Get average solar resource estimates for any latitude/longitude via NREL. Returns annual + monthly averages for: Direct Normal Irradiance (DNI, kWh/m²/day — solar concentrators), Global Horizontal Irradiance (GHI, kWh/m²/day — flat-plate panels), and Tilted-At-Latitude irradiance (optimal fixed-panel orientation). Sourced from NREL National Solar Radiation Database (NSRDB). Useful for rooftop solar feasibility, off-grid design, and renewable-energy modeling.