Any reason to schedule charging if you have flat rate electricity price?

JMG · Sep 21, 2015

I realize that the less amount of time the car is at a high SOC, the better. However, here is my question/dilemma:

My electricity company does not have a plan that includes cheaper electricity for off-peak. Electricity is the same price (.06kwh total :wink

regardless if you are pulling it at 1PM or 1AM. When I first had my Model S, I had it set to charge at 1AM just to minimize the amount of time it would sit at a high SOC. I normally charge to 85 or 90%.

However, I've also thought "What if I have an emergency at 8PM". Like a family member goes to the hospital 90 miles away, or some other unforeseen event that I"ll need all the miles I can get. I realize this is far fetched, but still. So how much harm would I do if I just cancelled the scheduled charging and let the Model S start charging as soon as I get home from work up to 85 or 90%? I drive anywhere from 80-130 miles a day, depending on if I go visit any clients. It would just make me feel a little better if we had to rush out of the house one evening, going ahead and having a fully charged vehicle versus one that only has 115 miles on it.

How much real damage would I be doing to have the car sit at 90% for an extra few hours everyday?

efusco · Sep 21, 2015

Probably minimal impact. I schedule at 3:30am to charge to 90% so that my average SOC will be lower as I think it's better for the battery, even if the impact is minimal and to assure I have the full 90% charge when I start my day. The other reason might be 'big picture' for helping balance the grid and using electricity at off peak times, even if there's no obvious financial benefit.

Rockster · Sep 21, 2015

I'm in north Texas and during the spring and summer months I schedule off-peak charging just to help minimize demands on the grid.

AmpedRealtor · Sep 21, 2015

My electric company is doing everything it can to make life hell for those who want to install solar panels. I don't mind charging at 80A during peak load. Serves them right.

RandyS · Sep 21, 2015

AmpedRealtor said:
My electric company is doing everything it can to make life hell for those who want to install solar panels. I don't mind charging at 80A during peak load. Serves them right.

I know it makes you feel better, but if a lot of people did that, it would require infrastructure expenditures that all ratepayers would have to cover...

eye.surgeon · Sep 21, 2015

Short answer, no.

Long answer, your so lucky to have such cheap electricity. Here is CA even with an electric vehicle plan and solar, my peak rate in summer is $.44/kwh and my low overnight is $.10

ZachShahan · Sep 21, 2015

Generally speaking, it would help society.

Electricity demand is lowest in the middle of the night, so you will limit the need for peaker power plants & transmission improvements (to a small extent, of course). Additionally, certain power plants take so long to shut down or start up that they run through the night generating electricity that are not needed, and thus extra emissions. If you use electricity at that time, you may cut electricity generation (again, to a small extent).

In other words, it would be a nice thing to do.

MorrisonHiker · Sep 21, 2015

I recently had two 14-50 outlets installed. Combined with the existing 6-20 and 5-20 outlets, my housemates and I could conceivably have up to 4 cars plugged in at once. It will be years before we have this 'problem' but we plan on using scheduling to limit how many cars would actually be charging at once.

Hopefully in the coming years multi-EV households will be more common and EVSEs will communicate better with each other to determine charging priority and charge each car accordingly. Until then, I'll just plan on using a staggered schedule approach and schedule the car(s) with the longest commute(s) to start/finish before those with shorter commutes. If we do ever get 3-4 EVs all needing to charge at once, I would also dial back the amps used on the 14-50 outlets so that the 6-20 and even a 5-20 could all charge at once over the 100 amp line.

TL;DR: If you have multiple EVs, you might need to schedule charging.

liuping · Sep 21, 2015

eye.surgeon said:
Short answer, no.

Long answer, your so lucky to have such cheap electricity. Here is CA even with an electric vehicle plan and solar, my peak rate in summer is $.44/kwh and my low overnight is $.10

I wish our rates in San Diego were that low.

EV-TOU2 rates are $0.48 peek/ $0.172 super off peak. If we did not have solar, AC these last few weeks would have cost a fortune.

lucy · Sep 21, 2015

I am asking from a place of Tesla ignorance so be gentle...

would it be better to wait until later to let the batteries cool off? I have always let my electric mower cool down before recharging, because that's what the manual said to do.

