The objective of the thesis is to develop and approbate models for energy supply, focusing on optimisation of long-term planning in energetics and securing a sustainable development in terms of use of energy resources. The object of the research is energy supply system in Latvia, comprising interrelated elements of power supply and district heating system. The subject of the research is models for energy supply analysis, planning, and forecasting as well as their applicability for evaluating the securing of energy resources. The nominated tasks for the objectives of the thesis include the analysis of technological, economic and management aspects of energy supply in Latvia, the comparison of energy system models available globally, the preparing proposals for renewable energy sources integration and for analysis of reciprocity of power supply and district heating system by applying the developed hybrid system dynamic model. General theoretical research methods have been analysed and employed in the research, including induction and deduction, analysis and synthesis, systemic approach, along with specific methods, e.g. mathematical modelling, system dynamics, correlation regression, analysis of scenarios, strategic decision making, classification, the balancing and expert evaluation. Principles and proposals have been drawn up in respect of: - the analysis of interaction between electricity supply and district heating and its influence on the national indicators of the efficiency and the securing of energy supply; - the enhancement of the optimisation methods used up to now in the energy sector, by assessing the integration of RES in electricity and heat production; - as a result of regional level analysis, development scenarios for power generation capacities have been obtained for a specific conjuncture of external factors. The research results have been used for developing practical proposals for electricity balance of “Latvian Energy long-term strategy 2030 – competitive energy for society”, for optimisation of the operations of the hydroelectric power plants and combined heat and power plants run by AS “Latvenergo”, in study “Analyses of Energy Supply Options and Security of Energy Supply in the Baltic States”, as well as in the State Research Programme sub-project “Explore the competitiveness of latvian enterprises in foreign markets and make proposals for its strengthening”.