The benefit of a hybrid system is strongly dependant on the system design and the control strategy that will be used. This paper suggests a method to evaluate the optimal control strategy of a hybrid electrical system to optimize its design from the point of view of fuel consumption taking into account this interaction. Analytic models are used to describe the system and the interactions between components. A first optimization is made to minimize fuel consumption using one system configuration on a typical consumption cycle. This algorithm is ready to be using with a higher level algorithm in order to find an appropriate design of the system.