Introduction: 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

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

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

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

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

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

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.

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