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Science, Maths & Technology

Why not throw a solar dinner party?

Updated Thursday, 1st June 2006

Get your science hands-on - follow our instructions and enjoy a solar-powered supper

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You can use any solar powered devices to cook your dinner, although photovoltaic cells (solar panels that make electricity) are borderline cheating! The more guests and the more food cooked the better - and yes, the food does have to be hot. So, gazpacho followed by ice cream does not count!

Below are a couple of designs for very simple solar cooking devices. The first is suitable for flat food (eggs, for example), and the second will do sausages.

Of course, make sure your meal is thoroughly cooked through before you eat it! We look forward to hearing about your solar-cooked food.

Solar cooker number 1 - Pizza box oven

Pizza box oven Made from a pizza box and perfect for pizza cooking, or maybe eggs. When we tested this device it easily reached a temperature of over 107 degrees C - and that was not even at midday. Give it a try and let us know how you do.

What you need:

  • One large corrugated pizza box
  • Black card
  • Mirror card or foil
  • Newspaper
  • Cling film or blank OHP sheets
  • Scissors, Tape, PVA glue

What to do:

  1. Take the pizza box and draw a square on the lid of the box that leaves a 3cm border. Cut out three of the four sides of the square so that you have a flap. Open the pizza box and gently score the flap along the uncut edge before sticking a piece of the mirror card to the inside surface of the flap.
  2. Now you need to line the inside of the box with black card. Place a sheet on the base of the box and make four rolled up sausages of newspaper to go along each side of the box. These rolls give your solar powered pizza cooker more insulation.
  3. Now double-glaze the hole in the box lid. Tear off a couple of pieces of cling film or acetate that are the size of the pizza box. Tape one piece of film over the outside of the hole in the lid and pull it tight, then open the box and secure another piece of film to the other side.
  4. You are now ready for action. Place the box in full sunlight and angle the lid flap so that it reflects the sun, through the double-glazing and into the box.

How it works:

The silver surface on the flap reflects the sunlight into the box, while the black card inside will help the pizza box to absorb the sun's heat, which in turn helps to cook the food inside the box. The rolled up newspaper will help to insulate the box and hold the heat from the sun. When we gave this a try we achieved temperatures of over 107 degrees C - which is definitely enough to cook things, like eggs for example.

Solar cooker number 2 - Sausage sizzler

Sausage sizzler The solar sausage sizzler is a bit more tricky to make and watch out for all of those cocktail sticks. However, once built it makes short work of a sausage or two (we used Frankfurters sausages). Have a go, and let us know if you succeed.

What you need:

  • A strip of thick mirror card or mirror plastic (We used a piece 70 cm by 25 cm)
  • A thick corrugated cardboard box (About 40 cm by 25 cm)
  • Cocktail sticks
  • A skewer at least 30 cm long
  • Craft tools and glue

What to do:

  1. The key to this solar oven is to make a parabolic reflector. The simplest way to do this is to use the measurements listed below. However, for those of you with a mathematical bent, the formula is given at the bottom of this page.
  2. Start by taping down the base of your box and gluing the top flaps open, to make the box a bit less wobbly. Now carefully draw a grid of pencil lines on one long side of the box. The lines should be 2 cm apart and cover 40 cm by 20 cm (i.e. 21 vertical lines and 11 horizontal). Now the hard part! Draw an identical grid on the other side of the box, such that the two grids line up. Mark the left-hand side -20, the right +20 and the central line 0. Use the data below to mark the parabola on both sides of the box.
  3. Once you have marked out the parabola, push a cocktail stick through each point on the curve. Cut your mirror card to the correct width and slide it into the box, so that it lies on top of the cocktail sticks in a parabola. Now secure the card in place with more cocktail sticks pushed through the card over the top of the mirror.
  4. Finally, push the skewer through the box, at the focal point - which should lie on the "0" line, 5 cm up from the base of the parabola. Feed a sausage onto the skewer, place in the sun and rotate the skewer regularly. Hey presto - solar sausage sizzler.

How it works:

The clever thing about a parabola is that it focuses light from the sun to a point - or in this case, a line that is perfect for sausage cooking. Mathematically the parabola is defined as y2=4ax, where a is the position of the focus vertically from the base of the parabola. The data points below uses a=5 cm and generates a curve that fits neatly in a 40 by 20 cm box.

Parabolic reflector measurements
Horizontal axis Vertical axis
-20 20
-18 16.2
-16 12.2
-14 9.8
-12 7.2
-10 5
-8 3.2
-6 1.8
-4 0.8
-2 0.2
0 0
2 0.2
4 0.8
6 1.8
8 3.2
10 5
12 7.2
14 9.8
16 12
18 16.2
20 20




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