1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Electricity Cost vs MPG

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by CaliforniaBear, Oct 12, 2012.

  1. CaliforniaBear

    CaliforniaBear Clearwater Blue Metallic

    Joined:
    Oct 9, 2012
    1,179
    289
    0
    Location:
    Northern California
    Vehicle:
    2012 Prius
    Model:
    Plug-in Base
    Electricity cost is the big factor in determining the equivalent mpg for the Prius Plug-in or any electric vehicle. If you have a green, low-cost source of electricity plug-ins are a big winner. If you get all your electricity from PG&E in California it may be a different situation. They have a progressive system for charges: Basic KWHours at $0.12, 100% to 130% of basic at $0.14, above that $0.30 per KWH. Check your electricity bill to see how much you pay.

    Shown below is my spreadsheet (sorry for the lack of column alignment). As you can see for the Prius Plug-In if the cost is 0.14 or 0.12 per KWH the effective mpg is very nice, at 0.30 not so much. Unfortunately any additional electricity at my house is at the higher rate. How about at your house?

    Electricity per KWH 0.30 0.14 0.12
    Charging KWH 5.4 5.4 5.4
    Cost/charge 1.62 0.76 0.65
    Miles/charge 12 12 12
    Cost for 40 miles 5.40 2.52 2.16

    Cost of a gallon 3.80 3.80 3.80
    Equivalent mpg 28.1 60.3 70.4
     
  2. Tracksyde

    Tracksyde Member

    Joined:
    Sep 21, 2011
    1,429
    761
    0
    Location:
    So Cal
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    Your "Charging kWh" is incorrect. Its closer to 3.2 kWh consumed from the wall. The battery's capacity is 4.4 kWh, but its not utilized 100% for battery longevity and health.

    But being in Southern California Edison territory, we're on a tiered rate plan also. I could go with the EV rate plan if I wanted to fork out for the modifications to accept a 2nd meter, but I'm not willing. As such, I'm at about $0.28 per kWh. At anything less than $4 a gallon, its a close call if you're talking financial reasons.

    But I figure I'd rather plug in each night than need to go to the gas station a few more times a year. Also I get "free" electricity from work, which pads my pocket an extra $0.70 or so per day.

    Lastly, consider that gasoline is always going up and will probably continue to rise for the foreseeable future. Looking back at my old car's fill-up records, its hard to believe I was paying $1.75 per premium unleaded gallon at one time.. and just yesterday, I had to fill up the wife's car at $4.65 per regular unleaded gallon.
     
  3. devprius

    devprius /dev/geek

    Joined:
    Jan 2, 2006
    979
    291
    0
    Location:
    San Francisco Bay Area, CA
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    PG&E actually has 2 more higher tiers, both at 34 cents a kWH. This applies to anything that is above 200% to 300% of baseline, and anything above 300%. It sounds like you don't go above tier 3 ever. Tier 5 used to be higher, but they redid all the tiers and tiers 4 & 5 were combined.

    When I first got the car, I ran the numbers, and as long as gas remained above $4 a gallon, it was worth plugging in, no matter what tier I ended up in at the end of the month. I've since put solar on the roof, switched to a TOU rate schedule, and charge at night when rates are about 11 cents, so it's definitely worth plugging in.
     
  4. CaliforniaBear

    CaliforniaBear Clearwater Blue Metallic

    Joined:
    Oct 9, 2012
    1,179
    289
    0
    Location:
    Northern California
    Vehicle:
    2012 Prius
    Model:
    Plug-in Base
    Thanks for two interesting responses.

    I'm not so sure about the 3.2 KWH since the specifications say you need a 15 amp circuit. Of course that could just be for a safety margin (9 amps actual would be a rather large margin) OR it could be that charging systems aren't 100% efficient and it really takes most of the 15 amps. It would be good if someone could make a measurement with a clip-on ammeter. Charging at work is nice, however, I'm retired :)

    I suspected there were higher tiers, fortunately I don't get there.
     
  5. terpsmandan

    terpsmandan Member

    Joined:
    Sep 26, 2012
    143
    13
    0
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    You are all going to hate me. I am on municipal electric and pay 2.97 cents per KWH. So it costs me less than 10 cents to "fill" my battery. I wish that my commute was less than 75 miles one way.
     
  6. priuskitty

    priuskitty PIP FAN

    Joined:
    Nov 18, 2011
    2,286
    335
    0
    Location:
    Clawson, Michigan
    Vehicle:
    2015 Prius Plug-in
    Model:
    Plug-in Base
    my Kill A Watt meter says 11.79 amps @ 120 volts
     
  7. John H

    John H Senior Member

    Joined:
    Jun 4, 2012
    2,208
    557
    0
    Vehicle:
    2007 Prius
    Model:
    N/A
    I suspect that PG&E have some provisions for EV charging so that you don't get kicked into the 3rd tier quite as fast. You might want to call them and tell them that you are using at least 100kWh ($30 at tier 3) for EV charging and they may qualify you for a different tier scheme or just credit/rebate you for $20 every month.
     
  8. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    17,035
    10,010
    90
    Location:
    Western Washington
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Electric code safety margin requirements limit a 15 amp circuit to just 12 amps of intended load. Since Kitty's charger is running at 98% of that allowed load, Toyota didn't add more margin than already required by the NEC.

    While most customers have 20 amp circuits (16 amp design load), so don't.
     
