The power industry is changing very rapidly because the electricity markets are becoming competitive and renewable electricity is coming in to the market place. The new competitive markets have also ancillary services, which will change the competitive positinos of power plants completely. In the new markets renewable energy and flexible generation should be combined optimally to achieve competitiveness. The main emphasis in the book is to plan an optimal capacity mix in national and decentralised power systems. The examples include eight cases of optimization of systems with and without nuclear, with and without coal, and with and without wind power plants. The second edition of the book has a new chapter on planning of decentralised power systems, in which wind energy optimisation in isolated and interconnected systems will be made. The chapter includes also optimisation of combined and heat power systems. Another new chapter is also dedicated to environmental control and global warming issues.