The paper analyses the role and the technical and economic indicators of different electricity generation sources in the transition to "carbon-free" energy. A simplified method is proposed for estimating the minimally justified price of selling electricity from thermal power plants (TPPs), renewable energy sources (RES) and new maneuverable natural gas capacities is proposed. It is shown that the price of electricity from RES and new maneuverable capacity has a decisive influence on the amount and fixed period of return on investment in construction, as well as on the capacity utilization factor (CUF), which depends on the mode of operation of the power plants. Comparative estimates of the CUF of different electricity generation sources are presented. It has been shown that the cost of electricity from RES, new peak and maneuverable capacity is significantly higher than the cost of electricity from thermal power plants during the payback period. It is proved that at present the reserve for the reduction of the power shortage and the load regulation is available only in the thermal generation, and the conditions for the possibility of its effective use are the maintenance of the proper technical condition of the pulverized coal boiler units and the sufficient fuel base. To ensure acceptable electricity prices, RES and new control capacity should be phased in, using existing TPPs and CHPs to balance both the weighted average price and the regulation of power system load modes. Keywords: thermal power plants, coal, natural gas, gas turbine, steam-gas, gas-piston power plants, renewable energy sources, cost of electricity supply.