Solar Radiation The mean annual and monthly solar energy received per horizontal square metre (MJ/m2) has been calculated for South Africa. The model used to estimate total or global (i.e. direct plus diffuse) radiation is based on two components:
A geometric model estimates solar radiation based on latitude, altitude, date, time, orientation and slope. The atmospheric component deals with radiation loss due to cloud cover and atmospheric constituents such as water vapour, dust, and salt crystals i.e. the 'transmissivity' of the atmosphere. Total radiation is estimated by adjusting the predictions from the geometric model by the transmissivity predicted by the atmospheric model. Solar duration and solar radiation data, collected over a 40 year period at 130 sites by the South African Weather Bureau, were used to create and verify the various components of the model.
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