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Weird Data from PG&E

Discussion in 'Model S: Battery & Charging' started by mposki, Jul 18, 2015.

  1. mposki

    mposki Member

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    2 week old 85D owner and just looked at my PG&E usage by day. The other day I charged and believe that u needed to put in, at most, 20 kwh yet the bill seemed to show I sucked down 40kwh between 12 and 2 which is the time I have my car set to charge. Is this something that I can have my local SC look at my logs about? Any thoughts or insights?
     
  2. cpa

    cpa Member

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    mposki,

    You do not give us enough information to be able to give you a reasonable guess. Was your charging the only electrical activity occurring at your home at the time? What sort of charging configuration do you have at your home? If you have an HPWC and dual chargers you can get 80 amps with 240 volts, or 19.2 kWh. Two hours at that rate is pretty darn close to 40kWh.

    If you do not have dual chargers or only used a 40A source, then your usage for two hours would be about your 20kWh figure.

    Was this midnight to 2AM or noon to 2PM?

    I would also set my charging display to show kilowatts added, and not mileage. Then after charging is completed, compare the amount recognized by the car to your PG&E usage graph. Make sure you are not using any other household appliances, and turn off your HVAC unit during your test period. That might give you better insight too.

    We live in the Central Valley, and we used to leave the HVAC on all night, and sometimes it would kick in for 30-40 minutes while we slept.
     
  3. miimura

    miimura Active Member

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    Post the chart from PG&E MyEnergy to illustrate what you're talking about. Here's a sample of mine. I have solar which is why it goes below zero.

    PGE Usage Day View.jpg

    That chart is 15 minute bars of metered kWh energy. The big fat spike is 40A charging. It's an old image I had sitting around. I'm guessing it's 14 bars at 2.8kWh = 39.2kWh. It includes the "dark draw" from my house overnight too. If you have it open on the PG&E site, you can hover over each bar and it will tell you the actual time period and metered energy. For example, 01:00-01:14, 2.85kWh
     
  4. mposki

    mposki Member

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    So in reviewing it was about 12 kwh from 0:00 to 1:00 then 19 kwh from 1:00 to 2:00 and then 9.5 kwh from 2:00 to 3:00. I am using a HWPC with a dual charger running at 80A. What seems quite odd about it is that it was less during the first hour. I am charging to 90% and did not think I was that close to 50% but maybe I was. Really it is just that the pattern seems weird as I would assume that the first hour it would be running at more kwh as it was more empty. Do these details help, am I over-worrying?
     
  5. Khatsalano

    Khatsalano Member

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    Do you know what is your base load? Even just lights, refrigerator, wifi routers, and other electronics will be a couple hundred watts base. I'm assuming you don't have A/C.

    Also keep in mind that there is loss ... 20 kWh through your meter isn't 20 kWh into your battery. There are loses from the meter to your HPWC, from your HPWC to your car, and from the inverters in your car itself. Nothing is 100% efficient, not even a simple piece of copper wire. :)

    - K
     
  6. miimura

    miimura Active Member

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    Do you have any way to know exactly when it started charging? 12kWh in the first hour and 19kWh in the second hour probably means it started at 00:22, all else equal.
     
  7. David_Cary

    David_Cary Member

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    My thought exactly.

    I have a higher resolution monitor and the car always starts at full speed charging. There is no taper that I've ever seen but I don't think I've ever range charged at home. The Leaf tapers at about 95%.

    The y axis seems to be labeled incorrectly 3kwh?, It should be more like 20 kw.

    Unrelated but I see no reason to max out your chargers every night. Slow and steady is more gentle. Does it matter much - no. But when 3 neighbors do the same thing at midnight, you might blow a transformer. You also create the most heat in the chargers and battery by doing that. Can they handle it - sure. Is it ideal - probably not.
     
  8. Owner

    Owner Active Member

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    don't have time to look at your numbers in detail, but your pattern looks exactly like mine. I don't have dual chargers. You can compare yours to mine:

    Annual Solar Panel Check | TESLA OWNER
     
  9. brucet999

    brucet999 Active Member

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    Part of the difference is in conversion. Don't forget that AC to DC conversion efficiency is around 85%, so PG&E will show about 17.5% more AC kWh than the battery receives in DC.
     
  10. miimura

    miimura Active Member

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    #10 miimura, Jul 20, 2015
    Last edited: Jul 20, 2015
    No. It is correct. They are graphing metered energy (kWh) during the given interval. 3kWh for a 15 minute interval is a 12kW power draw.

    Edit: New graph added with bar data shown.
    PGE Usage Day View 150704.jpg

    This specific graph has two EVs charging during the highlighted period. One at 240V 40A and another at 120V 12A. The remaining approximate 120V 3A is background draw of other stuff in the house, which is also shown by the tiny bars at the beginning of the chart.
     
  11. sorka

    sorka Active Member

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    That's strange. I'm only losing about 1 kWh for each 20 kWh that the battery records going into it. I had expected to lose more but don't appear to be.
     
  12. RAW84

    RAW84 Member

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    How do you get this number?
     
  13. sorka

    sorka Active Member

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    This based on how much PG&E says I used in my hourly data usage graph vs how much the car said it charged. My baseline usage is 241 watts when everything is turned off in the house. So the periods I used to calculate that show 241 watts per hour before and after. I subtracted that base off of the amount actually used to charge and then subtracted what was reported by the car from that.
     
  14. RAW84

    RAW84 Member

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    In the post I quoted and underlined above it seemed you were saying the battery was recording how much energy was going into it while charging and you could see that.

    I take it you're just looking at the kWh from the "Trips" section of the menu?
     
  15. CHG-ON

    CHG-ON Still in love after all these miles

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    I am sure it has been mentioned. Sorry for not reading everything. In a rush.

    Without a separate meter, you simply cannot tell. Unless, of course, you unplug everything in your house (not for me!). Give it some time and you will better understand what the cost is.

    Make sure you get the PGE EV rate plan. Then it is dirt cheap to charge. It took me two billing cycles to understand just how cheap it is to charge.
     

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