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

JBee

Well-known member
First Name
JB
Joined
Nov 22, 2019
Threads
18
Messages
4,752
Reaction score
6,129
Location
Australia
Vehicles
Cybertruck
Occupation
. Professional Hobbyist
Country flag
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.
A couple of things that might be interesting:

Solar can produce just as much in the morning as in the afternoon, but can only produce as much as the grid has load, meaning that most solar in the morning has restricted output leading to less exports. This is not because of the sun varies it's output between the two times of the day though. In a lot of cases it is also dependent on how well the local time zone meridian overlaps with local solar time. For example: In Nashville the sun rose today at 6:43 AM and in the same time zone (GMT -5) it rose in Fort Stockton TX at 7:46 AM. This obviously changes when the solar midday is, and how human activity is scheduled in comparison.

Tesla Cybertruck Charging cars at home at night is not the way to go, Stanford study finds EULP_Region1_Calibratio


In regards to ToU pricing the main problem is actually ToU itself. If you follow the graph above you will see that depending on the time of year the peak load in a household varies considerably, but peak household use remains dominate in the late afternoon and evening. This is because a lot of households follow a similar regimen, being; wake up, have breakfast, leave house, return to house in the afternoon (with kids) where household activities start, incl. dinner etc using power until late evening and finally sleep.

So even if ToU pricing would incentivize more even consumption, how do you go about changing these typical use profiles without disrupting how people go about their lives? Even if you would half the price I doubt you would see a 10-15% change in the usage profile. It's just not practical enough.

Another interesting element of the profiles above is also just how much cooling overlaps with potential household solar production, and how much of this load until 4-6PM could come from solar instead f the grid. In fact nearly half of the consumption in summer is cooling load that also follows the household occupancy pattern. Another option here would be use cheap and cost effective thermal storage (Insulated water tanks using thermal mass) to offset the evening peak into the solar production times, and with solar together essentially halving household demand in the summer. This load does not have to be electrical, and does not need it's own battery storage, which reduces the cost for running battery storage for the rest of consumption in the house.

Obviously, it's also evident from the graph that household EV charging overnight will increase the peak period until the morning. But here it is important to realise that the load of a EV charger when operational, typically exceeds normal household consumption some 2-3x. And as previously posted, only can use non-solar utility provided power to charge at those times.

"If" you had enough space on your house roof with correct orientation, you could actually take a large bite out of the middle of the daytime household consumption, which would give networks some more capacity during the day. But sadly as soon as the sun goes to low angles in the afternoon, that nasty evening peak will remain, and possibly even get worse as more households are built. But... if the EV's had V2G, or at least V2H, then those peaks could also be "buffered" out with battery storage.

In an ideal fashion, as is also proposed by the report, the EV's would charge at work, from solar during the day, and bring renewable energy home for use in the peak evening period when the sun goes down and everyone is at home.
Sponsored

 

Crissa

Well-known member
First Name
Crissa
Joined
Jul 8, 2020
Threads
126
Messages
16,227
Reaction score
27,092
Location
Santa Cruz
Vehicles
2014 Zero S, 2013 Mazda 3
Country flag
Please don't listen to jbee on solar stuff.

No, the grid isn't overloaded by solar. If that were true, it would get overloaded when we all have AC or space heaters running. it's more that enough to handle residential solar.

And no, solar is more limited from the direction of the panels than the load on the grid. Solar panels pointed south or west aren't going to pick up much energy when the sun rises. We don't have that much solar yet for it to reach that point that it's often limited by the load.

*sigh*

-Crissa

PS... that's too harsh on JBee. He's right on so much of the rest of it, especially that EVs can be used to solve many of these load mismatch problems. Apologies for seeming harsh.
 
Last edited:

JBee

Well-known member
First Name
JB
Joined
Nov 22, 2019
Threads
18
Messages
4,752
Reaction score
6,129
Location
Australia
Vehicles
Cybertruck
Occupation
. Professional Hobbyist
Country flag
Please don't listen to jbee on solar stuff.

