Alex Kee has 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 insulative 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."
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.
- Granada 2006 conference paper: The Solar Kettle-Thermos Flask: A Cost Effective, Sustainable & Renewable Water Pasteurization System for the Developing World