Low-cost Wooden Solar Box Cooker

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Last edited: 1 February 2017

The Low-cost Wooden Box Cooker Photo credit: Sankha Subhra Datta

Sankha Subhra Datta has attempted to reduce the cost of a conventional wooden solar box cooker. The cooker is very appropriate for rural applications. Its easy construction reduces cost of labor, and allows it to be built by semiskilled village artisans by using simple hand tools and with locally available raw materials.

Instructions

Constructional Features

Detailed construction features of the cooker is shown in the construction plans. The top opening cooker box is made of a half inch thick wood. The inner sides and bottom of the cooker box are covered with aluminum foil to direct solar radiation towards the cooking pots. The foil is pinned to the wooden box. Because of this reflecting surface, the wooden cooker box itself will not absorb radiant heat. Also, there is not much heat loss due to conduction from the foil to the wooden box, wood being a poor conductor.

Most of the absorbed heat is retained in the cooking pots. The cooking pots should not be direct contact with the foil to avoid damage to the foil. They are to be kept on pot stands (common ring shaped stands made of steel wire available in utensil shops). A slotted seat is provided near the top of cooker box for cover glazing made of 3mm thick transparent window glass.

Cooking pots are to be placed side by side inside of the cooker by opening the hinged glass cover. A south facing booster reflector is hinged as the lid of the wooden cooker box. The frame of the glass cover is made from GI (galvanized iron) sheet. The Booster Reflector is made by fixing mirror glass on a GI sheet frame. The reflector can be tilted to desired inclination by adjusting the stays provided for the purpose.

To make a leak proof joint in between the wooden seating and closed cover glazing, pieces cut from an old car tube are used as gasket material. For proper seating of the gasket, small grooves may be cut at the top of the wooden box seating. The gasket is also used inside of metallic channels of the cover glazing for sealing the glass pane. Gaskets are attached using an epoxy adhesive.

The cooker measures 46cm (18 in.) x 30cm (12 in.) inch x 15cm (6 in.). The length of the cooker, greater than its width is designed to increase the time between reorientations. The diameter and the height of the two aluminium cooking pots are 5 inch and 3.2 inch respectively. Cooking pots are painted dull black using an nontoxic black paint.

Test Results

• Intensity of solar radiation: 0.6 KW per sq.mt
• Reorientation is done in every 30 minutes interval.
• Ambient temperature: 28 degree Celsius
• Peak temperature of empty cooking pot lid: 130 degree Celsius.

Cooking performance:

• Time taken for cooking 0.5kg of rice (weight after preparation): 2hrs 15min.
• Method of cooking- One part of rice mixed with water twice of rice volume and then placed in cooker.
• Time taken for cooking 200gm Dal (lentil soup): 2hrs 30min.
• Method of cooking- One part of Dal mixed with water (twice the volume of Dal) and then placed in cooker.
• Time taken for boiling two potatoes: 2hrs 30min.
• Method of cooking- Potatoes are diced and cleaned with water and then placed in cooking pot without adding water. The wet surface of potato after water cleaning is sufficient for preparation of potato. Potato rather will not boil if water is added in the pot.
• Taste of prepared food: Good

Approximate Cost Estimation (for prototype making)

<(Say, Rs.800 in Indian currency)>Rs. 790

<td(Say, Rs.800 in Indian currency)>Rs.790

1.	Wooden for cooker box-	Rs.70
2.	GI sheet, 2ft x 2ft, for cover glass frame and reflector back: \\(sheet for reflector back support and for frame of cover glazing)	Rs.60
3.	Two Aluminium pots	Rs.80
4.	Two pot stands	Rs.40
5.	Aluminium foil, 4ft x 1.5ft @Rs.15 per ft.	Rs.60
6.	Mirror glass 1.5ft x 1ft @ Rs.40 per sq.ft-	Rs60.
7.	3mm thick plain window glass- 1.5ft x 1ft @Rs.20 /sq.ft	Rs.30
8.	Dull black paint (DUCO paint):100 ml.approx @ Rs.215 per Lt-	Rs.20
9.	Paint for wooden box:	Rs.30
9.	Gasket material and adhesive-	Rs.50
10.	Hinge, stay links, handle, plastic seat, clips, screws etc.	Rs.90
11.	Overall labor cost	Rs.200
Total

Tools Used

Hand Saw, Hand Drill, Hand Shear, Rubber and Wooden Mallets, Pliers, Screwdriver Set, Wrench Set, Measuring Tape etc.

Manpower Requirement

• Carpenter: For making wooden cooker box -- one person, 2 hours.
• Sheet metal worker for glass cover frame and reflector frame making -- one person, 3 hours.
• Tin smith for soft soldering of joints at corners of glass cover frame and relector frame -- one person, 1 hour.
• Fitter for final assembly work -- 1 person, 2 hours.

See also

• Construction plans for this cooker

Contact

See Sankha Subhra Datta.Sankha Subhra Datta