4 ms·
> grid already exists, people can charge at home, easier to build EV infrastructure, etc. I find it really interesting how people tend to repeat these "facts"
by robomartin 5y ago
> grid already exists, people can charge at home, easier to build EV infrastructure, etc.
I find it really interesting how people tend to repeat these "facts" over and over again and nobody fires-up Excel to go through some math and see if any of it makes any sense. I have. And I can't see how the infrastructure can possibly support a transition to a fully electric ground transportation system, well, ever.
Basic numbers:
How much power do we need to support the entire US fleet of cars going electric?
The simplest assumption is one where 100% of the fleet uses 8 hour long charge cycles:
daily charge energy 50,000 Wh
cars 300,000,000 cars
long charge 8 hours
fast charge 0.5 hours
Portion charging long 100%
Portion charging fast 0%
% of long-chargers charging simultaneously 100%
% of short-chargers charging simultaneously 0%
Total daily energy requirement 15,000 GWh
Cars long-charging simultaneously 100,000,000 cars
Cars short-charging simultaneously 0 cars
Power for simultaneous long charging 1,875 GW
Power for simultaneous short charging 0 GW
Total power requirement 1,875 GW
This isn't realistic, you are not going to have 300 million cars charging simultaneously during the same eight hours. Or, are we?
If every hour we have, say, 1/8 of the entire fleet plug in for eight hours to charge, what's the maximum number of vehicles that will be charging simultaneously at any point in the day? The assumption is that car will charge for eight hours and be off charge for 16.
Well, eight hours into the day we will, in fact, have 300 million cars charging simultaneously. After a full 24 hours from the start of this approach, the minimum number of cars charging simultaneously will be 187.5 million and the maximum 300 million.
So, yes, at peak utilization we will will have 300 million cars, requiring that we deliver 50 kWh in 8 hours, which means a peak requirement of 1,875 GW.
This means we need nearly two thousand giga-watt class nuclear power plants to support a fleet where 100% of the vehicles will slow charge.
What happens when some percentage of the fleet needs to fast charge? I am defining fast charging as delivering 50 kWh in 30 minutes:
daily charge energy 50,000 Wh
cars 300,000,000 cars
long charge 8 hours
fast charge 0.5 hours
Portion charging long 80%
Portion charging fast 20%
% of long-chargers charging simultaneously 100%
% of short-chargers charging simultaneously 20%
Total daily energy requirement 15,000 GWh
Cars long-charging simultaneously 240,000,000 cars
Cars short-charging simultaneously 12,000,000 cars
Power for simultaneous long charging 1,500 GW
Power for simultaneous short charging 1,200 GW
Total power requirement 2,700 GW
Now we need 2,700 giga-watt class nuclear power plants in order to be able to deliver the power needed to support the bulk of the fleet slow-charging and the remainder fast-charging spread across the day.
TWO THOUSAND SEVEN HUNDRED nuclear power plants.
Even if I am off by a factor of ten (I threw this together and it is very simplistic), that means nearly 300 nuclear power plants to be built in, say, 30 years. We have to build ten per year and we had to get started yesterday.
This is the kind of thing I look at when I talk about not reducing reality to single variables. The amount of energy we delivery by using petroleum is of a scale that is hard to imagine. To go electric we have to find alternative means to deliver some percentage of that energy (because electric cars are more energy-efficient than IC vehicles) to every car on the road every day. This task is far from being simple. Beyond that, the unmitigated mess that US politics has become over the last few decades virtually guarantees we cannot build a single nuclear power plant, much less ten, fifty or a hundred.
I think we are going to have some number of people driving electrics and, in the hubris of it all, we are going to ignore the fact that we are going have to burn twice or three times more coal to charge those cars every day. It has all the potential to be a larger mess than what we currently have.
I would love for someone to take the time to develop and publish a better model than my mindlessly-simple quick calculation. I know a lot of subtlety could be introduced. That said, I somehow don't think we can escape physics.
My guess is we will reach the limits of our available power generation capacity at some number in the low millions of electric vehicles, not sure that means tens of millions. At some point we will face the reality that the energy we transport today in liquid form will have to be provided in electrical form. If that happens in ten years and we suddenly decide "oh, shit, we can't make enough power!" either we get very good at building nuclear power plants at a staggering rate or the fleet of electric vehicles will reach an asymptotic balance point and that will be it for a while.
There are no alternative realities here. Physics doesn't tend to grant free lunches.
Request: I you (plural, anyone) are going to refute the above and say something like "we will use solar". Please, pretty please, with sugar on top: Do the math first. Most people don't. Hence the problem.
