Last updated: 19 January 2016
How to make Solar tea using black marbles and a double glass tea cup.
- Double glass wall tea cup (if available. Otherwise single wall will work)
- Glass saucepan lid or pyrex lid
- Mirrors or reflectors
- Black glass marbles
- Preheat water in the tea cup with black marbles with the lid on until bubbles and steam are present.
Water starts vaporizing from just over 50 degrees centigrade. The lid will start forming condensation soon after this temperature is reached. This is only half way to boiling.
Bubbles on the black glass marbles will form as steam is created on the surface of the marbles.
I keep a teapot on the aluminium tray in front of the mirrors all day, and used the preheated water at around 80 degrees to start making a cuppa.
If there is a sealed lid to the glass container then more heat is retained, such as a pyrex whistling kettle. However, if you are just making one cup at a time, why not bypass the kettle and give this a try.
I have a double walled glass container with marbles as a preheated warm hot water on the aluminium tray which is my minimalistic solar set up all through summer, so there is usually hot water to start with by the time I need a cuppa in the garden.
Test temperature with a thermometer if you need to pasteurize or boil the water first before adding the teabag.
- Add tea bag
- Place back in the focal area of the reflectors
- Remove tea bag
- Spoon out marbles
- Add milk and sugar as required.
When the water is hot in the reflectors tiny bubbles form on the sides of the black marbles.
When the water is close to boiling the bubbles on the sides of the black marbles will be rising to the surface to release steam.
The time it takes depends on your reflectors, cloud cover and temperature.
As this process is going to take a few minutes on a sunny day, make a kalidoscope mirror wedge vertical panels on your horizontal base reflector to speed the process up. Make the focal line match when you want the water boiling, which may be 20 minutes time, so cast a shadow a little to the east to give the sun time to come over to your focal line in 20 minutes time, to avoid overshadowing.
Explanation of the reflective geometry of a kaleidoscope solar cooker by curlydock: