[rubylark]

In this context, they are speaking of electrical efficiency, i.e. the amount of power lost to system impedance during transmission, not some abstract concept like effectivity. The efficiency of a transmission line is expressed as a ratio of power received at one end of the line over the power sent at the other.[1]

[1] https://en.m.wikipedia.org/wiki/Electrical_efficiency

[AlexandrB]

The cost still matters because if the losses cost less to replace than the superconducting material costs to install, no one will use it. So parents point still stands. It doesn't matter how high the electrical efficiency is, what matters is cost efficiency.

[ABCLAW]

This is only true to a point. Evaluating incremental cost benefits on the basis of the delta of energy loss along specific lines ignores the state change that occurs when main trunk elements of the grid become lossless and energy generation and storage solutions can be deployed in a near-location agnostic manner.

As with all toy models being applied to the real world, there are important factors to model in that aren't immediately obvious.

[kerkeslager]

Who's "they"? If anyone is talking about electrical efficiency they shouldn't be because cost efficiency is what matters for a transmission line. Transmission maintainers have no reason to care if a wire transmits with 100% electrical efficiency if it's cheaper to lose some electricity than pay for the perfectly electrically-efficient wire.