In the paper alternatives for expansion of the Macedonian electricity supply system are presented. MESSAGE tool is used for modelling the system, for developing the scenarios, to analyse cost optimal energy pathways and to determine the optimal electricity generation technology mix. The calculations for the period 2020-2050 are made in a 5-year interval. Two scenarios are developed: Scenario 1 – BAU (Business as Usual) scenario, where the current energy structure prevailed, with trends like the current development. The electricity demand is satisfied by coal-fired thermal power plants, gas-fired thermal power plants, hydro power plants and renewable power plants. Scenario 2 – Green scenario, where gas-fired thermal power plants and nuclear power representative with small modular reactors are base load technologies, and also intensive construction of production capacities on renewable energy sources is forced. By making further analysis, the possibility of flexibility in the construction of new facilities within the interval, economic indicators, and appropriate impact on the environment are obtained. In order to make an economic analysis for a particular technology, calculations are made for parameters that are standard for projects, such as: net present value, benefit – cost ratio, payback period and internal rate of return. The environmental impact is analysed of aspect of CO2 emissions.

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In the proposed paper scenarios for expansion of the Macedonian electricity generation system are investigated. In order to determine the optimal electricity generation technology mix sufficiently enough to feed the country electricity demand MESSAGE tool is used. The planning period for the case study is from 2020 (base year) to 2050. The environmental impact, for each scenario, is also analyzed of aspect of CO2 emission.

The paper presents the methodology of operation modes for hydropower plants (conventional and pump storage) in a complex hydroenergy system. Operation involves water management in generating and/or pumping mode of hydropower units taking into accounts technical characteristics of the power plants facilities (turbine/generator and pump/motor systems), reservoirs characteristics considering all hydraulically connected infrastructures, as well as the hydrological conditions (for run offs and turbine inflows). The purpose of the operating mode for the entire hydropower system is to maximize financial profits from electricity generation, taking into account market electricity prices, electricity needs, with respecting the technical requirements and of course avoiding or minimizing overflow. Operating regimes depend on the electricity market price, the tariff models and the duration of each tariff (base, peak), the technical characteristics of the units and the hydrological conditions. The model application is presented at the hydropower Complex on the Crn Drim river with existing construction and new facilities that can be upgraded in the future. The results are presented for long-term and short-term planning of the system operation under various technical and hydrological conditions. The model can be used to perform preliminary analyses in order to improve hydroenergy systems with additional installed capacity of the existing system. Selected outputs are presented with appropriate comparisons and conclusions.

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