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True added cost of home EV charging on PG&E

Discussion in 'California' started by miimura, Jun 13, 2014.

  1. miimura

    miimura Active Member

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    #1 miimura, Jun 13, 2014
    Last edited: Jun 13, 2014
    Calculating how your electric bill will change after you bring home your electric vehicle is not easy in California where we have tiered electrical rates. However, I have done an analysis of the true added cost to charge an EV in the SF Bay Area on PG&E. This analysis is based on actual SmartMeter data from two different homes with different usage profiles. Of course, your situation may be significantly different than these two cases, especially if you live in the East Bay where the AC demand is much higher than western Santa Clara County. All EV charging is assumed to take place during the Off-Peak hours of 11pm-7am.

    The first home is a ~1,700sf 2BR 2BA single level detached townhouse in Cupertino. A retired couple lives there. This is what I consider to be a small home and their average electric usage is about 425kWh/month with only December and January over 500kWh.

    TownhousePGampEAnalysis_zps3c2a4db7.jpg

    Choosing the best rate plan, Schedule EV, would result in an increase of about $60 per month to the electric bill at the townhouse. This comes to approximately 6 cents per mile. Staying on the same rate plan that most people use, E-1, would result in a bill increase of more than $120 per month, doubling the incremental cost of EV charging.

    The second case is a single family home in Los Altos with 5BR 4.5BA ~4,800sf in two stories. A family of 4 lives there including two elementary school children and one parent works from home most of the time. The average usage is about 700kWh/month for most of the year, with Nov-Jan over 800kWh and peaking at just over 1,000kWh in December.

    SingleFamilyPGampEAnalysis_zps5bcad901.jpg

    You can see that the average monthly bill without an EV is MUCH larger for the larger home. This is primarily due to the tiered rate system that penalizes high usage. The larger house is already paying over $160/mo for electricity, so adding EV charging and using a non-tiered rate adds less than $25/mo to the bill. That's only 2.5 cents per mile!


    The details of the Townhouse analysis can be found in a PDF here. That PDF contains the actual usage and the projected usage with EV charging calculated on E-1, E-6, E-9A, EV month by month.
    The single family analysis can be found in a PDF here. The spreadsheet that I used to do these calculations is here. It uses SmartMeter data downloaded from PG&E to do all the calculations. Rates in the Excel workbook are from the Tariffs effective 5/1/2014.
     
  2. lloyds

    lloyds Member

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    Actually very cool info here. Thanks for sharing. Personally, adding the 2nd P85+ is costing us about $100 extra per month and we are running on a Solar City system now w/ E9 rate at 0.04 / kw from 12am-7am. I drive about 100 miles daily, so it's quite a bit and I make it out to supercharger about twice a wk
     
  3. miimura

    miimura Active Member

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    PG&E rates were revised August 1, 2014. This is not unusual, it happens all the time. However, this is the first time in 3 years that the baseline quantities have been changed. For example, territory X which includes all of Santa Clara County and most of the temperate zone up and down the state has been decreased from 11.0kWh/day Summer and 11.7kWh/day Winter to 10.1 Summer and 10.9 Winter. That will push people into the higher tiers with less usage. Tier 3 (130% of Baseline) where the rates really start to go up used to start at 429kWh/mo, but now start at 394kWh in the summer. E-1 rates now jump from 17c/kWh to 26c/kWh at that level. They have actually made the ramp less steep by raising Tier 1 & 2 rates and lowering tiers 3, 4, and 5. Tier 3 used to be 32c/kWh and 4 & 5 used to be 36c/kWh.

    Determine Your Baseline Quantity

    Schedule E-9, the old EV rate plan was changed in a similar way - the rates on the lower tiers were increased and the rates in the higher tiers were reduced. The cheapest Off-Peak rate is now slightly over 5c/kWh while it used to be slightly under 4c/kWh. The tier 4 & 5 Off Peak rate is now just under 17c/kWh, down from 21c/kWh.

    In any case, if you're on Schedule EV, the baseline changes do not affect you since that rate schedule does not have tiers. EV rates were reduced across the board. You will now pay slightly under 10c/kWh Off-Peak in Summer and Winter, a reduction of about 0.1c/kWh.
     
  4. astrotoy

    astrotoy Member

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    Thanks for all the work. We are on the EV rate schedule and are closer to the Los Altos home example. We always charge starting at midnight, so we are on the approximately 10 cents/kwh rate (almost the same summer and winter). We do have a bunch of solar panels on our roof, so much of our peak load is offset by the solar. However, since the peak tiers do not correspond to the peak of the solar energy, we are still paying a fair amount at the highest tier and second tier.

    I have done rough calculations and it appears that I am paying an excess of around 10 cents per kWh for running the Tesla. At about 333 watts/mile, that works out to about 3 cents per mile. I'm sure there are some inefficiencies in charging that I am not calculating.
    On the other hand, our month long trip to LA to visit our daughter's family was greatly subsidized by Tesla, using the SC's for free at Harris Ranch, Lebec, and even a few visits to Hawthorne, along with some free charges at Whole Foods in Westwood and the free public lot in Beverly Hills.
     
  5. ken830

    ken830 Model S (Res#P12,447)

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    Thanks for summarizing the changes! Reading PG&E rate schedules always requires so much concentration. Comparing two of them to find changes is not something I want to do.
     
  6. miimura

    miimura Active Member

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    Each page of the tariff has a unique Effective Date for that page. The Baseline table is on its own page, so that is how I knew how long it had been since the Baselines had changed. Changes are noted in the margin (N for New) and all rates have (R) or (I) next to them indicating if they have been Reduced or Increased. Also, when you're replacing the values in a spreadsheet with the new ones you quickly get a feel for how much they're changing.
     
  7. rnlass2

    rnlass2 Member

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    Incredibly helpful. Called SoCal yesterday and pretty much got what you said in suggested changes (I look like the townhouse profile). Was not offered the non-tiered plan. Suggestion was to have one full month of my current standard and then compare. Thanks to your clarifications I will no longer be trying to compare watermelons to elephants. I wasn't even close to apples and oranges in thinking. Thank you.
     
  8. miimura

    miimura Active Member

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    SoCal Edison has a different rate structure. From what I've heard, they push people to get a dedicated meter for EV charging even though the up-front cost of installation by your electrician usually exceeds $2,000. Their "Home + EV Plan" (TOU-D-TEV) is good for off-peak charging, but can really jack up your bill if you use A/C during the day. Because their peak hours are 10am-6pm weekdays, you can really earn some big summertime credits with solar on this rate plan. I strongly recommend anyone with an EV and SoCal Edison service to get solar if at all practical. Their rate structure makes the payback come quicker than other places.
     

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