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The declining cost of renewables, the need for cleaner sources of energy, and environmental protection policies have led to the growing penetration of inverter-based resources such as solar photovoltaics (PV), wind, and battery energy storage systems (BESS) into the electric power system. The intermittent nature of these resources poses multiple challenges to the power grid and substantial changes in the conventional generation and electrical power delivery practices will be required to accommodate the large penetration of these renewable power plants. The impact of large solar PV penetration on both generation and transmission systems, and the use of BESS to mitigate some of the challenges due to solar PV penetration has been studied in this dissertation. One of the major challenges in evaluating the impact of inverter-based resources (IBR) such as solar PV systems is developing an equivalent model adequate to represent its operation. This work proposes a detailed solar PV model suitable for analyzing the configurations, design, and operation of multi-MW grid connected PV systems. This model which takes into account the contributions of the power electronics control and operation was used to evaluate the impact of transient changes in solar PV power on an example transmission system. The benefits of a battery system configuration connected to the grid through an independent inverter were analyzed and its operation during transient conditions was also evaluated. After developing a detailed solar PV and BESS modules for analyzing the effect of IBR on transmission systems, an innovative approach for evaluating the impact of solar PV plants on both generation and transmission system based on a practical minute-to-minute economic dispatch model was proposed. The study demonstrates that large solar PV penetration may lead to both over- and under-generation violations, and substantial changes to conventional generation dispatch and unit commitment will be required to accommodate the growing renewable solar PV penetration. The terminal voltage of a battery pack varies based on multiple parameters and cannot be modeled as a constant voltage source for a detailed analysis BESS operation. A novel approach for estimating the equivalent circuit parameters for utility-scale BESS using equipment typically available at the installation site was proposed in this dissertation. This approach can be employed by utilities for monitoring energy storage system operation, ensure safety and avoid lithium-ion battery "thermal runaway". The new methods developed, configurations and modules proposed in this dissertation may be directly applicable or extended to a wide range of utility practices for evaluating the impact of renewable resources and estimating the maximum solar PV capacity a service area can accommodate without significant upgrades to existing infrastructures.