Disclaimer: I know this isn't the first thread about the IC2E biogas production chain (e.g. here and here ) and I fully understand that using an electric heater on the fermenter won't provide a net surplus of energy. That's not what I think the real problem is.
In real life, nuclear power can be characterized as having very high capital (infrastructure) cost, but very low running (fuel) cost. By comparison bio-fuels (e.g. corn ethanol) can be characterized as requiring a very significant amount of input material, and the debate regarding bio-fuel sustainability centers on just how much land will be required for farming.
I had hoped IC2 would follow that dichotomy. Fission reactors in IC2 already require a lot of infrastructure (pressure vessels, containment vessels, reactor components, steam turbines - it's quite a lot!), and I kinda expected that meaningful biogas production would require large fields of automated farms but relatively few processing machines. Instead, IC2 Biogas production actually requires very little farming, but quite a lot of machines.
I set up a single Macerator (without overclockers) to process a carrot farm, feeding into a single Bottling Plant to produce Biomass. I then set up a small array of 4 Fermenters, heated by Liquid Fuel Fireboxes. I found that I had a large excess of biomass, so I added more Fermenters. I still had excess biomass, so I added even more Fermenters. And I still had excess biomass. That's when I decided to crunch the numbers:
Macerator: produces 1 biochaff every 300 ticks = 0.00333 chaff/t
Bottling Plant: produces 1000mB biomass per chaff = 0.0033 * 1000 = 3.33mB/t
Fermenter: consumes 10mB biomass per operation. At 32HU/t (liquid fuel firebox), it took roughly 12 seconds per operation (~240 ticks) = 10 / 240 = 0.041667mB/t
Number of fermenters required to use all the biomass = 3.33 / 0.041667 = 80!
Is my math wrong somewhere? Please let me know if I'm missing something! Because this would mean that: One single macerator will provide enough biochaff to run 80 Fermenters! After accounting for biogas spent on heat, that will provide fuel for 53 Semifluid Generators, for a massive ~848EU/t. That's a lot of machines, and the materials would cost ~1000 iron, ~500 copper, ~1000 rubber, ~1500 tin.
I'm not saying that infinitely renewable 850EU/t shouldn't take a lot of resources - that's fair. My concerns are:
1) Providing the macerator with enough carrots to run constantly only requires only 8 carrots every 15 seconds. If my math is right, 107 vanilla carrot crops should be able to keep up. That's not a big farm IMO. Furthermore, a single carrot will provide ~32k EU each, about 4 times the EU from a piece of coal. This seems overpowered.
2) A complete setup would have a tiny little farm connected to >200 machines. This seems imbalanced.
3) It would be fun if biogas production required fewer machines but lots more plants to provide contrast against existing options like fission reactors.
For these reasons it might make sense to tweak the Fermenter to consume much more biomass per operation. Say, from 10mB to 100mB. With just this change, the effective EU/t from each Fermenter would stay the same, but you'd need 10x as many plants to feed it. You would need one Macerator for every 8 Fermenters, producing 80EU/t (net). Each carrot would produce about 3000EU. That's still a fair bit of energy, but not huge.
Or better yet (IMO), why not increase both biomass consumed and biogas produced? Let's say biomass from 10mB to 160mB and biogas from 200mB to 240mB. This increases the effective EU/t from the Fermenter, but electric heaters would still not be viable. Each carrot would yield about 2825EU, and you wouldn't need as many machines - just 1 Macerator for every 5 Fermenters. As an added benefit, each Fermenter would be able to fuel exactly one Semifluid Generator, so construction designs could be quite compact. You'd need just 18 machines to handle to handle the production of 107 blocks of farmland, producing about 75EU/t (net). Much more reasonable.
Thanks for reading my wall of text! Thoughts?
tl:dr; biogas production doesn't require enough plants. Fermenters should consume more biomass per operation.