This study explores the performance of the Duke Energy Progress/Carolinas (DEC/DEP) electric power system under eighty-five configurations combining different capacities of utility-scale photovoltaics (PV) and energy storage (lithium-ion batteries). The different configurations include PV installations capable of providing 5% to 25% of the systems energy and batteries with varying power capacities and storage of 2, 4, and 6 hours. A cost-based production model comprised of a day-ahead unit commitment and a real-time economic dispatch simulates the optimal operation of all the generation resources necessary to supply hourly demand and reserve requirements during the year 2016. The model represents in detail the generation fleet of the system, including 221 nuclear, natural gas, coal and hydro power generators accounting for an installed capacity of 37.8 GW. Results indicate that minimum carbon abatement costs for the configurations studied are obtained when the power capacity of the batteries is~12.5% of the PV capacity. For levels of PV penetration (measured as expected annual share of energy) above 17%, higher decarbonization targets are better pursued with increased storage capacity than with more PV. For more ambitious targets (e.g. $> 30\%$ ), carbon dioxide emissions reductions require increases in both PV and storage capacity. Like previous studies this analysis confirms the decreasing marginal value of storage especially in systems that already have important shares of low carbon generation, such as DEC/DEP where ~50% of the generation is provided by nuclear plants.