You may be asking at this point, ’What is Solar Fire? ’
To be honest, I don’t know.
Solar Fire was once upon a time an open source solar project, to develop low-tech high-power solar concentration designs, that anyone could participate in and take in their own direction. That being said, people participated and took it in their own direction! So it quickly became impossible to fit everyone under one definition and so Solar Fire became a fairly fuzzy concept potentially appropriated by anyone.
Now that that’s settled, the next question you may be asking is, ’Why should I build a solar concentrator? I’ve never needed one before ... right?’
Wrong. If you’ve ever lit some wood on fire, small or large, you’ve used a solar concentrator.
When you burn a tree, or any bio-carbon, the tree becomes a solar technology taking the sun’s rays and concentrating it in chemical bonds, storing energy to later be unleashed when you light the tree on fire. Unfortunately, as solar technologies go, trees are notoriously inefficient. Only about 1 percent of the solar energy that originally fell on the tree is delivered to the end user’s fire pit. Estimates may vary depending on region, accounting methods, and lumberjack/stove efficiency, but even absolute ideal conditions wouldn’t be very efficient as photosynthesis is at max 10 percent efficient.
As the foundation of the bio-sphere as we know it, trees have a lot going for them, so much so that burning them isn’t really a good idea in any case.
So upgrading our rudimentary solar technology to reflective mirror based solar concentrators, can allow us to easily reach efficiencies upwards of 80 % efficient and temperatures above 1000 C°. What this means is that for the amount of energy access we’d use significantly less land.
But before we get all excited we have to ask the question of why tree-burning has become so popular, even taken for granted. The answer is that tree-burning-technology is extremely simple for the user; just collect trees and light them on fire, a technique we mastered some hundreds of thousands of years ago. Tree burning is straight forward and easy ... as long as there are trees but we’ll ignore this detail for now and concentrate on the positive points that made tree-burning-technology such a success in order to compete with it.
Now, in terms of usability, there are also basic things going for mirror-concentrators, notably not needing to collect firewood, but in order to take a hack out of tree burning globally, a fairly simple alternative to tree-fires is required.
Hence the need for some sort of “solar fire”, a direct-light-concentrator that shares enough of the characteristics of our old technology to compete with its popularity.
Why are fires so popular?
First, fires are really hot, easily over 400 C° allowing us to do most of our tasks. Second fires are fairly low-tech and widely accessible (for now). Third, fires are easy to scale to whatever small and large fire we need. Burning things is also scalable in the sense that when we started this practice there didn’t seem to be any limit to what we could burn, it was a globally viable technology.
So to recap, we need a technique that is hot, low-tech, and scalable both in terms of meeting the energy requirement of a specific human and for all of humanity.
For direct solar concentration, neither attaining high temperatures nor scalability should pose a problem. Solar concentrators can go up to 5000 degrees and scalability is pretty straightforward, simply capture more light and there is about 172 petawatts of energy the earth receives from the sun, so we’re unlikely to run out of the resource any time soon. However, doing all this and keeping it simple and widely accessible is the challenging point.
Enter the Batant, the Solar Fire Demonstration Model of roughly 1 square meter of mirror providing 800 Watts.
Why build the puny demonstration model when you want more power!
People wanting more power is what got us into this mess in the first place, so a less ambitious approach may be required some times.
One thing we have to get clear right away is that what I am about to tell you may not actually work ... for you.
I made this construction guide to work for me, but you may be different, have different skills, different materials on hand, etc.
So, by building the small model you’ll be able to take this technique and rebuild it better, stronger than it was before. You will of course encounter problems in doing this and so it’s far better to meet and solve these problems with a structure you can look down to, rather than find out you’ve repeated a mistake a few hundred times.
Also, after your initial success you may want to start building more concentrators! Or train people to build more. Not only can you maybe make some coin but more importantly maybe make your whole extended community far more resilient. For this you may find it helpful to have on hand a demonstration model you can lug around.
But do not be worried, in the second series of articles I’ll go through the construction of a bigger version of this concentrator with 29 meter squared of mirror providing roughly 20 Kilowatts of thermal energy. Except for a the size difference and a few additions you’ll see that the basic method for building the 1 square meter model is exactly the same as the 29 square meter model, or anywhere in between. In the third installment I’ll go through the construction of a roughly 6 meter square oven, providing 3000 watts.
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