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Understanding Tesla's TOU modes.

Discussion in 'Tesla Energy' started by Sylvia Else, Sep 1, 2018.

  1. Sylvia Else

    Sylvia Else Member

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    This is something I posted on Whirlpool, but I'll post it here too.

    I've been trying to fathom the rationale for Tesla's TOU modes of operation.

    Powerwall Modes of Operation with Solar

    "It can save energy capacity to charge from a higher priority source later in the day."

    Given that the only sources are solar and grid, does this make any sense? Any solar that's not used now either for charging or for consumption has to be exported. In the absence of variable solar export tariffs based on time of day (which the Powerwall doesn't know about anyway), is there any conceivable benefit to be had from exporting solar now, so as to leave room for charging from solar later.
     
  2. cwied

    cwied Member

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    The algorithm seems to be set up for Net Metering in the California style, where the solar export tariff equals the import price (hence the "Net"). I was wondering if they set up the configuration differently in Australia to accommodate the concept of export tariffs, but from your comment it sounds like that's not the case.
     
  3. Babaron

    Babaron Member

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    Not sure I understand the question but I got the impression that using the excess power generated by solar to export to grid vs charge pw could be made based on time of day/night. Credits and charges can vary based on the time of day so it might make more sense to export when credit would higher and similarly, charge pw from grid when cost of energy from grid is lower. In other words, use grid to charge when grid cost is cheap, and use pw to power when grid cost is higher.

    Does that clarify or did I miss the question?
     
  4. CA-Gbm84

    CA-Gbm84 Member

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    My understanding of it is there are more than 2 sources depending on your TOU schedule, and energy usage. I believe in Australia it is assumed that the export value is very low or zero, in contrast the net-metering in some US areas.

    Sources - I can think of at least 5 to charge from (more if there is variable export rate).

    1. Solar - Net
    2. Solar - Gross
    3. Grid - Off-peak
    4. Grid - Shoulder
    5. Grid - Peak

    In your example, the priority is not just charge now or not, but also charge from gross or net solar. In both cases the export will be zero, but charging from gross will increase import (hopefully during off-peak!)

    Eg - High peak consumption day (or low PV production)

    Consumption: 5 kWh (peak)
    Solar production: 5kWh (off-peak/shoulder).

    In this case you need ALL solar to be charged, ignoring round-trip efficiency losses, to have covered the peak consumption. If you had charged from net, you would be short.

    Eg - Low consumption (or high PV production)

    Consumption: 3 kWh (peak)
    Production: 5 kWh (off-peak/shoulder)

    In this case charging from gross production is excessive as you have increased your off-peak/should consumption by 2 kWh, which is not needed, you've just swapped free energy for cheap energy (and incurred more RTE efficiency losses).

    Then you have to consider how much energy is currently available, the actual price of each period, and the expected production/consumption - so not a trivial optimization.
     
  5. NinjaVece

    NinjaVece Member

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    For those using the Powerwall 2 in Advanced: Cost Saving Mode, here are some aspects of the Powerwall 2 software to be aware of:

    First, let's get the terminology straight that Tesla uses: Off-Peak is what Tesla calls the blue portion of the display when identifying TOU time periods. Shoulder-Peak is the grey portion of the display and Peak is the orange portion of the day.

    Most grid operators do NOT include a Peak period for their weekends - only Off-Peak and Shoulder-Peak (blue and grey). Thus, while you generally set up your Week Price Schedule to include all colors (Peak, Shoulder-Peak and Off-Peak) at their appropriate times, you would only set up your Weekend Price Schedule to include Shoulder-Peak and Off-Peak timeframes (the grey and blue colors).

    This leads to a problem, however, with how Tesla decides to recharge the Powerwall 2. When you are in Advanced: Cost Saving mode, the system will ONLY recharge the Powerwall 2 on days that there is a Peak time set. If there is no Peak time that day, there will be no recharge of the Powerwall 2 from the day before.

    That means that if you had your Reserve set to 40% and your Powerwall 2 was used on Friday to that level, on Saturday AND Sunday, it will NOT recharge the Powerwall 2 back to its 100% level. On any day without a Peak setting, it will leave the Powerwall 2 at the level last used the day before.

