Cell capacitance is a well-known parameter in silicon solar cells. Its effects on the power units, specially on the S3R, is also well known since it has to be taken into account to design them. The capacitor energy is discharged into the power switch and the dissipation increases. Moreover, it introduces a delay in the energy transfer from the array to the main power bus. In triple junction solar cells, this parasitic element becomes far more complex and is not so well characterized. This paper addresses this issue and proposes a large signal model to be used in combination with a S3R.