The book addresses energy as a means of entropy generation, which is a prerequisite for all processes occurring on Earth. The available energy carriers are distinguished between renewable and non-renewable. For the latter, their availability is calculated using mathematical models, taking into account the development of population numbers and living standards. Based on physical laws, it is examined to what extent renewable energies can replace the loss of non-renewable energies. At the same time, these laws define a limit that growth processes on Earth must not exceed.