    This is fundamentally a BAD policy and Tesla Powerwall Tech Support has agreed it is. The software needs to be updated to have the system update the Powerwall 2 to full 100% power WHENEVER the solar panels are active and the system is not in a Peak setting. The reason is that the Powerwall 2 is left for two days in a reduced state (the example 40% Reserve) and if a power outage were to occur between Saturday and Monday, the system would not be able to be at its best to back you up during that outage.

    There is a work-around until Tesla corrects this error. Simply apply a 30 minute Peak period at some time for the Weekend Price Schedule (example: from 2pm to 2:30pm) and the Powerwall 2 will be used a small amount for house power yet not delve deep in the power cycle for those two days. You will be able to minimize deep power cycles by 2/7ths (Saturday and Sunday) or 28% reduction each week while still keeping the Powerwall 2 'topped out' for random grid outages between Saturday and Monday.

    We all want our Powerwall 2s to last as long as possible while both cost shifting through Peak periods under TOU and protecting against the random grid outage that can occur. Minimizing battery cycles during the years it is in operation extends the Powerwall 2's life while it continues to function as a cost shifter when needed and a back up device when necessary.

    Once Tesla fixes this obvious error, you can go back to simply showing Shoulder-Peak and Off-Peak in your Weekend Pricing Guide.
     
    • Informative x 1
  6. NinjaVece

    NinjaVece Member

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    Sylvia, if you are using a Time Of Use (TOU) Pricing Schedule, the only setting you should be on is Advanced: Cost Saving. Once you set up the Off-Peak, Shoulder-Peak and Peak daily timeframes for Week (Monday through Friday) and Weekend (Saturday and Sunday) times, the system will charge the Powerwall 2 during Off-Peak and Shoulder-Peak times and expend the Powerwall 2's battery when you enter the Peak time period. During Peak time period, the solar panels will feed the grid unless they need to help the battery past 5kW house usage at any time during that expenditure.

    Once the Powerwall 2 is expended to the Reserve level you set, it will stop providing power and the solar panels will take over house power needs until it falls below the house needs and then the grid will contribute. Finally, if the Peak period lasts into the evening (most do), the grid will return to fully power your house.

    Now, since the solar panels were directed to feed the grid while the battery was in operation, there will be a 'grid credit' that will be available even when you return to grid usage to avoid the ACTUAL Peak pricing. The idea is to balance your Reserve level and 'grid credit' to completely avoid true grid Peak charges. Hopefully, Tesla will update their software to better show this 'grid credit' (a suggestion I've made to them) so that TOU usefulness is at its highest with regard to the Powerwall 2.

    Now there is a bug in the software (see another of my posts in this thread) which doesn't allow the Powerwall 2 to recharge over the weekend if you don't have and Peak times associated with it. My suggestion (again, see my post) is to simply add a small dummy half-hour Peak period for the Weekend Price Schedule. It won't power cycle the battery on your Powerwall 2 very far and it allows it to recharge on the weekends.

    Let me know if you have any questions.
     
  7. NinjaVece

    NinjaVece Member

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    I believe the software follows the CA model (I'm in CA and use the Powerwall 2 in Advanced: Cost Saving mode as you describe). It isn't yet sophisticated to handle tariffs and the like.
     
  8. power.saver

    power.saver Supporting Member

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    I discovered this too, and did a similar thing. But I put the weekend dummy peak at 11:30pm-12 midnight to minimize the discharge to when demand is lowest.

    I also eliminated entirely the shoulder periods, because including them causes the PW to discharge in an evening shoulder after the peak with energy it stored during the morning shoulder. This incurs the 89% round trip loss, and discharge should never occur at a tariff equal to or less than a charging tariff. I my case, for weekday, I have peak 2pm-8pm (SCE) and the rest off-peak. For weekends, it's all off-peak except for the 1/2 hour dummy peak 11:30pm-12 midnight.

    The result is essentially the same. Fully charged by mid-day Saturday, and only minimal cycling on weekends. Monday's are my best days, as I can return all morning shoulder and peak solar to the grid.
     
