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 | 07. März 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 | 08. März 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 | 09. März 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 | 09. März 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. März 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. März 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. März 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. März 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. März 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. März 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 | 02. Mai 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 | 02. Mai 2019

Oops can't edit BANNED

DermMD | 02. Mai 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