الأسبوع 20 · المحور الثالث، الوحدة الثالثة، المفهوم 3.3 «مصادر الطاقة المتجددة» (أ): طاقة الشمس وطاقة الرياح · 3 دروس
2
The Sun gives energy
Discovery Education Science P4: Term 2, Unit 3, pp. 56–69
GoalExplain that the Sun gives light and heat, list uses of solar energy, and draw the energy change in one example.
New words
solar energy · energy from the Sunsolar panel · a flat panel made of solar cells that makes electricity from sunlightradiation · energy that travels as light and heat, for example from the Sun
Explanation
The Sun is a star, a huge ball of very hot gas far away from us. It gives out light and heat, which travel through space and reach Earth. We must never look straight at the Sun. Sunlight warms the land, the sea and the air, and plants use it to make food. People use solar energy in several ways. A solar water heater has a dark panel on the roof: the sunlight heats the water inside it, which is stored in a tank. This is common on roofs in Egypt. Some cookers use curved mirrors to gather sunlight. A solar cell changes light into electrical energy, and solar panels are made of many cells. The electricity can be used at once, for example by a street light, or stored in a battery for night. Farmers can run water pumps with solar panels.
A solar street light. In the day the panel gets sunlight and makes electrical energy, which a battery stores as chemical energy. At night the battery gives electrical energy to the lamp, which gives out light.
Item
Hours
Units per hour
Total units
panel makes
6
3
18
lamp uses
8
2
16
A panel makes 3 units of electrical energy each hour for 6 sunny hours: 3 × 6 = 18 units. A lamp uses 2 units each hour for 8 hours of night: 2 × 8 = 16 units. 18 − 16 = 2 units are left over, so the battery can run the lamp all night.
A solar water heater on a roof in Aswan. The panel is dark so that it takes in more of the sunlight. The sunlight heats the water, and the hot water goes into a tank. No fuel is burned.
Class activity
Draw the sun’s energy. Choose one use of solar energy (a solar water heater, a street light or a calculator). Draw it with arrows and boxes, and label each box with the form of energy: light, thermal, electrical or chemical. Add a sentence saying why we must never look at the Sun. Show your drawing to your family.
Practice
1
Name two things the Sun gives to Earth.
Light and heat.
2
What energy change does a solar cell make?
Light energy into electrical energy.
3
A panel makes 4 units an hour for 5 hours. How many units?
4 × 5 = 20 units.
4
Why does a solar street light use a battery?
To store energy for the night, when there is no sunlight.
