Bloody batteries and solar panels
Other technologies can make efficient use of copper, but batteries and solar panels cannot.
The reason is voltage: High voltage equipment only needs a small amount of current to transfer a high power, lower voltage systems need more current, and power losses due to resistive heating in the copper wire go as the square of current (I^2 R).
Lithium battery cells only produce about 4 volts, and solar cells only produce 1 volt. To have more volts, you need more cells in series i.e. more points-of-failure in series, so high-voltage batteries and high-voltage solar panels are unreliable, because one failure in a string of 1000 series-connected cells will disable the whole string. So batteries and solar cells tend to operate at low voltages and high currents, i.e. they need lots and lots of copper.
If I want to make a 10kW solar panel, I could either use 1000 cells in series at 10A, or 100 cells in series at 100A. The latter is 10 times more reliable, by some reliability metric. But it requires 10 times more copper to push 10kW around at 100A with the same losses than it does to push the same 10kW around 10A.
So either I go for low-reliability, or use more copper to reduce the resistance.
Motors, transformers and generators on the other hand, don't have electrochemical or photovoltaic cells in series, they just have longer coils of wire to generate higher voltages. It's easy to make a high voltage generator or transformer, we just need good insulation, and that insulation doesn't really degrade much with time, provided it is kept at a sensible temperature. The reliability of motors and transformers scales much better with voltage than it does for batteries and solar cells.
Batteries also have the problem of balancing of course. so the more cells in series, the more that small variations in cell capacity will reduce the overall capacity: Because the whole series string takes the same current, and if any one cell goes below 2V or above 4.4V, the whole pack is in serious trouble.
The next problem I can see with copper, is low-voltage (240V) local power distribution. Again, losses go as I^2 R, and the cable under my road is rated for 400 Amps. One electric shower is 40A, one EV charger is 40A, and one heat pump is 40A. But my street has 30 houses, so the underground cable regularly overheats and fails. (and while doing so, it is incredibly inefficient)
As the cable is overloaded, it heats up, and the power lost in the cable goes with the square of current as voltage is lost across the cable resistance. So when I turn my shower on, the lights dim slightly as the voltage drops.
If I bothered to, I could even measure this voltage drop and calculate the resistance (and the power loss) in the local mains distribution. But on average it is around 15% just for the last leg between the 11kV-240V substation and your house.
The kicker is that any electronic DC-DC load such as a computer, battery charger, or "inverter" appliance will automatically draw more current as the input voltage drops. This leads to exploding underground cables because as the voltage drops due to overload, the DC-DC regulator tries to keep a constant power, which leads to more current, and remember losses go as I^2 R. Even R is not constant, it goes up with temperature.
So TLDR, expect power cuts on Monday and Tuesday as more people fire up their air con units. Grid transformers may overheat. We may also run out of cooling water for some power stations too.
</doom>