Thanks

Cosmacelf · Sep 21, 2015

Home charging does not heat the Tesla battery appreciably. Your mower says that because it is a much smaller battery with no active cooling system.

If you have no TOU rate, I would charge whenever it made sense for me. Maybe the utility/regulator will get a clue someday.

techmaven · Sep 21, 2015

Texas's grid is not connected to other grids. There's enough wind power at night to drive prices into negative territory in some cases. If you charge late at night when others are not using much electricity, you have the lowest carbon footprint electricity going into your vehicle.

Of course, you might not care about this aspect. It depends on what your SoC is when you get home - if you regularly come home with very little and cannot accommodate occasional longish trips as a result, then delaying charging doesn't necessarily make sense for you. But if you can, you should wait until the wee hours to charge in order help both your grid and the overall carbon footprint.

You can search "wind power negative prices" to look at articles like this one:

Texas electricity goes negative: Wind power was so plentiful one night that producers paid the state to take it.

Khatsalano · Sep 21, 2015

If you can, you should always charge during off-peak hours to make it easier on the utility grid. Off-peak electricity is cheaper to procure wholesale during off-peak hours, and lower costs for your utility means lower rates for you in the long run. Also, off-peak generation tends to be more efficient and uses "cleaner" parts of the generation fleet as opposed to on-demand peak units. Basically, you're doing the environment a solid when you use electricity off-peak as much as possible.

- K

lucy · Sep 21, 2015

Cosmacelf said:
Home charging does not heat the Tesla battery appreciably. Your mower says that because it is a much smaller battery with no active cooling system.

If you have no TOU rate, I would charge whenever it made sense for me. Maybe the utility/regulator will get a clue someday.

Thanks, Cosmacelf, I have seen posts about the garages getting warm during charging, so wasn't sure if it was a factor.
this winter I'll be wishing for that!

David99 · Sep 21, 2015

Many good points about grid load and off peak generation.

The other aspect that works to your advantage when charging the car at night is that you keep the battery at a lower level for a longer time instead of charging right when you come back home. It is a know fact that Lithium batteries age quicker when their state of charge is higher. So charging at night timed so it finishes in the morning when you leave for work is the best way to keep your batteries healthy.

yobigd20 · Sep 21, 2015

JMG said:
How much real damage would I be doing to have the car sit at 90% for an extra few hours everyday?

zero. zip. zilch. just plug it in to charge every time you pull into your house. no need to schedule late night charging.

rxlawdude · Sep 21, 2015

liuping said:
I wish our rates in San Diego were that low.

EV-TOU2 rates are $0.48 peek/ $0.172 super off peak. If we did not have solar, AC these last few weeks would have cost a fortune.

SDGE has the highest rates in California. Even SCE, which is no saint, only charges $.11/kWh for EV-TOU off-peak.

Too bad the window for the EVSE submetering pilot ended, as you could have gotten a free submeter for your EVSE, and be billed solely for the EV consumption at the lower rate while not requiring the rest of your home (with solar) to be on a TOU plan.

We're on the tiered SCE rate Rate Schedule D, and with our 6.6kW PV solar, heavy daytime consumption for A/C and a couple of koi ponds, there's no way I'd move to whole-house TOU.

AmpedRealtor · Sep 21, 2015

RandyS said:
I know it makes you feel better, but if a lot of people did that, it would require infrastructure expenditures that all ratepayers would have to cover...

I know, and I'll eventually get over it. But at least allow me the illusion of "sticking it to the man"

lol

JeffVanEpps · Sep 21, 2015

liuping said:
I wish our rates in San Diego were that low.

EV-TOU2 rates are $0.48 peek/ $0.172 super off peak. If we did not have solar, AC these last few weeks would have cost a fortune.

Holy cow. I was feeling a tad annoyed at my rates, but no more. Is that at least the total for supply plus delivery?

davidc18 · Sep 21, 2015

we plug in every time the car is in the garage. generally set to charge at 10 amps, sometimes higher if we are doing a lot of driving during the day. I really like starting each day with a "full" tank, and we are looking forward to a future completely free of stops at the gas station.

Any reason to schedule charging if you have flat rate electricity price?

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