> IANAElectricalEngineer, but given that most high voltage transmission lines are DC anyway, surely it would be more efficient to not convert to AC outside of a town and then back to DC in every device.
It's complicated.
HVDC is used for long-haul transmission lines because it's more efficient and there isn't the need to do a lot of converting between voltages. But it has to be high voltage to work -- at lower voltages, the losses would be too large and you'd need to use much thicker cables.
When you're near consumers of electricity, though, you need to convert those voltages to something more reasonable that your customers can use (and not all of them use the same voltage -- you have to account for industrial uses too). It is far, far more efficient to shift voltages up and down with AC vs DC.
The current system of using HVDC for long-haul transmission, and converting to AC when you're near customers actually using the electricity, is pretty much the most efficient way to do it. Power companies and grid operators have a very strong economic incentive for maximizing this efficiency.
Biting the hand that feeds IT
