Solar Cooking
Last edited: 30 December 2015      

SK-TF: Prototype Models

SK-TF (Solar Kettle-Thermos Flask) 0.75m nominal tube length

A reflector is attached to the bottom of the solar thermos tube to significantly increase the performance of the otherwise idling bottom half of the tube.

In 2005 Alex Kee developed a solar water pasteurizer and storage device called the Solar Kettle-Thermos Flask (SK-TF). Its primary component is a solar vacuum glass tube, also known as an evacuated tube, made of borosilicate glass (Pyrex(r)). The inner-most glass layer has a dark external coating that heats up in sunlight. The outer-most glass layer is transparent, allowing sunlight to pass through. The air has been removed ("evacuated") from between the layers, creating an insulating vacuum. "One of the setbacks of any solar thermal water heating system is that when you want hot water most - like in the morning to make hot beverages when the sun is still asleep - it fails you," says Mr. Kee. "The SK-TK is not just a solar kettle; it is also a 'Thermos' flask that keeps water hot overnight with thermal loss of less than five degrees Celsius."

SK-TF diagram.jpg

Use is straight forward: simply set up the included tube stand, insert the tube, adjust the angle toward the sun, fill the tube with up to two liters of water, and cork the opening. According to Mr. Kee, pasteurization temperatures are usually reached in one to two hours.

The Solar Vacuum Glass Tube Collector (SVGTC) delivers free solar energy generated boiling water within two hours. Made from strong "Pyrex" (borosilicate) glass, these new generation co-axial selective coated solar vacuum glass tube collectors is more than 70% efficient in converting solar infra-red energy into thermal energy.

Solar infra-red energy penetrates the transparent outer glass tube, right through the vacuum layer and gets absorbed by the black selective coating on the outer side of the inner tube.

Solar thermal energy generated from solar infra-red energy by the Solar Kettle-Thermos Flask (SK-TF) sterilizes and kills most if not all water borne pathogens making it potable and safe for drinking through the solar water pasteurization or boiling processes.

Given that vacuum is an excellent thermal insulator, the heated water remains hot as very little thermal energy can escape through the inner tube to the outer tube of the SK-TF.

For added thermal insulation performance, the outer side of the inner tube has not one but two selective coatings: electro-statically spluttered adsorptive black coating (Aluminum Nitride) on reflective silver coating (Aluminum).

To preserve the longevity of the coatings, a barium ring is placed within the vacuum to absorb any nitrogen or oxygen that may be out-gassed post vacuum sealing.

The vacuum insulation is so efficient that overnight, the thermal loss is less than 5°C, doubling up the Solar Kettle as a Thermos or Vacuum Flask to provide hot water in the morning even before the Sun is up, a critical feature inherently deficient in most solar energy devices.

Besides the solar pasteurization and boiling of water, the SK-TF which stagnates at a high temperature of 220°C delivers baking hot dry heat to bake and autoclave.

At the heart of the SK-TF design and purpose is personal empowerment where it is the individual rather than the group is empowered to manage and ensure his or her own drinking water safety. It is hoped that with personal empowerment, there will also be personal ownership and responsibility so that the end result is a community that is self reliant where personal hygiene is concerned.

The SK-TF is not only for the aid receiver, but also the Personal Solar Survival Tube (PerSisT) for the aid giver to ensure his or her own drinking water safety because the last thing the aid giver wants is to also be a victim in the field.


  • January, 2011: The SaVeTaO (Solar Vacuum Tube Oven), a bigger diameter version (4 inches iso 2 inches diameter opening) of the SK-TF is already in commercial production and sales. With the SaVeTaO, cooking, baking and autoclaving become more viable and versatile given its bigger diameter opening that can accomodate hand access for easier handling and cleaning.


  • February 2011:

See also[]

External links[]


See Alex Kee.