Practical activity: How to build a solar oven

Objective:

The sun represents an important source of energy, but can we also use it inside the house? In this activity we explain how to build a simple solar oven with a plastic box. And for the crafty ones, at the end you will find instructions to build a solar oven in the shape of a parabola.

Solar oven in a box

Material

• Black paint.
• A paintbrush.
• Two large rubber bands.
• A clear plastic box (iced cake).
• A glass lid.
• Two photo reel jars, filled with cold water and closed.

Process:

1. Paint the inside of the plastic box black.
2. Place one of the film canisters inside the plastic box.
3. Tighten the glass to the box with the rubber bands to prevent leakage between the edges of the box and the glass, but be careful when handling it! You don't need to tighten the rubber bands too much.
4. Set up your box in full sun, take the second jar and place it next to the box, outside the box.
5. After 30 minutes, remove the glass and dip your finger in the water from the two jars.

How do you feel?

Explanation:

The water that was inside the box is hotter than the water that was left in the sun. The sun's rays pass through the glass and enter the oven: they heat the two pots in the same way.

The black color absorbs the light and transmits its heat to the water. Inside the oven, everything becomes a heat source and emits infrared rays, which are heat rays.

This glow is stopped almost entirely by the glass that serves as a lid and prevents the hot air from escaping; the box prevents the heat from being lost to the ground, remaining inside: this is the greenhouse effect. On the contrary, the heat rays emitted by the canister left in the open air, reheat the surrounding air, which circulates freely around the cylinder and prevents it from heating up as much as the air inside the oven.

Application:

Solar collectors work thanks to the greenhouse effect. They are large boxes covered with glass, which have their interior painted black and contain a set of black tubes. The water that circulates inside is heated thanks to the absorption of heat by the black color and the effect that this color has on the greenhouse effect.

Video: Build a solar oven in a shoe box

Parabolic solar oven

Elements of the System:

• Solar Oven
• Parabolic surface.
• Reflective sheet.
• Focus locator structure.
• Support base.

For the parabolic surface, an antenna dish used for satellite TV will be used, it will only be necessary to clean it to be able to safely glue the reflecting surface, adapt the support base, and mount the locator, as can be seen in the section "structure of the focuser".

The reflective sheet is made of aluminized plastic, which will be cut in strips of about 3 cm. so that, when glued with impact glue, they adapt perfectly to the surface.

The locating structure of the spotlight consists, as can be seen in the photograph, of three rectangular tubes, which can be displaced for each other. The smallest one has a clamp and a holed stem in which the material or container to be placed in the spotlight can be clamped.

The iron support base consists of a circular base in the center of which welded the column, which will hold the reflecting parabola. This should be as heavy as possible to give it stability.

Schematic diagram

Process

The parabola concentrates the sun's rays at a point called focus, the sum of all the rays (infrared radiation), consequently, their energy is added generating an increase in temperature resulting in burning wood, boiling water or frying eggs, etc. A parabola is defined as a curve in which all its points are equidistant from a point (focus) and an axis (parallel rays), consequently, any ray that strikes a parabolic surface parallel to the axis will be reflected passing through the focus.

Activities that can be carried out with the solar oven

• Conics: description and calculations.
• Axes of the generating parabola.
• Length of the generating parabola.
• Reflecting parabolic surface.
• The focal distance of the solar furnace.
• Amount of heat generated by the furnace.
• Mechanical energy that we can obtain.
• Energy power that the oven is capable of supplying.
• Ecological cooking activities (protein denaturation).