What it shows
A panel cooker uses flat foil-covered reflectors to bounce extra sunlight onto a dark pot sealed in a clear bag. It shows that sunlight can heat water without any fuel.
The science
Foil reflects most sunlight, so each panel sends extra light to the pot. The black surface absorbs that light and turns it into heat. The clear bag lets sunlight in but traps the warm air around the pot, as in a greenhouse, so less heat leaks away.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Two cardboard sheets about 50 cm square
- Aluminium foil and glue
- A small black steel or aluminium pot with lid
- A clear oven bag or large transparent plastic bag
- A thermometer (0 to 110 C)
- Two bricks or books to prop the panels
Safety
For this project: Never look at the bright reflected beam; wear sunglasses. An adult must handle the hot pot. Keep the water only warm to hot, not boiling, and never leave the cooker unattended.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Glue foil, shiny side out, smoothly onto both cardboard sheets and let them dry.
Stand the two panels in a V shape around the pot with the opening facing the sun.
Fill the pot with 300 ml of tap water and note the starting temperature.
Slide the pot inside the clear bag, close the bag loosely and set it between the panels.
Turn the cooker every twenty minutes so the pot stays in the brightest spot.
Read the temperature every ten minutes for one hour and record it in a table.
Repeat with the panels removed so you have a control pot in the same sun.
Plot both temperature curves on one graph and compare how far each rose.
What you should see
The pot between the foil panels warms noticeably faster and reaches a higher temperature than the control pot. The gap between the two curves shows how much the reflectors add.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why is the pot painted black?
Black absorbs more sunlight and turns it into heat.
2What does the plastic bag do?
It traps warm air so heat is not carried away by the breeze.
3Why keep a control pot?
It lets you see the effect of the reflectors alone.
4Is a solar cooker a renewable energy device?
Yes, sunlight is not used up.
Take it further
Change the panel angle in steps of 15 degrees and find the angle that gives the highest temperature.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Science Projects for Class 6 to 8
Working models matched to middle-school science topics