Get the Offline ArchiveFree lifetime updates

Panel Cooker

3 min read

A panel cooker is a funnel-shaped cardboard reflector covered in foil, with a black pot sealed in a clear heat-resistant bag at its centre; it reaches 100-120°C and cooks rice, beans, stews and bread with no fuel. Its net power is only tens of watts, so 2 kg of water takes about 2.5 hours to reach 100°C: put the meal on in the morning and plan for slow cooking.

Part of Solar Cooking & Pasteurization

A panel cooker is the simplest solar cooker: reflective panels that bounce sunlight onto a dark pot enclosed in a transparent bag.

How Slow Is Slow?

Inputs, assumed: the reflector gathers sunlight over an effective area of 0.5 m² (a panel about 0.7 m across); 1,000 W/m² of direct sun; 15% of the incident power ends up in the pot; 2 kg of water starting at 20°C.

  1. Net power = 0.5 × 1,000 × 0.15 = 75 W.
  2. Heat to reach 100°C = 2 × 4.18 × 80 = 669 kJ.
  3. Time = 669,000 J ÷ 75 W = 8,920 s = 2.5 hours.

So even in a good midday sun, water takes about 2.5 hours to boil, and the parent page’s rule of starting 2-3 hours early is the plan. Food does not need to boil, but it needs to hold above about 60°C (Minimum Safe Temperatures); a pot of rice, beans or stew at 90-100°C cooks through over the following hours.

What You Need

  • Cardboard, a large piece cut to a funnel or petal shape (parent page: the CooKit design)
  • Aluminium foil, shiny side out, glued or taped smooth
  • A black pot with a lid, thin, dark and matte
  • A clear heat-resistant bag, or a large glass bowl to invert over the pot (parent page: a clear plastic bag; use one rated for oven use, since a thin polyethylene bag softens near the boil)
  • Bricks or stones to hold the cooker against wind
  • A support so the pot sits in the focal area without touching the ground

Method: Build And Use It

Step 1: Cut the cardboard, fold the panels so they curve toward the pot, and glue the foil on the inside, smoothing out wrinkles.

Step 2: Place the black pot in the bag, with air around it; close the bag so wind cannot cool it.

Step 3: Set the pot in the focal area of the panels on a stand, in full sun, away from wind.

Step 4: Face the cooker toward the sun and re-aim every 30 minutes or so; a shadow of the pot should fall on itself, not to one side.

Step 5: Check for 100-120°C by feel and by simmering; leave until the food is soft.

Common Mistakes

  • Wrinkled foil. Each wrinkle scatters light away from the pot.
  • Pot not in a bag. The wind carries the heat off, and the pot stays lukewarm.
  • A shiny or light-coloured pot. It reflects the sun away.

Safety

Glare, hot pots and escaping steam

The panels reflect strong sunlight into the cook’s eyes, so wear dark glasses and do not stare into the reflector. The pot, lid and bag are hot enough to burn, and opening the lid releases steam and scalding food; lift the lid away from your face. A panel cooker left unattended with its pot removed becomes a small concentrator that can scorch what lies at its focus.

What’s Next