"If the conversion losses were as high as 10%, why did anyone bother using HVDC for e.g. a mere 85 km stretch in the Trans Bay Cable?" 1. Because AC also has t

"If the conversion losses were as high as 10%, why did anyone bother using HVDC for e.g. a mere 85 km stretch in the Trans Bay Cable?" 1. Because AC also has transformation losses (2-3% per transformer. You need at least three (medium voltage, high voltage, medium voltage, low (house) voltage). 2. The answer is in the name, ain't it? It's underwater. AC coupling in a dielectric increases losses very significantly. The longest underwater line AC line in the world is only 135 km, in Greece, for this very reason. The Greeks probably couldn't afford the capital to instal a DC line instead and settled for higher losses. You pay for more expensive HVDC lines for three major purposes: 1. Underwater cables - see dielectric loss 2. Cheating on the synchronization 3. Long AC lines. This has many reasons: - Take the speed of light, and divide it by 200Hz (50Hz * 4) = 300 000 km/s /200Hz = 1500 km. That's as long as an AC line can be before you start to deal with impedance reflections. - Lowering losses. AC was famously adopted to lower ohmic losses by adopting high V. But, AC lines are coupled to ground (they're a massive capacitor to ground), so at a certain length you have to consider AC coupling losses that don't exist in DC "But even if they were 10%, that’s a multiplier not an adder so it makes a difference of 10% to final energy prices, it wouldn’t break anything (though it might shift the minima to batteries, as those are also cheap and getting cheaper)." I love how eagerly ppl dismiss 10% loss. I'm aware its a multiplicative - it's also an 11% increase in the amount of panels needed (1/0.9 = 1.1). You have to think of your losses in the inverse - how much added land you have to cover (and loose CO2 sinks to photosynthesis) The things that are "cheap and getting cheaper" are things at a certain scale. Everyone loves things getting cheaper at scale, but forget that things also get more expensive at scale. Batteries don't get cheaper once you start running against the bounds of how much electrode material is available. "I think you’re overestimating how much the losses matter. You only lose half your power from 20,000 km, adding an extra 10,000 km from wiggling around a bit takes you down to 34% of original generation" so from you're original 50%, to 34%, a loss of 34/50, implying an increase in land covered of 50/34, or about 50% more land you have to cover. 50% more land if I accept your hand waving argument that you'll only need an extra 10Mm to get from point to point. "“I am not qualified to discuss them” absolutely is not the same thing as dismissing them." "I'm not qualified to discuss them" absolutely is used, de facto, as a license to ignore. It maybe the most common human rationalization. "But my main point is more of we don’t need to tile the Sahara (or any single particular place), so it shouldn’t even come up in the first place." You have to tile something. The Sahara makes most sense lacking vegetation. But sure, tile Ireland and see how much the local appreciate it.