The whole of nature is powered by free solar energy. Only plants are able to make use of that energy without some physical effort — even that is debatable. Animals (including everything that is capable of moving from one location to another) are physically incapable of taking advantage of that free solar energy without the input of labour. (Perhaps I should define ‘labour’ as used here: the act of moving a body from one location to another; the act of applying some process to a body in order to transform it from one physical state to another.)