You’ll need

  • A small cardboard pizza box
  • Black paint and a paint brush
  • A pencil (or pen)
  • A ruler
  • A craft knife
  • Scissors
  • A permanent marker
  • Aluminium foil
  • Craft glue
  • 2 sheets of thick, clear plastic, cut to about the same size as the pizza box lid (plastic sheet protectors work well)
  • Sticky tape
  • 4 sheets of newspaper
  • String
  • A nail or small pencil
  • Food to ‘cook’ (marshmallows, chocolate, and cheese on biscuits work well)
  • A clock or timer

What to do

Warning!

Knives are sharp. Ask an adult for help cutting the box.

  1. Gather your materials on a flat surface.
  2. Paint the inside and outside of the pizza box with the black paint and let it dry.
  3. Close the pizza box so that the lid is on top.
  4. Use a ruler to measure a point 5 cm in from one edge of the lid of the box. From that point, draw a straight line, parallel to the edge of the box.
  5. Repeat step 4 for the other edges. You should end up with a square that has a frame 5 cm wide surrounding it.
  6. Place the box on the table so the lid opens in front of you, and the hinge of the lid is at the back.
  7. Close the lid and use a craft knife to cut through the front, left and right sides of the square to make a flap in the lid. Make sure you don’t cut the back side of the square because this will be the hinge for the flap.
  8. Lift the square flap and make a crease at the hinge.
  9. Use a permanent marker to trace the shape of the square flap on a sheet of aluminium foil.
  10. Use the scissors to cut out the square of aluminium foil, making sure it is the same size as the square flap on the pizza box lid.
  11. Glue the aluminium foil square to the underside of the square flap (the side that faces into the box). Make sure there are no creases in the foil.
  12. With the lid still closed and the flap open, place one sheet of plastic over the square opening and tape it to the cardboard ‘frame’ of the lid.
  13. Open the box and tape the other sheet of plastic to the inside of the lid over the square opening, taping it to the inside of the cardboard ‘frame’.
  14. Loosely roll up some sheets of newspaper and tape them to each inside edge of the box.
  15. Close the box.
  16. Carefully push a nail into the back edge of the box (the edge that runs parallel with the hinge of the lid and square flap).
  17. Tie one end of the string to the nail.
  18. Open the flap and tape the other end of the string to the top of the square flap so that it holds it open. Don’t trim the string because you will need to adjust the angle of the flap.
  19. Open the box and place the food inside.
  20. Close the lid and take the box outside to a sunny location.
  21. Turn the box and adjust the length of the string so that the underside of the square flap reflects sunlight into the oven.
  22. Measure how long it takes to heat the food so that the food is warm to touch and appears different (melted, gooey, glossy).

Questions to ask

Does the aluminium foil absorb or reflect sunlight?

Does the black paint absorb or reflect sunlight?

What does the clear plastic do?

Why are there 2 layers of plastic?

What does the newspaper do?

How long did it take to warm your food? Did different types of food take different times to heat up?

How could you improve your oven so that it heats food more quickly or so that it makes the food warmer?

Change the design of your solar-powered oven to see which design warms food the best. You could try different paint colours, different box sizes, different insulating materials, different window sizes, and different sizes or more flaps with aluminium foil.

What's happening

This solar-powered oven uses sunlight to warm the food. Light is a form of energy that can pass through clear objects, be absorbed by dark-coloured objects, and be reflected by light-coloured or shiny objects.

In this activity, when energy from sunlight hits the aluminium foil, it is reflected into the pizza box, through the sheets of clear plastic. When the light hits the cardboard box, the energy is absorbed by the black paint. This makes the box heat up, warming the food.
The newspaper helps trap the heat inside the pizza box. Heat naturally flows from warmer places to cooler places. When the box warmed up, it became hotter than the air and objects around it. This meant that the heat energy from the box slowly moved into the surrounding area. Things like wood, paper and straw don’t transfer heat well, so they can act as a barrier to help keep the heat inside the box. These types of materials are called insulators.

As long as energy is going into the oven faster than it is coming out, the oven will keep getting hotter.

Transcript

Tim: Hi everyone, my name’s Tim and I from the Questacon Science Squad. Today I’m going to show you how to make a solar powered oven. To do this.

You need:

  • pizza box, which has been painted black
  • a thumb tack
  • a piece of string
  • a nail
  • some chocolate

(Tim says ‘yum, yum, yum, yum, yum’)

  • some clear plastic sheets and,
  • some aluminium foil

So, the first step is to cut out a window from the top of the pizza box.

(Tim lifts a flap that’s been cut out)

I’ve measured five centimetres from this side, this side and this side and left a hinge along the bottom here.

(Tim points at each side to demonstrate his measurement)

Once you’ve done that, you can take one of the pieces of plastic, lay it across the top. Take some tape, tape it along one hedge here.

(Tim inserts the sheet of plastic and tapes it to the top of the box)

Take two more pieces of tape and tape along the other edges. And you want to give this a double glazing effect, so they can open it up and take another piece of plastic, get some pieces of tape and tape this across the top.

(Tim opens up the main part of box and inserts the plastic sheet to the other side where the insert has been cut out)

OK, that piece is held in. Take two pieces of tape and put one piece across the bottom and one more piece of tape at the top – just across this edge here and hold it down.

(Looking at the screen Tim applies the tape to the top right corner)

So, you can close that up now.

(Tim closes the constructed box)

And we’re going to make a mirror edge along this piece here.

(Tim lifts the cut out flap up)

To do that, take your aluminium foil, hold it at the base and then just fold it across the back.

(Tim is attaching the aluminium foil to the insert)

To give you a nice, smooth mirror surface. Scrunch it across the back. And that is your mirror surface. You want to be able to adjust this mirror, because at the moment you want to make it so the sun can go straight in there, to do that you can take a piece of string and a thumb tack. Put the thumb tack through the piece of string and push that through the top.

(Tim puts the thumb tack through the string and then secures the string to the foiled insert)

Swing this around.

(Tim swings the box around 180 degrees)

Push a nail through the base, just here.

(Tim inserts the nail through the middle of the base of the box – not all the way though)

Take the string and you can adjust the string around the nail to whatever level you want it to be.

(Tim is securing the piece of string to the nail at the back of the box by winding the string around the nail)

So, just wind it around a few times, push the nail in.

(Tim pushes the nail right into the box and then turns the box back around 180 degrees)

And once you have that, you can open it up, put your chocolate inside.

(Camera zooms in as Tim opens the lid to the main part of the box and puts a piece of chocolate inside)

Point it in the direction of the sun.

(Tim adjusts the foil panel)

And you can wait for the chocolate to melt.

(Camera zooms out on the box and back to Tim)

If you want to find out to make your own solar powered oven, head to the Questacon Science Squad website

Did you know

Have you ever seen a house with a large, black rectangle and a cylindrical tank lying down on the roof? These things with tanks are not solar panels, and they don’t make electricity. They are used to heat water for washing and cleaning. They use exactly the same ideas as your oven, except instead of food, the oven has a row of black water tubes in it. If you pump water through these tubes, the water heats up, and you get hot water without using much electricity.

If you leave a garden hose full of water lying on a hot driveway in the Sun for an hour, then turn on the tap, the water that comes out will be hot at first.

Energy from sunlight is called solar power. It is a renewable energy source, which means that it can be used over and over again. Solar power is considered a ‘clean’ energy resource because it doesn’t create as much pollution as burning fossil fuels, such as coal and natural gas.