Introduction: Saving the World With a Giant Solar Death Ray

Picture of Saving the World With a Giant Solar Death Ray

So you have finally gone and done it- you've gotten a giant fresnel lens and you have mounted it so you can use the 1000+ square inches of solar collection to really heat things up.

Then what?

Laugh your Maddest Scientist all you want, because it is time to use those powers for good, and not evil.

Step 1: Safety

Picture of  Safety

Be safe! The solar concentrator is not a toy*, and can cause real damage in a matter of moments.

  • The most important thing is good eye protection- the focal point is incredibly bright, and you WILL hurt your eyes if you look straight at it!
    I use a pair of polarized sunglasses underneath a cheap set of welding glasses. This cuts the reflection down to a tolerable level.
  • Keep pets and children away- the focal point for my set up is just the right height to burn a dog- or a baby. It only takes a moment, especially if you are heating metal.
  • Don't leave it unattended- as the sun travels across the sky, the focal point will move. With my set up, I have to readjust it every 10 minute or so. Make sure yours won't accidentally traverse something flammable.
  • When you aren't using it, store it safely. I keep mine in a basement with no windows. If I have to move it, I wrap the lens in an opaque blanket. This protects the lens, and keeps it from starting a fire by accident.

*OK, maybe it is kind of a toy, but it is a dangerous one.

Step 2: Frying Eggs

Picture of Frying Eggs

A obvious choice, and a classic one. Nothing demonstrates more concretely just how hot the focal point is than this, because it relates it to an activity most of us are familiar with. It gives you a good intuitive sense of how hot the focus is, and just how careful you should be.

Would you touch a stove? No, so don't get near the focal point.

My lens will fry an egg in a few minutes on a fall day, or roughly the same amount of time that my stove does. I expect it will cook quicker during the high heat of summer.

Once you have fried an egg, why not try something a little more complex?

Step 3: De-icing Your Steps

Picture of De-icing Your Steps

Maybe a different frame would work better, but mine was not very good at this. The focal length is fixed, so only one of my steps is getting heated.

Since it is a concentrator, it is effectively acting as a sun shade for every piece NOT in the beam. Fortunately, the heated water flows away from the focal point and melts the surrounding ice. Kind of like this concept, but without the infrastructure.

I tried to use it to melt snowbanks faster, but the frame was too awkward to do it well. Maybe next winter.

Step 4: Making Charcoal, Char Cloth, or Biochar

Picture of Making Charcoal, Char Cloth, or Biochar

By putting organic material in a mostly sealed container, you can heat it to a point that drives off volatile gases and water, and leaves just the carbon behind. Depending on what you use, this can be called charcoal, char cloth, or just biochar.

Charcoal is pretty handy to have around. It burns steady and hot. It also has a lot of uses for filtering, and artists use it to draw. Like I said, lots of uses.

Charcloth is the result of heating small pieces of cloth. It is often used by survivalists, because it can catch and hold a spark like few other materials.

Biochar is a catch all term for generic organic material. It is used as a soil additive, and is supposed to be good for the soil.

All of the above tend to be very energy intensive to make. In the old days, they used to use as much as 50% of the wood chopped as fuel to turn the rest into charcoal. How wasteful! Using a solar concentrator means that 100% of your material can be used, instead of burning it as fuel.

I use a very small tin as my heating vessel. It gets hot enough to vaporize the paint off the side, which reveals shiny metal. This is bad, because shiny means less efficient heating. I've tried to stain the metal with the smoke from inevitable fires from the solar death ray.

Step 5 of this instructable shows a good solar char cloth setup.

Step 5: Environmentally Friendly Weed Killing

Picture of Environmentally Friendly Weed Killing

You don't want to use poisons to kill weeds around your food garden- the garden club bylaws are pretty clear on that. But hoeing is such hard work!

Why not boil water to dump on the weeds while you work? No chemicals, no residue, and no effort on your part except to collect the hot water and pour. Oh yeah, and make sure that no one gets blinded by your setup or burns the garden down.

Here, you can see several weeds that have been boiled next to one that wasn't. The heated water is fast and effective, and leaves no trace behind. Preheating the water you intend to boil makes the process go faster- in my case, I filled a 500 ml water bottle from the hose, and left it in the sun while the pan of water was heating.

