ABSTRACT
Available solar radiation at a given location – latitude, longitude and height above sea level – needs to be determined as a basis for any calculations of how much energy may usefully be harvested for a project. It is usually modelled by totalling three components: direct beam shortwave radiation, sky diffuse and ground reflected radiation. Solar radiation is modified during its journey to the ground by scattering and absorption by air molecules, aerosols and clouds, which affects wavelengths differently. The solar spectrum changes throughout the day and with location, so standard reference spectra are deployed to permit comparison of photovoltaic devices. To determine the position of the sun it is necessary to know: the solar elevation; the solar azimuth; the latitude of the location; the longitude of the location; the equation of time; and the declination.
