Sustainable energy technologies

3.1.5. Hay Box Cooker

It is a simple well-insulated box lined with a reflective material into which a pot of food is placed. Food is cooked in 3-6 hours by the heat retained in the insulated box. The insulation greatly slows the loss of conductive heat. Convective heat in the surrounding air is trapped inside the box and the shiny lining reflects the radiant heat back into the pot. Simple hay box cookers could be introduced along with fuel saving cook stoves in areas where slow cooking is practiced. How these boxes should be made, and from what materials, is perhaps best left to people belonging to different regions. Ideally, the hay box cooker should be made of inexpensive and locally available materials and should have standard pot sizes used in the local area.

b) Inner surfaces of the box should be of a heat reflective material, such as aluminum foil, to reflect back the radiant heat from the pot.

c) A simple, lightweight hay box can be made from 60 x 120 cm sheet of rigid foil-faced insulation and aluminum tape.

d) Hay box cookers can also be constructed as box-inside-a-box with the intervening space filled with a good insulating material. Required thickness of the insulation will vary based on the efficiency of the insulating material.

e) Some of the good insulating materials, suitable for ‘Hay Box Cooker’, with suggested wall thickness are given in Table.3.2.

f) Box can be made of wood, cardboard or any combination, but the lid should be airtight.
Instruction for Using Hay Box: a) Cooking with Hay Box Cooker requires some adjustments as given below:
- Less water should be used since it is not boiled away,
- Less spicing is needed since the aroma is not boiled away, and
- Cooking must be started earlier to give enough time to the food to be cooked at lower temperature than over a stove.

b) Hay box cookers work best for large quantities of food, as small amounts of food have less thermal mass and cool faster comparatively. Combination of two or more smaller amounts of food may be placed in the box to cook simultaneously. Food should boil for several minutes before placing in the box. This ensures that all the food is at boiling temperature, and not just the water.

c) The hay boxes perform best at low altitudes where boiling temperature is highest. They should not be expected to perform well at high altitudes. One great advantage of hay box cookers is that the cook no longer has to keep the fire burning, watch or stir the pot once it is in the box. In fact, the box should not be opened during cooking, as valuable heat is lost.