A Community and Forum For Aquaponic Gardeners

Using a Fresnel Lens to Heat Water

We've just started researching this little gem, so haven't acquired the lens yet...but checking around!

A Fresnel (the 's' is silent I think) lens is found in big screen TVs. Pick up a non-working rear projection TV off Craigslist, or wherever.

A guy on YouTube, fencekid, has quite number of videos relating to this. Check out the one about building the frame here. Then also check they way this guy recycles the TV box as a frame here (he rabbit-trails a bit but gets to the point).

Different sizes offer different results, fencekid again...see here.

If anyone here is doing this, or does one, please share in this forum. When we get the parts, I'll try to assemble a video...especially if it works well!

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Permalink Reply by Jack Dunbar on December 31, 2014 at 11:23am

Sounds like a great idea. It's very cold here in the Northeast and now I know what I can do to rid myself of boredom. I have some ideas. I just need to locate a Fresnel lens. Please keep us posted if you decide to build something.

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Permalink Reply by Will bryan on January 1, 2015 at 9:12am

This looks like it could work awesomely for heating a fish tank, would probably even need a temperature controlled timer to either cover the frenel or stop the pump (but then you have the heat exchanger not being cooled).

Of course like he says, you need to track the sun somehow to maintain focal for best heat, but might not need that just to keep the tank warmed.

At night of course you would dump a lot of heat from the day and run the risk of freezing, but might be a really nice experiment to run with graphs tracking temperature.

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Permalink Reply by Bill Edmonds on February 17, 2015 at 9:15am

Yes, a Fresnel lens can achieve high temps if you don't mind adjusting it every ten to fifteen minutes. But I would be more inclined to consider a parabolic or "cusp" reflector as less adjusting is required and I prefer the lazy way of doing things. Google either one and see what comes up. Just a couple more options you may want to consider. Good luck.

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Permalink Reply by Will bryan on February 17, 2015 at 9:32am

You could easily use a computer and small motor with solar power to adjust the lens to track the sun

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Permalink Reply by Michael & Kristine Stoddard on October 14, 2015 at 5:02pm

How to get 2000ºF Solar Power -- The King of Random

This might give you an idea of how much power you'll be dealing with. It's insane and you'll want to do your research before you set your tank, (or your fish) on fire.

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Permalink Reply by Pieter Swanevelder on October 15, 2015 at 12:06am

Sun insolaiton is typical 1000W/sqm for overhead sun (90deg) - the lens only concentrate that power in to a very small area - thus the high temperature obtainable at the focus. i.e. the energy available to heat your water stays the same. You'll be better off using a _wind_ isolated_ coiled black irrigation small diameter PVC pipe (as in passive swimming pool heating - but with a transparent cover added) as it is better match to the desired working temperature of your AP system.

Also - check safety with lenses - that focus spot don't give your eyes a second change.