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The Future of EV Home Charging and the Grid

Discussion in 'Energy, Environment, and Policy' started by gnuarm, Jan 17, 2019.

  1. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    READ MY LIPS! THIS IS NOT ABOUT GENERATION OR TRANSMISSION!!! This thread is about local distribution. Before anyone posts another comment about the time related excess capacity in generation and transmission learn the difference between transmission and distribution.

    A good example is the telephone network. They phone system has layers of interconnection. If a phone in Frederick, MD wants to talk to a phone in Fremont, CA, the Frederick phone is connected to a switch in Frederick which connects that phone to a trunk which takes the call to Baltimore where another switch connects it to another trunk that connects to a switch in Chicago, which uses another trunk to connect to a switch in Oakland, etc until it reaches the switch in Fremont that connects to the phone there. As the call goes up the tree to a main trunk, capacity can be maxed out at any point, any switch may be overloaded or any trunk lines between switches may be overloaded. So even if the system works just fine 99.99% of the time and the person you are calling only uses the phone 1% of the time, there is a chance you will not be able to make your call because the next town over has a big fire and lots of people are calling to make sure their family is ok.

    In the same way, adding a relatively small number of relatively heavy loads can overload a nearly maxed out local distribution network on a cold winter night when residential demand is at it's peak.

    This has nothing to do with the generators on the dam 50 miles away or the transmission lines that Ross Perot said we should have built to carry wind power from the central plains to the coasts. LOCAL DISTRIBUTION. Look it up and learn something about it before you reply. Thanks.
     
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  2. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    I'd like to make one point about the carbon impact of charging EVs. Yes, not all electricity comes from burning carbon. But two points mitigate that. One is that a significant portion of the power plants still burn coal, in 2017 it was still 30%, while natural gas supplies 32%, nukes are at 20% and renewables are at 17% (hydro 7%, wind 6%, biomass 2%, solar 1%, geothermal 1%) and petroleum just 1%. Worse, the energy in coal is from virtually 100% carbon producing the maximum amount of CO2 possible. At least in an ICE a significant portion of the energy comes from turning the hydrogen into H2O.

    EIA - Electricity in the United States is produced with diverse energy sources and technologies

    The efficiency numbers don't pan out either. Most power plants are only a little more efficient than the car engine. Then there are transmission losses and losses in charging the battery and powering the engine in an EV, so the raw numbers actually work out to be about the same. The EV however, has regeneration which helps reduce the use of energy. So when all issues are factored in there is not a large advantage to EVs in terms of generating carbon... yet! As more and more solar comes online and wind production increases this can change.
     
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  3. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    The issue is not average. They don't size the distribution grid based on average use over the month or year. They look at the total demand of each piece of the grid so they can size the distribution transformers and wiring. This size must be sufficient for the maximum demand at any time.

    Some people will talk about the "average" home usage over time and look at the peaks. To use those numbers you have to multiply by the number of homes to get back to a total number for sizing equipment. But no one cares about the average over the day, month or year unless you are counting beans perhaps. Equipment has to be sized to the peak demand.
     
  4. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    Maybe, maybe not. Compared to my TOU plan I would get something like 450 kWh a month for $30. I'm pretty sure I only use around 250 to 300 kWh per month from home for charging.

    Do they give you a Tesla charger? I suppose it is another brand that lets them meter and control the usage? What is the charge rate capability? Does it have to be installed permanently or does it plug into a 14-50 plug?

    I'm interested in this because this is the sort of thing that will be needed to prevent major overhauls to local distribution... which happens to be the topic of this thread.
     
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  5. mspohr

    mspohr Well-Known Member

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    The phone network doesn't work like that anymore. It's all packet switched now like the Internet.
    Local distribution is not a problem. The distribution wires are sized for Max load (afternoon, not when EVs charge). The power company may have to upgrade a local transformer here and there as more people charge but that's it.
    My local transformer is only 25 kW with 5 houses and two Tesla's. No problems yet but if more neighbors get EVs, they may need a bigger transformer.
     
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  6. mspohr

    mspohr Well-Known Member

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    Just wrong. ICE engines are only 25% efficient (20% if you count well to wheel). Fossil fuel power plants are greater than 80%.
     
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  7. brkaus

    brkaus Well-Known Member

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    Regions are all different due to weather, energy types available for heat, etc. Here is some data for New England that appears to show higher peaks in summer. I looked at New England as there is less Natural Gas in the area I think. Texas has much lower load in winter due to natural gas.

    Anyway -

    ISO New England - Energy, Load, and Demand Reports

    The ISO New England Control Area net summer peak load of 25,899 MW (gross peak was 29,660 MW after reconstitution) occurred on August 29, with a WTHI of 82.0.

    The ISO New England Control Area actual winter peak load of 20,599 MW (23,528 MW after reconstitution) occurred on Friday, January 5, with a dry-bulb temperature of 7.6oF.

    ---

    Regarding control, there are wifi connected J1772 EVSE that could be remotely controlled. In theory, an external box could be added to an HPWC and act as a master and provide control for up to 3 daisy chained HPWC devices.
     
