A number of solar thermal power plants have been planned by the Algerian state for the horizon of 2030, for the purpose to achieve the self-sufficiency from solar electricity and its exportation. The main objective of the present paper is annual performance and economic assessment of an Integrated Solar Combined Cycle System (ISCCS-18) of 68.2 MWe with 18 MWe solar field, using parabolic trough collectors. This power plant has been designed and simulated through the software IPSEpro for Naâma site in Algeria. For this purpose five power plants cases have been investigated in terms of performance and economics analysis, namely, (i) Gas turbine, (ii) conventional combined cycle, (iii) ISCCS without fossil-fuel back-up system, (iv) ISCCS with fossil-fuel back-up system, and (v) Solar Electric Generating System (SEGS). The parameters of the annual performance analysis include annual energy production, net annual efficiency and capacity factor. The economic analysis includes environmental, investment, fuel and Operation and Maintenance (O&M) costs, and the Levelized Electricity Cost (LEC) calculation. The obtained results have shown that the LEC of the ISCCS-18 is 4.22 ¢/kWh; about 43% higher than the combined cycle with consideration of environmental cost, and saves around 21 million US$ in fuel consumption and reduces about 0.45 million tons in CO2 emissions in 30 years operating period in comparison with conventional combined cycle. Also, the results have shown that about 4 % improvement in the net annual efficiency of the ISCCS-18, as well as the annual solar share is 8.0 %. According to this solar share and to the Algerian regulations, the project owner will receive premium of 100 % of the LEC of the total produced electricity by the ISCCS-18.