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NEM 2.0: Non-bypassable charges and Powerwall modes

Discussion in 'Tesla Energy' started by Az_Rael, Aug 14, 2018.

  1. Az_Rael

    Az_Rael Supporting Member

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    I have now seen two bills since we had our solar +2 powerwall install turned on. I am currently sporting a $314 "energy generation credit" with my solar energy after just 2 months, however my June bill was $23 in NBC's and my July bill was $34 in NBC's. If I project those forward 12 months, that works out to several hundred $$ just in NBCs.

    I have been running the powerwalls in "balanced" mode for the most part as we don't have a lot of off peak generation. My initial thought was to maximize the amount of solar being sold back to the grid during peak hours . However, looking at my NBCs I am now wondering if self-consumption mode might be the better option as I think that may reduce the amount I am pulling from the grid on a daily basis vs the cost-saving or balanced modes.

    If I end up with a net credit at my true-up bill, then I think I just get paid at the crappy wholesale rates. But if I go to self-consumption, I might be able to reduce my NBC's each month, which might work out to more benefit than running a net positive for the year.

    I feel like I would need a PhD to actually do the math, so I may just set it to self-consumption and run it for a few months to see if my NBCs are reduced in any noticeable manner.

    Anyone else on NEM 2.0 with Powerwalls taken a look at this?
     
  2. cwied

    cwied Member

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    I think this is the right trade-off: if the NBCs are greater than the difference in cost between when you charge and when you discharge, then it's advantageous to do self-consumption instead of exporting more. If they are the same, you can just extend the peak period to make the Powerwalls discharge more and reduce your NBCs.

    The reality is that with NEM 2.0, you'd really want a charging mode that charges only from excess solar, which I don't think currently is possible with time-based control.
     
  3. GenSao

    GenSao Member

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    In general, you'll still come out ahead if your battery is filled with solar power generated from off peak (and perhaps partial peak) times. Actual savings will vary based on your utility rate schedule. I am in PG&E Land on an EV rate schedule (EV-A).

    For PG&E, non-bypass charges are approximately $0.0211/kWh based on:

    $ 0.0141 Public Purpose Program Charge
    $ 0.0002 Nuclear Decommissioning Charge
    $ 0.0013 Competition Transition Charge
    $ 0.0055 Department of Water Resources Bond Charges​

    Consider the cost of round-trip power loss of 11% (100% - 89% Efficiency) for a Powerwall to defer non-bypass charges with solar stored at partial-peak or off peak rates.

    Summer
    Partial-peak rate, $0.251/kWh x 11% = $0.0276/kWh
    Off-peak rate, $0.123/kWh x 11% = $0.0135/kWh ​

    Winter
    Partial-peak rate, $0.199/kWh x 11% = $0.0219/kWh
    Off-peak rate, $0.126/kWh x 11% = $0.0139/kWh​

    I agree that self consumption made may be best to minimize the chance of excess energy generation and being paid wholesale rates. Ultimately, the Powerwall help minimize the cost of peak rate energy costs with a side benefit of mitigating non-bypass charges.
     
  4. Az_Rael

    Az_Rael Supporting Member

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    OK good info here, thanks!! I have switched the powerwall over to self-powered and we will see how that affects my NBCs as well as keeping an eye on my credits as the year progresses.
     
  5. cr0ntab

    cr0ntab Member

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    The timing of this post is incredible.

    I was literally thinking about this last night while I was looking at my bill.

    Same deal, ~2 months of solar with powerwalls.

    Only $70 banked in credit though :rolleyes:

    I had also switched my pool to run at night to use the "cheap" power, but I'm now thinking that was a bad move.

    I was planning to switch back to self-powered to see how things went.

    I've been running on Cost Saving for the last 3 weeks, I just switched it to Balanced this week.....the usage patterns are nearly the same.

    I need to run the numbers though, I'm on SCE so the rates and NBCs are a little different than what was posed above for PG&E
     
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  6. NuShrike

    NuShrike Member

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    The utilities have basically made the banked credit worthless because it's non-refundable. You'd only need to bank enough to literally cover cloudy-days (few hundred $ for the year?), and then the rest of the time is fighting the NBCs.

    All that messaging they put out to move major appliance usage to night-time? It's now better to move them to daytime to avoid the NBC hit. Ironic.
     
  7. cwied

    cwied Member

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    Don't forget that some of us don't have a 100% offset. For us, the banked credit has full face value.

