When to charge ev?

When to charge ev?

Anyone have insight on which option would be more optimal for me or for the grid?

1. Tell my car to charge during the day, so that I'm using solar power directly to charge and not using the grid at all to charge.

2. Send my excess solar power to the grid during the day when it tends to be more heavily used and then charge at night from the grid.

Tesla-David | 7 maart 2019

We have 13.2kWh solar system with 2-PW2's and also have two Tesla's (MS and M3) living in Edmonds, WA, and generally charge our cars during peak solar production period, so as to eliminate or drastically reduce our grid usage. With our system we produced 252% of our electricity needs last year in our all electric home, including charging both Tesla's, and actually exported 60% of our excess solar energy back to grid. We actually had zero energy usage from grid after our PW2 installation from June through October last year with our setup. My personal goal is to be as independent of grid as possible while still being hooked up to grid. The PW2's have been an absolute game changer for us.

thenagivator | 8 maart 2019

I agree with Tesla David. I like to charge during peak production. When there have been low production days due to cloud cover, I re-think my charging cycles based on my electric company's rate structure. Right now, we have a period known as "super off peak". It runs from November to April. I will use that time frame and then the off-peak time frames. I am careful to never allow my car to charge during Peak time as that results in the highest charges. That can easily happen if you are charging midweek on a cloudy day, with most rate plans and most power companies. Just check your rate plan and that will likely answer your questions. The amount that my power company reimburses me for the power I send to the grid is not worth it. It's better than nothing, but my best scenario is always to use as much as I can when I'm generating it and use as little power as possible when I'm not.

Mediumed | 9 maart 2019

There are many variables including can you charge your car and meet all of your home energy needs during the daylight hours? if not then you will be drawing power from the grid when there is the most demand on the grid as opposed to drawing from the grid at low demand times. If you can meet all of your demands in the daylight hours then that would be best. Then there is the matter of net metering where you live. Some utilities will pay you one to one and others will not. If they pay you one to one then you could charge late at night when the demand on the grid is low. Some utilities will give you extra low rates for electric car charging and others will not. You have to check with your utility to be sure.

Model X Guy | 9 maart 2019

We have solar but always try and charge at night when the power company has excess power that can go to waste if not used.

teslariley | 13 maart 2019

Thanks for the responses. We've only had our system for a month, but so far most days have plenty of solar to charge the car. Also, our electric company does not pay us for extra power, just net metering, so as long as we produce more than we use, I don't think there's any financial difference to us.

It makes sense to me that charging at night like Model X Guy said might be the greenest option unless there are other issues I'm not aware of.

Tesla-David | 18 maart 2019

@teslariley I would take issue with your statement that charging EV's at night is the greenest option. If you have TOU and your solar system is not sufficient to charge your EV's and provide necessary energy to your home, I would agree that charging at night provides the best, less costly option. For us it makes zero sense to charge our EV's at night, for reasons summarized below.

We are fortunate to live in a non-TOU state, where our utility costs do not vary throughout the day/night, as we have uniform rate of $0.10 kWh here in WA. We also have a sizeable solar system (13.2 kWh), that enabled us to provide 252 percent of our electricity needs for our all electric home and also fully charge our two Tesla's (MS and M3) last year. We installed 2-PW2's last June, and they enabled us to dramatically reduce our grid energy use, with zero grid usage from June through October, last year. With a full year of PW2 use, we should be over 300 percent this year easily. Last year we exported 60 percent of our solar energy back to grid, so we are effectively operating as a microgrid, at least for 9 months of the year. We operate our 2-PW2's in self-powered mode and they have worked incredibly well to satisfy our energy requirements and reduce our grid energy usage. We are also fortunate to live in a state where we get paid $0.54 kWh for every kW we send back to grid with Net Metering. These incentives will sunset next year, but have helped us to pay off our solar system within 7 years of purchase.

teslariley | 19 maart 2019

Thanks for the details, Tesla-David. This is getting closer to the meat of the question I was really trying to ask.

If everyone could remove or significantly reduce their grid usage as you have, that is clearly the greenest option. However, assuming most of a city's power is coming from the grid, which I think is still the general case, is it greener to stop using the grid as much as possible or to help supply the grid during its peak load and then charge from the grid during its off-peak hours?

I haven't found any real data either way, which is why I'm asking this question. Thinking through it logically, I could see that reducing peak load would require less coal to be burnt to reach the peaks.

