There's 2 easy methods that I know of.
1. Cheap: Run some RP tubes at the bottom of the generators. The coal will automatically be put in those generators which need more fuel. If you have too much coal, you can put an overflow barrel after a restriction tube.
2. A bit more expensive: Use a router, this is the way to go, imo. You can make it super compact and make a block of say 5x5x5 generators and make the router fill all of them, by setting the router to fill at the bottom. Use some upgrades to make it faster.
There are other methods, but these are the methods I use or will be using.
Edit: ninja'd by 4 people :/
1. Cheap: Run some RP tubes at the bottom of the generators. The coal will automatically be put in those generators which need more fuel. If you have too much coal, you can put an overflow barrel after a restriction tube.
2. A bit more expensive: Use a router, this is the way to go, imo. You can make it super compact and make a block of say 5x5x5 generators and make the router fill all of them, by setting the router to fill at the bottom. Use some upgrades to make it faster.
There are other methods, but these are the methods I use or will be using.
Edit: ninja'd by 4 people :/