Abstract
Industrial gas turbines are central to electricity supply in hot-climate countries such as Iraq, yet their actual performance often deviates from design-point values because of high ambient temperatures, part-load operation, and component degradation. This study quantifies the operational, thermodynamic, and exergy performance of a 125 MW-class simple-cycle gas turbine in southern Iraq and identifies the principal sources of performance loss. High-resolution SCADA data (30,912 valid 15-min records) were analyzed over one full year using integrated energy and exergy balances. The unit operated predominantly at 75–90% of ISO-rated power, with an annual capacity factor of 0.41. At 90–100% load, the average net power output was 114.7 MW, the thermal efficiency was 0.321, the heat rate was 11,210 kJ/kWh, and the exergy efficiency was 0.343, corresponding to a 7–9% derating relative to ISO conditions. Thermal efficiency decreased by about 0.095 percentage points for each 1 °C increase in ambient temperature. Exergy analysis showed that the combustor accounted for approximately 59% of total exergy destruction, followed by the turbine (about 15%) and exhaust-related losses (about 21%). The results confirm the strong dependence of plant performance on ambient temperature and load. Near-term improvement should focus on sustained high-load operation and condition-based maintenance, whereas inlet-air cooling and waste-heat recovery should be evaluated in future techno-economic studies.