An approach to model the solar cell system with coupled multiphysics equations (photovoltaic, electro-thermal, direct heating and cooling processes) within the context of the resistive-companion method in the Virtual Test Bed computational environment is presented. Appropriate across and through variables are defined for the thermal terminal of the system so that temperature is properly represented as a state variable, rather than as a parameter of the system. This allows enforcement of the system power conservation through all terminals, and allows simultaneous solutions for both the electrical potentials and the system temperature. The thermal port built accordingly can be used for natural thermal coupling. The static and dynamic behaviors of the solar array model based on the approach are obtained and validated through comparison of simulation results to theoretical predictions and other reported data. The electro-thermal modeling method developed here can be generally used in the modeling of other devices, and the method to define the across and through variables can also be generalized to any other interdisciplinary processes where natural coupling is required.