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Off Peak charging advice

Discussion in 'Model S: Battery & Charging' started by Firewired, Nov 26, 2014.

  1. Firewired

    Firewired Member

    Joined:
    May 23, 2013
    Messages:
    367
    Location:
    San Antonio, Texas
    My Model S is projected to be produced in mid December and I need advice on off peak charging. I am in Texas and our electricity is pretty cheap compared to a lot of other places at $0.10/Kw anytime 24 hours a day. My current energy usage on average is 4500 Kwh/month before the car. I inquired to our local utility to see if there were any cheaper rates to charge off peak, and this is the off peak plan they have:

    $10.50 Service Availability Charge
    Summer Billing (June - September)
    $0.160 Per KWH for all On Peak KWH
    $0.051 Per KWH for all Off Peak KWH
    Non-Summer Billing (October - May)
    $0.105 Per KWH for all On Peak KWH
    $0.051 Per KWH for all Off Peak KWH

    I wasn't sure that was such a good deal as during the summer my hot Texas AC use will go up an additional 6 cents a Kw. What do you all think better to stay with the current plan or go for the tiered pricing? Thanks for any insight and advice.
     
  2. bollar

    bollar Disgruntled Member

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    Location:
    Southlake, TX
    What are the off-peak hours?

    If you're not home during a workday, and you use the car a lot, maybe it will work out for you, but my guess is not.
     
  3. dennis

    dennis P85D

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    Location:
    Silicon Valley CA
    In general, these plans only work to your advantage if you have solar PV at your home so you can reduce or eliminate the on-peak charges. In most cases the bulk of the usage is on-peak if you don't have solar.
     
  4. jcaspar

    jcaspar Member

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    Aug 19, 2013
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    Location:
    Sacramento
    You need to find out your peak/off peak hours. Here in this part of California we have pretty long off peak hours.
    Winter: 10pm to 4pm off peak
    Summer: 10pm to 2 pm off peak
     
  5. Firewired

    Firewired Member

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    May 23, 2013
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    Location:
    San Antonio, Texas
    Thank you for your input. This is their definition:

    The On Peak and Off Peak Monthly Consumptions will be the KWH's as determined by CPS Energy for the respective On Peak and Off
    Peak Periods. The On Peak Period is defined as 12:00 noon to 10:00 p.m. inclusive each weekday and all other hours are defined as the Off Peak
    Period. The following holidays will be considered Off Peak: New year's Day, Martin Luther King, Jr. Day, Memorial Day, July 4th, Labor Day,
    Thanksgiving Day and Christmas Day. Also, when any holiday listed falls on Saturday, the preceding Friday will be considered the holiday, and
    when any holiday listed falls on Sunday, the following Monday will be considered the holiday. All other hours are defined as the Off Peak
    Period.
     
  6. Cosmacelf

    Cosmacelf Active Member

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    San Diego
    #6 Cosmacelf, Nov 26, 2014
    Last edited: Nov 26, 2014
    Let's see. 29.7% of the hours during the week are defined as peak.

    If your usage stayed constant 24x7, then your blended rate would be 29.7% x .165 + 70.3% x .05 = .084 which is cheaper than your $.10 per kW/hr you now pay and you get to charge your car at the cheaper rate.

    Let's assume a pretty bad case scenario where during the peak rate time, your usage is double that during the non peak time. So 2 kW would be consumed every hour during the peak hours for every 1 kW every hour in the non peak times. So your energy consumption would be (10/24 * 5 * 2)/7 = 59.5% at the expensive rate.

    So, 59.5% x .165 + 40.5% x .05 = .118 per kW/hr. Which is more expensive.

    That's all in the summer. In the winter, it's a good deal regardless of the peak/non peak consumption pattern assuming your regular rate is $.10 year round.

    Now all this isn't factoring in the cheaper charging rate for the car. If you drive an average 12,000 miles per year, that's 1,000 miles per month at say 400 wh/mile (factoring in some charging inefficiency), that's an extra 400 kW/hr per month. So roughly 10% of your bill would be at .05 or .10 per kW/hr depending on which scenario.

    So ... It's close to break even for the worst case scenario. Personally, I would switch rates now and see what it does to your bill. You can always switch back.

    And given rates are going to keep rising, yes, a PV system makes sense...
     
  7. David_Cary

    David_Cary Member

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    Location:
    Cary, NC
    Agree with above. I don't know if it was realized or mentioned - summer is only 4 months.

    So you are only getting penalized for 4 months and then only 5 days a week.

    I went to a TOU when I got an EV. Also at that time, I got solar and an energy monitor. Obviously solar changes the equation completely. But skipping that, I was able to throw nearly all my hot water heating to off peak. I have a heat pump and in the winter I save a much bigger amount that a/c would have cost (if I didn't have solar).

    The hot water thing is pretty easy. Most tanks have 2 heaters. You set the lower one a little higher temp and put that on a timer. The upper one will still run if needed during peak but it mostly won't ever run.

    Having NG changes this of course.
     
  8. linkster

    linkster Member

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    Apr 22, 2013
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    Location:
    USAX2
    I installed a timer on the entire hot water heater that is energized 1am - 5am. I only have to override the timer when we have guests and its only a 50gal tank.

    Intermatic EH40 240-Volt Electronic Water Heater Timer - Wall Timer Switches - Amazon.com
     

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