The global energy transition from fossil fuels to Renewable Energy (RE) is dominated by wind and solar photovoltaic (PV) systems. In Namibia, this transition is mainly dominated by solar PVs, with a rapid increase in grid-connected solar PV plants over the past nine years due to the Renewable Energy Feed-In Tariffs (REFITs) introduced in 2015. This initiative aimed to reduce reliance on imported power and help the country achieve its 70% RE target. However, the increasing integration of solar photovoltaics stations to our grid poses new challenges of grid instability due to the intermittent nature of solar energy and the lack of natural inertial response from inverter-based generation units. Currently, there are no reports that thoroughly present the impacts of increased penetration of the solar PV plants on the Namibian grid’s frequency stability. Therefore, this study focused on evaluating the impacts of increased solar PV penetration on the Namibian grid frequency stability. The analysis was conducted in the DIgSILENT Power Factory software tool, whereby the Namibian grid was modelled and simulated under four PV penetration scenarios: 0% PV, 30% PV, 44% PV, and 73% PV to assess the frequency response under each scenario, following a generator trip event. The simulation results demonstrated that increasing the PV penetration leads to frequency instability, whereby the frequency deviates beyond the permitted threshold of 49–51 Hz. Specifically, the 73% PV scenario resulted in a frequency sag of 48.77 Hz, which poses risks of power equipment damage and blackouts. As a mitigation measure, Battery Energy Storage Systems (BESS) and Grid-Forming Inverters (GFMIs) were recommended and implemented within the model to mitigate frequency instability. With these measures in place, it was observed that the Rate of Change of Frequency (RoCoF) was improved, thereby reducing frequency deviations.