JUSTIFICATION CRITERION OF ECONOMIC EFFICIENCY OF JOINT USE OF TRADITIONAL AND RENEWABLE ENERGY SOURCES
One of the main tasks of electric power supply of medium and small-scale enterprises is to ensure the functioning efficiency of electrical systems connected with renewable energy sources. To date, there is no unified methodology for assessing the effective functioning of electrical systems with the rational replacement of traditional energy sources with renewable energy sources in the North-West Russia. Energy supply systems with renewable sources have their advantages and disadvantages. An advantage is that such systems do not have the elements associated with the extraction, transportation and processing of fossil fuel; they also do no feature the hazardous atmospheric emissions. The energy transport distance is shorter, usually owing to the absence of supply networks. A disadvantage of such systems is the cyclical character of energy flow from the sources (e.g. wind and sun) throughout the year, season, and day. Therefore, the use of these energy sources imposes certain restrictions related to the uneven supply of solar and wind energy. The idea is to use economic and mathematical methods to assess the optimum substitution of traditional energy resources with solar, wind and biogas energy by introducing the weighting factors, which take into account the intensity of use of renewable energy sources under specific meteorological conditions and technical and economic indicators. The first stage of implementation of the proposed idea is to identify the efficiency criteria and to develop a justification method of the criterion of technical and economic efficiency of joint application of traditional and non-traditional energy sources. Under availability of the initial data, this method will allow to calculate the optimal ratio of energy carriers while maximizing the use of renewable energy sources.