No, the grid isn't overloaded by solar. If that were true, it would get overloaded when we all have AC or space heaters running. it's more that enough to handle residential solar.

And no, solar is more limited from the direction of the panels than the load on the grid. Solar panels pointed south or west aren't going to pick up much energy when the sun rises. We don't have that much solar yet for it to reach that point that it's often limited by the load.

*sigh*

-Crissa

PS... that's too harsh on JBee. He's right on so much of the rest of it, especially that EVs can be used to solve many of these load mismatch problems. Apologies for seeming harsh.
lol ok. Thanks for compliment btw.

So how much solar do you have on your particular network?

I heard that on April 3 this year California had 97.6% renewables feeding it's grid, producing some 26GW of power of which solar was more than 15GW (57%).

What am I missing?

Have you heard of solar network curtailment?

And please don't start with the regulatory capture stuff, this is a technical problem, that I am trying to come up with solutions for. I'm not on "their" side, whoever "they" might be, rather am pragmatically discussing the issue of network management.

Feel free to add relevant information to the conversation, or refute mine. :)
 

ldjessee

Well-known member
First Name
Lloyd
Joined
Apr 22, 2020
Threads
14
Messages
1,148
Reaction score
1,357
Location
Indiana, USA
Vehicles
Nissan Leaf, MYLR, Kaw 1700 Vaquero
Occupation
Business Intelligence Manager & Analyst
Country flag
I am sorry, but I find this article impossible to believe.

The reason I think this is that most electricity is used during the day, especially peaks at 'dinner' time for most locations, assuming not mid summer where inefficient AC compressors really spike daytime use.

Use is so low at night, in those places that do have time of use, sometimes people are PAID to take electricity (negative costs).

Tesla has software in their stationary battery products to take advantage of these conditions.

Why would charging at night save money or burn more fossil fuels? Usually if there is more demand during the day, they have to fire up those very inefficient (and expensive) peeker plants.

The only way that charging during the day over night makes sense is if the charger is powered by solar panels... but even then, if you have panels on your house or place of work, then a battery pack can let you time shift between energy production and energy usage.

Look at these charts for USA regional power usage. Given the same grid is providing power for those huge summer spikes, not sure how charging at night is a problem.

Tesla Cybertruck Charging cars at home at night is not the way to go, Stanford study finds region_timeofday_average_usage_chart2


And, looking at the 'study' at the source, the source publication does not call it a study, they call it an Article, not something peer-reviewed nor up to the standards that such a thing would be if it was presented as a Analysis or Review... according to their Content Type definition.

I know most power companies are happy with setting up EV charging at night, because they have excess base load capacity that they have to lower the price or give away to get people to take at night in some places, so getting a customer base (EV owners) a special plan for them to charge at night makes them happy, more money, and they do not have to build more capacity yet nor use expensive peeker plants.

As other have stated, more solar (or wind) generation tied to batteries the better.
 

fritter63

Well-known member
First Name
Mark
Joined
Jan 21, 2020
Threads
33
Messages
1,422
Reaction score
2,877
Location
Atascadero
Vehicles
2018 Model 3 LR, 2019 Model 3 SR+
Occupation
Retired Software Engineer, Woodworker and guitar builder extraordinaire
Country flag
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).
let's stop assuming and use real life numbers/examples: My wife! :)

Daily work commute: 34 miles round trip (but up and over Cuesta Grade, 7% grade, several hundred feet elevation gain (and loss for regen).

Nightly charging: Starts at midnight when off-peak rates start, finishes just after 2 hours

Power used to charge the car is offset by the solar panels, which charge the power walls, and then are put back on the grid.

So our charging is generated by solar, but stored on the grid/batteries.

And if we DO use grid power, it comes from nuclear power!

We do have a slight deficit on solar generation, but I'm not sure it's worth adding more as we're close to retirement and daily commute about to go to zero.....then we'll be trying to eBike as much as possible!
 


