Solar dryer
A box with a black base and mesh tray dries mango slices, chillies or grains. Very useful for farming families.
The big idea
Drying food saves it from spoiling. A solar dryer does it faster and cleaner than spreading food on the ground.
You will need
Tick things off as you gather them.
Step by step
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Step 1: Paint the inside black
Paint the inside of the box black, especially the base. A dark base soaks up the heat.
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Step 2: Make the tray
Stretch the mesh over a frame and fit it inside the box, a few centimetres above the floor, so air can flow under and over the food.
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Step 3: Add the clear lid
Cover the top with a clear plastic sheet, slanted, tilted to face the Sun. Seal the edges with tape.
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Step 4: Make air holes
Cut small holes near the bottom at the front and near the top at the back. Warm air rises and leaves at the top, drawing fresh air in at the bottom.
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Step 5: Prepare and weigh
Wash the fruit and slice it thin, about 5 mm. Weigh the slices and spread them on the mesh. Set aside an identical batch to dry in the open as a comparison.
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Step 6: Dry in the Sun
Put the dryer in full sun with the clear lid facing the Sun. Keep it off the ground.
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Step 7: Weigh each day
Weigh both batches each day. Record the drop in weight. Which dries faster? Which stays cleaner?
What to look for
- Food in the dryer loses weight faster than food in the open.
- It stays free of dust, flies and birds.
- Thin slices dry faster than thick ones.
An example of the pattern you should see, not measured data. Your numbers will differ, and that is fine.
Why it works
The clear lid lets sunlight in and keeps warm air from escaping. The black base turns light into heat. Warm air holds more moisture than cool air, so water leaves the food and is carried away through the top vent. The warm air moves on its own, because hot air rises. Drying removes the water that microbes need to grow, so the food keeps for months.
Try this next
- Compare slices of different thickness.
- Measure the temperature inside the dryer and outside.
- Try drying chillies, tomatoes and herbs.
Stay safe
Wash your hands and the fruit first. Cut slices with a blunt knife with an adult. Never eat food that smells bad or has mould.
Link to the grid
Using the Sun directly for jobs like drying, cooking and heating water saves electricity that would otherwise be made at a power plant.
Learn how the grid worksMore sun power experiments
Mini solar panel circuit
A small solar panel lights an LED or spins a toy motor. Test it in sun, in shade and at different angles.
Solar cooker
A cardboard box, foil and plastic wrap trap the Sun's heat. Melt chocolate, warm water or cook rice.
Solar water heater
Black-painted bottles or pipe in the Sun heat water. Measure the temperature as it rises.