[en] Highlights: • Comparative techno-economic analysis of wet- and dry-cooling systems for the steam condenser of a combined cycle power plant. • Development of a novel cooling system selection procedure based on site climatic conditions. • Investigation of the influences of site meteorological parameters on the thermoeconomic performance of different cooling systems. • Determination of optimal steam condensing temperature based on site ambient conditions. For combined-cycle power plants, the two most dominant steam condenser cooling options are the wet-cooling tower and the air-cooled (dry) systems. The wet cooling system is commonly installed on plants located in areas with available water sources, while the dry system is typically preferred in areas where water is scarce. However, owing to the increasing regulations on water conservation, water usage costs and improvements on cooling system designs, a new approach is required for the optimal selection of plant cooling systems, incorporating site climatic conditions, amongst other considerations. This study presents a comparative techno-economic analysis of a steam turbine cycle with wet- and dry- cooling systems for five typical tropical locations in Nigeria with different climatic conditions and water usage costs. The results show that in the hot (ambient temperatures $>$33 °C) and dry regions (relative humidity $\le$31 °C) and high relative humidity values ($\ge$76%), the performance and cost implications of the plant with dry cooling was more favourable due to lower system sizes and costs requirements. Parametric investigations revealed that high ambient temperature increased the size and costs requirements of air-cooled systems while relative humidity significantly influenced the total power consumption of water-cooled systems.