Charging cars at home at night is not the way to go, Stanford study finds

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Charging cars at home at night is not the way to go, Stanford study finds
The move to electric vehicles will result in large costs for generating, transmitting, and storing more power. Shifting current EV charging from home to work and night to day could cut costs and help the grid, according to a new Stanford study.
By Mark Golden
The vast majority of electric vehicle owners charge their cars at home in the evening or overnight. We’re doing it wrong, according to a new Stanford study.
Tesla Cybertruck Charging cars at home at night is not the way to go, Stanford study finds EVcharging-555x370

If the common charging of electric vehicles at home in the evening or overnight shifts to daytime at work as more cars go electric, then that would restrain extra costs for electricity systems, according to a new Stanford University study. (Image credit: Amy Adams)
In March, the research team published a paper on a model they created for charging demand that can be applied to an array of populations and other factors. In the new study, published Sept. 22 in Nature Energy, they applied their model to the whole of the Western United States and examined the stress the region’s electric grid will come under by 2035 from growing EV ownership. In a little over a decade, they found, rapid EV growth alone could increase peak electricity demand by up to 25%, assuming a continued dominance of residential, nighttime charging.
To limit the high costs of all that new capacity for generating and storing electricity, the researchers say, drivers should move to daytime charging at work or public charging stations, which would also reduce greenhouse gas emissions. This finding has policy and investment implications for the region and its utilities, especially since California moved in late August to ban sales of gasoline-powered cars and light trucks starting in 2035.
“We encourage policymakers to consider utility rates that encourage day charging and incentivize investment in charging infrastructure to shift drivers from home to work for charging,” said the study’s co-senior author, Ram Rajagopal, an associate professor of civil and environmental engineering at Stanford.
In February, cumulative sales of EVs in California reached one million, accounting for about 6% of cars and light trucks. The state has targeted five million EVs on the road by 2030. When the penetration hits 30% to 40% of cars on the road, the grid will experience significant stress without major investments and changes in charging habits, said Rajagopal. Building that infrastructure requires significant lead time and cannot be done overnight.
“We considered the entire Western U.S. region, because California depends heavily on electricity imports from the other Western states. EV charging plus all other electricity uses have consequences for the whole Western region given the interconnected nature of our electric grid,” said Siobhan Powell, lead author of the March study and the new one.
“We were able to show that with less home charging and more daytime charging, the Western U.S. would need less generating capacity and storage, and it would not waste as much solar and wind power,” said Powell, mechanical engineering PhD ’22.
“And it’s not just California and Western states. All states may need to rethink electricity pricing structures as their EV charging needs increase and their grid changes,” added Powell, who recently took a postdoctoral research position at ETH Zurich.
Once 50% of cars on the road are powered by electricity in the Western U.S. – of which about half the population lives in California – more than 5.4 gigawatts of energy storage would be needed if charging habits follow their current course. That’s the capacity equivalent of 5 large nuclear power reactors. A big shift to charging at work instead of home would reduce the storage needed for EVs to 4.2 gigawatts.
Changing incentives
Current time-of-use rates encourage consumers to switch electricity use to nighttime whenever possible, like running the dishwasher and charging EVs. This rate structure reflects the time before significant solar and wind power supplies when demand threatened to exceed supply during the day, especially late afternoons in the summer.
Today, California has excess electricity during late mornings and early afternoons, thanks mainly to its solar capacity. If most EVs were to charge during these times, then the cheap power would be used instead of wasted. Alternatively, if most EVs continue to charge at night, then the state will need to build more generators – likely powered by natural gas – or expensive energy storage on a large scale. Electricity going first to a huge battery and then to an EV battery loses power from the extra stop.
At the local level, if a third of homes in a neighborhood have EVs and most of the owners continue to set charging to start at 11 p.m. or whenever electricity rates drop, the local grid could become unstable.
“The findings from this paper have two profound implications: the first is that the price signals are not aligned with what would be best for the grid – and for ratepayers. The second is that it calls for considering investments in a charging infrastructure for where people work,” said Ines Azevedo, the new paper’s other co-senior author and associate professor of energy science and engineering in the Stanford Doerr School of Sustainability, which opened on Sept. 1.
“We need to move quickly toward decarbonizing the transportation sector, which accounts for the bulk of emissions in California,” Azevedo continued. “This work provides insight on how to get there. Let’s ensure that we pursue policies and investment strategies that allow us to do so in a way that is sustainable.”
Another issue with electricity pricing design is charging commercial and industrial customers big fees based on their peak electricity use. This can disincentivize employers from installing chargers, especially once half or more of their employees have EVs. The research team compared several scenarios of charging infrastructure availability, along with several different residential time-of-use rates and commercial demand charges. Some rate changes made the situation at the grid level worse, while others improved it. Nevertheless, a scenario of having charging infrastructure that encourages more daytime charging and less home charging provided the biggest benefits, the study found.
Rajagopal and Azevedo are also co-directors of the Bits & Watts Initiative at Stanford’s Precourt Institute for Energy. Other co-authors of this study are Gustavo Cezar, PhD student and a staff engineer at Stanford’s SLAC National Accelerator Laboratory; and Liang Min, managing director of the Bits & Watts Initiative.
This work was funded by the California Energy Commission, the National Science Foundation, and the Bits & Watts Initiative with support from Volkswagen.

