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Consideration of the feasibility of building combined power plants (CPP) based on renewable energy sources (RES) and the choice of parameters, type of equipment, layout, and design solutions is based on an assessment of economic efficiency, the indicator of which is the ratio between the required investments and the achieved technical and economic effect. An accurate assessment of economic efficiency is a rather difficult task since it is necessary to take into account a large number of factors, for example, specific features of design solutions, operating conditions of the CPP depending on the requirements of the consumer, the stochastic nature of the manifestation of energy resources, the possible mode of operation of the CPP for the needs of individual consumers and others. An approach based on the minimum cost criteria has been widely used for the economic justification of the objects under construction for a long time. In rigidly centralized economic management, such an approach based on ensuring optimal construction planning played an important role in increasing the scientific validity of economic decisions. It proceeded from the global and national economic goals of economic development. In the conditions of a free market economy, a method of evaluating the effectiveness of taking into account all the main features of it is necessary.

Energy plants based on renewable energy sources can be combined according to the type of energy source (hydro, solar, wind with or without hydro storage). Currently, not enough attention has been paid to assessing the economic efficiency of combined power plants incorporating a hydraulic accumulator. When designing combined power plants, it becomes necessary to choose the composition of such plants and evaluate their economic efficiency. The purpose of this study is to justify the possibility of applying the present value method to select the composition of combined heat and power plants and assess their economic efficiency. The research used the following methods: review, synthesis of existing literature on the subject, system analysis, collection of data on different types of power plants, and calculation of their economic efficiency. A computer program has been compiled with Turbo Pascal 7.0 for the calculations. The calculations have shown that a cost-effective option is a combined power plant based on a wind power plant and a hydropower plant with a hydro accumulator.

In our country, a lot of attention is paid to the development of the energy sector. A lot of work is underway to modernize existing capacities and commission new capacities. At the same time, the unit capacities of units and power plants also increase, which ensures faster commissioning of capacities in the power system and an increase in the efficiency of power plants. Attention is also paid to the development of power plants based on renewable energy sources (hydraulic, solar, wind, etc.). One of the most important tasks in the power industry is to cover peak minimum and maximum loads, which is becoming increasingly important in connection with the growth of the power system's capacity. As is known, according to world indicators, the maneuverable capacities should be about 25% of the total power of the EPS. The most promising maneuverable capacities are hydroelectric power plants. However, in our country, hydroelectric power plants account for about 14.3%. This task will become more complicated with the introduction of capacities based on solar and wind energy and the commissioning of new hydroelectric and thermal power plants in the Republic. This is because RES capacities have a significant discontinuity even during the day, and the water resources in the Republic are primarily for irrigation and drainage purposes and are significantly variable during the season. One way to solve these problems in the world is the creation and use of pumped storage power plants (PSPP). The peculiarities of the creation and use of pumped storage power plants in our region are that the available hydro resources of our region are mainly of water management importance, while the task is also to increase the energy efficiency of existing reservoirs. Based on the foregoing, we can say that the development of methods for determining the economic efficiency of pumped storage power plants, taking into account direct and indirect effects, taking into account the peculiarities of their use in energy and water management systems of Uzbekistan is the main task for the present time. To solve the set tasks, a new methodology and program for substantiating the technical and economic indicators of pumped storage power plants in Uzbekistan's energy and water management systems have been developed. The schemes of using pumped storage power plants at four energy and water management facilities, that is, the Tuyamuyun hydro subunit, Arnasai, Talimarjan, and Khodjikent reservoirs, were considered, and for these facilities, based on the developed methodology and program, their technical and economic parameters of the pumped storage power plant were determined. Based on the results obtained, it can be said that using the PSPP in four facilities, it is possible to generate a total of about 418 MW of capacity and more than 930.0 million kWh of electricity, as well as to save 139 thousand tons of fuel equivalent per year, with this, the annual economic efficiency will be about 700.0 billion sums.