I could also be convinced that it doesn't really matter when you charge since the total draw from the grid is the same whether you are drawing the power at night or your neighbor who doesn't have solar is drawing the power for his A/C during the day. This would only be true if there's a linear relationship between coal burnt and power produced. If there are diminishing returns as you generate more power, then reducing the peak would still be better.

I'd love to hear additional thoughts on this topic.

Tesla-David | 19 maart 2019

@trslariley Agree my goal is to use less fossil fuel (coal, natural gas) generated energy as possible.Again I am lucky up in Washington State as most of our electricity is hydro generated with only small amounts coming from fossil fuel sources,and those sources will be shut off within 20 years. I love being a micro grid producing virtually all our energy off our roof. We only rely on our electric grid for 3 months of year (November through January) to supplement our solar during Winter. In heavily coal generated electricity states, charging during non peak hours makes sense when you don’t have enough solar to cover your needs for EV charging.

PalmVegas | 23 maart 2019

I live in TOU California. We have Solar Panels and 2 Powewalls and are getting the Tesla Car Charger installed for our new M3.
My question: Is the Car Charger best placed on 1) the protected house circuits (with Powerwalls) OR 2) outside the Protcted Circuits, directly to the Grid??

Which configuration gives better savings?
Can’t seem to find this answer to this question on the Internet.

I have a query out to the company that installed our Solar and Powewrwalls.
However, the Tesla Recommended electrician who is going to install the Car Charger is telling m it should be connected directly to the Grid.

Any advice would be appreciated.

Tesla-David | 24 maart 2019

Can't really answer your question about cost savings, but our HPWC is set up within the protected house circuits + PW2's, and this setup has worked very well for us. With our PW2's in self-powered mode we are only use grid energy between November and mid-February, when our solar production is insufficient to full charge the PW's and cover our home/EV charging needs. We then rely on the grid to offset the difference. I live in a non-TOU state, and we don't need to worry about the lower power rates as we have a uniform rate 24/7.

DermMD | 2 mei 2019

I started a topic along these lines but it did not post. Maybe I have been burned from starting new posts. My thinking, and I could wrong, is that for me in MD where we have Net metering at retail value and not wholesale price, it does not matter when you draw from the grid. As long as you produce more than you consume in Kwh over a period of 12 months aggregated you're free to draw from the grid whenever you want. Over 12 months the power company aggregates your total draw and cuts you a check if you want for your excess production.
In the same vein, my thinking is that I do not want to tax my Powerwall installation too much with frequent charges and discharges so I can keep this setup for say 25 years. Hence use powerwall as backup only. Indeed in my state, my Net metering behaves as a Giant battery storage for my solar produced energy. I believe I have convinced myself in this line of thought and I may be blinded to other views. Comments, please.

DermMD | 2 mei 2019

Oops can't edit BANNED

DermMD | 2 mei 2019

I believe I'd connect to the house panel if your Solar Panels produce enough for consumption to answer your direct question. Additionally however, even if you did not produce enough for your consumption the Powerwall management portal allows you to manage your electricity use and export really good. So I see no point connecting separately to the grid with 2 Powerwall setup which is sufficient for whole house backup including car charging.

tslavin | 19 oktober 2019

Love that I found this and maybe a little late to the convo but I live in Texas and we don’t have TOU as far as I know. I’m getting solar panels installed but have a contract (with a penalty for ET) with my current REP. Texas is a deregulated energy market and these REPs sell electricity to the consumers. Net metering isn’t provided by this REP but there’s a few that do. My question is should I charge during the day if I don’t have net metering?

jrweiss98020 | 20 oktober 2019

tslavin: Yes. You should try to program all your high-load activities (EV charging, PW charging, dryer, oven) for when the PV panels are producing power. That way you will use all that solar power directly, and will not have to worry about the price difference for selling to the grid.

DermMD: In your case, it just doesn't matter (WA treats us the same, with net metering). Use your electricity as you need it. From all the discussion and graphs I've seen, you can discharge your Powerwalls to 20 or 25% SOC every night, and have 30 years of life in them. Just to ensure backup in case of grid outage, I restrict my PWs to 50% in the winter, because I cannot predict what days will produce enough power to fully recharge them. Since you cannot control the high level to which they charge (unlike the cars), restricting low states is your only option.

gregbrew | 21 oktober 2019

Charge your EV when electricity is cheapest. The cost of electricity is how the utility tells you when *they* want you to use the most. Don't forget that there is an approximate 10% loss of energy as it makes a round-trip through your Powerwall battery, so this should also factor into your cost calculations.

asdfasdfa | 24 oktober 2019


PapaSmurf | 15 december 2019

If you work from home, it is an easy choice. Program the Tesla car to recharge between 9 am and 3 pm. Or perhaps as little as 10 am to 2 pm.

