But if they are spraying herbicides... that means something grows there.
Do you see how that doesn't make any sense at all? If nothing grows there... why do they have to "spray for weeds"?
Because weeds are plants. If weeds are growing there... THEN PLANTS GROW THERE. Weeds are only weeds because we don't want them growing in a spot.
And apparently, the OP doesn't know that electricity always reduces power over distance. Being generated by solar cells, coal furnaces, or nuclear fission doesn't change that. 40% is normal. It can be reduced by materials and distance. But losing power is expected.