Written By Ben | Last Updated Thursday, Nov 5, 2015

Make a fresnel lens solar furnace from scrap!

What is a Fresnel Lens?


You can think of a Fresnel lens as a flat magnifying glass off made out of plastic they where first used in the early light houses to channel the light, today they can be found in a lot of household gadgets, toys and certain types of televisions if you would like to know more about the science of how they work be sure to check out this wiki: https://en.wikipedia.org/wiki/Fresnel_lens

There are two types of Fresnel lens Spot and Linear. A spot Fresnel lens uses multiple flat segments, arranged in a circle, thus focusing light on a small spot.

This type does not produce a sharp image, but has application in solar power, such as focusing sunlight on a solar panel. Where a linear Fresnel lens uses multiple flat segments, arranged linearly, thus focusing light on a narrow band.

This type does not produce a sharp image, but has application in solar power, such as focusing sunlight on a pipe, to heat the water within.

For the best results you want to use a “Spot” Fresnel lens.

Where can I find a Fresnel Lens for free?

Well to get a high enough temperature your going to need quite a decent sized lens at least 32" the best place to find them, is in old rear projection TVs and luckily these days, not many people want nor have the room for them, so you can pick them up very cheap! even free… sometimes! if you can’t get your hands on a TV or don’t want the hassle of puling one apart you can also buy a Fresnel lens off ebay! but if want you shipping can be a bit expensive!

How to disassemble a rear projection television?


To be honest it’s pointless for me to explain how to take a TV apart as they are all different and put together differently, this video may act as some guide: https://www.youtube.com/watch?v=348PUYaoGm8

The TV may have multiple things that look like a Fresnel lens but there will only be one, and this is the rough order of most rear projection TVs.

1. Outer cover - Some TVs have a clear layer on the very outside.

2. Lenticular lens - outer screen with thousands of vertical lines. The reason for these is to spread each pixel outward so you can see the screen from the side. It will probably rip apart as you separate the layers.

3. Fresnel lens - this is the innermost layer - clear with millions of “circular ridges” on one side and what we want :)

What to do with the Fresnel Len?

All you really need to do is make a adjustable frame out of wood.

Some other uses

Fresnel Lens can be used to:
  • Heat water for pool or bath.
  • Boil water for hot drinks.
  • Cook meals.
  • Power steam and sterling engines.
  • Make Electricity.
  • Melting metals.
  • Engraving wood and other martial.
  • Starting fires (with ease so be careful)
  • Purifying Water.
  • Lots of fun

Related external links

1. Stirling engine powered by a Fresnel lens 2. How to get 2000ºF Solar Power - Finding a lens from a TV