One of the practical uses of the thermoeconomic models is to find a trade-off between efficiency and cost in the design of a power plant. Usually, the thermoeconomic analyses involve a thermodynamic model of the power plant and an economic model dedicated to assess the costs. In combined cycle gas turbine (CCGT) power plants, the thermodynamic model usually calculates the performance and the energy balances of the power plant at the design conditions. However, nowadays, after several years of CCGTs operation experience, data of annual operation may be found, which differ to some extent from the design conditions. This paper shows a methodology to achieve thermoeconomic optimisations of CCGT power plants taking into account the frequent off-design operation of the plant. Therefore, the aim of the work is to improve the thermoeconomic design of the power plant by means of considering a more realistic annual operation scenario. In addition, the methodology is applied to optimise several CCGT configurations operating under different scenarios of energy production. The results of the optimisations are compared to those obtained with usual thermoeconomic models based on design conditions performance. (C) 2010 Elsevier Ltd. All rights reserved.