Powerwall 2: TOU/Rate Arbitrage

[MP3Mike]

In other words, if I wanted all power to source from the Powerwalls first, then self generating solar, then grid if needed would that ever be possible?

The standard mode for a PW2 with solar is "Self-consuming" which would be where available Solar is used to power your loads, if you have more Solar than load it charges the PW2, once the PW2 is full excess solar power would go to the grid. If you have less solar available than demand pulls power from the PW2 until you hit the lower SoC limit you set at which point it would start pulling from the grid.

The whole idea being to use as little peak grid power as possible.

 

[abasile]

In other words, if I wanted all power to source from the Powerwalls first, then self generating solar, then grid if needed would that ever be possible?

This is a great question, and I'd also like to see Tesla implement that functionality. As an example, consider the following hypothetical scenario:

1. It's afternoon, peak rates apply, and the sun is shining.
2. The solar panels are generating 1.5 kW (AC).
3. Total home loads are 1 kW.
4. Normally, the surplus 0.5 kW would be getting exported to the grid.

However, since peak rates apply, we'd prefer to draw on the battery for the 1 kW of home loads, and export the full 1.5 kW that's coming from PV. That seems completely legitimate and within the intent of NEM.

 

[MP3Mike]

However, since peak rates apply, we'd prefer to draw on the battery for the 1 kW of home loads, and export the full 1.5 kW that's coming from PV.

There is ~10% loss in going into/out of the PW so that does increase your "costs" somewhat.

 

[Ulmo]

I have a question that I'm not googling to an answer about the PW2.....

I've got 6kW solar today on TOU at SCE in Southern California with net metering. I currently am a NET CONSUMER off the grid, but with TOU I'm able to time-shift my usage in a very advantageous manner such that at the end of my 12 month true-up period, I've got about a $500 credit on my bill. SCE then wipes the slate clean, sends me a check for pennies on the dollar (like I get a check for $50 vs the $500 credit) and we rinse and repeat. Fast forward a few months when my Model 3 starts to consume lots of kWh. My estimates show that my EV usage will completely wipe out the $500 credit and probably cost me about $500 per year in night time, low cost, consumption.

Now, for my question. This is not your typical green save-the-world question. If I get a PW2, can I time-shift it's function to continue to leverage the TOU that I'm currently benefiting from? Meaning I would want to ONLY use the PW2 to fill up at night and discharge during the day to produce enough credit to fully offset my expected EV usage (again, that's approximately 3kWh/year).

The PowerWall stores 14kWh. Do you mean 3MWh/year?

Would my usage qualify for SGIP?

SGIP specifically discourages this through enforcement through use statistics; there are particular % and amounts you have to meet that makes this use a disqualifying thing in most attempts to do such.

Can I operate my way some percentage, then a required way another percentage and still qualify? Any guidance appreciated!

Good question.

These questions will be better answered within a year. Some people might figure out aspects of it sooner.

 

[Az_Rael]

I just talked to a Tesla Rep because they are ready to install my Powerwalls. She was evasive about the chances of getting into Step 3. When I pushed her, she said that there are still customers who put their deposit down in March that didn't gotten into Step 2 due to the developer cap. My suspicion is that they will fill their Step 3 developer cap with the existing backlog. She seemed to be hinting that I might miss it given that I didn't put my deposit down until July.

I also was told that I can't apply for SGIP after the system is installed. This seems to be different than what others in this thread have been told.

Are you in PG&E territory? Here is what they are showing on the statewide developer cap now:

I wonder how that will play out with my Install? Maybe I can snag one of the few remaining step 2 slots since I am in SCE territory and step 2 is still open?

 

[ohmman]

mod note: consolidating old posts into this thread, so there may be some flow issues in posts prior to this one.

 

[siucity]

This is a great question, and I'd also like to see Tesla implement that functionality. As an example, consider the following hypothetical scenario:

1. It's afternoon, peak rates apply, and the sun is shining.
2. The solar panels are generating 1.5 kW (AC).
3. Total home loads are 1 kW.
4. Normally, the surplus 0.5 kW would be getting exported to the grid.

However, since peak rates apply, we'd prefer to draw on the battery for the 1 kW of home loads, and export the full 1.5 kW that's coming from PV. That seems completely legitimate and within the intent of NEM.

This is how I'd like it to work also, but it seems like it's not currently possible.

For those of you who did the whole house backup option, and you charge your car at night during off-peak rates, is there a way for the app to stop the car from charging when it knows there's a power outage? It won't be instantaneous, but even within a few minutes would be fine so the car doesn't drain the Powerwall(s).

 

[ohmman]

For those of you who did the whole house backup option, and you charge your car at night during off-peak rates, is there a way for the app to stop the car from charging when it knows there's a power outage? It won't be instantaneous, but even within a few minutes would be fine so the car doesn't drain the Powerwall(s).

There is no such functionality right now, but I agree it's a good idea and a necessity in the long run for the app. I'd settle for just a push notification when power goes out in the meanwhile..

