arXiv:2610.34089v1 Announce Type: new Abstract: This study presents a two-layer optimization framework to determine the optimal sizing of PV, wind, and battery storage co-located with existing hydroelectric plants to support rapidly increasing data center loads while minimizing cost, grid reliance, and transmission upgrades. The outer layer uses Particle Swarm Optimization (PSO) to select capacity combinations, while the inner layer performs rolling-horizon dispatch simulations to model hourly energy balance among PV, wind, hydro, and BESS, considering operational constraints. Two case studies were analyzed. At The Dalles Dam (Oregon), favorable wind resources and land availability enabled deployment of 111.2 MW PV and 117.9 MW wind, with no BESS required. Hydro flexibility allowed the system to meet the load with minimal grid support. In contrast, Conowingo Dam (Maryland) faced land constraints and limited renewables to 130 MW PV, leading to higher grid dependence. Co-locating hydro with renewables significantly enhances reliability and cost effectiveness by leveraging hydro's dispatchability to balance daily and seasonal variable generation from PV + Wind, reducing the need for storage or costly grid imports. This analysis provides a framework to meet the 99.9% availability targets of this new load type on the grid with sustainable energy resources.