I'm trying to get a grip with how power works in this modpack. First question: How should I generate my first RF energy? Since documentation is often wrong or outdated, I ran a few tests.

First off, a Heat Generator from Mekanism will take 8 seconds to turn 1 charcoal into 800 Joules (Mekanism's unit of power; not to be confused with Buildcraft MJs). That's 100 J/s, or 40 J/t. Since 1 MJ is 25 Joules or 10 RF (and I confirmed those are the current values), that means a Heat Generator will turn a piece of charcoal into 320 RF at a rate of 4 RF/t.

By contrast, a TE Steam Dynamo turns charcoal into 24,000 RF at a rate of 80 RF/t. That means you get 75 times more power per charcoal from a Steam Dynamo, and generate it twenty times faster.

Turning to Ender IO, we have the Stirling Generator. 1 charcoal in it will generate 40,000 Joules over 80 seconds; that works out to 16,000 RF at a rate of 10 RF/t. That makes it only 2/3s as efficient as the Steam Dynamo, and a whole 1/8th as fast...but it's cheap, and doesn't require water, so it seems balanced. And it's still faster than the Heat Generator.

The BC Stirling Generator the same speed (10 RF/t), but it's significantly less efficient. 1 charcoal ends up being only 9537 RF. That's almost half what Ender IO gives.

Finally, a IC2 Generator produces 16,000 RF from a charcoal, putting it in line with the Ender IO Stirling Generator.

For reference, an AE system with two 1K drives and a crafting terminal consumes 26 RF/t. That means you would need just over 1/4 of a Steam Dynamo, just under 3 Stirling Engines, or seven Heat Generators. And you'd use a charcoal every 50 seconds with the Steam Dynamo; in the same time you'd have used 75 charcoal with the Heat Generators; 1.5 charcoal every second.

I guess the TL;DR here is that when starting off, just make a TE Steam Dynamo unless you're very short of copper, in which case make Ender IO Stirling Engines. (You need eight to match one Steam Dynamo, but at 1 iron, 1 redstone, and some stone and wood each, and no need for water, you still come out ahead). But whatever you do, steer clear of the Mekanism Heat Generator; it's a trap for the unwary that will turn your fuel into frustration.

(Discussion: Is the Heat Generator even working right? Is this a bug? The power output is ridiculously low; so low in fact that when I hooked it up to my AE system I spent about an hour fruitlessly trying to find the bug that was stopping the power from being transmitted. Then it hit me: The reason no power was being sent to the AE system was because there was no power to transmit.)

Edit: As /u/Omegatron9 pointed out, the Heat Generator isn't that bad if you use it right. Worst case, build a Heat Generator, use 100 charcoal to enrich 6 iron ingots in the infuser, then use those to build a wind turbine and cast the Heat Generator into a volcano. Or if at all possible, build a Stirling Engine or Steam Dynamo, and use a couple charcoal instead. :) Still, even if using only Mekanism, the Heat Generator era can be brief. But don't ever try and run your AE system off them like I was. ><

Edit2: New conclusion! Wind Generators are okay; Hydrogen Generators are better. Solar Generators aren't worth it, and the Heat Generator should never be used to burn fuel, but is okay-ish in passive mode if you make like, twenty of the damn things.