 

[wwhitney]

Hello,

I'm a PG&E NEM 1.0 customer with a 2.3 kW solar installation. I'm a little unclear on the upshot of the PG&E Non-Export Interconnection agreement that I understand will be required as part of getting a Powerwall 2. Does it effectively prohibit TOU arbitrage? I can imagine a few different rules that would summarize the effects of the two agreements together:

A) No restriction, export power limited only by hardware.
B) Export power at all times <= 2.3 kW (or perhaps 3.3 kW?), no restriction on time of day.
C) Energy exported over the course of one day <= solar energy created that day, no restriction on time of day.
D) Export power at any given time <= solar power production at that time.

Obviously (A) would be preferable for me, and it seems like some posters are reporting that for transformer sizing, PG&E is assuming (A). And if I export power only during the evening peak of the CAISO net demand curve (duck curve), then that would be good for the grid, CO2 reduction, etc. But perhaps the tariffs haven't caught up with this idea yet?

BTW, do other California POCOs have similar non-export restrictions on the Powerwall?

Cheers, Wayne

 

[miimura]

I skimmed the PG&E Battery Interconnect rules document which lays out the classification of and approval process for battery interconnection. The Non-Export Interconnection is the easiest type of interconnection to get because it bypasses the additional studies that may be required for others.

My understanding is that with this type of interconnection, the battery is not allowed to discharge into the grid at all. That is what Non-Export means. However, that does not mean that nothing behind your meter can export any longer. The solar may continue to export as normal. So, according to your A-D classifications, my understanding is that Non-Export Interconnection is (D). In addition, to get SGIP or the Federal Investment Tax Credit, the battery must be charged with renewable energy.

If you combine these requirements, the best arbitrage that you can do is to charge the batteries from the time the sun comes up (usually after the 7am Part-Peak rate begins) and fill it up before the Peak rate period begins. For Schedule EV, that is 2pm M-F and 3pm Sa-Su. Once the Peak period begins, the battery should satisfy all loads inside the house and all of the solar should be allowed to feed into the grid to earn NEM credits. When the Peak period ends at 9pm, the battery should go idle until solar generation starts again in the morning unless there is a grid failure. The reason that I don't want the battery to do anything for the rest of the night is that the value of energy during Part-Peak from 9pm-11pm is equal to the solar generation that will fill the battery in the morning. The Off-Peak from 11pm-7am is even cheaper than the the solar generation. If you discharge at all during the Part-Peak you're just adding cycles to the battery pack with no return, or giving away money if you discharge during Off-Peak. The less battery you use during the evening, the earlier your solar will fill the battery and start earning you NEM credits.

I am fully aware that this regime is not currently implemented in the Tesla firmware. It also greatly reduces your self consumption percentage. By default, the Tesla PowerWall firmware will maximize self consumption. In markets where TOU is not in play or your feed-in tariff gives your solar generation much less value than consumption, maximizing self consumption is the most advantageous strategy. However, in the California power market, especially for those on NEM 1.0, the best strategy requires these TOU adjustments. Hopefully, Tesla's programmers are cognizant of this and provide this level of control in the forthcoming "TOU" software update.

 

[wwhitney]

In addition, to get SGIP or the Federal Investment Tax Credit, the battery must be charged with renewable energy.

I don't believe that is correct for the SGIP. In which case if the Non-Export agreement plus NEM 1.0 yields the restriction I call (D), then the best strategy would be to charge the Powerwall from Off-Peak power only, and power all house loads from the Powerwall during Part Peak and Peak periods.

Cheers, Wayne

 

[abasile]

I don't believe that is correct for the SGIP. In which case if the Non-Export agreement plus NEM 1.0 yields the restriction I call (D), then the best strategy would be to charge the Powerwall from Off-Peak power only, and power all house loads from the Powerwall during Part Peak and Peak periods.

I believe you are correct with respect to the SGIP only. However, to claim the full ITC, the Powerwall does need to be charged from renewable energy, so the arbitrage strategy laid out by miimura would be the way to go.

One of our cars is a Nissan LEAF with a small battery (smaller than the two Powerwalls that we plan to install), so it's sometimes necessary to charge it during Peak periods just to keep up with the day's driving. That'll help us get closer to the level of self consumption required by SGIP.

 

[wwhitney]

I'm a PG&E NEM 1.0 customer with a 2.3 kW solar installation. I'm a little unclear on the upshot of the PG&E Non-Export Interconnection agreement that I understand will be required as part of getting a Powerwall 2. Does it effectively prohibit TOU arbitrage?

So I have some updated information. The PG&E Non-Export Interconnection agreement is apparently only for installing a Powerwall without solar (or other renewable generation). If you have solar, then you get a different Interconnection Agreement, in my case the "Net Energy Metering Interconnection for Solar And/or Wind Electric Generating Facilities of 30 Kilowatts or Less with Energy Storage of 10 Kilowatts or less."

