Reliability issues in power systems with DG

Even, or may be particularly, in the time of disintegration, deregulation and competition in a power system, its reliability is one of the most important criteria which must be taken into consideration during planning and operation phases of its life. In many countries the increase of generating capacity takes place in small units of so-called distributed generation (DG). They use primary energy conventional sources as well as renewable energy sources (RES), and in many cases produce electricity and heat (CHP). Using of renewable energy sources is one of the crucial components of the sustainable development, giving rationale economic, ecological and social effects. Electrical energy sources can be qualified into two groups: with production dependent on unpredictable external sources of primary energy, and others. The most difficult is to analyse those, production of which depends on renewable energy sources like: hydro energy, the Sun, and wind energy. This paper presents chosen aspects of power system reliability modelling and evaluation, including distributed generation.