The availability of solar resources across the United States varies significantly, depending on geography and atmospheric conditions. This resource, defined as the amount of solar radiation received, dictates the viability and efficiency of solar energy projects. Understanding where this resource is most abundant is the first step for developers and homeowners looking to harness the sun’s power.
How Solar Resource Potential is Measured
The solar industry and government agencies quantify solar resource potential using two commonly cited measurements: Global Horizontal Irradiance (GHI) and Direct Normal Irradiance (DNI). GHI measures the total solar energy received on a horizontal surface, including both the direct beam from the sun and the diffuse light scattered by the atmosphere. This metric is the standard for assessing the potential of fixed-tilt and rooftop photovoltaic (PV) systems.
DNI, in contrast, measures only the solar radiation arriving directly from the sun on a surface perpendicular to the sun’s rays. This measurement is relevant for Concentrating Solar Power (CSP) and Concentrated Photovoltaic (CPV) technologies, which require a clear, direct beam of sunlight to focus the energy. Solar resource data is collected using ground monitoring stations and estimated through sophisticated models that integrate satellite imagery and atmospheric data. Average daily GHI across the continental U.S. ranges from approximately 2.9 to 6.2 kilowatt-hours per square meter (kWh/m²).
The Arid Southwest: Maximum Resource Zones
The region with the greatest solar resource in the United States is the arid Southwest. This area includes the desert regions of Arizona, New Mexico, Nevada, and Southern California. These states exhibit the highest annual average solar irradiance values due to favorable geographic and climatic conditions.
The Southwest benefits from low humidity and minimal cloud cover, allowing the sun’s energy to reach the ground with little atmospheric interference. Many parts of this region experience over 300 days of sunshine per year, maximizing generation hours. Average annual solar irradiance in this core resource zone can reach between 6.0 and 7.0 kWh/m² per day, a value significantly higher than the national average.
This area’s advantage is pronounced in both GHI and DNI, making it suitable for all types of solar installations. High DNI values are appealing for utility-scale CSP projects, which rely on the intense, direct solar beam. The combination of clear skies, high sun angles, and an arid environment creates a corridor for maximum solar energy harvesting. This concentrated solar resource has driven considerable investment in large-scale solar infrastructure across these states.
Secondary High-Irradiation Regions
While the Southwest holds the top position, several other regions across the country also possess strong solar potential. The High Plains, encompassing parts of Texas, Oklahoma, and Kansas, represents a secondary resource zone. These central states benefit from a large number of clear-sky days, particularly during the summer months, which supports substantial solar energy production.
Texas leverages its vast land area and high levels of sunlight, boasting ample irradiance for both residential and utility-scale projects. Regions in the South and Southeast, such as Florida, receive high solar intensity due to their lower latitude. Even though these areas contend with higher humidity and more frequent cloud cover than the Southwest, their proximity to the equator ensures a strong baseline solar resource.