The rules for exporting are contained in the Electric Schedule NEM tariff, (https://www.pge.com/tariffs/tm2/pdf/ELEC_SCHEDS_NEM.pdf ). Section 11 covers NEM Paired Storage, and 11(g)(i) describes a billing procedure for Small NEM Paired Storage (under 10KW Energy Storage) using the California Solar Initiative Expected Performance Based Buydown (CSI EPBB Calculator) to estimate the solar system's output each month. That estimate is a cap on energy export credits for the month. If the system exports more energy than that estimate, you get lose credit for the extra, starting with the peak rate period. I.e. PG&E will credit you for the cheapest cap's worth of energy that you export.

The rate arbitrage strategy for this is clear: use the Powerwall to time-shift all generation to the Peak period each day, and all consumption to the Off-Peak period each day. Plus pay attention to the export cap for each month. I guess we'll see how much control the coming TOU option for the Powerwall will provide and how close we can easily get to this.

Cheers, Wayne

 

[abasile]

The rate arbitrage strategy for this is clear: use the Powerwall to time-shift all generation to the Peak period each day, and all consumption to the Off-Peak period each day. Plus pay attention to the export cap for each month. I guess we'll see how much control the coming TOU option for the Powerwall will provide and how close we can easily get to this.

My understanding is that Tesla is not going to support the use of the Powerwall to time-shift energy exports. In other words, the Powerwall will not discharge into the grid. This is consistent with the NEM agreement that Tesla recently had me execute for two Powerwalls, and I quote below, italics added:

2.7 Generating Facility Nameplate Rating (kW): 10 kW
2.8 Generating Facility CEC-AC Rating or Equivalent (kW): 10 kW
2.9 Estimated monthly energy production of Generating Facility (kWh): 0 kWh

That said, the Powerwall could, in theory, be used during Peak hours to offset all home energy consumption, exclusive of solar PV generation, and thus allow every single kWh of PV generation to be exported to the grid during those hours. For example (note that I previously suggested essentially the same thing on this thread), if at a given moment during Peak hours we are using 3 kW of power inside the house and our solar panels are generating 2 kW, then the 3 kW of demand could be met by the Powerwall and the entire 2 kW of PV could be exported. I hope that Tesla will end up supporting this.

 

[miimura]

So I have some updated information. The PG&E Non-Export Interconnection agreement is apparently only for installing a Powerwall without solar (or other renewable generation). If you have solar, then you get a different Interconnection Agreement, in my case the "Net Energy Metering Interconnection for Solar And/or Wind Electric Generating Facilities of 30 Kilowatts or Less with Energy Storage of 10 Kilowatts or less."

The rules for exporting are contained in the Electric Schedule NEM tariff, (https://www.pge.com/tariffs/tm2/pdf/ELEC_SCHEDS_NEM.pdf ). Section 11 covers NEM Paired Storage, and 11(g)(i) describes a billing procedure for Small NEM Paired Storage (under 10KW Energy Storage) using the California Solar Initiative Expected Performance Based Buydown (CSI EPBB Calculator) to estimate the solar system's output each month. That estimate is a cap on energy export credits for the month. If the system exports more energy than that estimate, you get lose credit for the extra, starting with the peak rate period. I.e. PG&E will credit you for the cheapest cap's worth of energy that you export.

The rate arbitrage strategy for this is clear: use the Powerwall to time-shift all generation to the Peak period each day, and all consumption to the Off-Peak period each day. Plus pay attention to the export cap for each month. I guess we'll see how much control the coming TOU option for the Powerwall will provide and how close we can easily get to this.

Cheers, Wayne

This is very interesting because it highlights that NEM installations in PG&E territory over 2 PowerWall units will be more onerous. They really don't want you to use the battery to export more than what your solar is generating. Also, when you have 3 PowerWalls, you must have a large (10kW+) solar array because you cannot have more than 150% battery power over your generating nameplate power. If your battery system is at or below 10kW, it doesn't matter how much generation you have.

Also, my reading of that last provision, g.ii) and Special Condition 4 earlier in the tariff means that if you have more than 2 PowerWalls, battery discharge in excess of your behind-the-meter loads will not receive any NEM credits. Interval metering could enforce that condition down to the individual metering intervals, which in residential could be 15 minute intervals.

 

[wwhitney]

I believe that with PG&E, the interval for residential account is 60 minutes; 15 minutes for other accounts. At least, that is what I was told with respect to Non-Bypassable Charges and NEM 1.0 versus 2.0.

[In related news, I was concerned that adding a Powerwall to my existing PV system could force a transition from NEM 1.0 to NEM 2.0, but was just told today by [email protected] that it would not.]

Cheers, Wayne

 

[miimura]

I believe that with PG&E, the interval for residential account is 60 minutes; 15 minutes for other accounts. At least, that is what I was told with respect to Non-Bypassable Charges and NEM 1.0 versus 2.0.

[In related news, I was concerned that adding a Powerwall to my existing PV system could force a transition from NEM 1.0 to NEM 2.0, but was just told today by [email protected] that it would not.]

Cheers, Wayne

From my initial residential solar install in Dec 2012 until December 2016, I had a NEM SmartMeter that reported 15 minute intervals. At that point, they changed it to 1 hour intervals. In the process, they made all my prior data inaccessible and refused to make any effort to recover it and send it to me. Nah, I'm not bitter at all...

Before:

After: