UNESCO resource kit - science and technology educa...

------------------------ UNESCO Module 21: Photovoltaic systems
Monitoring the Sun's radiation
The amount of sunlight arriving varies during the day, and it varies from day to
day. Here are two ways to monitor the Sun's radiation:
• Use a home-made sundial. Record the position of the end of the shadow
every 30 minutes during the day.
• Use a light sensor connected to a datalogger. This will record the light level
during the day, and you can then print out a graph. Alternatively, use a light
meter and record readings every 30 minutes.
Once you have collected some information, you can work out the best places and
times for using solar technology to harvest energy from sunlight.
Safety: Never look directly at the Sun/ as this can damage your eyesight
Using the results from your sundial experiment, you can fill in a solar log sheet
like the one shown here. Use a compass to work out the direction of the Sun
when it reaches its highest point (when the shadow is shortest). Estimate the
angle of the Sun using the length of the stick and the length of the shadow.
(Hint: you can use your maths trigonometry skills for this, or draw a scale
diagram.) You could plot a graph to show how the angle of the Sun above the
horizon changes during the day.
Set up your light sensor and datalogger to record how the light level changes
during the course of a day. Things to think about:
• Where will you position your sensor?
• In which direction will you point your sensor?
• How can you test your equipment to check that it is running correctly?
When you have a graph to show how the Sun's radiation changed during the
course of a day:
• Try to explain the shape of the graph, and any sudden changes in light level.
• Suggest how the graph would be different at different times of the year.
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