To read all stories about Stanford science, subscribe to the biweekly Stanford Science Digest.
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Tesla Cybertruck Charging cars at home at night is not the way to go, Stanford study finds EVcharging-555x370
Tesla Cybertruck Charging cars at home at night is not the way to go, Stanford study finds EVcharging-555x370
Tesla Cybertruck Charging cars at home at night is not the way to go, Stanford study finds EVcharging-555x370
Tesla Cybertruck Charging cars at home at night is not the way to go, Stanford study finds EVcharging-555x370



https://news.stanford.edu/press-releases/2022/09/22/charging-cars-honight-not-way-go/
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egandalf

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Agree with all of this. Two additional points I'd like to add.

1. You've not seen my mother-in-law doing laundry. That dryer absolutely is capable of being run 5+ hours per day!! :)

2. I think the average commute is something like 30-ish miles? Even if we round up to 40 as an average, that would mean most EVs would only charge for 1-2 hours per day, most days. Maximum 3. That's including power-hungry vehicles like the Cybertruck.

Let's assume a 40-mile round-trip commute. Worst case (or lead foot) we get 2mi/kWh, so that would mean using 20kWh for that commute. Even if we only install a 32-amp capable level 2 charger, that's, approximately 6.6kW going into the vehicle (rounding down to commercial voltages). So absolute worst case is charging for 3 hours for an average commute.

If the commute is 30mi and we can draw a full 48-amp (11kW) level 2 at home (what I have installed) then we're talking 1.5 hours tops at 500Wh per mile. My wife's Model Y would recharge in less than an hour (which is what we typically see).

But the biggest difference that I see is that we're looking at a continuous draw for that time. A relatively quick ramp up to 32/48A and an abrupt end at that amperage (or rapid taper, perhaps) when the charging limit is reached (assuming not charging to 100%). Even dryers don't use the full 32A continuously. It's a spike to get up to temps and then a lower amperage to maintain those temps.
 

Throwcomputer

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Seems easily solved with more solar/charging stalls in the world.

-Crissa
Problem is a concern but is overstated, given in 10-20 yrs solar roofing and power wall style battery storage will be common in most houses. So your night charging will have zero to minimal effect on the grid.
 


JBee

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Agree with all of this. Two additional points I'd like to add.

1. You've not seen my mother-in-law doing laundry. That dryer absolutely is capable of being run 5+ hours per day!! :)

2. I think the average commute is something like 30-ish miles? Even if we round up to 40 as an average, that would mean most EVs would only charge for 1-2 hours per day, most days. Maximum 3. That's including power-hungry vehicles like the Cybertruck.

Let's assume a 40-mile round-trip commute. Worst case (or lead foot) we get 2mi/kWh, so that would mean using 20kWh for that commute. Even if we only install a 32-amp capable level 2 charger, that's, approximately 6.6kW going into the vehicle (rounding down to commercial voltages). So absolute worst case is charging for 3 hours for an average commute.

