Solar Engine

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The purpose of the Solar Engine project is to produce electrical power from concentrated sunlight. We already have several large Fresnel lenses to gather the sunlight, and will build a steam engine, Stirling engine, or something similar to convert the sunlight to electricity. Why do it? Because we can, and because it is awesome.


Obsolete rear projection televisions contain large Fresnel lenses. We acquired three such TVs for free and removed their lenses. Their properties are:

Name Height Width Focal length Focus pattern
Clear 31" 41" 45" dot
Wide 25" 44.5" 36.5" 4" line
Gray 27" 36" 30.75" dot


Ideally, a mount will do three things:

  1. Keep the lenses planar and stable
  2. Track the Sun
  3. Allow multiple lenses to focus on a single target.

Currently we have mounts (TV bezels) to keep two of our three lenses planar. We are working on more sophisticated mounts.

Related Links

Project Log

Jan. 8, 2011

The sun was totally gone by the time we all got to the space, so we couldn't melt or burn anything today, but that gave us an opportunity to do some work on the lenses.

We measured the dimensions and focal lengths of the 3 lenses we have in our inventory. We did this by placing a light bulb at one end of the workshop, turning off the lights and projecting an image of the bulb through the lens and onto the garage door. It turns out that one of the lenses actually produces a 4" line while the other two produce points.

A frame was built for the clear 31x41" lens using scrap strips of mdf, brackets and bolts. This frame will keep the lens planar and sturdy. Currently the lens is the only layer in the frame. We plan to add a protective layer of acrylic over the lens side to keep it clean. The lens surface is accumulating dust and scratches, so keeping it protected will be important for the long term. The frame is built so that that the lens rests against the bolts instead of having the bolts go through it.

Constructing the frame.
Constructing the frame.
The completed frame.

Jan. 22, 2011

We had some decent sun so we played around with the clear 31"x41" fresnel lens which recently got framed for stability. This time we had welding masks so we were able to do some more prolonged experimentation. The first target was coins, again, which were quickly destroyed. We were able to melt a nickel, made of a 75% copper 25% nickel alloy, which reformed into a football-shaped ball of metal once it cooled.

Alan brought in the Hero's engine he built recently which is essentially a steam-powered device that spins when the liquid inside is boiled. When heated, steam shoots out of two small curved pipes on either side of the chamber, causing the device to spin. We were able to generate a decent flow of steam out of the tubes using the fresnel lens, and next time plan to mount the device on a wire using fishing swivels to see if we can get it to spin.

The cinder block we used as a test bed also succumbed to the concentrated sunlight. We targeted the block in several places, turning the concrete and cinders into a red hot molten mixture which cooled into a smooth black glass. Using an IR thermometer we measured temperatures as high as 630C. The instrument wasn't calibrated specifically for what we were doing, so that number may not be accurate, but gives us a indication of the kinds of temperatures we're able to achieve using concentrated sunlight.

Turning cinder block into glass.
Coins destroyed by concentrated sunlight.
Steam from the Hero's engine.
Heating the Hero's engine with a fresnel lens.

Jan. 29, 2011

Melted steel!

Focusing the fresnel on a steel pipe.
Notice the spot in the threads just above the half length where the threads are disrupted because the steel was melted on the surface of the pipe.
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