In order to evaluate the value of cogeneration, usually static-simplified criteria are used, neglecting the entire energetic context and the dynamic interaction between cogeneration and the centralized electric system. Therefore, a dynamic method, based on simulation of scenarios, is proposed. For a given demand for heat and electricity, two scenarios are worked out: a scenario where no additional cogeneration is installed and a scenario where cogeneration is added, possibly also resulting in a more moderate expansion of the central power system. To correctly portray the dynamic response of the central power system, it is simulated. The use of this method on concrete possibilities for cogeneration in Belgium, demonstrates the need for this dynamic method. For industrial cogeneration, the static simplified method seems valid because of the high and constant utilization of this form of cogeneration. In the case of cogeneration in the commercial sector, however, where the heat demand is only present during a limited period of time, the static method is not valid and the environmentally friendly nature of this kind of cogeneration is less obvious. As a general conclusion, it can be stated that every specific possibility for cogeneration has to be evaluated separately in its own overall energetic context, including the entire electricity generation system.