The solar Concentrator is hot enough that bubbles will form almost instantly at the focal point, but it will take about ten minutes for the heat to disperse through the water.

Step 6: Sterilizing Soil

Picture of Sterilizing Soil

Soil for planting is often sterilized, so that any seeds from weeds or parasites are eliminated, ensuring that only the plants you want are free to sprout. Many people use large sheets of black plastic to heat the soil with solar power, but that takes weeks. You can put the soil in the microwave or oven for smaller batches, but why waste energy? The solar concentrator can easily hit the 200F that is recommended.

Here, I have placed the soil out of the focus point, and probably should have placed it even lower. In the video, you can see that it only takes a minute or two for the soil to start smoking- those are the organic components of the soil vaporizing. I understand they can become toxic if the temperature goes too high. Low and slow are the way to go here- no need to roast or melt it.

I've added the cooked soil to my tomatoes, which could use some more dirt to replace some lost to erosion.

Step 7: What Else? You Tell Me.

I look forward to suggestions on other environmentally friendly ways to use a solar concentrator. I'll try out feasible suggestions in the comments over the summer and report back how well they work.

Something I think would be interesting would be to try generating power- perhaps with a Stirling engine, or a Biolite stove.


ridalyn (author)2014-06-11

Solar Smoker, I drawed ya a picture.

ridalyn (author)ridalyn2014-06-11

It occurred to me that the smoke would build up on the inside of the lens so I would recommend adding a plate of regular glass between the lens and the enclosure, that way you can clean the glass easily between batches of smokables.

jkimball (author)ridalyn2014-06-11

This is a very good and feasible idea! As a vegetarian, I don't often think about this sort of thing very often.

I've been considering putting some sort of "smoke shield" in front of the lens already, because things burst into flames on a regular basis under it. (it set the DIRT on fire!)

What is the temperature range for a smoker?

Bill WW (author)2014-06-10

Excellent Instructable. There have to be some great applications for using concentrated sun radiation to produce useable energy. The typical solar panel in use currently is only about 15% efficient. So from the 1000 w/m^2 we get from the sun, a solar panel will only produce 150 w max.

You could try using your lens as the heat source for a Stirling engine, but the engines we hobbyists make are pretty inefficient. If you are interested, however, take a look at my Instructable:

You would focus your lens on the top plate, and cool the bottom section

Also, performance of most solar cells (photo voltaic cells) is enhanced by concentrating the sunlight upon the cell - but of course to a limit.

You said: "The solar Concentrator is hot enough that bubbles will form almost instantly at the focal point, but it will take about ten minutes for the heat to disperse through the water." The bubbles are most likely dissolved air the comes out of water when heated.

jkimball (author)Bill WW2014-06-11

That's a very fine Stirling Engine- I could only dream to make one half as nice. I'll probably have to purchase one, since it is unlikely that I will find one in the garbage to salvage.

Bill WW (author)jkimball2014-06-11

A small steam engine might be a better option. You could focus the concentrated sunlight directly on the boiler. I think you could really generate electrical power that way. A steam engine is much more efficient than the kind of Stirling engines we can build.

Also, to get an idea of the heat at the focus, try melting various materials fo which you know the melting point - try lead (melting point 620F) or 95/5 solder, the solder commonly used for copper pipe, (450F).

AuntieAbuse (author)2016-04-28

Excellent titorial j. I'm currently on the path to self-sufficiency and
energy respect. I've watched a few YouTube videos featuring the Fresnel Lens, nothing as large as yours it must be said, and am aware of the massive potentials of this application. My interest has been reignited... Large THANKS

fred3655 (author)2015-05-04

I wouldn't tie up an Arduino building a solar tracker. You could use optical components and a stepper motor. You could build a sauna, heat a tube or coil of water into steam. I was thinking solar oven too. As for a smoker, just use a long tray for wood chips & the moving beam works in your favor. Get a round piece of glass & rotate it through the smoker window to keep it from getting too smoky.

bgoldberg1 (author)2015-03-08

Have you considered using your solar collector to brew, or perhaps even roast, coffee?

