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Home charging vs Chargepoint at work

Discussion in 'Charging and Infrastructure' started by ng0, Sep 12, 2017.

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  1. ng0

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    So with deliveries approaching, I started getting a little nervous about the cost of charging my Tesla at home. Here in San Diego, the cost per kWH could reach as high as $0.50. Now I don't know much about Chargepoin+ but the chargers outside of my work say they cost $0.75 per hour and looking at the screen it says 6.6kW. I could be reading that completely wrong, but by my calculations that would be $0.113 cents per kWH. Even at the lowest possible rate I could get at my house, it wouldn't be anywhere close to that. Does that mean it would be best for me to charge at work as often as possible? Am I looking at that right or do I have something wrong?

    Thanks!
     
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    • SoFlaModel3

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      Do you have off peak rates in San Diego? We don't have it in Florida, but if you do, you can ensure the car only charges when rates are lower for you.

      As for your main point of the question. I'm not 100% sure so hopefully someone confirms.
       
    • JWardell

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      Wow, why are your electric rates so high? Especially down in sunny San Diego, I would imagine you should install solar all over your home and it would pay for itself in no time!

      Your math is correct, and I never looked at it that way...here charge point charges 50 cents/hr, which comes to 7.6 cents per kWh, which is half what I pay at home. Not to mention it is half the price of the $1 per hour of street parking, not to mention the daily rate of my work parking garage (though there is a 2hr limit at the charge points and they are almost always occupied).

      Of course that means that your car is charging at the maximum rate, which may not occur at the top 10% of the battery or once it is charged, but for the rest of the time, good point, it is cheaper to pay for a charger!
      I assume the same might be true once Tesla starts charing for superchargers.
       
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      • ng0

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        Thanks for the responses! Yea, I'm absolutely planning to get solar, but right now I'm trying to plan around my potential home renovation/expansion. If I build a second floor, I'd have to redo the roof anyway. I'm not clear on how charging my model 3 will effect my electricity bill, but from what I can tell I'll for sure be consistently up in the tier2+ category and it'll be upwards of $0.42 plus fees for that. You make a good point about chargepoint not necessarily charging at the fastest rate, but even then I'd guess I'll still be in the $0.20 or less range per kWh.
         
      • Derik

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        The chargepoint location in front of my work is $1.50 an hour (6.6 kwh charger) but 1/2 mile away my work has some that are $0.75 an hour for the same thing. So I'm thinking it is going to be cheaper to park and walk the 1/2 mile to my building.

        I don't live in SDG&E area, I live in an area with SCE and they have super off peak which drops them to around $0.13 on a couple of the planes from 10 PM till 8 AM.

        Even at the super off peak rates it is still cheaper to use the Chargepoint stations as long as they are under $0.85 an hour at 6.6 kwh.

        I've got solar on my house, but it was sized for my usage a couple years ago. So far it's covered all of my electricity needs plus some extra. Not going to come close once I get my model 3.
         
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        • ng0

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          Thanks for the response! Sounds like your line of thinking is very similar to mine. I'm not sure if I'd be willing to walk the half mile you're talking about doing, but it's definitely a good discount. Maybe some day you'll be able to drive to work and have your car drive over to the charging station, charge and come back to pick you up later. ;-)
           
        • Derik

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          Maybe that FSD package is starting to look nicer. But still, it's a chargepoint charger, I don't think there will be an automated charger around here for a while.

          Maybe I can make friends with the security guard. :D

          I'd walk the 1/2 mile for 50% off. Assuming I need 75 kwh it's ~$17 vs ~$8.50 every couple days. Plus the walking might do me some good. Damn engineering job always keeping me in a cubical.
           
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          • ng0

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            hahah.. I definitely feel you. I work in a cube all day so every so often I try to go outside and take a little walk. I guess a mile before and after work isn't bad, but then you can't go anywhere for lunch unless someone else drives. :)
             
          • RandyS

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            ng0, Check out the EV-TOU2 rate...You're currently on the tiered DR rate, and charging your car will put you into the second more expensive tier. If you switch to the EV-TOU2 rate, which is time of use based, the cheapest time to charge the car is after midnight. So you can set the timer and plug in the car when you get home...
             
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            • ng0

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              Thanks for the suggestion! I looked into that and it's really tempting to switch over. I'm just not sure if it'll be worth it for me. I have a baby at home all day with a/c running during the summer so 50 cents per kWh is pretty pricey for peak hours.
               
            • RandyS

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              The time of use periods will be changing on December 1 due to the shift in the real-world peak on the power system. Changes to TOU times will be as follows:

              summer season will be 1 month shorter (June 1 to Oct 31) and winter season will be 1 month longer (Nov 1 to May 30).

              On Peak: 4-9pm
              Super off peak: midnight to 6am on weekdays, midnight to 2pm on weekends
              Off peak: all other times

              March and April: new super off-peak time from 10am to 2pm

              You can do a spreadsheet to calc it out...One thing I tell folks is that you have to think of annual costs with this rate. The benefit of EV-TOU2 is that during the entire winter season, which will be 7 months of the year, the 3 TOU prices are just a couple of cents apart no matter how much you use. It's only the summer season that has the higher peak price, and it's only 5 hours a day. Charging your car after midnight will tip those scales in your favor...Most people benefit from the rate...
               
            • ng0

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              Thanks again for all the great info! You're right, I really do need to do a spreadsheet and figure out which plan would be best. Things have changed significantly for me in the past year with having a baby, so our A/C units are running a lot more than they used to. Also, people are home with the baby all day, so all of a sudden we're using electricity a lot more during the peak hours. San Diego really only has a month or two a year where A/C is necessary.

              I looked at my SDG&E account and it says that I could've saved $55 by using the "Time of use plus plan" this past year. I'm not sure if that would still apply with the baby and the new car, but definitely something to consider!
               
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              • ng0

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                It's funny, I went to another one of my company's buildings right down the street that has the same chargepoint charging stations and sure enough the cost was $1.50. I think those are controlled by the company next to ours though. I can only assume that our company is somehow subsidizing the cost to bring it down to $0.75 per hour. Hopefully the ones here stay that way and the 4 charging stations don't fill up!
                 
              • Derik

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                If it is a building 8 vs building 7 thing then we might work at the same place.
                 
              • ng0

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                hahaha.. awesome! :) We'll have our own Model 3 club soon! :p
                 

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