[lazide]

It’s really difficult to make solid state components that work at million+ volts.

It’s comparatively quite easy to make transformers that work at million+ volts.

So anytime you need to do any sort of voltage boosting, conversion, or the like, DC is going to be expensive and relatively fragile compared to AC.

If it’s just once, that’s not bad. If it’s often, that sucks.

[sangnoir]

> It’s really difficult to make solid state components that work at million+ volts.

You can split (or add up) the million volts as transmitted at either end so the individual components only work across a small fraction of the 1MV potential difference. This is how can get 12V from 1.5V batteries or use 1V LEDs from a 12V line.

[londons_explore]

That principle doesn't work as well at high voltages because generally it's a pain for a rack of equipment (such as solar panels) to have a potential between them and ground of 1 million volts.

[lazide]

Yup, high voltage has special challenges because even super tiny leakage currents (which are normal unless extreme precautions are taken) transmit significant power and cause extreme breakdowns rather quickly in most materials.

At very high (million+ volts) we’re talking even quantum tunneling effects producing enough current to cause material breakdowns. It’s pretty nuts.

It’s a big reason why glass and ceramic are so commonly used at those voltages as insulators - they are one of the few materials stable enough and electrically insulating enough to last long term.

Splitting things up like being discussed works when it’s possible to do so without creating even more leakage current paths, which is extremely difficult to do with sizable equipment in the million+ volt range. Folks eventually were able to do so, which is why HVDC eventually became a thing, but it is far from easy or cheap. My understanding is almost all HVDC lines run at lower voltages than their equivalent AC counterparts do as well, due to these technical limitations.

HVDC currently tends to be used for longer runs, where AC inductive losses exceed the equivalent capital costs challenges HVDC has. AC has significant inductive loss issues when run under ground or undersea.

At low voltages, those same leakage currents can’t transmit enough power to damage things or even cause measurable power losses, so don’t matter.

These effects starts being noticable in the > 1kv range, significant in the > 10kv range, quite problematic in the > 100kv range, and very difficult (maybe impossible using known material science in some scenarios) to deal with in the >= 1MV range.

Semiconductors have the added challenge that they often have noticeable leakage currents even in the low voltage ranges (even with specialized designs) and it makes it even harder.

[https://www.nationalgrid.com/sites/default/files/documents/1...]

Additionally, Arc faults in DC transmission infrastructure are extremely difficult to control, as unlike AC there is no zero-voltage crossing point (as there is no waveform, in general). So unlike AC, arcs are not likely to self extinguish, and require complete interruption of current flow. Which is actually a really hard problem to solve for several reasons at the power levels involved here.