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Best time-of-day for charging with Puget Sound Energy (WA state)

Discussion in 'Model S: Battery & Charging' started by deonb, Mar 29, 2013.

  1. deonb

    deonb Supporting Member

    Mar 4, 2013
    Redmond, WA

    PSE in WA of course don't currently charge time-of-day usage fees.

    However, I still wanted to make sure I charge my vehicle at the best time of day so as to optimize grid and green energy usage. I thought it may be a good idea for other PSE EV customers to also be mindful of this, so that that PSE don't feel compelled to have to charge for time-of-day usage in order to handle the increasing demand for EV's, which sounds like they are considering. Charging at specific times will of course be easier for us after the 4.3 software update.

    I contacted PSE about their actual recommended time-of-day, and here is the response I got from Patrick Leslie (in short - 11pm to 5am):


    Hi Deon,

    Congratulations on your Tesla purchase! Thanks for your excellent question and for your concern about reducing impacts on the grid and the environment.

    We don’t currently have a time of use rate because given the relatively small number of EVs on the system, the cost to implement outweighs the benefits. We anticipate that will change once we reach approximately 10,000 vehicles. We’re currently at about 1,500. We’re seeing about 1.1kW of peak-coincident load per EV. To put that in perspective, our system peaks at about 5,500,000 kW. Our system peaks daily in the early morning and mid-evening, and critical peak typically occurs in the 5-7 am timeframe on the coldest day of the year. In general, charging between 11p and 5a is the best to reduce grid impacts. But let me reiterate that our grid is robust and we hope that EVs are adopted widely. The benefits of increasing throughput during off-peaks hours great exceeds the cost to upgrade transformer and prepare the grid in other ways.

    As for reducing your environmental impact, our energy mix varies greatly by the day, month, and season. It’s practically impossible to make a general rule as to the best time to charge. We have a large share of hydro generation, so during spring runoff our entire region can have surplus hydro for limited periods. During other times of the year, we may be using more “thermal” generation (fossil fired). Wind is a growing share of our mix, but it comes and goes as it pleases and we generally balance the variability with hydro. How we dispatch generators also depends on what’s happening in the electric markets as far away as California. In general, our coal plant runs baseload, so your EV will not affect the dispatch of that plant. Most of the generation “on the margin” is hydro and natural gas, therefore if you are charging during peak periods, the additional load from charging your vehicle will likely come from a simple or combined cycle natural gas generators, or from shifting hydro generation around. I apologize if this isn’t clear, but there’s no cut-and-dry answer.

    If you wish, you could sign up for our Green Power program, which supports local green power projects in the Northwest.

    Thanks for your interest,

    • Informative x 1
  2. TurboFroggy

    TurboFroggy Member

    Dec 5, 2012
    Everett, WA
    Yep I always charge after at least 10PM just to be kind to the grid and the local transformer. I have been eagerly awaiting 4.3 so I can just set the timer like our 2 year old Leaf can do already. I have been plugging in then going to my Tesla app on my Windows Phone and stopping the charge. I then start it charging when I got to bed at 10PM. Between the Leaf and the Model S we are drawing around 14KW from 10PM until 1AM then 10KW from 1AM until around 4AM. However we put 35.69KW/h of power onto the grid today from our solar, whoohoo!!
  3. pilotSteve

    pilotSteve Active Member

    Jul 14, 2012
    Vancouver WA
    @deonb - thanks for your post and the info. I am on Clark County PUC and I had one of their engineers come to my house to see the HPWC in operation. They were amazed to see 80A/240V draw (my entire large house was running about 17A so charging was a 5x increase) but our neighborhood was fortunate that they upgraded to 7.5kVA transformers and underground feeds to the distribution is quite robust. The engineer hooked up a recording amp meter to my utility feed and recorded the HPWC coming online and ramping up to 80A. He was impressed with the gentle startup even with the eventual high currents.

    I asked about TOU they said very similar things. No TOU plans yet for Vancouver. Ours was the first Tesla they'd seen or heard about and it took some explaining so they understood the battery size and consequent charge requirements of the Model-S vs. a Leaf for example.

    They thanked me for calling them and for educating them on EVs.
  4. olanmills

    olanmills Member

    Jun 20, 2012
    Wow thanks for posting that info, it was interesting. However, I really think it will be impossible to make any sort of positive impact just by choosing your charge times as an individual; the majority of people either won't know or care about such factors. What would really happen is that if it actually becomes a concern, PSE will have to implement incentives/disincentives to use electricity at different times, and the most straightforward idea is of course rates that vary at different times of the day.

    You know what could be even cooler? Smart meters with rates that vary based on real-time conditions, and of course, the customers would need to be able to easily see those current rates in order to decide how much electricity they wanted to use at that time.

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