Valorisation of resources with the cogeneration of electricity and heat from the incineration of wastes is an important issue in modern societies. Present decision models aiming with minimizing the total costs associated with the optimum choice of configuration (synthesis), component design (dimensioning), and operation of waste incineration/cogeneration units. In fact, the time factor which greatly affects certain key decision parameters such as the amount of wastes to eliminate and the electrical and heating demands places on the system (to name just two) renders the problem of synthesis design and operation very complex. The thermoeconomic methodology presented below is a general approach which can be used to respond to the questions: when to invest and reinvest and which technology, configuration, component capacity and performance and modes of operation to adopt. The problem consists of developing the thermoeconomic models (typically very non-linear, continuous and/or non-contiguous) which can be used to minimize the time integral of total costs, optimizing simultaneously the configuration, design and operation of the installation over its entire economic lifetime. The system considered in the paper consists of a waste incineration cogeneration power plant which may include several incinerators, one condensing steam turbine, one extraction steam turbine and one auxiliary boiler.