jkimball (author)bgoldberg12015-03-08

I don't feel I have enough control over temperature to roast something usefully. Can you roast coffee in a pan? (I don't drink coffee, so I have never tried to make it.)

dbaugher (author)2014-10-27

As a scrapper I'm going to try using this idea as a heat source on circuit boards to remove the components. Right now I am using a heat gun and holding the board still. If this can cut down on my electricity consumption then holding the lens still in its frame and moving the board around is an easy enough change to make in my procedure. Thanks.

jkimball (author)dbaugher2014-10-27

Temperature control will be an interesting problem, as you'll have to keep from setting the board on fire or roasting your parts. Depending on the size of the lens you have, you could try keeping the focal point wide (and thus safely low heat) and preheat the board, then use the heat gun for a controlled heat to pop out the components.

muddwasher101 (author)2014-06-26

You could possibly use this to heat air such as an underhouse circulation system for winter that would heat floors or possibly heated air entering a pipe and dispersed into a green house, smoker, dehydrator. Harnessing the energy indirectly rather than directly onto surfaces, I think would be safer and more useful.

jkimball (author)muddwasher1012014-06-26

I think you are correct about "indirectly", and that's why this may not be a good fit for heating.
Since it is a concentrator, the total heat energy is focused to a point, but the rest of the area is in shadow. A traditional solar heater would be more effective and efficient, I think, because the concentrator would need more infrastructure to handle the "heat dispersal" part.

Maybe someone with more math can tell us whether it is better to heat a large volume of air slowly, or a small volume of air quickly.

Kilt Y (author)2014-06-11

Don't laugh, but I'd be curious how quickly it could sterilize waste for humanure applications: off the grid, in areas without water, and in emergency situations.

A specific poop recepticale could be designed and placed in the focal point to kill of nasty micro-organisms for quicker composting.

jkimball (author)Kilt Y2014-06-26

I would try this, as I have read "The Humanure Handbook" too, but my wife gave me a look so this will not be happening in my backyard anytime soon.

I think if I tried to defecate in a metal box, and then cook it in the yard, it would be the last straw for the HOA.

I hope someone else gives it a try and reports back, though.

xxxCHICAGOxxx (author)2014-06-25

the king of random already did this and posted it on instructables I recommend you check out his channel

his YouTube channel is king of random

This is so awesome!

Thank you! What would you do with it if you had one?

Smite my enemies, obviously.


fixfireleo (author)2014-06-10

hmmm. can you string a few of those together and aim it at DC?

dojers (author)fixfireleo2014-06-18

This soooooo needed a "Like" button! :)

dojers (author)2014-06-18

I'm loving your idea of a "toy" - course, I'm a bit of a pyro so anything that makes fire is up my alley :)

xarlock667 (author)2014-06-11

So, can you place a mirror at the focal point and turn it into a proper laser? Can you then make a bank of them and use their combined heat to melt steel like water under a blow torch? The whole point of a death ray is to be EVIL. Evil is Good. Eddie Murphy said it so it must be true!

nickiwoll (author)xarlock6672014-06-11

Yes, if you put another inversed lens there, shaped like this: )( then you could use it as a beam.

xarlock667 (author)nickiwoll2014-06-12

What about a bent mirror? Shaped like this ---> )| Would that have the same focusing ability? I just found one of those huge lenses outside and want to put it to bad use. Um... Good use. Yeah, thats the ticket! LOLZ

Bard (author)2014-06-11

If that lens came from a projection Tv then I would recomend using a sheet or too of glass to protect the thing. They scratch really easily another thing too if you have salvaged the mirror as well you could have your self a monster weapon on your hands.

Eh Lie Us! (author)2014-06-11

Ok, you asked for ideas. Are you sitting? No? Then go to another instructable on how to build a chair. Good?

I believe that it can be used for blacksmithing. Hold on, people. A few years back I took a class at the local junior college on it and I was amazed but turned off by the use of energy (propane or coal) I managed to get one of these Fresnel lenses from a TV that was gettign pitched and was blown away by the power. Mine focuses in a circle. Some out there focus the heat in a bar shape. Anyway, the issue is to spread out the heat uniformly throughout the work piece. So I thought, BBQ rotisserie motor! Maybe a way to connect the piece so it heats evenly? Those motors will turn slowly for hours near heat sources (BBQ grills).

