3 ms·

Thanks! So, I had interpreted your previous comment as saying that using the average miles driven per day is a bad way to estimate the total energy (per day) ne

by drdeca 4y ago

Thanks! So, I had interpreted your previous comment as saying that using the average miles driven per day is a bad way to estimate the total energy (per day) needed. But I guess you instead meant, not that the problem from averaging came from averaging miles over people and using that to get energy use per day, but rather averaging energy use per day over both people and days, when max power is also important, and is perhaps currently the limiting factor?

robomartin 4y ago
> max power is also important, and is perhaps currently the limiting factor? Precisely! That's what I learned after spending time creating a reasonably granular simulation. Everyone talks about energy. This allows for hand-wavy arguments that end-up being false. I am not claiming that people do this intentionally or maliciously, BTW. Until someone takes the time to truly understand the realities of widely deployed EV's, it is impossible for them to understand what the problem looks like at scale. The hand-wavy statement usually takes the form of "just charge at night/work/off-peak", etc. What is not immediately obvious in this way of thinking is that this isn't at all a solution. It's hard to think in terms of aggregate demand. No matter how you charge, slow, fast, distributed across the day/week, etc. At the end of the day, what you discover is that there's an unavoidable steady-state power generation and delivery requirement. Energy is power spread over time. Energy is great, but it does not address the needs this second, or the next. That's power. And that's the issue. Not sure I provided this link before. I ended-up confirming my estimate many years after I came to this conclusion when someone finally asked Elon Musk the question. Here's his answer: https://www.youtube.com/watch?v=TcI6FaaDp8g&t=3510s https://www.youtube.com/watch?v=TcI6FaaDp8g&t=3510s
robomartin 4y ago
> I had interpreted your previous comment as saying that using the average miles driven per day is a bad way to estimate the total energy (per day) needed. I should address this separately. The average isn't a good metric because it applies what is often a bad indicator of central tendency to the entire population. In addition to this, what matters in the case of electric vehicles isn't how many miles someone drives per day but rather how they charge. Here's an extreme exaggeration to illustrate the point: Let's assume three groups, each with a million cars. Let's also assume they all drive exactly the same miles, whatever that might be. The final assumption is that you can fully recharge the energy used in a day by slow-charging in 12 hours. Let's define rapid charging as taking two hours. In other words, it's three times faster than slow charge. Here's charging behavior for each group. Every day: Group 1: All 1 million cars plug in to slow charge at 1/12 the rate between 6 PM and 6 AM Group 2: 25% of the cars plug in to rapid charge every hour, starting at 6 PM Group 3: All 1 million cars plug in to rapid-charge at 6 PM All three groups require the same energy to recharge their cars. They drive the same distance. We'll call that 1 million units of energy. Trying to keep it simple, if delivered in one hour, that's 1 million units of power. Let's call Group 1 our baseline. They use 1 million units of energy and require 1/12 the power to deliver that energy over 12 hours. We can service this million car cohort with a power system that delivers 1/12 the power for 12 hours. Group 2 is interesting. Here's the number of cars charging per hour over the four hour period. 6:00 PM 7:00 PM 8:00 PM 9:00 PM 10:00 PM 250K 250K 250K 250K 250K 250K 250K 250K -------------------------------------------- 250K 500K 500K 500K 250K The first subgroup plugs in 250K cars and is on there for two hours. An hour after that subgroup plugs-in, the next 250K cars plug in for two hours, and so on. The last line represents the number of total cars plugged in for rapid charging per hour. The first hour we only need 125K units of power, which is 1/8 of a million. More than the Group 1 case. However, due to the overlap, we can't supply this group with a power plant delivering 1/8 the power, we need 250K. The last case is one where 100% of the cars plug in to charge simultaneously and for two hours. The 1 million in energy is delivered in two hours, which means we need a power plant capable of delivering 500K units of power for two hours. Imagine these groups exist in the same city. We have to build a new power plant to support their charging needs. What metric do we use? Average miles driven? That's pretty much irrelevant. This might give us a (likely bad) idea of how long they will have to charge. It will not tell us how big of a power plant we need to build. How about we build it to Group 1 requirements? 