Solar Irradiance

Direct insolation is the solar irradiance measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation (the solar radiation that is scattered or reflected by atmospheric components in the sky). While the solar constant varies with the Earth-Sun distance and solar cycles, the losses depend on the time of day (length of light's path through the atmosphere depending on the Solar elevation angle), cloud cover, moisture content, and other impurities.

Radiation quantities are generally expressed in terms of either irradiance or radiant exposure. Irradiance is a measure of the rate of energy received per unit area, and has units of Watts per square metre (W/m2), where 1 Watt (W) is equal to 1 Joule (J) per second. Radiant exposure is a time integral (or sum) of irradiance. Thus a 1 minute radiant exposure is a measure of the energy received per square metre over a period of 1 minute.

The 3TIER's solar map (click to enlarge) is based on actual, half-hourly, high-resolution visible satellite imagery observations via the broadband visible wavelength channel at a 2 arc minute resolution.

These data have been processed to create more than 10 years of hourly of Global Horizontal Irradiance (GHI), Direct Normal Irradiance (DNI), and Diffuse Horizontal Irradiance (DIF) by 3TIER at a horizontal resolution of roughly 3 km.

By looking at where you live on the map and using the colour coded legend showing W/m² you can gain a rough idea on how your solar system might perform.

You can a better appreciation by using an irradiance calculator located here. This calculator is based on data collated over a 22 year period to provide monthly average insolation figures. This information is then used to calculate the average daily power generation a photovoltaic system will produce in any given month.

(http://www.solamaps.com/solar-pv)