The Lightning Rod is a single block generator that can generate large bursts of energy during rain and in particular during thunderstorms. It needs an uninterrupted tower of Iron Fence blocks (from IC2) stacked on top of it, and there must be nothing between the top of the fence and the sky. The top of the rod should be over Y 128, and the longer the fence rod, the greater the chance (having at least 8 fence blocks and a top on or above Y 128 will have maximum chances).
Assuming an 8+ fence rod construction with a top on or above Y 128, lightning will strike the rod once every 12.8 seconds (every 256 ticks) during thunderstorms. During rain, there's a 10% chance of this happening, so on average every 128 seconds.
Each bolt will charge the Lightning Rod block with 50 000 000 EU that can be extracted at up to 512A of its tier. However, the block will void just over 1% of its stored energy on each tick, so unless the power is extracted rather quickly, it'll be lost. Care must be taken to maximize the number of amps that can be extracted without setting any cables on fire.
A full 16 slot battery buffer can accept up to 32A each. Using 5 battery buffers would hence extract 160A. This could extract something like ~15.9 M EU per bolt from a HV Lightning Rod.
64 -> 16 Amp Transfromers
There are high-amp transformers that can accept up to 64 A and output 16 A of its target tier. Using 5 of these would extract 320A. From a HV Lightning rod, this would extract ~22.5 M EU per bolt.
Molecular Transformer (and other machines capable of handling near unlimited energy intake)
A Molecular Transformer can accept all 512A of a Lightning Rod if placed adjacent to it. From a HV lightning rod, this should be able to accept ~27.5 M EU per bolt.