Home vs Public charges: which one cheaper?

Discussion in 'Clarity' started by qtpie, May 3, 2018.

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  1. qtpie

    qtpie Active Member

    We live in Alameda County, east side of San Francisco area. When I checked our recent utility bills for the past few months (before getting our Clarity), our electric rates (per kWh) is 21 cents for Tier 1 and 28 cents for Tier 2. PG&E only allows 327 kWh per month in Tier 1, then rate jumps to Tier 2. These rates are before taxes and other additional charges. My wife can charge at her work place for only 15 cent/Kwh. I can charge at my work for $1/hour.

    It looks like charging in public is cheaper than charging at home. Is my calculation right on this? Thanks.

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  3. KentuckyKen

    KentuckyKen Well-Known Member

    Qtpie, I think you’re right.
    Obviously $0.15/kWh wife’s work place charger is cheaper than $0.28 or $0.21 at home (even more so more if you count taxes/fees), so the question is does $1/hr at your work place turn out cheaper?

    Assuming work charger is a full Level 2 32 amp EVSE, then you can fully charge from 0 EV/2bars in about 2hr15m for around 47 EV miles using EPA #s. That’s $2.25. I think EPA uses 33 kW/ 100 miles and several posts have said they see 14-15 kW usage per full charge so those two figures kind of agree. So if you assume you’re getting 15 kW for $2.25 over 2.4hr, that’s $0.15/kW ($0.16/kW using 14kW/full charge).
    So then your work charging is cheaper than home electric rate and roughly on par with your wife’s work charging costs.
    And that means to avoid marital discord over who gets to drive the Clarity to work.... you need another Clarity!

    OK, now my head hurts. Can some one check my math and assumptions and/or come up with a better way to calculate this?
    Last edited: May 3, 2018
  4. Wall-e

    Wall-e Member

    Look into time of use rates, if you have low usage during the afternoon know as on peak you can reduce your rates. I am in Southern California under SCE territory, I switched to time of use rates. We charge at night which is 0.13 cents/kWh in the winter and 0.12 cents/kWh there is a 0.55 cent daily charge so effectively those rates are 0.02 cents higher

    PG&E is regulated by the CPUC and so is SCE so I think your rates will be very simular
  5. jdonalds

    jdonalds Well-Known Member

    Those are some high rates. It looks to me that you're better off charging away from home for the present time. I'd keep a watch on the rates to make sure things don't flip on you. Also compute the price of gas into the equation. It may be cheaper to use the engine. This is one of the benefits of a PHEV.

    How about looking into solar. There are several ways to install solar including a lease plan that will cost you nothing to install.
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  6. marshall

    marshall Well-Known Member

    It's not surprising that you are getting a better deal during the day as they have too little demand between 9am to 3pm due to solar energy, especially in the spring and fall.

    I read a while back that they when asking for approval from the regulators to supply grants to install charging stations at work locations.
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  8. delrey

    delrey New Member

    I live in Alameda county too. I have PG&E. I switched to the EV plan, time of use. In the summer rates are higher, but winter evening rates are 12 cents per kWh.

    Maybe look at the pg&e rate comparison tool? It's decent.
  9. bfd

    bfd Active Member

    Your wife is getting a decent deal. Let's say you spend $2 for 2 hrs of charge. As mentioned, at level 2 charge, that should just about fill your battery.

    At her rate, she'd spend about $1.80 for that same two hours of electricity… (I'm assuming 12 kW @ $0.15/kWh)

    Your at home price would be almost double that (at $0.28/kWh). Even if you go TOU, and charge in the middle of the night on super off-peak plan, you're still better off charging at work if you can, since the lowest rate (right now down in the far southwest corner via SDG&E the price for super off-peak is $0.228/kWh year-round). Off-peak for winter is a penny more, so it's OK to charge during the day. But summer peak rates for TOU shoots up to 53.7¢¢/kWh! So there's no charging from 4PM to 9PM.

    Within 5 years, the entire state will be on TOU, so enjoy the tiered rates while you still can - but realize that by using an extra 10-20 kWh or electricity a day, you will soon be well past tier 2 into tier 3. SDG&E instituted a "high-user" charge - basically a 4th tier that was just whacked. Seems like your best choice for now is to charge up at work and maybe just depend on the home charging for weekends or top-offs.
  10. Viking79

    Viking79 Well-Known Member

    CA has a ridiculously messed up power grid. I can't believe how high rates are. Here they are about 11 or 12 cents/kwh for residents, and maybe 7 or 8 cents/kwh for businesses. (Without time of use billing.)

    This was a good read on CA power issues and massive over supply: http://www.latimes.com/projects/la-fi-electricity-capacity/
  11. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    I'm gobsmacked that any place you actually have to pay to charge would be less expensive than charging at home, but I'm certainly not going to argue with KentuckyKen or his math!

    I think this goes in the "Strange but true" file.
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  13. M.M.

    M.M. Active Member

    Have you looked at EV-A and decided it won't save you money?

    You look like you're probably on E-1 (non-time-of-use tiered) or similar, which generally speaking is a really bad deal with an EV unless you use very little power ordinarily, you also don't drive much, and for whatever reason you tend to use most of your electricity between about 1pm and 9pm. Once you get past even a modest amount of driving, you're in Tier 2, which costs a fortune--similar to peak rates on other plans, but all day.

