The accelerated introduction of renewable energy sources (RES) in electric power systems makes it necessary to carry out studies to evaluate their impact and ensure a stable operation. The objective of this article is to carry out an evaluation of the frequency stability in the Cuban National Electric System from the point of view of the inertial response with the massive introduction of photovoltaic solar farms and Battery Energy Storage Systems (BESS). A theoretical description of the inertial response and frequency stability problems in an electric power system is shown, and how it is affected by the introduction of solar photovoltaic generation (PVG). It shows how it is possible to use BESS devices to achieve a synthetic inertial response and the control algorithm implemented for this purpose is presented. The Cuban Electric Power System is modeled with the participation of BESS in a concentrated model; the values of inertia constant, RoCof and frequency nadir are calculated for different penetration scenarios of solar PVG. The results obtained are analyzed and a general assessment is given on the stability of the frequency in the studied scenarios.