ABSTRACT
Diffuse horizontal irradiance (DHI) is dened as the solar irradiance that has been scattered by molecules, aerosols, and clouds in the atmosphere and received on a horizontal surface (refer to Figure 6.1). Another perspective on diffuse irradiance is that DHI is the skylight portion of the global horizontal irradiance (GHI) remaining after removing the direct normal irradiance (DNI). DHI is measured by a properly shaded pyranometer, or it can be computed from measurements of DNI and GHI using Equation 4.1. Light reected by objects above the surface contributes to the DHI, but light reected from the horizontal surface is not included. However, the radiation reected from the surface that is subsequently reected back to the surface by the atmosphere is included; that is, multiple scattering components are included in DHI.
