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Can I control rate of charging at home? Solar, peak meter charge

Discussion in 'Charging Standards and Infrastructure' started by nursebee, Dec 16, 2015.

  1. nursebee

    nursebee Member

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    #1 nursebee, Dec 16, 2015
    Last edited: Dec 16, 2015
    Hello,
    We have solar power on our house, produce all we need. We are still connected to the utility, pay about $30 a month for that honor, plus about $7 per peak kwh. Judging from records we expect our peak demand to run 4-7 kwh each month. Here are my questions then:
    1. If we had a Tesla, could we program the car for when it would charge and at what rate?
    2. If the car can't be told what rate to draw power, what kwh does it draw on 110V, 220V(nema 14-50), or home charging station?

    In less than a month we have excess generation of >250kwh. If our daily drive distance is 30 miles, some 60 milers, doesn't this seem like we could power our car with solar electricity if we can keep the peak demand charge down? Our regular direction of longer distance travel has convenient superchargers.

    Thanks for your input.

    Edit below, found this chart on Tesla site. WOW.
    We actually rent out rooms on Airbnb, installed a 14-50 outlet about 2 years ago. Nobody has come, but damn! It could cost up to $70 in peak meter charge for letting a tesla charge on that outlet and we only rent out for $50. LOL
    Gotta rethink this. echarge.PNG
     
  2. spottyq

    spottyq Member

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    The MS can draw anything from 1A* up to 40A (or 80A with dual chargers.) in 1A steps at whatever voltage you provide it.
    Since you should be recharging it with 220V (it really does not make any sense to use 110V, especially if you want load management) you can control the power usage of the car with a granularity of 220W.

    The best way to do this would be to get your EVSE to communicate with your electrical meter in order to know how much to draw at each instant; the EVSE would communicate that to the car (via the pilot signal) and the car would follow these instructions.

    The good news : the MS follows the pilot signal down and up when charging.
    The bad news : no charger that I know of can communicate with the electrical meter. It is possible to make your own EVSE and to integrate such functionality, however it requires the will to tinker and some programming skills.

    Hope this helps you.

    *I'm not sure if it can actually get down to 1A.
     
  3. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    The minimum limit is 5A, I believe.
     
  4. Rocky_H

    Rocky_H Member

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    Are you sure of those units with saying it’s $7 per kwh? Where I live in Idaho, our electricity cost most of the year is 7 CENTS per kwh. I can’t imagine anywhere on the planet that it is 100 times higher than that! Even in really expensive parts of the country, it’s only about 30 to 40 cents for peak times.

    Anyway, on the programming capabilities, here is how that works. You can set in the car a programmed time of day for charging to start. That only applies for AC charging, though, since for Superchargers and CHAdeMO, you are obviously wanting to use it as soon as you are plugging it in. You can flip that timed setting on or off as needed, like if you’re on a trip, you may want to use a business’ charger during lunch. As to the current, when you set the current level, it will remember that current level tied to that GPS location, so when you charge there, it will always use that current again at that place. Yes, 5A is the minimum.
     
  5. nursebee

    nursebee Member

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    Yes I am sure of the units. netmeter.PNG
     
  6. MorrisonHiker

    MorrisonHiker Beta Tester

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    #6 MorrisonHiker, Dec 16, 2015
    Last edited: Dec 16, 2015
    Looks like they might have the wrong units there. If you look at C, it has both dollars ($) and cents (¢). I think it should just be cents for C...and probably B as well. I'm sure they aren't charging $13.668 per kWh. $0.13668 (or 13.668 cents per kWh) is much more likely.

    This reminds me of the cell phone company that listed data charges as something like $0.01 cents per gigabyte. It's either $0.01 or .01 cents. BIG difference!
     
  7. nursebee

    nursebee Member

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    That at is the charge for the peak demand, the highest draw from them. In other words, they have to recoup money for periods of high demand such as high ac usage cause they have to buy expensive power then.
     
  8. MorrisonHiker

    MorrisonHiker Beta Tester

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    Ah, thanks for the explanation. I didn't see it was for peak usage (nor the kW vs. kWh difference). That makes more sense...so your peak charge might be 1 or 2 kW, not 900 kWh (example usage for the entire month)!

    Still..the units for C are wrong. It should be dollars or cents, not both.
     
  9. Rocky_H

    Rocky_H Member

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    #9 Rocky_H, Dec 16, 2015
    Last edited: Dec 16, 2015
    There we go. Thanks, @nursebee for showing that. Yeah, the demand charge is from the rate of energy use, not amount of energy. It does surprise me that it says (All kW). Most demand charge systems have that as a penalty thing above a certain level, so if you keep your usage rate below some threshold the whole month, you don’t get hit with any demand charges.

    @MorrisonHiker, Yes! That was Verizon math. If you have time, the blog site is still there telling the whole story of that, with recordings of his calls with idiot Verizon support people who can’t tell that there is any difference at all between “.02 cents per megabyte” and “.02 dollars per megabyte”.

    VerizonMath
     

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