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Step 3 Irradiation

The irradiation is obtained from the internet. The NASA developed a database based on information from satellites (cloud configurations during a long period). The database gives a good estimation of the solar irradiance on the ground. To find the relevant data, we direct you through the next steps. The result will be a table with monthly averages of the amount of “hours of full sunshine” at your project site.

• You start by clicking on the NASA Retscreen website

• Click on Renewable Software Application Inputs

• Click on Retscreen International data access

• Register yourself as user

• Now you will enter a screen, in which the Longitude and the Latitude should be given. To know these numbers, you can also use the tool ‘Pick a location graphically’. At zoom level 16 you can give your location quite accurately.

▲ Tool for looking up the co-ordinates of your project location.

• Now you click on ‘Submit for data’

• You will obtain a table on your screen with the monthly averages of various meteorological parameters. The most important is the third column of this table ‘Daily solar radiation - horizontal kWh/m2/day’. This column presents the irradiation.

In the figure below, this third column of the table is presented in a graphical way

▲ Irradiation on project site Ghana (7ºLatitude -2º Longitude) in ‘kWh/m2/day’. This unit can be translated into ‘hours of full sunshine per day’. Full sunshine is defined as irradiance of 1kW light energy.