If the commute is 30mi and we can draw a full 48-amp (11kW) level 2 at home (what I have installed) then we're talking 1.5 hours tops at 500Wh per mile. My wife's Model Y would recharge in less than an hour (which is what we typically see).

But the biggest difference that I see is that we're looking at a continuous draw for that time. A relatively quick ramp up to 32/48A and an abrupt end at that amperage (or rapid taper, perhaps) when the charging limit is reached (assuming not charging to 100%). Even dryers don't use the full 32A continuously. It's a spike to get up to temps and then a lower amperage to maintain those temps.
Time to buy a condenser dryer for the next mother's (in-law) day!

Who knew she was single handedly responsible for global warming? :p 🤣
 

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Agree with all of this. Two additional points I'd like to add.

1. You've not seen my mother-in-law doing laundry. That dryer absolutely is capable of being run 5+ hours per day!! :)

....
heat pump type clothes dryer

Heat Pump Dryer
ENERGY STAR certified heat pump dryers offer the biggest advantage to consumers with high clothes dryer usage and high electricity rates.
https://www.energystar.gov/products/heat_pump_dryer
 

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This.

All grid usage/generation is time-based. Most solar generation is in the afternoon, but peak usage is in the evening, for instance.

If the utilities switch to demand-based rates, then consumers will change their habits to get the better rates, and the market will adjust accordingly.
 

JBee

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This.

All grid usage/generation is time-based. Most solar generation is in the afternoon, but peak usage is in the evening, for instance.

If the utilities switch to demand-based rates, then consumers will change their habits to get the better rates, and the market will adjust accordingly.
If users were actually home to use their solar power at that time of day, and not at work trying to pay off their solar! :rolleyes:

Its just like rush hour traffic, that is only caused by business opening times.

People are stupid. Get rid of fixed business hours and spread the peak an hour or more each way, and hey presto you solve the traffic problem and peak load.

This whole fixed scheduling rubbish where everyone has to do the same thing at the same time lis the primary cause for so much peak loading, and instead of one simple scheduling change to get better ROI, we go and put in another 3 lanes, another network feeder, and more batteries etc, or build some tunnels so we can carry on doing things nobody' wants to do in the first place? 🥴
 

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If users were actually home to use their solar power at that time of day, and not at work trying to pay off their solar! :rolleyes:

Its just like rush hour traffic, that is only caused by business opening times.

People are stupid. Get rid of fixed business hours and spread the peak an hour or more each way, and hey presto you solve the traffic problem and peak load.

This whole fixed scheduling rubbish where everyone has to do the same thing at the same time lis the primary cause for so much peak loading, and instead of one simple scheduling change to get better ROI, we go and put in another 3 lanes, another network feeder, and more batteries etc, or build some tunnels so we can carry on doing things nobody' wants to do in the first place? 🥴
Maybe we could take turns having weekends and holidays, too? I’ll take Christmas in October
 


JBee

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Maybe we could take turns having weekends and holidays, too? I’ll take Christmas in October
I'll take Christmas in summer. Oh wait... never mind, that already is the case here. ;)

But seriously wouldn't it be cool to go on holiday without it always being overcrowded?
Get rid of schools I say that pump out dumb people that go to physical shops, and work in physical offices, that all need to live in the city to work. Programed obsolescence. One day we will look at our history and laugh at all the dumb people, especially ourselves. :eek:
 

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Wow. Stanford just lost credibility with me. This is a case of researchers who endeavor to find contradicting data to universally accepted truths, and while finding a grain of it, are vastly misleading. The overwhelming highest electrical demand on the electrical grid is during mid-day (especially in warmer climates, especially during summer). My state power co drops my rate to $0.017 / Kw-h if I charge my EV between 9 pm and 6 am. They are very aware of the improvement on their system if I choose to charge at night, instead of mid-day (when they are firing up natural gas generators to keep up with demand during the summer).

