While advancement of power generation and grid management technologies has enabled their broader applications, recent changes in climate are projected to impose obstacles to performance and operation of the systems employing these technologies. As more renewables are prioritized over fossil fuels to alleviate changes in climate, the power systems are in need of further research to help meet public and environmental demands by complementing renewable intermittency. In this thesis, the combined-cycle plant technology was modeled in the MATLAB/SIMULINK and verified at two different scales: 1) a 19MW UC Irvine central power plant; 2) a 600MW utility-scale power plant.

Three scenarios were generated using the Holistic Grid Resources Integration and Deployment (HiGRID) tool with the renewable penetration percentages set according to the original California Renewable Portfolio Standards (RPS): 33%, 50% and 80%. Each scenario presented how various power generating classes contribute to electricity demands for a year-long period. For the scope of this study, load-follower power plant contributions to the general load profile for a week-long period were extracted, normalized and input into the utility model for simulation.

The simulation results demonstrated possible consequences from increasing the renewable penetration to the grid. With the increasing penetration, the natural gas combined-cycle power plant needed to operate more dynamically as a load-follower to complement the renewables. The more dynamic operation of the power plant resulted in decrease of its efficiency from 63% to 44% and to 36% and its capacity factor from 75% to 59% and to 34% for the three scenarios, respectively.

To combat climate change and air pollution many electric utilities have implemented standards to prioritize power generated from renewable sources. However, their intermittency and dynamics have posed challenges to high use of these non-dispatchable resources such as solar and wind. Climate change will further complicate these challenges and thus, the reliable and efficient operation of the electric utility grid network. Among many available options capable of complementing the renewables, natural gas combined-cycle (NGCC) technology, with its high efficiency and flexibility, has demonstrated its potential as a load-following plant. The fleet of load-followers needs to operate at lower part-load and more dynamic operating conditions for extended periods of time to complement the non-dispatchable renewables. In this study, current and next-generation load-following technologies are physically simulated to determine implications of their dynamic operation in a current and future grid affected by increased renewables. For the current load-following technology, novel NGCC control and dispatch strategies are applied to improve an individual plant and grid performance. Compared to the respective base case, the control strategies have improved efficiency by up to 58 percentage points and dispatch strategies have reduced grid wide GHG emissions up to 54%. Furthermore, climate change impacts on grid operation are examined as they affect the renewable dynamics. In response, not only has capacity of the load-followers been increased but also their operation has become more dynamic to maintain grid reliability. In addition to dynamic dispatchability, transitioning to a 100% renewable grid requires power systems to be fuel-flexible with near-zero emissions. In this context, solid-oxide fuel cell gas turbine (SOFC-GT) hybrid technology is explored as a next-generation load-follower. The proposed system can achieve net efficiency >70% at distributed energy scale (100 kWel). With a developed control strategy, the system can complement high levels of non-dispatchable renewables without incurring component degradation and with its high part-load efficiency maintained >50%. On the other hand, the system can seamlessly operate with up to 72.9%v of hydrogen without any configuration modifications. These conclusions increase confidence that dynamic dispatch of highly efficient and renewable-fueled load-following technologies can facilitate a smooth transition into highly renewable electric grids.