  8. Big Dog

    Big Dog Member

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    Ok, I see what you are getting at, but strongly disagree that residential demand of a local residential grid is at its peak at night, cold or otherwise. Please post the data/reports to support your assertion.
     
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  9. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    That's not the point. It was an analogy. The way the electrical grid works is that way. The local grid does not see the same loads as the main grid which is feeding both residential and commercial distribution. So they will be loaded differently at different times of day. I am pretty sure I provided some numbers for my personal use. My max usage during summer peak times has been up to about 4 kW. My max usage on winter nights has been about 12 kW. This is not uncommon in much of the country where many homes are heated with heat pumps with electric backup. The local distribution capacity is pushed at a different time than the generation capacity which is pushed at the times when both residential and commercial customers have maximum overlap.

    My numbers show if you have just two of those five customers have heat pumps they can come pretty close to maxing out your local transformer with zero Teslas. Two Teslas charging at 72 amps (18 kW) will also max out the transformer. This is simple math. No?

    What about the lines feeding that transformer and the lines away from the transformer? What about the transformer feeding the line with your transformer?

    BTW, your 80% number on the efficiency of the fossil fuel generators is just plain wrong. You can find numbers from 30% to 45% here...

    EIA Efficiencies
     
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  10. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    None of this is relevant to the discussion. If you don't understand why, please research the difference between electrical generation, transmission and distribution. Thanks

    Yes, devices exist, but are they suitable for control by the utility? I believe I had mentioned the idea of an external unit to control HPWCs, possibly in another thread. But still, it all has to be done in a way that is secure and meets the needs of the utilities... such as potentially providing accurate metering of the power which is no small requirement requiring significant testing and certification.
     
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  11. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    I did post my personal numbers, didn't I? If not, I did just a few messages back.
     
  12. mspohr

    mspohr Well-Known Member

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    The local distribution system is designed to handle peak loads. EVs are not charged during peak times which is afternoon and evening. (Your anecdote is irrelevant)
    Power plants are twice as efficient as ICE engines.
     
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  13. wycolo

    wycolo Active Member

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    #53 wycolo, Jan 20, 2019
    Last edited: Jan 20, 2019
    > Heat pumps aren't that efficient in the northeast or west. [Big Dog]

    Real domestic heat pumps use 15 foot deep loops which offer a year-round optimum loop temperature which (magically) is cool in summer and warm in winter. But I doubt most heat pump installations bother with all that digging.
    --
     
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  14. adaptabl

    adaptabl Banned

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    Your number are wrong.
     
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  15. adaptabl

    adaptabl Banned

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    In cold climates there is not enough energy in that 55 degree loop to heat homes efficiently. We looked at that as a solution and natural gas was a winner by a mile for efficiency.
     
  16. wycolo

    wycolo Active Member

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    "Winner by 1.6 kilometers" would sound even better!

    If the loop was actually 55* there would be no problem. You could use just a simple heat exchanger without a pump to keep a base temp in the house. Having a house at 55* minimum all year would be nice.

    Of course there are maps of zones beyond which the attempt to extract heat from the earth becomes futile. Pure clay would be ideal for this; I've been down in a 7 ft deep ditch here in pure clay and sensed the great potential - imagining what it would be like at twice the depth. But the over abundance of beetle-killed lodgepole pine hereabouts dictates wood burning over digging a loop.
    --
     
  17. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    The distribution part of the electrical grid is designed to handle the peak distribution loads. The peak distribution loads happen at different times than the peak generation and transmission loads because the residential loads do not have the same timing as the commercial loads which are typically on different parts of the distribution grid.

    My anecdote is VERY relevant because every home with a heat pump is doing the same thing when the weather is too cold for the heat pump to work effectively. Even without considering heat pumps, the loads placed by EV charging are very significant compared to the typical loads on the residential distribution grid. You need to understand that the electrical grid is not a unified entity with homogeneous characteristics.

    A better analogy would be roads. You have widespread gridlock at rush hour with many arteries clogged. In your neighborhood the roads are likely busy, but not clogged. However, before rush hour, the road in front of the high school gets clogged at 2:30 when school lets out. Local congestion with it's own rhythm.

    If you can't accept these facts you are simply in denial.
     
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  18. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    So what are the correct numbers?
     
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  19. gnuarm

    gnuarm Model X 100 with 72 kW chargers

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    Dude, I have no idea where you are getting your information, but you are wrong. A 55 degree ground improves efficiency of a heat pump tremendously. The only problem is they are expensive to install and maintain. You can read about ground based heat pumps on many web sites. Do me a favor and don't post further on the ground based heat pump issue since it is off topic in this thread.
     
  20. Lloyd

    Lloyd Well-Known Member

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    I can see a time coming where the power companies will dictate when you will have the best rate to charge to help balance the loads. One area for example may have block A, b or C. A starts charging at 11 pm, B starts at 1:00 am, C starts at 3:00 am etc. This way there is not a huge load change and demand when the rates first drop.
     
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