This paper deals with the electromagnetic modeling of large and complex electrical structures by means of large scale parallel systems, such as Grid Computing (GC) and super-computer. Transmission-Line Matrix (TLM) modeling method is applied to homogeneous volumes. The planar structures are modelled with the mode matching approach. The results prove the benefits of the GC and supercomputer environments to solve electrically large structures. A prediction model for computing performances on grid, based on a hybrid approach that combines a historic-based prediction and an application profile-based prediction, has been developped. The predicted values are in good agreement with the measured values.