Water Lens - These are useful for solar cooking experimentation and general fun with a big magnifying glass. This project is very simple almost primative like making a drum, that you can set things on fire with. This lens was made from a rusted out old barrel, 1 Yard of clear vinyl and some twine. It is very easy to build and to demonstrate. You need the sun fairly over head, a few fat stones to level the base and a bucket or container with a few gallons of air temperature water. Air temperature water is best because cool water straight from a hose will tend to cause condensation on the vinyl until it more closely matches air temperature.
Water lenses are fairly safe for group learning exercises. This is because the lens directs light down and away from the eyes. Molded plastic could be made available for classroom teaching but vinyl works well enough. In fact most any clear plastic sheeting will work like this on a circular frame, even square frames work but not as well. Water lenses can also be sealed and different materials can be used such as oil to demonstrate the refraction differences of oil and water.
These devices can be used for solar cooking, but the width of the lens would have to be larger for serious or large scale cooking projects. So these devices are more useful for safe and inexpensive learning exercises like heating up some hotdogs or pasteurizing water.
Water Lens - Cooking One way to cook with a water lens is to place a black pan with a on it pancake all sealed in an oven bag. Then adjust the focus of the lens by changing the height of the pan like by putting a box under it. This will also work with a small box oven. To make a small box oven place a box with the top facing up and put a piece of clear vinyl over the top and use some twine to hold the vinyl down. Most vinyl is surprisingly heat resistant and makes a good clear lid for a box oven. If you have plastic oven bags, that can be used instead of the vinyl. When you are done place your baking tin inside and under the lens.
Solar Water Pasteurization Experiment
1. Get a clean pickle jar
2. Paint the jar black, but use some tape to make a window to look inside of jar.
3. Make a small hole in the lid to let pressure escape.
4. Get some pond water and observer moving organisms under microscope.
5. Fill jar with pond water and twist-tie a clear plastic bag around the jar.
6. Chart different solar cooking times and observer water activity under microscope.
7. Get a small clear glass container and put some beeswax in a tube.
8. When the wax melts the water should be pasteurized, check under microscope.
9. Have class make some observations and look up the melting temperature of beeswax.