in the overall efficiency of global energy conversion from primary energy to services was about per cent cullen and allwood a in other words global primary energy demand could be reduced to only one ninth while the same energy services were provided if all energy conversion devices were operated at their theoretical maximum efficiency in more practical terms but still assuming an almost perfect world global primary energy demand could be reduced by per cent or to less than one fourth while the current level of energy services were provided mainly through a shift to passive systems cullen allwood and borgstein this is in line with the popularized overall factor and factor improvements von weizsacker lovins and lovins