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Solar Biochar at Home

An idea: solar biochar at home

A while back I read about biochar. I think it was not-too-long after I attended HOPE 2020, and it felt like there were a few ideas floating around that pointed towards diverse, local approaches to climate change (solarpunk feels associated with this). I think it was also shortly before or after I read this article in Scientific American, plus countless sources/articles looking at how adding carbon to soil can be a good method of carbon sequestration, while also improving crop yields and reducing disease in plants (which means less fertilizer and pesticide).

Is this worthwhile?

Now, my understanding is that we’re past the point where everyone making small changes (like recycling better, or turning off lights) is going to make much difference in what happens over the next 30-50 years. That might be wrong, but even if it’s true, I think finding ways to let individuals and small organizations make positive, real environmental impacts is worthwhile for a couple of reasons:

So, probably not actually a useful thing, but the thought is roughly this: can you make biochar (targeted at amending soil, not for use as fuel) at home, safely, with minimal emissions (most methods seem to produce lots of smoke), and without a lot of energy input (minimal fuel/electricity to run the process). I know there are solar grills, so could the sun supply all the heat required to produce biochar?

Is this feasible?

Of course, someone has to be doing this already, right? I looked around a bit, and while I’m not the best at googling I really don’t think there’s evidence of people doing this. I did find this small-scale biochar kiln at, which seems like good option, but isn’t something I’d put in my backyard. Can we do better?

Well, first, how reasonable is the idea of using solar power? The kiln described at sounds like it generally runs at about 475°C, though elsewhere on the website they list 300-550°C as optimal for soil biochar (Wikipedia agrees, roughly). I know a CSP plant can heat salt to several thousand degrees C, but those tend to be bigger than my backyard. Let’s look at a few solar grills.

All of the above use reflection (as opposed to, say, a big lens), and it seems like the 1.5m diameter parabola is the only one that could run anything at the temperature we want, but that implies to me we don’t need a massive solar array, a few square meters might be enough.

Seems like this might be something I could make.

Principles/goals & notes

Some goals to keep in mind:

And a few additional thoughts on construction:

Anyway, I think it’s an interesting thing to think about. I doubt I’ll try to build one, but you never know.

Last modified: 2022-07-31 21:39:49 -0400 -0400 • For full version history, see github
Tags: idea climate-change memetic-approaches backyard-engineering