UNESCO resource kit - science and technology educa...

UNESCO Nodule 21: Photovoltaic systems ---------------------
Measuring the Sun's energy
Page 2
We can measure the energy of the Sun at the surface of the Earth in units called
'kilowatt-hours' (or kWh for short). 1 kWh is the amount of energy used by a
small electric fire in one hour, or the energy that a single hundred-watt light bulb
consumes in ten hours. In fact, your electricity meter at home or school
measures the electricity that you consume in the same units - kWh.
The Sun's energy that is available for collection depends on the intensity of the
light, and on how long the Sun shines. Sunny summer days, when the Sun is
high in the sky, give more energy than cloudy winter days. Close to the Earth's
poles, the Sun does not move high in the sky, so the energy supplied by the Sun
in the course of a year is greater near the Equator, and less near the Arctic and
Antarctic.
Tobe able to compare the Sun's energy in different parts of the world, we
measure how much energy falls on each square metre of land - we say
kilowatt-hours per
square metre (or kWh/
m" for short). Then we
add up all the energy
that arrives from the
Sun in the course of a
year.
Use the world solar energy map to answer these questions:
Measuring the Sun's
energy helps us to find
out how much solar
energy we can use for
our own purposes. It
can also tell us how big
our solar panels need
to be to collect enough
of the Sun's energy.
5 Compare northern Russia and central Australia. Which one receives more
solar energy each year? Can you say how much more?
6 Imagine that you are designing an emergency phone for use in remote areas.
It will be powered by a solar PV system. Would you need the same size of
solar collector in each country (Russia and Australia) to gather equal
amounts of energy? Try to explain your answer.
7 List as many reasons as you can why some parts of the Earth receive more
energy from the Sun in a year than others.