To repeat myself: Even if I am off by a factor of ten, the excess power generation capacity we would need to support a fully electrified ground transport system is of staggering proportions.
- fossuser 5y agoNot my area of expertise, but people that claim to be experts suggest that global electricity generation is enough: https://www.barrons.com/articles/theres-enough-electricity-in-the-world-for-electric-vehicles-heres-who-will-charge-them-51605368406 https://www.barrons.com/articles/theres-enough-electricity-i... My intuitive guess is your simple model is wrong, but I'm not an expert.
- robomartin 5y agoThanks for the link. Sadly, no, the "analysis" in the article --and I am being kind-- is overly simplistic. This is the kind of hand-wavy thing I've been running into when I look for prior work on the subject. Here's an analogy that might convey the nature of the hand-waving: A typical home swimming pool requires 20,000 gallons of water. Let's say the average flow rate of a good quality garden hose is 20 gallons per minute. That means you can fill that pool in 1,000 minutes, or, about 17 hours. Can you fill the pool in 8.5 hours if you use two hoses? No. Why? Because your plumbing will establish a limit on just how much water you can flow per unit time. Anyone who has ever dealt with plumbing understands this. In some installations, if you flush the toilet and someone is taking a shower they get burned because less cold water flows to mix with hot water. In my home, when the sprinkler system is on there's a marked difference in flow rate everywhere in the house. What if a thousand of your neighbors want to fill their 20,000 gallon swimming pools simultaneously? Could they? Very likely not. Well, not in 17 hours. The large pipes supplying water to a neighborhood have a flow rate limit as well. Under normal usage they are adequate for the usage profile of a certain number of homes in a neighborhood. Are these pipes designed and specified to manage twice that design rate? Likely not. And certainly not five or ten times. Most neighborhoods in the US are supplied with drinking water from large water tanks strategically located higher than the homes they service. This isn't universal across the entire nation but it is very common. Here comes the next problem. Filling a thousand 20K gallon swimming pools requires two million gallons of water. This, over and above the water required for all the other things people do with water, from drinking to flushing the toilet. A typical neighborhood water tank might hold one or two days of water, as defined by the typical usage for the area. It certainly does not hold an extra two million gallons to dispense over 17 hours. As the water level decreases due to either normal or abnormal usage, pumps are engaged to maintain water level. Once again, these pumps are sized for typical usage as it might pertain to the specific installation. They are not sized to provide a massive step change in water pumping from the main aqueduct into the neighborhood tank. As you can imagine, this analysis can extend beyond neighborhood tanks and explore issues with aqueducts, water treatment plants, etc. What these articles do is they say something like "the world capacity is N GWh. We need 1/2N GWh for electric cars. We only use 1/2N for everything else. We have what we need." Well, no. We don't. There's also a confusion between power and energy. Power is energy per unit time. Put a different way: There's a huge difference between walking a mile and running a mile. What these articles ignore is that the electric car charging problem is like the neighborhood swimming pool issue. When everyone in the neighborhood wants to charge their cars in eight hours or less, what you need isn't just the energy (the water level in the pool), you also need power, you need to be able to deliver a lot more gallons per minute at every home, street, neighborhood, town, city and region. Exiting power plants cannot do this. Furthermore, by definition, if we want coal power plants to deliver twice their average power to charge cars, you have to burn at least two times the coal you were burning before. Hence me reaching for nuclear power plants...because any other option would be somewhere between unrealizable (the plant just can't produce twice the power) to unthinkable (pollution). Put a different way: Let's say your city is fed by a 1 GW nuclear power plant today. Everyone is driving gasoline cars. Median load factor for nuclear power plants is in the order of 80%. That means you only have a 20% excess capacity. Now everyone buys electric cars and, of course, everyone wants to charge them as quickly as possible, with some willing to wait overnight. Well, your power plant will not be able to supply this extra power. We don't design power plants to be twice or three times larger than what we need. Which means you'll need to build one or two additional plants as soon as possible. I have yet to see a study of model of electric car charging energy and power requirements that passes the physics test. Lots of hand-waving and "trust me, I am a <insert appeal to authority>" but no numbers. Science is about numbers. My attempt isn't complete at all. However, like I said, even if I am off by a factor of ten, we have a problem. Heck, we likely have a problem if I am off by a factor of 20. I think what everyone is counting on is everyone covering neighborhoods with solar power. As the owner of a 40 panel array I built myself to, among other things, power my CNC shop and, after expansion, support electric vehicles, I can tell you without a shadow of a doubt that the idea of a clean solar future for electric cars is a fantasy. My energy logs say so. I would need somewhere in the order of three to five times the array to truly be "green" as far as electric vehicle charging would be concerned. Any way you look at it, that is impossible.