Forestry farms and harvesters will consume a lot of energy if you let them. They are cycle based. Everytime they have enough energy for one cycle, they will execute it, up to 1 cycle per tick. In the config files you can set how many blocks are checked during each cycle (performance.planter and performance.harvester). If it finds something to act on (an empty space to plant in, a finished crop to harvest), then it will stop its current cycle there and pay a one-time energy cost to act on the block (trees have several blocks that need to be paid for individually), then wait for the next cycle to be paid for to resume scanning.
Now, I don't know how much energy a cycle or an action costs, but with harvesters checking up to 200 blocks per cycle on default, up to 1 cycle every tick, you can easily see that even with a 21x21 area to scan there's absolutely no reason to let the farm run that fast. Things need to grow first before they can be harvested, after all, and growing takes time! So in the default setting, giving each farm or harvester around 1 MJ/t yields acceptable enough results.
Note that resource output scales a bit with power input. If the farm harvests grown crops/trees/whatever faster, and replants harvested spaces faster, then new things will grow faster. Thus you will get more stuff in the same time if you give the farm more power. This is especially true for tree farms, where the canopy of grown trees inhibits the light level available for nearby saplings. But this scaling is not proportional; you won't get a doubling of output for a doubling of input, and the higher you go the smaller this effect becomes.
There is also a setting in the difficulty subconfigs that lets you adjust the energy cost of cycles and actions for planters and harvesters, but last I checked it was not working properly. Myself, I just reduce the number of blocks per cycle by half in order to increase the overall energy need.
Now, I don't know how much energy a cycle or an action costs, but with harvesters checking up to 200 blocks per cycle on default, up to 1 cycle every tick, you can easily see that even with a 21x21 area to scan there's absolutely no reason to let the farm run that fast. Things need to grow first before they can be harvested, after all, and growing takes time! So in the default setting, giving each farm or harvester around 1 MJ/t yields acceptable enough results.
Note that resource output scales a bit with power input. If the farm harvests grown crops/trees/whatever faster, and replants harvested spaces faster, then new things will grow faster. Thus you will get more stuff in the same time if you give the farm more power. This is especially true for tree farms, where the canopy of grown trees inhibits the light level available for nearby saplings. But this scaling is not proportional; you won't get a doubling of output for a doubling of input, and the higher you go the smaller this effect becomes.
There is also a setting in the difficulty subconfigs that lets you adjust the energy cost of cycles and actions for planters and harvesters, but last I checked it was not working properly. Myself, I just reduce the number of blocks per cycle by half in order to increase the overall energy need.
