In this paper, the effect of using three solar fields in a solar thermal power plant has been evaluated. Two separate solar direct steam generations are used to provide a portion of the energy required by the high-pressure turbine and low-pressure turbine. The third solar field is used for molten salt energy storage. If the energy stored during the daytime is not enough, the fossil fuel boiler will provide the rest of the energy needed. Given the current price of natural gas, the use of solar energy is not cost-effective, regardless of environmental issues, government incentives or external costs, such as health costs. Furthermore, the use of solar energy for the power plant was unable to make a significant reduction in electricity cost, regardless the 3.5$/MMBTU natural gas price. However, considering the complexity of the solar system, the use of solar energy for the price of the current natural gas is not recommended. By increasing the price of natural gas, the use of solar energy is more economically feasible. The results of the study show that the use of three solar fields (two separate solar fields to produce superheated steam for a high-pressure turbine and low-pressure turbine and a solar field for energy storage using molten salt as thermal energy storage medium) rather than one solar field reduces electricity consumption by 1.83%-13.78% for the price of 9 $/MMBtu natural gas. Although each of the first and second solar fields produce different energy quantities, and therefore, require different field areas, the field coefficient of the field is the same for both solar fields. (C) 2019 Elsevier Ltd. All rights reserved.