3 ms·

"Which is going to be a fixed amount regardless of distance" Sure, but knock off another 10% "I would expect HVDC to be a dead end already if it made a differ

"Which is going to be a fixed amount regardless of distance" Sure, but knock off another 10% "I would expect HVDC to be a dead end already if it made a difference to my conclusion." I didn't get that. Could you re-phrase? "Surely a web is the best topology? " My point you're underestimating the line length since you cannot connect generation to consumption with a straight line. Also, the hub-spoke or a web network would need the connections to be much larger than needed for that city (since the city would also need to transmit to it's neighbors) "While true, I’m not even going to try to play at global geopolitics; [..] worsen the performance of my opinion and give your criticism the best possible chance." You cannot dismiss cultural concerns. Look what happened in Kabul last week!

ben_w 5y ago
> Sure, but knock off another 10% > "I would expect HVDC to be a dead end already if it made a difference to my conclusion." > I didn't get that. Could you re-phrase? 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? 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). > My point you're underestimating the line length since you cannot connect generation to consumption with a straight line. Also, the hub-spoke or a web network would need the connections to be much larger than needed for that city (since the city would also need to transmit to it's neighbors) 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, and even then webs usually have high-capacity connections between important locations and lower-capacity links from the high capacity nodes to the low use nodes. Is anywhere in the US more than about 2400 km from the coast? Because 2400 km is a multiplicative loss of 0.918 compared to whatever losses you get from a trans-oceanic link to wherever (0.77 from Algeria to DC, according to distance from Wolfram Alpha, likewise 0.66 from Queensland to San Francisco). And the USA already has (several) grids, so you’d probably just want to link any global HVDC connection like this into each grid, rather than to each city. > You cannot dismiss cultural concerns. Look what happened in Kabul last week! “I am not qualified to discuss them” absolutely is not the same thing as dismissing them. 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.
- sasfasaf 5y ago
  "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.

ben_w 5y ago

> Sure, but knock off another 10% > "I would expect HVDC to be a dead end already if it made a difference to my conclusion." > I didn't get that. Could you re-phrase? 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? 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). > My point you're underestimating the line length since you cannot connect generation to consumption with a straight line. Also, the hub-spoke or a web network would need the connections to be much larger than needed for that city (since the city would also need to transmit to it's neighbors) 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, and even then webs usually have high-capacity connections between important locations and lower-capacity links from the high capacity nodes to the low use nodes. Is anywhere in the US more than about 2400 km from the coast? Because 2400 km is a multiplicative loss of 0.918 compared to whatever losses you get from a trans-oceanic link to wherever (0.77 from Algeria to DC, according to distance from Wolfram Alpha, likewise 0.66 from Queensland to San Francisco). And the USA already has (several) grids, so you’d probably just want to link any global HVDC connection like this into each grid, rather than to each city. > You cannot dismiss cultural concerns. Look what happened in Kabul last week! “I am not qualified to discuss them” absolutely is not the same thing as dismissing them. 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.

sasfasaf 5y ago
"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.