Average daily solar exposure maps

These maps show the average daily global solar exposure over Australia for each month, season and annually.

Download: Grid
Average annual daily solar exposure

Product code: IDCJCM0019

What do the maps show?

These maps show the average daily global solar exposure over Australia (each month,season and annually) for the period 1990 to 2019.

Global solar exposure is the total amount of solar energy falling on a horizontal surface. The daily global solar exposure is the total solar energy for a day, and is typically between 1 and 35 MJ/m2 (megajoules per square metre).

The amount of solar energy reaching the ground depends on a number of factors; two of the most important are the position of the sun in the sky and the extent of cloud cover. Cloud cover can be quite variable and is determined by the local weather conditions and seasonal patterns. However the position of the sun in the sky is predictable and changes over the course of a day, reaching its highest point at "solar noon". The height of the sun at solar noon varies during the year.

The annual solar exposure map shows an area of higher solar exposure across central and northern Australia, with lower solar exposure in coastal areas in the south. Areas of inland Australia have a lower moisture content in the air (see relative humidity maps) and therefore less cloud cover. This reduced cloudiness directly influences the amount of solar exposure at the surface. Coastal areas, especially in the south, have a higher moisture content, greater and more frequent cloud cover and therefore a lower solar exposure.

The influence of the sun's position on solar exposure can be seen in the monthly climatologies, in particular in the map for June. The further south you are in Australia, the lower in the sky the sun appears, and the amount of solar exposure is lower. In contrast, during the summer months of December and January the sun is higher in the sky and there is more solar exposure. Solar exposure in the north is reduced at this time due to cloud cover associated with the tropical monsoon.

Solar exposure maps can be compared to the sunshine duration maps, which have a similar pattern.

How are the values calculated?

The Bureau of Meteorology's computer radiation model uses visible images from geostationary meteorological satellites to estimate daily global solar exposures at ground level. At each location the image brightness is used to provide an estimate of the solar irradiance at the ground. Essentially, the irradiance at the ground can be calculated from the irradiance at the top of the earth's atmosphere, the amount absorbed in the atmosphere (dependant on the amount of water vapour present), the amount reflected from the surface (surface albedo) and the amount reflected from clouds (cloud albedo). These instantaneous irradiance values are integrated over the day to give daily solar exposure in megajoules per square metre.

Creative Commons By Attribution logo Unless otherwise noted, all maps, graphs and diagrams in this page are licensed under the Creative Commons Attribution 4.0 International Licence