    If you drive a moderate amount to a lot, and either don't use that much electricity otherwise or can avoid the heaviest use during peak period (afternoon/early evening), EV-A will definitely be your best bet--just make sure your car (or charger) is programmed to start charging at 11pm. Then you're only paying 10 or 11 cents per kWh to fill up the car, and while peak power will be really expensive it's still only about what you're paying for Tier 2, and there are no caps. Non-EV time of use is also probably better, but unlike EV-A it still tiered, so is only likely to be worthwhile if you don't drive much and don't use much home power, either.

    Incidentally, math-wise, the Clarity is rated at about 3.2 miles/kWh and 42 miles/gallon, which is to say that at Alameda-lowest price of $3.35/gallon using the ICE is the equivalent of about 25 cent/kWh energy (actually probably 22 cent due to charging inefficiencies). EV-A is about half that if you only charge at night (and you might also save money on your household bills if you usually ended up in Tier 2 anyway or can shift use outside peak period).
    Last edited: May 4, 2018
  14. Wall-e

    Wall-e Member

    That link contains a lot of fluffy "information". A lot of California's power comes from natural gas and renewable energy. One of those you do not have control over. During a hot day you might need both to supply enought power otherwise you would have to drop load. Transmission lines have a high utilization during the hot days (we have plenty of them). The solar and wind farms are in the desert far away from people. The Natural gas plants are near the coast (need to bring it to the people). The power company doesn't own power plants, they purchase power from independently owned operators. When demand is high the price is high. When its not hot or electricity demand is lower they sit idle.

    This is the point of time of use rates. To discourage high usage during high demand. When utilization is low they sell it cheaper
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  15. M.M.

    M.M. Active Member

    California has made some poor energy market decisions in the past, and they do factor in to some of today's cost of energy, but trying to point to generation capacity as the sole reason for California's relatively expensive energy is an oversimplification. Some of the reason, for example, is simply that the state has decided to prioritize renewable build-out over cheapest-possible energy.

    That said, I'm not as plugged in to CAISO energy markets as some people I work with and know, so I can't comment more specifically on how accurate overall that LA Times article is in its conclusions, one way or the other.
    Just to note, somewhere around 35-40% of the PV in California is small behind-the-meter systems at the residential or commercial scale, so a fair amount of that generation happens near the point of consumption. Which doesn't actually change much--in most parts of the state intermittency is a much bigger factor in utility markets than constrained transmission.

    Getting way off topic here, but power flow issues do drive cost, and actually the current time-of-use rates lag the duck curve resulting from surprisingly rapid PV adoption statewide. It's getting close to the point where on sunny days, particularly in the spring and fall, the period around noon should be cheaper than the middle of the night--utilities and CCAs are occasionally paying negative marginal rates for energy at those times due to comparative oversupply. The oversupply, of note, isn't necessarily due to having too many plants online--you'll need those plants a few hours later after the sun goes down and everybody gets home from work. It has more to do with the relative inflexibility of most large power plants. PG&E actually recently replaced my county's main plant with one that can be adjusted from 100% output to nearly 0 on a very short timescale, in preparation for more renewable-based variability.
  16. qtpie

    qtpie Active Member

    Thanks everyone for your replies. We always thought that charging at home should be cheaper, because we don't have to pay for the "convenience" and other fees imposed by the company who owns the charging stations. I guess this math proves us wrong.

    We have switched our rate plan to EV-A and plan to charge our car mostly during off-peak hours. We'll see if rates would be better in bills for next few months.
  17. Viking79

    Viking79 Well-Known Member

    Most of the electricity fee is actually in your physical grid connection. In the US utilities tend to under price that connection fee and charge based on usage. This allows them more control over how much they charge. Your work probably pays a much lower rate than you do at home per kwh, they probably pay a higher grid cost or just buy a lot more kwh so they are charged less per kwh. So any usage delta doesn't tend to cost them as much as it might cost you at home.
  18. Timothy

    Timothy Active Member

    In most places your instincts would have been right. In NC it is certainly cheaper to charge at home (not counting free charging stations).
  19. Mikep00

    Mikep00 Active Member

    All depends upon the ‘math’ for your area. Here locally, pay public chargers on average cost double what it would cost to charge at home. ~$0.50/hr at home versus $1/hr at public charger.

    Which is still very reasonable all things considered.

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  20. bobcubsfan

    bobcubsfan Active Member

    We have had solar since 2009. We generate more than we use (LADWP will not refund the overage) so it costs nothing to charge the Clarity nor did it to charge the Leaf with a much larger battery pack.
  21. bfd

    bfd Active Member

    Many of us are now paying (indirectly and directly) for the successful lawsuits over backcountry fires. Every year there's another REALLY big one, and somehow it always turns out to be somewhat attributable to ignition from a wire. Even if that ISN'T the case, the PoCos are replacing as many wooden utility poles - think about the cost here - with metal or composite ones - and as fast as they can. So we're paying for that directly. We're not supposed to be paying to compensate them for losses due to fines and lawsuits, but 'Transmission' and 'Interconnection' hide a multitude of these costs. With the rapidly changing climate, we're in for lots more of these "seasonal" firestorms - as well as the costs involved in recovering from them. "Seasonal" may just end up being year-round within 50 years or so…
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  22. bobcubsfan

    bobcubsfan Active Member

    Another reason to go solar.
  23. Atul Thakkar

    Atul Thakkar Active Member

    How much does typically in USA does it cost for 10KW system which is very standard in Canada ?
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