Technology

Villagers in Awuju, Zhengga, Quma, Bailing, and Xiakeba Villages wanted more portable solar cookers and a means of heating their homes without having to spend long hours collecting fuel. In response to their request, SolSource Tibet has developed a solar solution which includes both cooking and heating functionalities.

The SolSource solution can be dismantled as quickly as a hiking tent and transported from home to field for the mid-day meal. Its earthquake-safe bamboo frame and legs that can be staked into the ground help it withstand the winds of the Qinghai-Tibet Plateau. While food is not being cooked, waste energy from the solar cooker is harnessed for household heating by affixing a heat transfer coil to the pot stand.

Diagram of the SolSource SolSolution, a 2-in-1 solar cooking and heating device.

Cooking Functionality

The SolSource solar cooker is strong enough to withstand the high winds of the plateau while remaining compact and light enough to be portable. It consists of a parabolic, 25-panel yak wool canvas with sewn mylar reflector. Underside loops on the canvas run the length of bamboo rods which form a light-weight and durable tent-like supporting frame. At the vertex of the parabola, the bamboo rods insert into a 1-meter long metal shaft that connects to four re-bar legs oriented in a 2m-by-2m “X” pattern base. In high wind, these legs can be staked into the ground to prevent tipping. In addition, the legs pivot inwards for easy transportation while two guide rails attached to the legs enable manual solar tracking.

A back view image of our initial prototype. Since the prototype was built in the US, local Qinghai materials were not available. Here, bamboo rods are replaced by fiber glass, yak wool canvas is replaced by crafts canvas, and the re-bar stand is replaced by steel and wood parts. This shows the flexibility of the design for adaptation to new materials.

The pot stand is comprised of a re-bar ring that rotates about the end of the extended shaft via a wing nut. This stand also doubles as a resting place for a heating coil. Since the dish is fixed with respect to the shaft, the pot remains at the center of focus during adjustments to the solar angle.

Cooker Specifications:

• Dish diameter = 1.5m
• Focal length = 0.6m
• Central opening diameter = 0.3m
• Parabolic constant = 0.15
• Mylar Reflector = 80% specular reflectivity
• Cooker provides 0.9 kw of energy

Our design can easily be adapted to changing functional requirements using this MATLAB program written by Orian Welling.

Heating Functionality

Our detachable solar heater harnesses the waste heat from our solar cooker and has the potential to heat households while simultaneously protecting bugs and guarding against unwanted fires. It employs 0.5-inch polyethylene (PEX) tubing as a conduit for heat transfer fluid. This, in turn, is clamped to a heat transfer coil comprised of metal tubing coiled vertically and of radius less than that of the solar cooker pot-stand to which it is detachably affixed. This maximizes the surface area for heat transfer from the reflected sunlight. Heat transfer fluid comprised of a 50-50 water/anti-freeze solution is driven through the coils using a simple gravity pump comprised of two 20-liter buckets, which serve as the source and sink.

Diagram of heating functionality and bucket gravity pump.

We also offer the option of a novel in-home hand-driven pump to replace the bucket gravity pump. We are currently preparing this design for provisional patent.

Heater Specifications:

• Although we constrain the maximum flow rate at ¾ liter per minute, the rate can be partially regulated by the user via a simple valve at one of the buckets. Thus, on cold days, users can increase the temperature of the water by decreasing the flow rate.
• With room temp at 20C and heated water temp at 70C, flow rate must be regulated at 1/4 liter per minute, and buckets must be lifted (water pumped), about once per hour.

Innovative Aspects

1. Incorporates bamboo poles in a tent fashion instead of a heavy solid-form pre-woven basket
2. Dual functionality wherein waste solar energy is used for indoor heating
3. Does not kill bugs because the collected energy is always in use
4. A single collector can be used for both cooking and house heating
5. Transparent: Easily maintained and repaired. Most parts are fixable by the family or local artisans
6. Size and portability facilitate nomadic and alternative usage scenarios in addition to offering a more flexible, distributed retail model
7. Can withstand high winds due to anchoring and a broad base

Additional Innovative Aspects

The design also features the following elements which have not previously been combined:

1. Resistant to weathering
2. At cooking height to eliminate squatting and stooping
3. Energy efficient
4. Portable and light-weight
5. Will not break easily during long-distance transport
6. No fires!
7. Allow traditional cooking practices to continue
8. Made from locally available, traditionally employed, and low-tech materials
9. Constant focus with respect to the pot
10. Affordable