How to make a solar tower

Investigate air density and find out how heat can create power

1. Make your fan
You’ll need a rectangle of black card around 30 centimetres long and 25 centimetres wide. You’ll also need a piece of paper, some scissors, a long pin, two similarly thick books and a small strip of card. Once you have these items, cut a square of paper ten centimetres wide, then make a cut from each corner towards the middle of the square, around two-thirds of the way to the centre.

2.Fold it

Now for the slightly fiddly part. Take one corner of the paper at a time and fold it in so that it touches the centre point of the square. This will create a kind of ‘pocket’ in the paper. Do the same with the other three corners, ensuring that these pockets all face the same direction, like the blades of a fan. Glue the folded paper in place at the centre of the square.

3.Create your tower

Next you need to create the solar tower. Take your black card and roll it into a cylinder shape — this will be the shape of your tower. Now take the two books you selected earlier and place them a few centimetres apart on a flat surface, then place your cylinder over the gap. This will allow air to enter the tower from the bottom and circulate up through the tube.

4. Add your fan
Take a small strip of card and bend it slightly to create a C-shaped piece. Stick this to the top of your tower on the inside to create a loop that looks a little bit like a handle for your cylinder. Then push the pin about half way through this strip of card and tape your fan on top of the pin so that it sits just above the tower’s opening.

5. See your solar power in action

Now place your tower near a sunny window to see what happens. Black items absorb heat, so by using black card you have created a tower that warms up the air inside it. What happens at it gets hotter? You should see that the fan on top starts to move as air is pushed up through the tube and cooler air is pulled in from the bottom.

This article was originally published in How It Works issue 106

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