The rise in global temperature has accelerated the demand for replacing fossil fuels with sustainable renewable energy. Alongside wind, waves and current energies in the oceans, there has been huge interest in developing large floating photovoltaic (FPV) plants in offshore environments. Applying FPV structures in offshore environments remains challenging due to harsh environmental conditions. This paper numerically studies a recently developed soft-connected FPV concept for harsh offshore conditions. The case of a small array consisting of 6 modules interconnected by soft ropes that were experimentally examined is considered. A numerical model for the time domain analysis is built using the commercial solver SIMO. The numerical model is calibrated and validated according to the available experimental results. Next, a parametric study is conducted to examine the effect of different mooring line pretensions on the global responses of the FPV array under regular waves. The study will provide a better understanding of the effect of mooring pretension on the global FPV design. Moreover, recommendations are presented for further optimisation and development of such FPV systems.