Thermoeconomic modelling for power plants under flexible operation: The case of a turbogas for CCPP generation

The power generation mix has deeply changed due to penetration of RES (Renewable Energy Sources) into the grid and fluctuation of the supply/demand of electricity. In Italy the power generation mix has relied on CCPPs (Combined Cycle Power Plants) so far. Therefore these plants, which were designed for base-load generation, are now called to cover the peak-load demand in order to maintain competitiveness and to balance the fluctuations of RES. This new asset will be essential for the reliability of the network in the middle term, until large storage capacity and smart grids are introduced. Indeed, plant operators face unknown response of the plants to the dynamic operation and a new structure of the production costs. It is therefore necessary to evaluate the internal cost structure of electricity generation in order to identify the best operation strategy for CCPPs in this new dynamic framework and to assess its consequences on capital and resources expenditure. The present work proposes thermoeconomic analysis as a tool to fulfil such objective, since it may provide a consistent cost allocation basis and a unique ground for weighing cost sources. The model is applied to quasi-steady operation profiles of a turbogas for CCPP generation. Thermoeconomic costs, exergoeconomic factors, relative cost differences are calculated as functions of the load profile and its slope, so that an evaluation of the capital and exergy expenditure of the different operation strategies can be carried out.