Hey biochar enthusiasts. I thought I'd provide a link to Primitive Technology's new video on a "Reusable charcoal mound":
This method is obviously not ideal for getting a homogenous batch of char. As you can see, there are a bunch of branches that haven't been chared all the way through. But, if you're like me and not as concerned with that sort of thing and just looking to build a biochar kiln completely free, then I would say that this is definitely worth a shot
I hope this finds someone, like me, who has been looking for a free earthen-based design for a biochar kiln.