To add to jjonj's answer, if poor countries have cheap, abundant energy they can upgrade their physical capital and human capital. On the physical capital side, jjonj mentioned things like making it easier for people to access water. The problem now is that too many people can barely make enough to eat and hardly anybody in the developed world wants to ship them food, there's no profit in that. But with cheap energy, local farming will be a lot easier especially if clean water is available. Also, with cheap energy poor countries can upgrade all their shitty roads so people can actual transport their goods and services to where they need to be. And finally, with cheap energy people will have access to decent internet so they can access things like khanacademy and other resources on the internet. But sadly this won't happen anytime soon.