1/12 power? Well, that means we'll have blackouts when the other groups plug in. That's not good. OK, Group 3 then? Same problem. Good for that group, yet, we can't supply the aggregate charging needs. Ah, the average of the power required by all three groups. Once again, the average is useless. The average of 1/12, 1/4 and 1/2 is only 28% of the power required to service all three groups. We need to build a plant that can deliver 833K units of power. I hope this oversimplified example illustrates why speaking of energy is pretty much pointless. The limiting factor is the ability to deliver power. And that power requirement, in the simplest of cases, is dominated the peak of the aggregated charging behavior. In fact, the real calculation is far more complex than that. It's what I call the "Florida/California Evacuation Scenario". How do we cover the case of everyone --and I do mean everyone-- needing to rapid-charge right now? A hurricane, flood, fire, etc. is coming. You charge right now, as fast as possible or tens of thousands of people could die. The answer is obvious: A widely distributed storage network "at the edge", much like gasoline stations at nearly every highway exit store gasoline. However, that answer can't be taken as hand-wavy magic that instantly solves the problem. Ignoring the fact that this infrastructure is nearly impossible to build today, that stored energy has to be delivered at a reasonable rate (power) over an equally reasonable period of time. It can't take three years to charge massive batteries at 200,000 charging stations nationwide. I'd say, maybe a few months, two to four? This is a power requirement over and above that required to service normal daily charging. This isn't a simple matter at all. Places like Los Angeles are going to have absolutely insane power deliver requirements. Small towns will be more manageable. The key point --and what I have been saying-- is that we need to stop lying to ourselves with false/useless metrics. It's about power. One can't just magically waive this requirement as Gavin Newsom has here in CA. No more new IC cars in 2030 could presumably mean two million new EV's per year sold after that date. That is not a trivial number of cars. Not to mention we probably going to have lots more EV's already by then. We have announced no new power generation and delivery projects at all. We have dumped (burned, really) over a hundred billion dollars into a high speed rail nobody is going to use (if it is ever completed). If we were serious about EV's we would have dumped that money into new power generation and distribution projects instead. The reason we are not is that the public discussions surrounding EV's are filled with fantasies and hand-wave-itis, which means the public isn't informed and there's no way to gain votes in support of new power generation projects. This is why I say we need to start to discuss the truth, rather than the fantasies we are being sold.
- Schroedingersat 4y ago
  So your entire argument is that the laws of physics need to get out of the way And you need to take several years of income from everyone in the country because you wanna fill up your car whenever you want without thinking about anything even an hour into the future?
  - robomartin 4y ago
    Please stop. I am tired of your insults and misinterpretation.
Schroedingersat 4y ago
Solving the max power problem by duplicating every EV battery so there is one stationary one and one in the car is vastly cheaper and actually physically possible. The net average power required in any given week is well under 600GW even assuming average efficiency is around 750Wh/km (1/4th of a tesla). But that said, fewer and smaller cars is a much better solution. Most car trips are unnecessary if you have reasonable infrastructure and don't make cornerstores illegal. 25mph LEVs and NEVs can serve most of the rest and can be powered purely on the sunlight that lands directly on them where 90% of people live. Trucking is a major issue if you don't want to spend those trillions on functioning rail instead, but no trucking company is going to pay $1/kWh just so there can be terawatts of idling nuclear capacity. They'd just build their own renewable+battery depots at $0.2/kWh.

