Our Masters Capstone Project is an Integrated Resource Plan (IRP) for Arizona's largest electric utility, Arizona Public Service Electric (APS). An IRP is developed by utilities to identify the optimal combination of demand- and supply-side resources needed to reliably meet forecasted demand for energy and capacity, including a planning reserve margin, over a future period. In addition to APS's obligation to serve the growing load in Arizona while minimizing costs, it is required by the state to adhere to the Renewable Energy Standard (RES) policy of 15 percent retail sales from renewable energy resources by 2025. The analysis described in the report aims to identify the optimal resource mix for APS to deploy to reliably meet the forecasted deficit and deliver 100 percent of its retail sales from zero-carbon sources by 2050, based on its recently announced goals. We analyzed three scenarios: Business-as-Usual (BAU), 100 Percent Clean Energy (Clean100) and 100 Percent Renewable Energy (RE100). The Business-as-Usual scenario serves as a reference, exploring what it would look like if APS only adhered to Arizona's current RES policy. The alternative scenarios explore two pathways to reaching zero carbon emissions electricity by 2050, using only carbon-free energy resources in Clean100 and only renewable energy resources in RE100. The results of our analysis show that while both alternative scenarios demonstrated the feasibility of a zero-carbon system, Clean100 provided the least cost pathway to achieving APS's zero-carbon electricity goal by 2050.