So, there are actually companies looking at generating renewable energy WHILE making biochar, one of them that comes to mind is in Australia - although their website seems to be gone here is an article that still exists https://biochar-international.org/pacificpyrolysis/

Basically they were (are?) for 12~ years were powering up to a [200kw generator proccessing up to 300kg](from my previous notes about them) of material an hour of dry biomass. Stuff like collected lawn clipping and branches. You could also use waste like paper sludge, sugar cane refuse, waste water sludge (feces and toilet paper), wood waste from milling, used grain from breweries and distilleries, organic waste from industrial sources etc.

Go watch videos on making char cloth, it's a similar process. With char cloth you basically take a can that's mostly air tight, poke a hole in the top, place natural fibers inside like some scrap denim, replace the lid and heat the contents. The gas that gets cooked off is actually flammable and can be a fuel.

The process they were using required a rather large machine and ended up not only producing biochar but output more energy than went into the system by being much more controlled and capturing the gasses.

I suspect you could also manufacture a system that instead just uses concentrated solar power to process material, instead of needing to get up to 1000C though you'd only need to get around 450C (based on past studies for optimal temperature for producing biochar with optimal soil drainage properties), you could pull the gas off of that and pipe it some distance away to another facility doing the same a more traditional way, using the gas as the fuel source for it.