Do Batboxes have a Loss themselfs?
If no, just hook up the Windmills directly to batboxes and have a Ton of batboxes down to your base.
You are forgetting the loss in wire going down. Copper can only go 4 before you need another bat box and while glass cable can go as far as tin and handle 512 eu, it takes lots of diamonds to make enough. this makes wind gens near useless for early bases unless your base is way up above the clouds.