JBee

Well-known member
First Name
JB
Joined
Nov 22, 2019
Threads
18
Messages
4,752
Reaction score
6,129
Location
Australia
Vehicles
Cybertruck
Occupation
. Professional Hobbyist
Country flag
I am sorry, but I find this article impossible to believe.

The reason I think this is that most electricity is used during the day, especially peaks at 'dinner' time for most locations, assuming not mid summer where inefficient AC compressors really spike daytime use.

Use is so low at night, in those places that do have time of use, sometimes people are PAID to take electricity (negative costs).

Tesla has software in their stationary battery products to take advantage of these conditions.

Why would charging at night save money or burn more fossil fuels? Usually if there is more demand during the day, they have to fire up those very inefficient (and expensive) peeker plants.

The only way that charging during the day over night makes sense is if the charger is powered by solar panels... but even then, if you have panels on your house or place of work, then a battery pack can let you time shift between energy production and energy usage.

Look at these charts for USA regional power usage. Given the same grid is providing power for those huge summer spikes, not sure how charging at night is a problem.

region_timeofday_average_usage_chart2.png


And, looking at the 'study' at the source, the source publication does not call it a study, they call it an Article, not something peer-reviewed nor up to the standards that such a thing would be if it was presented as a Analysis or Review... according to their Content Type definition.

I know most power companies are happy with setting up EV charging at night, because they have excess base load capacity that they have to lower the price or give away to get people to take at night in some places, so getting a customer base (EV owners) a special plan for them to charge at night makes them happy, more money, and they do not have to build more capacity yet nor use expensive peeker plants.

As other have stated, more solar (or wind) generation tied to batteries the better.
You're missing the point a bit here in that solar does not work at night at all and there is absolutely no capacity in the network to store it until EV"s can charge at night. Nor should there be a need for it if we can avoid it by other means.

Therefore the easiest way to do it is to charge when you have solar in the day time, and to do so you need to charge at work. That's it in a nutshell.

Don't really need a peer review to understand the logic of night vs day solar production.
 
Last edited:

JBee

Well-known member
First Name
JB
Joined
Nov 22, 2019
Threads
18
Messages
4,752
Reaction score
6,129
Location
Australia
Vehicles
Cybertruck
Occupation
. Professional Hobbyist
Country flag
let's stop assuming and use real life numbers/examples: My wife! :)

Daily work commute: 34 miles round trip (but up and over Cuesta Grade, 7% grade, several hundred feet elevation gain (and loss for regen).

Nightly charging: Starts at midnight when off-peak rates start, finishes just after 2 hours

Power used to charge the car is offset by the solar panels, which charge the power walls, and then are put back on the grid.

So our charging is generated by solar, but stored on the grid/batteries.

And if we DO use grid power, it comes from nuclear power!

We do have a slight deficit on solar generation, but I'm not sure it's worth adding more as we're close to retirement and daily commute about to go to zero.....then we'll be trying to eBike as much as possible!
Sorry that logic only works at this time if you have fossil/nuclear generation at night as baseload. There's not enough wind or hydro to charge every EV at night and there will likely never be.
A lot of solar energy is going to waste because of solar network curtailment, and then could be better used if they charged during the day.
 

Crissa

Well-known member
First Name
Crissa
Joined
Jul 8, 2020
Threads
126
Messages
16,227
Reaction score
27,092
Location
Santa Cruz
Vehicles
2014 Zero S, 2013 Mazda 3
Country flag
I am sorry, but I find this article impossible to believe.

The reason I think this is that most electricity is used during the day, especially peaks at 'dinner' time for most locations, assuming not mid summer where inefficient AC compressors really spike daytime use.

Use is so low at night, in those places that do have time of use, sometimes people are PAID to take electricity (negative costs).

Tesla has software in their stationary battery products to take advantage of these conditions.

Why would charging at night save money or burn more fossil fuels? Usually if there is more demand during the day, they have to fire up those very inefficient (and expensive) peeker plants.