  9. priuskitty

    priuskitty PIP FAN

    Joined:
    Nov 18, 2011
    2,286
    335
    0
    Location:
    Clawson, Michigan
    Vehicle:
    2015 Prius Plug-in
    Model:
    Plug-in Base
    I used a data logger to graph my charging sessions, you can view my charts at my thread "Attention Kill A Watt Nerds"
     
  10. rockfeller

    rockfeller Junior Member

    Joined:
    May 20, 2009
    88
    3
    0
    Location:
    CA
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    I fall in the same category,

    For Zip code 95117, winter pricing tiers are like this:
    Tier 1: 0-351 kWh $0.13 per kWh ,==46$
    Tier 2: 352-456 kWh $0.15 per kWh==16$
    Tier 3: 457-702 kWh $0.30 per kWh ==73$.
    Tier 4:703-1053 kWh $0.34 per kWh ,
    Tier 5:1054+ kWh $0.34 per kWh

    Before PiP I was in tier 1. paying about .13cents, about 46$,
    Now I do charge everyday night, and use about 3.2 kwh *30 ==100kwh + 351kww=451kwh monthly,

    If you see price range above,
    from Tier 2(i.e 46+ 16 $) to Tier 3(i.e 46+16+73) , it makes sense for me to not hit Tier3 but stay in Tier 2.

    So to increase my PiP EV ranges, I must stay in Tier 2 about 450kwh/month,
    To stay in Tier 2 ,here are the things I have changed at my house:


    1. Move to Gas Drier,
    2. Move to Gas Stove.
    3. Add motion-sensor based, battery powered LED lamps all over house like
    inside bathrooms, closets, kitchen, garage, wherever you tend to burn electricity
    These cost about 15$ for a 100-200 Lumen Lights, and last 6 months to 1 year minimum.
    My battery coast is about 15$/6 month if I buy in bulk.
    4. Replace all old power consuming appliance with Energy Efficient Star rated appliance.
    5. Remove all the charger from the Hook , use only when you need.
    6. Use Mac's, sorry windows lovers.
    7. Take PG&E smart day event seriously, generally 2PM to 7PM[go shopping]
    Rates at this time are .76 cents !!.
    8. Off-course replace all the lamps with LED or Fluorescent lamp all over house.
    9. Replace all Tube and LCD TV's with LED TV .
     
  11. John H

    John H Senior Member

    Joined:
    Jun 4, 2012
    2,208
    557
    0
    Vehicle:
    2007 Prius
    Model:
    N/A
    I applaud your desire to conserve electricity but would encourage you to re-evaluate the use of disposable batteries. Also, I will assume your hot water heater was already gas, or solar.
     
  12. rockfeller

    rockfeller Junior Member

    Joined:
    May 20, 2009
    88
    3
    0
    Location:
    CA
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    Yes, I already have gas water heater, if not should be good idea to replace one.
    Some I have 'rechargeable', but planning to replace all into 'rechargeable', not a bad idea.
     
  13. cwerdna

    cwerdna Senior Member

    Joined:
    Sep 4, 2005
    12,544
    2,122
    1
    Location:
    SF Bay Area, CA
    Vehicle:
    2006 Prius
    That is very cheap. Do you live in the Pacific Northwest?

    Those in CA will fall over when they see rates like
    2012 Rates (July 1, 2012)
    (and less so at Seattle City Light: Electric Rates & Provisions) vs. ripoff PG&E, esp. if their usage is well beyond the baseline.

    Ignore the demand charges unless you happen to have a draw of over 50 kW at a given time (seems pretty darn hard to do in a house).
     
  14. John H

    John H Senior Member

    Joined:
    Jun 4, 2012
    2,208
    557
    0
    Vehicle:
    2007 Prius
    Model:
    N/A
    A couple of Tesla's in the garage with dual chargers :)
     
  15. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    it's not about the money.
     
  16. wjtracy

    wjtracy Senior Member

    Joined:
    Sep 19, 2006
    11,309
    3,586
    1
    Location:
    Northern VA (NoVA)
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Owning a plug-in in CA has two benefits one is HOV access and the other is helping to solve CA smog problem by diverting some emissions to power plants located elsewhere. But saving money over gaso is not so important in CA.
    CA is a special case with elec supply issues and gaso supply issues, so if you own a plug-in you have some flrxiblity to deal with either upset case.
     
  17. terpsmandan

    terpsmandan Member

    Joined:
    Sep 26, 2012
    143
    13
    0
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    Penn Yan NY but we have a municipal electric, not NYSEG.
     
  18. John H

    John H Senior Member

    Joined:
    Jun 4, 2012
    2,208
    557
    0
    Vehicle:
    2007 Prius
    Model:
    N/A
    at $0.30/kWh, payback on a solar installtion would be fairly rapid, then you would have FREE fuel.

    I understand that solar installs in CA are a net positive home improvement for resell value.

    Home Improvement Returns: Solar Power Savings
     
  19. Corwyn

    Corwyn Energy Curmudgeon

    Joined:
    Mar 6, 2011
    2,171
    659
    23
    Location:
    Maine
    Vehicle:
    2007 Prius
    Model:
    II
    At $0.30 per kWh, and California levels of sun, you ought to be able to buy a solar array on a home improvement loan and reduce your monthly payments significantly, right now (forget payback).

    Assuming 5.5 sun-hours per day, a peak watt of panels costing around $4.00 installed, a 15 year home improvement loan at 3.25%APR, the cost per kWh of your electricity would be around $0.12 per kWh. So you would want to size your array to definitely keep yourself out of tier 3, and as much of tier 2 as you want/can.
     
  20. John H

    John H Senior Member

    Joined:
    Jun 4, 2012
    2,208
    557
    0
    Vehicle:
    2007 Prius
    Model:
    N/A
    with tax credits and such added that gets down to about $0.08 per kWh or lower. That is also $0.08 in pre tax dollars, so maybe $0.05 or less in after tax dollars. I know it's funny math, but a dollar saved is worth more than a dollar earned when the tax man is involved.