Last year when I was on Ohm Connect my MX could stop charging during and Ohm Hour. The setting was in the OhmConnect application. It really wasn't useful because my charging was always after 11PM and I don't think I ever saw an Ohm hour that late.
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Powerwall Arbitrage DEAD: San Diego's SDGE
- Thread starter Princeb
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I think it depends on how you're defining "normal". My main goal with the Powerwall is backup. Everything else I do with the Powerwall aims to try to offset the extra cost of the Powerwall over a traditional backup system. OhmConnect works fairly well for me for that purpose. If I were to self-consume instead, I'd end up paying more for my electricity because I would lose the round-trip inefficiency of the battery while forgoing the net metering in the morning. In addition, my CCA pays a bonus for net generation, so that makes it even cheaper to export rather than self-consume.
I agree that the long-term plan would be to sign up to Tesla's grid-stabilization program, but I'm not holding my breath for that. Given the experience with the TOU software release, I have a suspicion it's going to be a while until it's available. Neither Tesla nor the utilities seem to have a track record of moving quickly with this kind of thing.
I would assume that most people participating in this thread are charging at least one EV and are in California. Given those parameters, TOU rate differentials are going to be the biggest payback with Powerwalls. The round trip efficiency just doesn't matter when you have 2.5:1 to 3.5:1 Peak to Off-Peak rate prices per kWh. Currently, I use Self Consumption, but I manually set the Reserve high during Off-Peak hours to prevent discharge during those hours. During solar generation, the Powerwalls reach my 90% setting and also powers the house for a short time, then it reaches 100% and starts exporting. Export continues into the Peak hours, then drops off and the Powerwalls pick up the load so that there is no grid draw during the Peak period.
With the upcoming Time Based Control, I won't have to make any manual changes to the Reserve. It will also exaggerate the export by powering all the household loads from the Powerwall during the Peak Period and allowing all your solar to go to the grid and earn you more NEM credits at the Peak rate.
You mention Net Generation. If you are generating more kWh than you're using on an annual basis, then what I said above doesn't apply to you because you don't get the benefit of TOU arbitrage to the same degree. I am also on a CCA and they pay out all generation credits earned whereas PG&E will normally wipe out your $ credit balance and only pay you Net Surplus Compensation, if anything. EV drivers that end up with a credit balance at the end of the year but are still net consumers will get significant benefit from the CCA billing scheme.
Given that the powerwalls only charge from solar, isn't the effective arbitrage ratio less than 2:1, though? Assuming a 2 kW average usage on the PG&E EV-A rate plan and looking at the hours from 7-9 pm (which seems to be where I get the OhmHours more frequently), the arbitrage could save about $24 in a month. If the payout rates stay the same, it looks like OhmConnect could be as much as double that.
My intention with Time Based Control is to set the reserve to 100% at 7pm when my peak rate ends. I do plan to take advantage of the additional export during the peak rate period, though.
I'm not a net generator on an annual basis, but the bonus for net generation is paid on a per-bill basis. This means that my net export in the summer months is paid at retail + 1 cent.
My intention with Time Based Control is to set the reserve to 100% at 7pm when my peak rate ends. I do plan to take advantage of the additional export during the peak rate period, though.
I'm not a net generator on an annual basis, but the bonus for net generation is paid on a per-bill basis. This means that my net export in the summer months is paid at retail + 1 cent.
Actually, you are correct. The correct TOU differential to consider is Part-Peak (solar generation) to Peak (battery usage). PG&E EV-A is now:
Winter Part Peak: $0.204/kWh
Winter Peak: $0.330/kWh
Summer Part Peak: $0.260/kWh
Summer Peak: $0.473/kWh
So, your estimation of $24/mo during Winter is reasonable, but would almost $64/mo during the Summer at 10kWh shifted per day.
Also, remember that the CCA payout is only the Generation portion, not the total rates I listed above. The SVCE Generation rates were posted earlier in this thread.
I'm actually assuming only 2 hours of shifting per day, not 5. The idea would be still to shift the daylight hours, while saving the nighttime hours for OhmConnect. I'm assuming this would be 7-9pm. This means you would get the $38 for shifting the daylight usage and also get the OhmConnect payout. Given that San Diego's grid prices seem to fluctuate more than up here, I think it could potentially be even more than that.
It's not perfect, but I do think that on balance it should be at least slightly advantageous to use OhmConnect for a couple of hours a day. Since I'm on the E6 rate (no EV yet), it's a no-brainer for the next two years.
SoundDaTrumpet
Member
I agree. The only time an Ohm Hour overlaps with off-peak charging is on the weekends. Weekends are a different story. I set up my charging to happen around 8AM on weekends. This builds history of EV charging from Friday's commute and Saturday driving if any. I know this may sound terrible. The other demand response program from Juicenet has in past delayed my charging to start at 2AM. I have not seen any fluctuations in charge rate (solid 6.6kW) so Juicenet has not been adjusting charge rate after charging is initiated.
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Once we get Powerwall TOU control we should be able to reliably participate in Ohmhours before noon without worrying about clouds messing with the solar. It only requires manually changing the TOU rate period when an ohmhour occurs, but is otherwise passive.
