Why all Hatches produce coal?

[Ambaire]

Sage hatches are useless. If I need extra power, I'll put some dupes on hamster wheels for 1kcal a cycle.

Sage hatches need a redesign. That organic -> algae might be interesting. Or even.. rock to algae ^-^

[avc15]

smooth hatches useless? x.x

Sage hatches I'd say are more problematic, as you really can't manufacture enough dirt to feed many of them without your build requiring dupes to dig dirt. (digging incurs a 50% mass loss, did you know)

So maybe if you aren't using your dirt at all, as long as your base is composting something (sieve or outhouse byproducts) it might be worth having 4 or so sage hatches. But no good for large scale coal production