Reliability of power systems considering conventional and alternative sources of energy

Several methods, tools and measures have been developed which highlight the questions about the power systems reliability each from its particular viewpoint. The objective is to review the selected methods in the field of electric power system reliability keeping in mind the complexity of the system and its features. Their review is performed in sense of applicability to conventional sources of energy and in sense of alternative sources of energy. Particular importance is placed to alternative sources of energy, which power depends on weather conditions such as solar power and wind power, which may require different approach regarding the control of the frequency and the voltage. If the conventional sources of certain power are replaced with the alternative sources with variable power depending on weather parameters, the reliability of the system may decrease, if the replaced power is not sufficiently large. Defined power replacement has to suit requirements about sufficient power, about sufficient energy and about reliability, which should not be reduced.