240 volts and 30 amps = 7.2 kW (7,200 watts).

So if your house is likely mine, the minimum base load of the house (refrigerator, deep freezer in garage and some lights) is about 0.4 kW to 0.6 kW.

So if your solar system can exceed 8 kW during the middle of the day, then you can power the house and recharge the car without touching the grid. Just don't exceed your 30 amps on the car.

Of course, everyone has different numbers to plug into that calculation and time of the year will greatly affect your best midday max output. But you have to do that math for yourself as to what rate you can recharge your car without need the grid.

The highest I have seen my solar system produce so far is at 12.7 kW for a few minutes. So with a fully charged two Powerwalls allowing for 10 kW of continuous power, I could hypothetically recharge my Tesla at 240 volts and 80 amps.

240v 80 amps = 19.2 kW.
So if the two Powerwalls were at 90% or so and we were between 11 am and 1 pm when solar output likely exceeds 10 kW, I suspect I could recharge at 80 amps for about two hours on a good day, and still keep the basics in the house working at the same time. But just to be safe, make sure the AC and the electric water heater don't try to turn on during that time frame. Flip those circuits off on the panel.

Fun times with Powerwall 2 !!! First world problems !!!

getakey | 25 januari 2020

I have solar, EV, and just installed powerwalls. Looks like they removed the ability for me to control when the powerwalls charge from the app. I am on PG&E's EV TOU rate. I get very low rate from 11pm to 7am. How can I make sure the powerwalls do NOT charge my EV? this would mean I'm charging the EV with expensive rate electricity rather than the lower night rate. Not very happy that they removed that feature from the app

gregbrew | 25 januari 2020

If I'm not mistaken, the malfunctioning of the "Custom" settings is a bug introduced in the last firmware update (1.43.3). It should be fixed in the next one. If you need it sooner, others have reported that hitting the "RESET" button on the TEG made everything work again. Do so at your own risk.

That being said...I wish Tesla would allow us the *option* of getting the firmware updates. When mine is working just the way I expect it to, the last thing I want is a firmware update to fix compatibility with Zimbabwe.

Jones | 25 januari 2020

PG&E rates...
@Jagoedicke - I have been thru a succession of different PG&E rates in my decade+ of solar. The latest EV rates have actually become problematic for me because of the part-peak section.
The old E6 was best (which was replaced by E7) - both of which have now been discontinued and were replaced by TOUA. EV-A then became the choice until new rates were applied in November. EV-A is also being discontinued and replaced by EV-2. TOUA is also being discontinued and replaced by TOUB. Ultimately - come July 1, your choice will be limited to TOUB and EV2.
Bottom line - I did the math for me (10kW solar, 2 PW, Model 3) and TOUB is now optimal in terms of rates and time of use schedule.

getakey | 25 januari 2020

I'm on EV-A
Seems to work well for me, but I'll check out the math with TOUB
I have 11kW solar, 2 PW, i3. Started with 8kW, but swapped out dying gas furnace with heat pump so I added more panels. Haven't gone a full year with the heat pump and added solar. Only had solar 1.5 yrs. My first true up was $50.

I hope that losing the Advance custom setting is a bug.

getakey | 25 januari 2020

oops - I have 3PW. Given the state of the rebate program, buying 3 was the same price as 2

Jones | 25 januari 2020

I beat you on the true-up...2018 was $400 (rebate to me) and 2019 was $900 (rebate) which was mostly on EV-A. The new rate schedule for EV-A is predicted to reduce me to about $200 rebate. EV-B is predicted to zero me out - (in spite of the fact that I am a net producer of electrons). TOUB should get me back into the rebate territory.
All of the newest PG&E rate plans essentially devalue solar in terms of ROI and the only way to have any rational ROI is to have batteries. Higher expense, but (obviously) higher reliability in the face of power disruption and a slight edge on rate arbitrage.

getakey | 25 januari 2020

How did you get that much rebate? I thought any over production was only bought back at .02/kWh.
I was not aware that with solar, I cannot charge the powerwall from the grid. It seems as though the powerwalls will increase my electricity costs. I'll be charging the PW from solar when I could be getting the NEM credit.

