, which would be about a hundred   times what we’d need for a one hundred percent  renewable powered global electricity system.   Now, obviously not all of those sites will turn  out to be appropriate, so we need to keep our feet   well and true planted on the ground here. The ANU  itself points out that, apart from discounting any   00:07:56 urban areas and known areas of environmentally  protected zones, no other comprehensive   geological, hydrological, environmental, or  heritage studies were carried out as part of   their research project, so it’s highly likely that  only a relatively small percentage will prove to   be viable. But, even if it’s only one percent,  that still gets us over the line, doesn’t it?