US solar energy map. Southeast states are most suitable for solar energy projects. Click on map for full size.
On the picture above is map of US with average annual direct normal solar radiation. If you want to see full size map you should click on this picture. Resolution of this map is resampled to 40 kilometers. Model estimates of monthly average daily total radiation using inputs derived from satellite and/or surface observations of cloud cover, aerosol optical depth, water vapor, albedo, atmospheric pressure and ozone. Dark red are areas with high average solar energy radiation, and those areas are perfect for exploitation of solar energy for generating electricity, warming water, etc. Dark red areas in average are receiving more then 9 kWh of solar energy per square meter per day and that amount of solar radiation is definitely enough for exploitation. Dark grey areas are receiving less than 2 kWh of solar energy per square meter per day in average, and that amount of energy isn’t acceptable for bigger solar energy projects.
Near midday on a clear day, about 25 percent of the solar radiation is scattered and absorbed as it passes through the atmosphere. As a result about 1000 w/m2 of the incident solar radiation reaches the earth's surface without being significantly scattered. This radiation, coming from the direction of the sun, is called direct normal irradiance or direct normal solar radiation. Some of the scattered sunlight is scattered back into space and some of it also reaches the surface of the earth. The scattered radiation reaching the earth's surface is called diffuse radiation. Some radiation is also scattered off the earth's surface and then re-scattered by the atmosphere to the observer. This is also part of the diffuse radiation the observer sees. This amount can be significant in areas in which the ground is covered with snow. The total solar radiation on a horizontal surface is called global irradiance and is the sum of incident diffuse radiation plus the direct normal irradiance projected onto the horizontal surface. If the surface under study is tilted with respect to the horizontal, the total irradiance is the incident diffuse radiation plus the direct normal irradiance projected onto the tilted surface plus ground reflected irradiance that is incident on the tilted surface.
From this map we can clearly see that some US states are in very good position for solar energy exploitation. Arizona is without doubt the best located US state for solar energy projects. US states with great solar radiation levels are also California, Nevada, Utah, New Mexico and western parts of Texas. Best parts of California for utilization of solar energy are southeast regions with San Bernardino County as best placed County in California. Southeast California, south Nevada, southwest Utah and east Arizona are in fact the Mojave Desert. The Mojave Desert receives less than 10 inches (250 mm) of rain a year and is generally between 3,000 and 6,000 feet (1,000 and 2,000 m) in elevation. New Mexico is also located on very favorable position for solar energy, but states around Mojave Desert are receiving considerably more solar radiation per square meter than New Mexico. East parts of Texas are also located well for exploitation of solar energy, especially Mexico bordering Rio Grande area. If you look whole US map, then you can see that best solar energy areas are southwest parts of the country. One would think that Hawaii are best placed, but that is not true. Hawaii are receiving half of the amount of solar radiation that are receiving best parts of southeast US per square meter per day in average.