I'm curious what people out there think.

jkimball (author)Eh Lie Us!2014-06-11

My brother is a blacksmith, so I had already thought about potential uses for him. He turned me down though, because the focal point is so small compared to a full length forge he has now. My set up is just too unreliable for him to use.

I wanted to try to make lump charcoal for him so he has a renewable, high heat energy source for his ironwork.

Fikjast Scott (author)2014-06-11

this is a great project

Mozleron (author)2014-06-11

How about combining this with some sort of Arduino powered solar tracking system with a timer and shutters to better control the focal point and exposure time?

jayster454545 (author)2014-06-11

I could see this as being an excellent way to heat a green house in the very early spring so that plants in a cold climate could get a very early start. It could super heat a pressurized fluid container and the heat would even last into the night, but it would need a way to track the sun all day.

Chucknsc (author)2014-06-11

is there any handheld design out there that you could make or buy to use while walking around in your garden perhaps ?

jkimball (author)Chucknsc2014-06-11

I have several smaller lenses that are only the size of a sheet of paper. They are far more portable, but of course don't have the concomitant power of the larger lens.
When it comes to low-end solar, size matters.

ShutterBugger (author)2014-06-10

Some of those lenses will melt the surface of common bricks. The area is small, but still melted.

jkimball (author)ShutterBugger2014-06-10

My large lens won't focus tight enough to melt a brick- you can see that I use a large cinderblock as a rest for many of my projects. I have a much smaller lens that DOES focus to a fine point... but doesn't have the collection area to do it.
Ah well, that's the price of a free, recycled lens- no quality control.

miller (author)jkimball2014-06-10

Would it be possible to put your smaller lens in the path, if not at the focus, of the larger one? Wouldn't that increase the output? The question would be if the smaller one could handle the heat?

jkimball (author)miller2014-06-11

Oh, I have tried. I believe that fresnel lenses can't be used in series. I think that it would have to be fresnel lens 1 (converging) -> Plano convex lens (diverging) -> fresnel lens 2 (converging to tight point).
Euclid ( could probably work out the math for this in a matter of moments but I have yet to do so.

Radicalone (author)2014-06-10

Wasn't this done already by The King of Random?

That's Ok pretty much everything The King of Random does has been done before.

starphire (author)Radicalone2014-06-10

>Radicalone, to be fair this has been done by many people, for decades. A few individuals (such as the one you mention) have been very successful at producing good quality Instructables and videos showing DIY projects that aren't even close to new, or original save for perhaps a different source material or layout here and there. Often if you read or listen closely this fact will be acknowledged somewhere, as it should be.

omikeo (author)2014-06-10

heat some water for cleaning or a shower, try a mini steam turbine to change the energy to electric, store the heat in cooler weather for night release in concrete or ?

PhantomOfHeat (author)2014-06-10

Most would consider that a weed but it is not its plantain

Its edible and can be used to soothe bug bites and bee stings.

antioch (author)PhantomOfHeat2014-06-10

Excellent point! Indeed, plantain is one of the most amazing remedies for a huge variety of bug bites, including some very nasty ones.

obrienator3 (author)2014-06-09

If you were inspired by the king of random, you should give him some credit for the idea.

starphire (author)obrienator32014-06-10

Indeed. If you believe that individuals such as TKoR actually invented most of the projects they put up, including this one, then perhaps there is something wrong with the way they are being presented to the public that *they* ought to be acknowledging the folks who have done it before them (and published some kind of instructions for doing it). Edmund Scientific was selling giant fresnel lenses and suggesting DIY projects for exactly this purpose at least 40 years ago, before they were even being put into large screen TVs.

ManifoldSky (author)obrienator32014-06-10

Why would you even make that assumption? It's not like people have not been frying things with fresnel lenses since, well, fresnel lenses (and regular magnifying lenses before that).

jkimball (author)obrienator32014-06-10

I think his set up is far superior to mine, and he made better char cloth. I wish I had seen his before I tried with mine.

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