Sorry if this is stupid question, but I am just curious. And sorry if I posted in wrong forum but it seemed to um... Fit the most. And sorry if my English isn't perfect :). Ok now, the title might be a bit confusing. What I am looking for are the most efficient energy sources, which are small, relatively safe and transportable. They don't have to be existing technologies, I will be satisfied with theoretical technologies, or ones being developed. It can rely on super-rare and/or super-expensive minerals. Thanks in advance :).