The only way that charging during the day over night makes sense is if the charger is powered by solar panels...
Because most of the power generation added to the grid is solar. Eventually that base load generation will drop below the cost of solar.

-Crissa
 

ldjessee

Well-known member
First Name
Lloyd
Joined
Apr 22, 2020
Threads
14
Messages
1,148
Reaction score
1,357
Location
Indiana, USA
Vehicles
Nissan Leaf, MYLR, Kaw 1700 Vaquero
Occupation
Business Intelligence Manager & Analyst
Country flag
Last report I saw, more wind was being added than solar, but that was a couple of years ago.
 

BillyGee

Well-known member
First Name
Bill
Joined
Jan 22, 2020
Threads
8
Messages
708
Reaction score
1,534
Location
Northern California
Vehicles
Model Y P, Model 3 LR, Founders CT (Ordered)
Occupation
Technician
Country flag
I see the point, but what happens when people all start charging during the day? Same problem, different time slot.

A lot more homes need independent generation, either that or we need to shift towards better nuclear systems.
 


JBee

Well-known member
First Name
JB
Joined
Nov 22, 2019
Threads
18
Messages
4,752
Reaction score
6,129
Location
Australia
Vehicles
Cybertruck
Occupation
. Professional Hobbyist
Country flag
Diversity is key. But roof top workplace solar can do a lot of it in sunny areas.

I must point out that this whole charging EV's when the sun shines conundrum is ONLY relevant to where enough solar can be harvested during the day to do so at all. So it's only effective in summer in some locations at higher latitudes.
 

ldjessee

Well-known member
First Name
Lloyd
Joined
Apr 22, 2020
Threads
14
Messages
1,148
Reaction score
1,357
Location
Indiana, USA
Vehicles
Nissan Leaf, MYLR, Kaw 1700 Vaquero
Occupation
Business Intelligence Manager & Analyst
Country flag
Even last year, much more wind electricity was generated than via solar.
https://www.eia.gov/tools/faqs/faq.php?id=427&t=3

2.8% is solar, but 9.2% is wind.

If these off shore wind projects get approved, there will be a big jump in wind power generation.
 

fritter63

Well-known member
First Name
Mark
Joined
Jan 21, 2020
Threads
33
Messages
1,422
Reaction score
2,877
Location
Atascadero
Vehicles
2018 Model 3 LR, 2019 Model 3 SR+
Occupation
Retired Software Engineer, Woodworker and guitar builder extraordinaire
Country flag
Sorry that logic only works at this time if you have fossil/nuclear generation at night as baseload. There's not enough wind or hydro to charge every EV at night and there will likely never be.
A lot of solar energy is going to waste because of solar network curtailment, and then could be better used if they charged during the day.
I understand your point, but I think the future less centralized than it is now.

Decreasing cost of batteries will allow each house to store it's own solar for use at night (or charge the car at home during the day), and the grid itself could be backed by Tesla Megapacks (or similar green storage tech) rather than fossil fuel generation at night.
 

JBee

Well-known member
First Name
JB
Joined
Nov 22, 2019
Threads
18
Messages
4,752
Reaction score
6,129
Location
Australia
Vehicles
Cybertruck
Occupation
. Professional Hobbyist
Country flag
I understand your point, but I think the future less centralized than it is now.

Decreasing cost of batteries will allow each house to store it's own solar for use at night (or charge the car at home during the day), and the grid itself could be backed by Tesla Megapacks (or similar green storage tech) rather than fossil fuel generation at night.
I agree. I haven't really mentioned what I thought was a good solution until now, rather that short term this is a decent way to make some progress. At some point I expect the network to houses to diminish as there own generation and storage capacity increases and takes over most of its own load. At least in sunnier climates and if you have enough roof space for solar.

If you don't you might be able to use your EV to take energy home from work or shopping instead. Add some household efficiency, insulation and HVAC thermal storage and heat pump to reduce electrical load.

The overall net effect if all of these will be a significant reduction in network load, and the ability to time shift load, which will be better suited to fully utilise existing network capability.
Sponsored

 
 




Top