The article analyses the relevance of the problem of changing the structure of electricity and heat generation, taking into account the goal of increasing the share of low-carbon generation. The existing approaches to forecasting macroeconomic indicators, including the energy sector, are analysed. A new use of economic and mathematical modelling methods to build models of the sectoral balance is proposed. It has been established that a balanced economic and mathematical model that takes into account changes in the structure of energy generation and consumption can be an information base for calculating the need for investment in additional capacity. In this case, the investment capacity of the energy sector is calculated both on the basis of the first-order effects, expressed in the cost of energy capacities, and the second-order effects, expressed in the need to invest in enterprises for the production of energy capacities. The same model contains a calculation of the economic efficiency of investment, as well as a sensitivity analysis to changes in the input data for the calculation. The article concludes that the model developed according to the methodology being created can be a tool for justifying the targets for limiting carbon dioxide emissions under conditions of limited investment resources.