PowerCrops adds crops which generate power during growth. The crops grow like wheat. The crops only drop a single seed, and only when they're fully grown. Breaking a partially-grown crop drops nothing.
To craft a PowerCrop, first put 8 redstone around a wheat seed on a crafting table. This gives you Unrealized Power Seeds.
To realize Power Seeds, drop them on top of a generator, capacitor, etc. Each seed takes 10000 Forge Units (configurable as of 1.1.3+) to realize.
Once realized, simply plant the seed on farmland and it'll make power (configurable) each growth tick! But it probably isn't enough to power a power farm...
Note: You cannot craft/realize PowerCrops with EnderIO. This is for the same reason ActuallyAdditions Phantom Energyfaces don't work correctly with EnderIO. However, once crafted/realized, they do work normally with EnderIO.