Today I’ll be teaching you about a very cool and practical device that many off the grid families are making use of. The device that I’m referring to is the Fresnel lens.
What Is A Fresnel Lens?
This is a unique type of a lens that was designed by a French physicist by the name of Augustin-Jean Fresnel. The original Fresnel lenses were used in lighthouses. Their unique construction makes it possible for much smaller and thinner lenses to do the same job that very large convex lenses once did.
This meant that more powerful lenses could be manufactured with less material for use in lighthouses. The immediate benefit to this design was that ships could see the light from these lighthouses from much farther away.
Instead of a smooth convex lens, the early Fresnel lenses were made of several glass concentric annular sections which were known as “Fresnel zones”. This design made it possible to capture more of the ambient light that was put out by oil lamps and direct it into a focused beam that could be seen for many miles.
Most Popular Use Of The Plastic Fresnel lens
You might have a lens of this design in your home right now and not even realize it. Have you seen the plastic reading magnifier sheets that are designed to lie flat over a page of text? These Fresnel magnifier lenses are actually quite common. They only cost a few dollars and instead of using a traditional circular magnifying glass that only magnifies small sections of text, this type of a lens will effectively magnify the entire page.
Practical Uses for the Fresnel Lens Solar Concentrator
Perhaps one of the most practical uses for a large Fresnel lens is to use it as a solar concentrator. There are many practical applications of solar energy that don’t involve generating electricity from PV panels at all. Some that immediately come to mind are solar ovens, solar water heaters, and even solar powered steam engines.
In each of these applications, the ability to pass light from the sun through a large lens and concentrate it to a fine point can dramatically improve the usefulness of these devices. A solar Fresnel lens is the perfect choice because they are large but still lightweight. Their thin and lightweight design means that they can be easy mounted in a frame and manipulated without the need for heavy equipment to move them around.
Where To Buy Fresnel Lens
If you are just interested in doing some small scale experiments, you can buy one at your local supermarket. You’ll probably find them in the reading glasses section. You should expect to pay about $10 – $15 dollars for one of these small Fresnel lenses.
If you’re ready to go big, it’s not quite as easy to find a place to buy these lenses. One good source is greenpowerscience.com. They seem to do a good job of tracking these lenses down and making them available to us alternative energy nuts. They usually have a pretty good selection of previously used solar Fresnel lenses for sale. The typical Fresnel lens price is going to vary depending on the size, clarity, condition, and shape of the lens. For example: They have a framed 46 inch lens priced as low as $79 and a framed 65 inch lens priced as high as $299.
Greenpowerscience.com is run by Dan and Denise Rojas and they have some AWESOME videos on YouTube that demonstrate various alternative energy experiments that they have done. As a matter of fact, the video below is a great example from them that shows Denise making use of a large Fresnel lens to cook fish. The video demonstrates how someone can make use of one of these powerful lenses to do something that is really practical. We all have to cook our food and using this lens to cook with doesn’t require the use of any electricity or other type of fuel whatsoever!