Teardrops n Tiny Travel Trailers

Has anyone ever used a large fresnel lens for solar cooking?

These are the types of lenses used on school overhead projectors, or more importantly, old large screen projection TVs that are getting thrown away all the time.

I mounted a 3'x4' lens in a wood frame, and on a sunny day, I can melt pennies with it. No joke.

I'm wondering about using one to heat cast iron for cooking. Just focus the lens to the size of the pot or pan, instead of a penny-melting pin-point.

Anyone ever do this before? (We haven't had a sunny spring day yet since I've started wondering.)

-Ben

The bad thing about a solar reflector or lens is the sun moves in the sky. If you forget about it, it will burn or melt stuff you don't want burned or melted.

I haven't tried cooking with one but I have confirmed their efficacy for wanton, gratuitous destruction.

I was fiddeling with mine and focused it on a small section of back door trim and in a blink it was smoking.

I now have my projection tv fresnel lense mounted in a wood frame and plan on using it to evaporate gray water from my tiny house. I am looking for one of those old cast iron rendering pots ( witches caldron) to drain the gray water into then focus the beam to evaporate the liquids.

Bob
No septic sewer system or septic tank where you live?
Good Roads
Brian & Sandi

We were on Google earth yesterday looking at older aerial shots of the new property trying to determine where the septic field and the well may have been located. In the older pics it appears to have a small building on one side of the property I am guessing it to be a pump house and the opposite corner was a really nice green spot. As we all know "the grass is greener over the septic tank" according to Erma Bombeck. So until I locate them I guess my answer is NO at least not yet.

Bob Henry, how are you going to keep the lens focused on the gray water pot as the sun moves? Manually?

<Chas>

GuitarPhotog wrote:Bob Henry, how are you going to keep the lens focused on the gray water pot as the sun moves? Manually?

<Chas>

For the short term as an experiment it wil be stationary and only moved manually being careful that the beam can not focus on any combustable surface.

I have been looking at a somewhat Rube Goldberg contraption that powers a 12 volt car window regulator. There are 2 very small photo voltaic cells that power it right and left. and a shade guard that doesn't allow the sun to shine on either if in direct alignment with the sun.

Bob, for a sun tracker, it's easier to use 2 photo cells with a divider between that is tall enough to shade one of the cells as the sun moves. Then the tracker moves the assembly until both cells are illuminated equally. We used this method on a solar project in college (many years ago) and it worked well with fewer parts. You just wire it up so the motor drives in the direction of the cell with the higher output (i.e., no shadow).

<Chas>