Basically we can set it up so that every normal day all solar will go to the powerwall in the mornings to recharge from the previous evening and all household usages will be from the grid. On days with an Ohmhour, we can change the TOU so that hour is marked as "Peak Rate". The Powerwall will offset the house usage 100% and any solar will also go to the grid. Even if it's cloudy, we will have 0 usage from the grid, meaning we will always be lower than non Ohmhour days. If it's sunny, way lower.
Battery backup is useless, well, except for the one day or so every few years that your power goes out. However, the opportunity for arbitrage is most definitely alive and well in SDGE and elsewhere. The part that you have slightly incorrect, and was the part provided to you by the SDGE solar-EV specialist, is that "energy put back into the grid via Powerwall will be credited at retail pricing". The whole idea behind TOU shifting/arbitrage, with Powerwall anyway, is that of self-consuming (vs. grid export) the stored energy in the battery during peak periods, which in and of itself represents an avoided cost of $0.54/kWh, or the prevailing rate for customers on the EVTOU2 rate. Why would you ever draw from the battery during off-peak (which is $0.25/kWh) and results in unnecessary cycling of the battery because you can simply use grid energy at the same price and net meter your any extra PV generation? So while you're not really selling back during on-peak periods, by using the energy stored in the battery that was generated during the day at $0.25/kWh, you are sort of arbitraging and realizing an avoided cost rather than buying at $0.54/kWh.
So, the Powerwall as a backup solution is quite capable with 13.5kWh capacity (unless the grid is down for more than a few hours and you deplete capacity), but backup is definitely not worth the investment in my opinion. As for arbitrage, the Powerwall is lacking primarily due to the lack of a robust energy management system and inability to perform direct grid export functions. I'd suggest looking into JLM for an option for more robust TOU shifting/arbitrage/demand shaving capabilities.
The one thing to be aware of is that the utilities don't currently pay for negative demand. OhmConnect currently does pay for negative usage, but I wouldn't count on their continuing to do so if the utilities refuse to pay for it long-term. The utilities count all negative usage as 0 for both baseline and actual usage calculation.
Frankman60
Member
OK, that sounds pretty easy to do with the new TOU PW app settings. How long in advance does one know that a OhmHour is coming, and how long does it take for the PW to adjust to a change in the TOU settings in the app? I’m wondering if there is normally enough time to switch the PW TOU settings.
Generally you get one days notice. In rare grid emergencies you may get an hour's notice.
I've been getting around $800 a year from Ohmconnect. That might go up with the Powerwall, since I am not limited to after sunset hours anymore.
PM me if you don't already have a OhmConnect sign up referral code. (Both the referrer and referee get $20 when they sign up and use add smart device)
I've been getting around $800 a year from Ohmconnect. That might go up with the Powerwall, since I am not limited to after sunset hours anymore.
PM me if you don't already have a OhmConnect sign up referral code. (Both the referrer and referee get $20 when they sign up and use add smart device)
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Curious, do you charge EVs solely 12mn-5am and participate in ohn alerts? I signed up years ago, but never participated directly beyond reducing our usage. Now with PW2, we're can definitely self-consume through the most often 500-700pm times. The beauty is that we're granfathered with NEM 1.0 and 12p-6p peaks where we can charge up enough of the PW2 in shoulder, get solar production and then ohmconnect with the PW2. TOU options can't come fast enough since could just set and forget for the evenings anyways. I do wish had more roofspace for more panels!
12pm-6pm Peak is awesome since you can do set Ohmhours for only 6pm-8pm and can using as much as you want during off ohmhour days to increase your usage average. For me I probably won't do evening Ohmhours on summer rates kick in, since everyday I will be 0 or negative from 4-9pm (I've have solar for over 5 years, so I have the new peak rate period)
I usually charge from midnight until 5am. Recently I've been charging the Model 3 from 6-7pm, since winter rates are not really much cheaper peak or off peak. Then I use the Powerwalls to offset usage from 6-7 on Ohmhours days. It's a pain right now, since there is no TOU control. Once TOU is active, I'd do the morning system I described earlier, since that is no effort except to change the peak rate period on Ohmhours days. Usually they are only once or twice a week.
EscoguyS75
S75
I'm putting on more panels next month. My installer is a little backed up, but my bill with a Model S+a Model 3, 4000 sf/house with pool, should be less than $30/month after all is said and done. Still this is a touch of an odyssey. With SDG&E/PUC moving the peak rates, I have to have more generation than planned a few years ago. Of course, it will be a good feeling to be 100% renewable. I'm guessing longer term, they will shift the rates again and make power really cheap in the middle of the day when there is excess solar production. The policy should be to encourage people to charge when the supply is greatest rather than paying Arizona to take the excess. In that sense there is a risk that my assumptions about the long term value of power in the middle of the day may be invalid. If they do go for a more time sensitive/production sensitive market approach, then that could be very good for EVs and everyone could manage their charging to use the excess. That would also be good for Tesla as it would lower the cost of Supercharging. (leaving out demand charges).
At least, I'm looking at about a 6-7 year payback on the incremental investment. That being said, there are markets in Texas where night charging is FREE. So I'd like to think once people get the word that they can stop buying gasoline and pay zero for power in certain markets, that we'd see a bigger uptake in EVs. Especially for those who do a lot of driving which is very common in Texas. Truly Free Weekends Plan
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