by drdeca 4y ago

robomartin 4y ago

> max power is also important, and is perhaps currently the limiting factor? Precisely! That's what I learned after spending time creating a reasonably granular simulation. Everyone talks about energy. This allows for hand-wavy arguments that end-up being false. I am not claiming that people do this intentionally or maliciously, BTW. Until someone takes the time to truly understand the realities of widely deployed EV's, it is impossible for them to understand what the problem looks like at scale. The hand-wavy statement usually takes the form of "just charge at night/work/off-peak", etc. What is not immediately obvious in this way of thinking is that this isn't at all a solution. It's hard to think in terms of aggregate demand. No matter how you charge, slow, fast, distributed across the day/week, etc. At the end of the day, what you discover is that there's an unavoidable steady-state power generation and delivery requirement. Energy is power spread over time. Energy is great, but it does not address the needs this second, or the next. That's power. And that's the issue. Not sure I provided this link before. I ended-up confirming my estimate many years after I came to this conclusion when someone finally asked Elon Musk the question. Here's his answer: https://www.youtube.com/watch?v=TcI6FaaDp8g&t=3510s https://www.youtube.com/watch?v=TcI6FaaDp8g&t=3510s

robomartin 4y ago

> I had interpreted your previous comment as saying that using the average miles driven per day is a bad way to estimate the total energy (per day) needed. I should address this separately. The average isn't a good metric because it applies what is often a bad indicator of central tendency to the entire population. In addition to this, what matters in the case of electric vehicles isn't how many miles someone drives per day but rather how they charge. Here's an extreme exaggeration to illustrate the point: Let's assume three groups, each with a million cars. Let's also assume they all drive exactly the same miles, whatever that might be. The final assumption is that you can fully recharge the energy used in a day by slow-charging in 12 hours. Let's define rapid charging as taking two hours. In other words, it's three times faster than slow charge. Here's charging behavior for each group. Every day: Group 1: All 1 million cars plug in to slow charge at 1/12 the rate between 6 PM and 6 AM Group 2: 25% of the cars plug in to rapid charge every hour, starting at 6 PM Group 3: All 1 million cars plug in to rapid-charge at 6 PM All three groups require the same energy to recharge their cars. They drive the same distance. We'll call that 1 million units of energy. Trying to keep it simple, if delivered in one hour, that's 1 million units of power. Let's call Group 1 our baseline. They use 1 million units of energy and require 1/12 the power to deliver that energy over 12 hours. We can service this million car cohort with a power system that delivers 1/12 the power for 12 hours. Group 2 is interesting. Here's the number of cars charging per hour over the four hour period. 6:00 PM 7:00 PM 8:00 PM 9:00 PM 10:00 PM 250K 250K 250K 250K 250K 250K 250K 250K -------------------------------------------- 250K 500K 500K 500K 250K The first subgroup plugs in 250K cars and is on there for two hours. An hour after that subgroup plugs-in, the next 250K cars plug in for two hours, and so on. The last line represents the number of total cars plugged in for rapid charging per hour. The first hour we only need 125K units of power, which is 1/8 of a million. More than the Group 1 case. However, due to the overlap, we can't supply this group with a power plant delivering 1/8 the power, we need 250K. The last case is one where 100% of the cars plug in to charge simultaneously and for two hours. The 1 million in energy is delivered in two hours, which means we need a power plant capable of delivering 500K units of power for two hours. Imagine these groups exist in the same city. We have to build a new power plant to support their charging needs. What metric do we use? Average miles driven? That's pretty much irrelevant. This might give us a (likely bad) idea of how long they will have to charge. It will not tell us how big of a power plant we need to build. How about we build it to Group 1 requirements? 1/12 power? Well, that means we'll have blackouts when the other groups plug in. That's not good. OK, Group 3 then? Same problem. Good for that group, yet, we can't supply the aggregate charging needs. Ah, the average of the power required by all three groups. Once again, the average is useless. The average of 1/12, 1/4 and 1/2 is only 28% of the power required to service all three groups. We need to build a plant that can deliver 833K units of power. I hope this oversimplified example illustrates why speaking of energy is pretty much pointless. The limiting factor is the ability to deliver power. And that power requirement, in the simplest of cases, is dominated the peak of the aggregated charging behavior. In fact, the real calculation is far more complex than that. It's what I call the "Florida/California Evacuation Scenario". How do we cover the case of everyone --and I do mean everyone-- needing to rapid-charge right now? A hurricane, flood, fire, etc. is coming. You charge right now, as fast as possible or tens of thousands of people could die. The answer is obvious: A widely distributed storage network "at the edge", much like gasoline stations at nearly every highway exit store gasoline. However, that answer can't be taken as hand-wavy magic that instantly solves the problem. Ignoring the fact that this infrastructure is nearly impossible to build today, that stored energy has to be delivered at a reasonable rate (power) over an equally reasonable period of time. It can't take three years to charge massive batteries at 200,000 charging stations nationwide. I'd say, maybe a few months, two to four? This is a power requirement over and above that required to service normal daily charging. This isn't a simple matter at all. Places like Los Angeles are going to have absolutely insane power deliver requirements. Small towns will be more manageable. The key point --and what I have been saying-- is that we need to stop lying to ourselves with false/useless metrics. It's about power. One can't just magically waive this requirement as Gavin Newsom has here in CA. No more new IC cars in 2030 could presumably mean two million new EV's per year sold after that date. That is not a trivial number of cars. Not to mention we probably going to have lots more EV's already by then. We have announced no new power generation and delivery projects at all. We have dumped (burned, really) over a hundred billion dollars into a high speed rail nobody is going to use (if it is ever completed). If we were serious about EV's we would have dumped that money into new power generation and distribution projects instead. The reason we are not is that the public discussions surrounding EV's are filled with fantasies and hand-wave-itis, which means the public isn't informed and there's no way to gain votes in support of new power generation projects. This is why I say we need to start to discuss the truth, rather than the fantasies we are being sold.

Schroedingersat 4y ago
So your entire argument is that the laws of physics need to get out of the way And you need to take several years of income from everyone in the country because you wanna fill up your car whenever you want without thinking about anything even an hour into the future?
- robomartin 4y ago
  Please stop. I am tired of your insults and misinterpretation.

Schroedingersat 4y ago

Solving the max power problem by duplicating every EV battery so there is one stationary one and one in the car is vastly cheaper and actually physically possible. The net average power required in any given week is well under 600GW even assuming average efficiency is around 750Wh/km (1/4th of a tesla). But that said, fewer and smaller cars is a much better solution. Most car trips are unnecessary if you have reasonable infrastructure and don't make cornerstores illegal. 25mph LEVs and NEVs can serve most of the rest and can be powered purely on the sunlight that lands directly on them where 90% of people live. Trucking is a major issue if you don't want to spend those trillions on functioning rail instead, but no trucking company is going to pay $1/kWh just so there can be terawatts of idling nuclear capacity. They'd just build their own renewable+battery depots at $0.2/kWh.