I. Introduction
The successful development of humanity requires a reliable and cost effective power system. Similarly to labour and capital, energy is an essential part of the development process and the power system is playing a key role in the energy infrastructure. However, the modern power system is rather not suited for sustainable development of a modern society. It is heavily based on fossil fuels [1], which are depleting. Fortunately, society is accepting the challenge of transferring to a more sustainable power system, which was recently enforced by the 2015 Paris Climate Action Agreement [2].