• Imagine a world where there is no electricity or access to fuels for cooking.
• What potential ways could you use to cook food or to heat water?
• One solution that could be used is solar cooking, in this case we will focus on the concept of a parabolic solar oven.
• Discuss which STEAM roles might help in this situation: e.g. optical engineer, thermodynamics scientist, energy engineer, food scientist etc. Students can take on these roles if they wish.
• Briefly introduce parabolas and their properties.
• A parabola is a curve where any point is at an equal distance from a fixed point (the focus), and a fixed straight line (the directrix).f
• Use the link for a more detailed explanation and diagrams
  https://www.mathsisfun.com/geometry/parabola.html
• Explain that parabolas are found everywhere in the world including;
  
  • In nature
    
  • In Architecture
    
  • In everyday life they are especially useful for reflecting and focusing light in torches, vehicles headlights and household light bulbs.
    

• Guide teams as they carefully follow the step-by-step instructions to build a small reflective parabolic solar oven.
• If undertaking this outside, students can optionally use transparent acrylic sheets as a top cover, which helps trap heat. *Do NOT try this if using halogen lamps*.
• Step-by-step instructions for learners
  1. Cut out a parabola using the template page provided
  2. Use this parabola as a template to draw a parabola shape onto each of the 4 sheets of A4 corrugated cardboard and then cut the shapes out (leaving each group with 4 individual parabolas made of corrugated cardboard)
  3. Glue two of the parabolas together to create one of double thickness, then do the same with the other two parabolas as well
  4. Use a skewer to accurately create a hole through the focus points on each of the 2 parabolas (again using the parabola template with the focus point marked as a red spot)
  5. Use the glue stick to carefully cover one side of the A3 thin card, and one side of each parabola, with aluminum foil. Make sure the shiny side faces out and try not to create wrinkles as this will reduce the effectiveness of the reflective surfaces
  6. Wrap the thin card around the curved edges of the parabolas and tape it in place to create your solar oven, this should be wrapped all-round the parabola at each end to form a kind of a parabolic trough.
     
  7. Slide a skewer through the pre-pierced focus points of each parabola and make sure the skewer passes straight through the oven and out each side
  8. Now they have engineered a simple reflective parabolic solar oven with a cooking skewer

• Test the parabolic solar ovens with marshmallows and thermometers. See how fast the marshmallows melt, and / or what final temperature the ovens reach.
• Step-by-step instructions for learners
  
  • It’s time to cook! Load one or two marshmallows onto your skewer. Make sure they don't touch the foil, so light can reflect onto them
  • Angle your oven to face the sun, or if inside, the halogen lamp
  • *NOTE: Take extra care if using a halogen lamp as they can generate a lot of heat and you could burn yourself. Use protective gloves and wear protective eyewear*.
    *The following image below omits one side of the card/foil reflector*
    
  • It is important to explain the process that is happening, solar energy, in the form of sunlight is being converted into heat energy to heat and ‘cook’ the marshmallows.
  • The principles of the process are;
    1. Concentrating sunlight: the reflective metal surface is reflecting the sunlight so that it is concentrated and the energy is stronger at the focus point where the skewer and marshmallows are located
    2. Converting light energy to heat energy: the interaction between the light energy and the receiver materials converts light to heat and this is called conduction
    3. Trapping heat energy: this heat energy is now being ‘trapped’ within the parabolic trough and as more light energy enters it will continue to be converted into heat energy, this process can be increased by covering the top of the parabolic oven with the transparent acrylic sheet.
  • • The parabolic solar oven lets the UV light rays in and then converts them to longer infrared light rays. Infrared radiation has the right energy to make water, fat and protein molecules in food vibrate vigorously and heat up.
  • It is not the sun’s heat that cooks the food, nor is it the outside ambient temperature (though this can affect the rate or time required to cook) but rather it is the sun’s rays that are converted to heat energy that cook the food.

Once all the groups have completed the task and tested their ovens the teacher will decide which group’s oven worked the best based on the temperature it achieved and / or the level in which their marshmallows were cooked.