California EVA Gas/Electric Cost Calculator

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by Phil Edholm, Sep 23, 2014.

  1. Phil Edholm

    Phil Edholm New Member

    Joined:
    Sep 23, 2014
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    Location:
    Pleasanton, CA
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    We just bought a 2014 Prius Hybrid as we realized that the electric cost saving of the PG&E EVA ToD Tiering plan could save us almost the monthly cost of the car. However, the EVA tiering is really expensive during the day. My wife asked if she should plug it in and I had no idea. So I generated a gas to electric cost comparison tool that lets you enter the rate pricing, the price of gas and some other variables and it calculates the compared cost for the first 12.5 miles (that is what we are getting as we live up a hill). The tool is in Excel and the results are shown in the figure. As you can see, in the Peak Tier (2PM to 7PM Summers, 3 PM to 7 PM winters), it is actually 43%more expensive to use electric than gas based on the $0.38 per KWh. For us, my wife uses the car for a round trip early weekdays and this tool shows that it is worthwhile to plug it in if we are going to drive later in the day, but leave it off charge if not.

    Rate Calc.jpg

    Anyway, I loaded the file on my business wen site and you can download it if you want to do it for yourself. The yellow cells are the entry cells. The sheet is locked so it is not easy to screw it up, but there is no password, so if you want to change it, unlock the sheet. This is the URL to download the tool. The forum will not let me put a link in yet, so I am going to fake it out. Here is the link in a jpg, I will re post later when I get permission form the site as a copy-able link.

    Tool.jpg

    What is interesting is that nighttime charging is 62% less expensive than gas, wish it had a slightly bigger battery..... Anyway, hope some of you find and this interesting. I also added an image of the rate structures here that I posted for us to remember.

    PG&E Rates EV-A.jpg
     
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  2. se-riously

    se-riously Active Member

    Joined:
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    Location:
    SF Bay Area
    Vehicle:
    2014 Prius Plug-in
    Model:
    Plug-in Base
    I used a similar spreadsheet, but instead I downloaded my usage each day, each hour from the PG&E website and compared the EVA rates versus my E-1 rates. I even tried the EVA rate for 3 weeks before switching back to E-1. For my usage pattern, I found that:

    1) The PIP is unable to charge enough electricity to take advantage of the lower EVA off-peak rates and offset the higher mid-peak and peak costs during the rest of the day.
    2) To really save money, I'd have to do laundry on weekends only, or after 11 pm on weekdays, which wasn't feasible with a family of 4.
    3) The high peak rates discourage me from charging during the day, meaning that on weekends, it's cheaper to use HV mode even though I could have done the trip in EV mode if I had charged.

    I think the EVA rates are better if you have a Tesla, Leaf, Volt, etc. and a long enough commute where you can really "load up" during off-peak times.
     
  3. CaliforniaBear

    CaliforniaBear Clearwater Blue Metallic

    Joined:
    Oct 9, 2012
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    Location:
    Northern California
    Vehicle:
    2012 Prius
    Model:
    Plug-in Base
    I agree. the EV-A rate does not provide any benefit for the modest amount of kWh used by the PiP. Depending on your usage pattern the later Peak usage schedule may make EV-A more expensive than E-6. However, if you have a Tesla or other car with high electricity usage EV-A is a good deal. My calculations (similar to the OP) show that E-6 provides only a small advantage over E-1 because my solar panels keep me within the baseline (Tier 1) for most months. I'm considering going back to E-1 next "NEM year" to avoid the inconvenience of Time of Use.
     
  4. CaliforniaBear

    CaliforniaBear Clearwater Blue Metallic

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    Location:
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    Vehicle:
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    Plug-in Base
    Phil, that is a really great spreadsheet! I have a couple of nit-type comments. The battery capacity from 20% SOC to 85% SOC is about 2.86 kWh. (4.4 kWh battery total) Charging efficiency considering power from the wall is probably more like 90%. The word "Tier" is normally used in the progressive rate increases based on monthly totals. You might want to use Peak, Partial Peak and Off Peak per the PG&E rates. Many people get better than 48 mpg after the electricity is used up. On long flat freeway trips I get about 53 mpg. For mountain/hilly trips I get closer to 62 mpg due to the great regeneration charging of the PiP.

    Needless to say putting my numbers in the spreadsheet doesn't make much difference. With my solar panels and considering either E-6 (charging mostly at night) or E-1, my charging cost is about $0.14/kWh.
     
  5. Barbara R

    Barbara R Junior Member

    Joined:
    Aug 23, 2014
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    Vehicle:
    2014 Prius Plug-in
    Model:
    Plug-in Base
    I developed a mini-version of this for my own use and agree that most of the time during summer (May-October) it doesn't make sense to charge between 10 AM and 9 PM. I just bought my Prius and switched to a time-of-day plan but think I'll switch back in May. Thanks for posting this!
     
  6. bisco

    bisco cookie crumbler

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    can you switch back and forth whenever you want?
     
  7. CaliforniaBear

    CaliforniaBear Clearwater Blue Metallic

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    Location:
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    Vehicle:
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    No at least for folks with solar. I was allowed to switch in the middle of my first year to EV-A but that was an exception as far as I know. At the end of the year I switched back to E-6. As discussed above E-6 is somewhat better for the modest requirements of the PiP.
     
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