Over the last decade, the importance of electricity in the overall energy mix has been increasing. Trends show that by 2030, half of the electricity production will be from renewable energy sources, such as wind or solar energy. To complete and underpin such robust growth, the EU policies and national legislations related to the electricity market must introduce new instruments, taking into account new market players and cutting-edge technologies such as energy storage devices. The sustainability and security of the European electricity supply are strongly dependent on the successful integration of photovoltaic energy. This paper examines the deviation between day-ahead and intraday photovoltaic power generation forecasts compared to the real production regarding 1000 MWp photovoltaic systems. The aim was to determine the photovoltaic balancing requirement through real data relative to the day-ahead and intraday forecasts. Another goal was also to establish the photovoltaic grid balancing reduction potentials of lithium-ion-based and vanadium redox flow battery storage systems. As a result of this research, it was possible to present the magnitudes of the balancing power, the energy divergence, and the frequency in the examined 5-year period. In addition, by a second modeling concept, several energy storage capacity sizes (nominal net storage capacity) were simulated from the values of 10 to 10,000 MWh to estimate these grid balancing reduction potentials by using real, measured photovoltaic data.