How are you managing the PW to gain an advantage?

getakey | 26 januari 2020

Here's my main question of how the PW can help. In the summer, my peak rate is ~.50/kWh from 2pm to 9pm. Since I'm on the EV plan, I get off peak rate of .12/kWh from 11pm to 7am. Other hours partial peak is ~.33/kWh.

I'm over producing almost all hours the sun is shining.

Without PW, I would be getting NEM credit of .33 until 2pm and .50 from 2pm to 7ish. Then I'm charging my EV at .12 before 7am
With PW, I'm charging the PW during sun hours rather than getting NEM credit. Then when sun sets, I'm using PW to run the house. From 7ish to 9pm, its a wash. However, after 9pm, I'm losing money for every kWh I'm using the PW where the saved energy could have received .50 NEM credit. Its a wash for partial peak. However, I'm really losing money if the PW charges my EV instead of using the .12 from the grid.

How is the PW going to save any money?

Passion2Fly | 26 januari 2020

The PW will save you money if programmed correctly. You should set you peak times (under Advanced settings) to 2PM-9PM and off peak to 11PM-7AM. The rest is automatically considered shoulder time...

Here’s how it works:
- As soon as the soon rises, the Solar system will start charging the PW until 2PM.
- At 2PM the whole house will be powered by the PW and the ENTIRE solar production will be sent to the grid at $0.50/kWh.
- At 9PM, either the PW is empty and it shuts down until next morning, or it will continue to power the house until empty or until 11PM when the off peak kicks in...
- The PW will NEVER power the house during off peak schedules! If it’s not empty, it will stop until the next sun rise...

No worries, the Advanced setting is nicely designed...

gregbrew | 27 januari 2020

To clarify, the PWs will continue to power the house until their remaining capacity gets down to the set reserve value, which will be retained in case of a grid failure. If that value was set to zero, they will be empty. The reserve value setting is under the "Customize" section, along with the rest of the fancy stuff.

M3NOICE | 27 januari 2020

+1 @Passion2Fly That is exactly my setup.

Jones | 27 januari 2020

Tried posting several times and getting error message. Please pardon this "test message"

getakey | 27 januari 2020

Thanks Passion. The problem was that the Advanced/Time of Use function was not showing on my app. Today it appeared stating that it would not be available until 24 hours after install. So, yes I can see how to program it to take advantage of the rate differential.

getakey | 27 januari 2020

Just changed the settings. What is odd is that it is ~7pm right now.
PW is at 51%. House is using 1.2kW
Right before changing setting, PW was fulfilling house need.
Changed setting to Advanced/Time of use, and now power is coming from the grid. nothing from PW

Will continue to monitor

getakey | 28 januari 2020

There's something messed up in the app. I have it on Backup Only, but solar is feeding house not PW. No power going to PW at all and it is at 45%

Jones | 29 januari 2020

I used the exact scheme described by passion2fly and it gave me enormous rewards. Prior firmware messed up the ability to adjust times and schedules. Latest firmware (1.44.2) restored that function.

Passion2Fly | 29 januari 2020

It has been reported that SW 1.43.3 has issues. Call Tesla and asked them to push 1.44.2 to your PW.
Also, when you change any settings with your App, the PW doesn't receive the update immediately. It could take up to one hour for the updates to be pushed from the Tesla servers to your battery...

getakey | 29 januari 2020

the app seems to be settling down now. However, I think they setup my Powerwall under the wrong time zone. PW stopped feeding power to house at 7pm not 9pm. There was still >40% charge left. I changed the peak times and PW came back on. However those new time settings were gone today

I also seem intervals in Peak where the PW stops and energy is pulled from the Grid. Is something getting too hot and needs to cool? I'm usually only pulling 3 to 4kW. I would wonder what happens if there is a power outage

gregbrew | 30 januari 2020

PW2s are rated at 5kW continuous, 7kW momentary peak. If you have multiple PWs, they add together.

getakey | 30 januari 2020

I have 3 PWs. My question is during Peak, why would the PW completely stop sending power to house?
PW had ~50% charge

gregbrew | 30 januari 2020

Just speculation here, but do each of the Powerwalls know that there are two others? I think there's a configuration setting somewhere that tells them.

getakey | 30 januari 2020

my app knows that there are 3 total