Who is talking about other kinds of machines?
And if so, the paradox is, very few "native" MJ machines actually require power for long periods of time.
There is the BC quarry. Strips 16 chunks to the bedrock for hardly anything. Even the quarry (I find) works so fast that the real hassle is just re-locating it to a new site. Or just running it on a single combustion engine to keep it slow.
Other than the quarry, there are no BC machines that are not going to complete their operation almost immediately.
In RC - how many tracks do you need to make? I made an always on machine that processed iron into steel, wood into sleeper beds. I had a myriad of RC machines all hooked up, Ran it for 5 minutes and made a stockpile of railway beds I - months later - still havn't burnt through.
Forestry has its multiblock farms. They require a whole 2MJ/t to keep on going.
Which leaves us with gencraft / extrabees genetics machines. These are the ONLY native MJ devices I know that are hungry for 50MJ/t - and that 50MJ/t is so that you can get the gene operation completed "now" rather than waiting 5 minutes.
So a network of native MJ machines is mostly always in standby mode. The power system doesn't meet the needs of its own native MJ consuming devices?
With BC, RC and Forestry - It doesn't matter what power system you might have started off considering - if you have built a solid fuel boiler, you have a forestry tree farm - you can't find enough coal to run a solid fuel boiler unless you want to make your game an exercise in operating and relocating as many quarries as possible. If you build a forestry tree farm, because you say, want to try biogass, you quickly go back go to a solid fuel boiler because biogass has the energy density of a burp now, and you need to do *something* with all that wood its making. Unless you are located in an oil biome, even an oil well can't keep a liquid boiler going on a server with activity, and ongoing perdition means a centralized powerplant will exhaust it, powering mostly nothing, because (again) there are no actual buildcraft machines that actually require ongoing power, except for the quarry, and even the quarry at max size finishes in just a few hours and needs to be moved.