I have a video on a CC Fir Tree farm:
I'm in the middle of expanding my operations, and fir tree saplings now apparently work in a fermenter so it gets even better.
Before I started on my expansion, I was able to outpace two 36-HP boilers heating up with the charcoal it was outputting (and it is so ridiculously cheap to do). At the end of it all, I'm estimating that with 4 turtles, I will be able to support 6 36-HP boilers on charcoal alone -- with another 4 on bio.
(And yes, I know the setup is sub-optimal -- I could've used sawmills and burned wood instead of charcoal. If I was going for optimal, I wouldn't have made a bunch of coke ovens either)