Solar energy is the heat which comes from the sun. It is very clean and non-polluting energy so that it is best for humans using. Actually, the energy has been used since prehistoric times, and people has always used it in the simple way, such as cooking, burning, lighting etc. Also, it is free and renewable energy. Therefore, it is environmental protection to reduce some materials in the overage. So people use it neatly and we make the solar cooker to test its usability.

Solar cooker is one of the examples using solar energy. It is successful in cooking.

The energy of solar cooker is the energy comes from the sun. The sun is very far away from us, so the sun rays go to the earth in parallel line. When the sun rays hit onto the reflecting mirror directly, solar cooker will concentrate them at one point, such as the focus of the reflecting mirror. Therefore, it will meet at the focal point and cook the food eventually.

This effect results in the heating of enclosed spaces into which the sun shines through a transparent material such as glass or plastic. Visible light easily passes through the glass and is absorbed and reflected by materials within the enclosed space.

The light energy that is absorbed by black can placed underneath the sun is converted into IR radiation of longer wavelength and radiates from the interior materials.

• Most of this radiant energy is of a longer wavelength, and they cannot pass through the can and therefore is trapped within the enclosed space. So the glass will become hot because of this greenhouse

The solar cooker is just like the greenhouse, so the glass will become hot eventually.

The light energy goes to the box and reflects into the glass. We make the solar cooker which is like the box 2, because it faces the sun more directly so that the glass will be hotter than box 1 and will be more successful in cooking.

Solar cooker is a very good design for using solar energy. First, it uses the energy from the sun directly, so that you do not need to pay for the energy supply. It is used to enhance environmental protection.Next, using solar cooker is very safe in cooking. It does not need fire. While you are cooking, you would not worry because it can reduce the chance of having accident due to leakage of town gas. Lastly, the most important point is that solar energy is renewable energy source. Using it can protect our earth by reducing greenhouse effect.

Using solar cooker also has disadvantages.The cooking time is long so more time is wasted compare with using fire to cook.Sunlight usually appears in the morning, so we do not cook at night using solar cooker.The size of solar cooker is bigger than normal cooker, so it need more space to store it.

We used an iron can to heat water and painted it in black because dark-coloured surface may conduct heat well and reduce the loss of heat, so the water in the can absorbed the solar energy more efficiently. The solar cooker conducts heat to the bottoms of the can. To prevent the loss of the heat on conduction through the bottom of the cooker, the absorber plate is raised from the bottom using small insulating spacers.

The clad-wrap will prevent the heat loss by convection. In the box, hot air will rise up while the cold air will move downward. Hot air cannot escape away from the solar cooker as it is wrapped using the clad-wrap.

Solar cooker can absorb the energy which comes from the sun and the tinfoil will reflect it inside. As the cardboard is black in colour, it may absorb the heat energy more efficiently. Energy re-radiated will be absorbed by the water. Therefore, the temperature of water will rise.

We have used many materials in making the solar cooker. The main materials are:

Tinfoil ＊ Reflecting the light, heat from the

sun to the solar cooker

Cardboard ＊ Keeping the solar cooker warm

Reflecting mirror ＊ Reflecting the heat and

focusing it at one point

A can in Black colour ＊ Keeping the water hot

and reducing the loss of heat

Time (min) 0 5 10 15 20 25 30

Temperature(℃) 23 26 29 36 39 43 47

This is the table of our data recorded on the solar cooker. The water in our solar cooker rose about 24℃ eventually. It is better than the previous test because the temperature only rose 0.2℃ at the first test. We had changed the design. So it is more successful for us to use the solar cooker even though it also has some disadvantages.

After the test of the solar cooker, we are successful because the temperature of water rose about 24 ℃, from 23℃ to 47℃. The rise was more than what we had expected.The first time we tested the solar cooker, it did not work well because the temperature of water only rose 0.2℃. We tried to reduce the energy loss to the surroundings and change the design of the solar cooker. In our last test on the solar cooker, the sunshine was brilliant enough. We used the newly-designed solar cooker and put a convex lens above the solar cooker. As a result , we are very happy about the rise of temperature of the water.

In making the solar cooker, we had faced some difficulties, such as what materials we should use ,how to find the appropriate materials,etc. We solved these problems by ourselves. The main difficulty is how to make the box to keep water hot. We spent many times to solve these problems together. Actually, we have learnt and understood more about heat, application of physics principles etc. so we hope that we can make the solar cooker more successfully in the future. It is good for us to learn Physics.