    • Informative x 1
  9. Sylvia Else

    Sylvia Else Member

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    Thanks for the responses. I'm in NSW, Australia. The system is rather different here. Net usages is accumulated over short periods - in the order of seconds. If the net is an import, then it is accumuated to the import counter. If it is an export, it is accumulated to the export counter. Imports are charged at one rate (I'm on TOU, so the rate depends on time of day). The exports are credited at a different rate.

    So there's no notion of grid credit, and since the export credit rate is independent of time of day, there is nothing to be gained by exporting at one time of day in preference to another.

    For the record, my import rates are 13.6 cents/kWh in off-peak, 22.3 in mid-range (called "shoulder" here), and 42.7 in peak. My export rate is 12.5 cents/kWh. Consequently it never makes sense to export while discharging the battery, nor while the battery is not fully charged.
     
  10. cwied

    cwied Member

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    Interesting. Powerwall support told me the same thing, but that most definitely is not how my Powerwalls behave. Instead, my Powerwalls seem to maintain three bands in the SoC. The highest band is used in partial peak, the middle band is used for peak usage, and the lowest band is the backup reserve. For example, here is my usage last Sunday with a partial peak (5pm-7pm) but no peak configured:
    upload_2018-9-4_9-1-5.png
    Note that my shoulder is configured to end at 7pm to allow for demand reduction on weekends, which is why the Powerwalls stopped discharging at 7pm. My backup reserve was set to 25%.

    If you're sure about the algorithm your Powerwall is using, that might imply different algorithms are applied in different installations. My firmware version is 1.22.1.
     
  11. NinjaVece

    NinjaVece Member

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    Hmm, can you do me a favor and provide me with actual Tesla app photos? I'll show you what happened with mine. My setup is Off-Peak until 8am and Shoulder peak until 2pm (typical So Cal Edison TOU specs). When I set the Weekend rates to no Peak, the battery charged until 8am (minimal as my panels were just getting going then) until Should Peak as you can see in the first photo. When I changed it to a small Peak amount in the afternoon, the battery began charging during Shoulder Peak.

    You can see further in the Power Flow diagrams of 'before' and 'after':

    IMG_8631.PNG IMG_8632.PNG IMG_8633.PNG IMG_8634.PNG

    I'm still using 1.21.0 as 1.22.1 had a lot of issues on my system - but it may have been related to an errant router of mine that I have recently replaced. I'll ask for the 1.22.1 firmware to be re-installed to verify any changes.
     
  12. cwied

    cwied Member

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    Unfortunately I can't, since this was the day before yesterday, but I think that your post explains it. I think Tesla's explanation was oversimplified. It's not that it won't charge unless there's a peak, but that it won't charge during partial peak unless there's a peak later in the day. I have off-peak until 5pm on weekends (grandfathered PG&E E6 TOU rate plan).

    Note that my pvoutput graph includes all the same data as Tesla's app graph, but also includes state of charge, so you can see the interaction between state of charge and discharging/charging. The data comes from the Powerwall gateway, so it should be identical to what's shown in the app.
     
  13. MorrisonHiker

    MorrisonHiker S 100D 2019.12.1.1

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    I guess that explains why we still don't have the TOU option in Colorado. :(

    Here, I don't think we earn nearly as much during production. The paperwork was confusing as it appeared we'd only get like 1.5 cents/kWh so we went with the other option instead. When we do send power back to the grid, I believe we do get credits in kWh depending on peak/shoulder/off-peak periods (if that option is chosen).
     
  14. BJReplay

    BJReplay Member

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    The solution to this is both simple and complex...

    The simple part is the app needs to support you putting in the price you pay for grid usage, and the price you get paid for grid feed in for each time band. Then the app will be able to prioritise charging, discharging, and reserving power for a later higher priced period.

    The complexity comes in because it also needs to look ahead to the next day - for example, it may need to choose to save energy that it could discharge into part peak because it has looked ahead and seen that after the part peak, it will hit a peak rate before it has time to charge, so reserves energy to discharge into peak the next day. So it needs to be able to predict both today's load and solar, and tomorrow's to make good decisions.
     
    • Informative x 1

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