    Moving the appliance usage to the daytime is the right thing to do for the grid if you have solar. The NBCs do reflect a real cost, so I don't see it as the utilities being out to get us.

    One other note: my Community Choice Aggregator (CCA) actually pays out any balance over $100 each April. They also pay a bonus $.01/kWh for net production in each month. Maybe your community will decide to do the same thing some day. This applies only to generation, not transmission, but it looks like I'll probably be able to get some money back because there's a bigger differential between the different rate levels on the generation side than on the transmission side.
     
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  8. Bigtanuki

    Bigtanuki Member

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    I ran into the issue of less self consumption of solar then I wanted using the balanced setting. I found that by altering the Peak hours to start later than actual I was able to force the system to use excess solar later into the day. My particular solar situation gives enough solar to as late as 7 PM through the summer, for the most part. I'll be adjusting those hours soon.
    Changing the TOU hours seemed to cause a minor reset in the "learning" function of the PW system but it was minor and I was willing to live with the small usages of peak or partial peak power as the system adapted. I'll be adjusting the timing of peak and partial peak hours as the seasons progress but for now it seems to be working as I need it to. I don't expect Tesla to be able to build an app/system that can meet every one of my needs since the highly balkanized state of US utility regulations across the country make for nearly unlimited variables.

    For instances where our use during the day (real peak hours) exceeded the solar capacity it looked like the battery picked up the slack. This has been an issue when we were using a lot of AC the last few weeks or if we were doing cooking that required the use of the oven. Overall, I find that the issues with the time based control are far outweighed by the ability to let the program handle the swap to grid for vehicle charging. Prior to TBC I would manually switch modes to keep the vehicle charging on the grid and switch back in the morning. Missing just one swap drained the battery to reserve making the implementation less than what I wanted. YMMV.
     
  9. abasile

    abasile Conscientious investor

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    This is assuming that your annual total PV generation >= annual total electric usage.

    For those of us with PV shading issues who drive our EVs a lot, those banked credits are great because they pay for much of our excess usage. NBCs of about two cents per kWh won't change that.
     
  10. NuShrike

    NuShrike Member

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    Why would anybody put up PV with annual generation less than total annual consumption?

    Doesn't that defeat the "purpose" in so many ways of conservation of usage, properly sizing the system, not getting under-performing panels, etc?

    I understand shade, but there should be ways to size the system to compensate. I also understand localities limiting installation size, but NBC shouldn't exist in those localities.
     
  11. cwied

    cwied Member

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    I have only about a 90% offset for two reasons. First, my convenient roof space only had room for about 20 panels and with a slate roof I wanted them to minimize how much of the roof they were going to crawl over. Second, with TOU a 90% kWh offset is actually a full dollar offset.

    My goal is not to be fully grid-independent, but rather to pre-purchase the bulk of my energy from a clean source. Producing slightly less than I consume is the financial sweet spot, and it certainly beats consuming 100% from the grid from an ecological standpoint.
     
  12. Az_Rael

    Az_Rael Supporting Member

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    I only offset ~80% of my annual consumption for cost benefit reasons. To do 100% offset we would have needed close to 15kWh of panels. Due to the way netmetering works, I was able to install 11.75kWh that will still net me zero $$ at the true up for much lower initial costs. I am less interested in the conservation aspect of panels.
     
  13. GenSao

    GenSao Member

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    Utilities ensure customers do not make money on generation above and beyond their usage by the following:
    1. Generation over 100% of use (surplus energy) is reimbursed at wholesale rates. According to the PG&E FAQ, rate is $.03-.04 per kWh. Not the full retail rate nor the actual market rate at peak time.
    2. Approximately a $10/month Minimum Bill charges apply in PG&E land. Per the FAQ, "It was designed by the CPUC so that every customer, including those with very little or no energy usage, contributes a portion to the costs of providing electricity service regardless of how much energy you use."
    Our system was sized to 90% of our household use for those reasons.
     
  14. abasile

    abasile Conscientious investor

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    That is certainly true, but our roof is pretty much tapped out. All available area on our south facing roof is covered with high efficiency 360W panels with micro inverters, and our roof size is limited because we live in a modest-sized multi story house. We could potentially add reverse-tilted panels on our north facing roof, but that would be more costly and look odd. It would also help if we can work with our neighbor to cut back a large tree on their property that is responsible for a fraction of our shading.
     

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