While I would agree that when the majority of vehicles are charging at night the grid would benefit from smart assignments, and there is much development in that area, this article's general thesis is (IMO) somewhere between grossly misleading and flat wrong.
 
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Wow. Stanford just lost credibility with me. This is a case of researchers who endeavor to find contradicting data to universally accepted truths, and while finding a grain of it, are vastly misleading. The overwhelming highest electrical demand on the electrical grid is during mid-day (especially in warmer climates, especially during summer). My state power co drops my rate to $0.017 / Kw-h if I charge my EV between 9 pm and 6 am. They are very aware of the improvement on their system if I choose to charge at night, instead of mid-day (when they are firing up natural gas generators to keep up with demand during the summer).

While I would agree that when the majority of vehicles are charging at night the grid would benefit from smart assignments, and there is much development in that area, this article's general thesis is (IMO) somewhere between grossly misleading and flat wrong.
With the removal of most fossil fuel from the California grid, and the nuclear not being replaced, most power production will be solar. Hydro is also dropping, but mostly because we don't have enough water where we used to have plenty.

-Crissa
 

JBee

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Wow. Stanford just lost credibility with me. This is a case of researchers who endeavor to find contradicting data to universally accepted truths, and while finding a grain of it, are vastly misleading. The overwhelming highest electrical demand on the electrical grid is during mid-day (especially in warmer climates, especially during summer). My state power co drops my rate to $0.017 / Kw-h if I charge my EV between 9 pm and 6 am. They are very aware of the improvement on their system if I choose to charge at night, instead of mid-day (when they are firing up natural gas generators to keep up with demand during the summer).

While I would agree that when the majority of vehicles are charging at night the grid would benefit from smart assignments, and there is much development in that area, this article's general thesis is (IMO) somewhere between grossly misleading and flat wrong.
Primarily it's about optimizing existing infrastructure and leveraging EV's themselves to support more renewables.

The problem is that there is a lot of solar during the day from households that can't be dispatched through the networks without overloading it. This results in network voltage rise which in turn automatically throttles household solar exports. The solar inverters can only operate within the predetermined parameters of the power connection and many can't import VARs to reduce network voltage whilst exporting, like other "spinning generation" can. This is lost capacity.

The other issue is that the household solar is not always on the same part of the network that the cars charging at day would be, meaning extra network capacity needs to be installed to transport the energy required. The simpler option is to have solar installed at work and charge at work during the day, which puts little to no extra load on the networks, and reduces overall network generation as well, saving fuel. On top of this EV's with V2G could also provide storage buffer to flatten the peak whilst parked at work, meaning they would further increase RE network penetration, and further reduce the need for networks overall.

We really need to change how we look at EV's and how they should be used, until now ICE have had little to no interactivity with the electricity network, except for running the fuel pumps at the service station.

In contrast EV's with V2G are both network load and power providers from storage. They are also physically relocatable network assets. The trick to make the most of them is to not interfere with the primary use, namely to drive from home to somewhere else, which simply means leave enough range in the tank to get o your next destination when you unplug. In both locations they are parked and can be connected, and especially at work, they can have profound net positive effects on network stability and generation, which in turn opens the door for more RE.

It might be true that the utilities are providing off-peak power for cheaper, but a lot of that energy is not RE rather fossil, as many large generators are not capable of being switched off, meaning the utility can only throttle them down, resulting in lower electricity market price for off-peak.

Obviously, no solar at all can be produced at night, making all EV charging at night currently grid dependent. But that does not mean that it is physically receiving electrons from a renewable source, rather mostly from fossil base load, except if you have wind or hydro if that is nearby. So to get EV's to charge from solar, you need to charge them during the day, and during the day most vehicles are at work, and whilst they are parked there they should be charged from local embedded solar. Which all results in better resource allocation and utility, and provides networks with more capacity to increase renewable use.

This is all very similar to rush hour traffic where one half of the motorway is packed for one part of the day, and in the opposite direction at another part of the day. Where as at night it's empty. All because of time of use and poor resource utilization. The road doesn't stop working at night, it's just that we humans all go to bed.
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