Thermo-economic and environmental study of solar hybridization for existing fossil-fueled combined cycle power plants: comparison of two practical approaches

This study investigates the technical, economic, and environmental feasibility of integrating solar energy into existing combined cycle power plants. A design method is developed based on the parametric study of steam turbine behavior and evaluation of the power augmentation capacity in the reference combined cycle. Considering the minimum requirement for major changes in existing equipment, the practical limitations of the retrofitting process have been identified. Two different hybridization approaches, superheating and vaporization schemes, are proposed and evaluated under off-design and quasi-steady conditions. The investigation demonstrates that integrating superheated solar steam at the high-pressure level of HRSG leads to the recovery of the dominant share of the available recoverable power. The results show that the mentioned integration scheme requires a slightly larger solar field and can increase the average output power of the reference steam turbine from 118 to 140 MW. The levelized cost of electricity (LCOE) for the hybridized plant is more competitive than the similar stand-alone solar power plants. While the LCOE of the additional solar electricity to the referenced combined cycle has been calculated equals to 64.86 $/MWh for the best case, the total LCOE has grown from 38.99 $/MWh for the combined cycle to 39.63 $/MWh. The environmental analysis shows that the annual CO₂ emission is reduced by 25,453 tons. This study demonstrates the techno-economic viability and environmental benefits of solar hybridization, providing insights to guide the retrofit of existing power plants in other countries and climatic conditions and facilitate the transition towards more sustainable electricity generation.