Insignificant: EEs can lower the losses by increasing the line voltage [0], at the expense of other challenges (namely taller pylons). It's about 5% over the length of the line.

Consider the other losses:

- Thermal (gas turbine) cycle: 40-60% lost (the big one) - Transformer loss: 1-2%. You pay this every time you step up/down, so it adds up. - Capacitive coupling: I dunno, but length dependent. It has to be about the same as Ohmic losses since once it's large you switch to DC lines (and take an Ohmic loss hit from lower V) - You're house's power factor (which, unlike industrial users, you're not charged for).

[0] in the sixties very large V lines were introduced (0.75 - 1.0 MV ??). They work, but it's not considered worthwhile.