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PowerWall: Peak, shoulder and off-peak

PowerWall: Peak, shoulder and off-peak

I am having trouble understanding the difference between the Powerwall Advanced setting for peak, off-peak and shoulder.

I understand that the general rule is that power will first be taken from our solar panels, then from the battery if solar is not sufficient, and finally from the grid if solar and the battery do not have sufficient power. Does this rule change based on peak, off-peak and shoulder times set?

Or is it something else that changes, such as when the PowerWall tries to charge itself?

Jones | 24 December, 2019

Here is the guidance I sent to a colleague who just finished his installation.
All assumes you are on a time of use (example is northern California).
Backup-only - Your solar will charge your batteries as a first priority to get them to 100% and the solar will keep them at 100% in preparation for a grid failure. If you have excess solar production, it will power the house and if you still have excess, you will send it to the grid. You probably will never use this option. You are still connected to the grid. Your batteries are always in a reserve mode and do not cycle. You are essentially a solar house with a battery backup - prepared for the apocalypse.
Self-powered - Your solar is used to power the house as a first priority and any excess is used to charge the batteries and if there is still excess, you send it back to the grid. When the sun goes down, your batteries kick in and power the house and will continue to do that until they get to the reserve level (whatever you set as emergency backup reserve) and then you will draw from the grid. You are still connected to the grid. Your batteries cycle up and down every single day. This is the conceptual equivalent of being off-grid…you just stay connected so that if your batteries get to the minimum reserve, you start taking from the grid. Again - this is the setting for you to use to get as far into the carbon offset region as is possible. You can probably do this year round, since your normal usage is so low. I cannot. I have to keep a much higher reserve capacity than you because of the shit I keep turned on 24x7.
Advanced - this allows you to input your time of use rate schedule and the system takes care of the arbitrage to give you the maximum $ value for your solar production. Essentially, it will use the batteries to power the house during peak (max $ time) so that you can avoid buying from PG&E at their highest rates. If there is sufficient capacity in your batteries, it will also carry you thru the “mid-peak” rates as well so that all of your actual PG&E usage (if your solar will not fully power your house all of the time) is at the lowest rates. As part of this - it will shunt all of your solar production to PG&E during the peak and mid-peak times so that you essentially sell them your solar output at the highest possible dollar. This is the setting that I use and thru this, I actually get paid for my solar production at the highest rates…even though I am a net consumer of electrons, PG&E still sends me a check…this year, the check is currently about $900. PG&E accountants are not stupid - they have seen this usage and they have calculated a whole new schedule and rate plan that started on November 1. They will not permit me to make that much money in the future. I expect that after I get my check this time, the new schedule and rates will probably reduce my annual arbitrage advantage to about $200, depending on how much driving I do.
Storm watch - this uses a signal from Tesla to get you to max charge on your batteries in expectation of an outage so that when the expected outage occurs, you start it with full batteries and have maximized your chances of getting thru the entire outage with the lights on and zero impact (while your neighbors sit in the dark). The one feature of this setting is that when they send the signal, your batteries suck up electrons from the grid…it is the only time that happens…all other cases - your batteries will charge only from solar. TURN THIS ON.

Here is my recommendation - put your setting to backup only in order to get the batteries to 100% as quickly as possible. Once they are fully charged…kill the breaker that connects you to the grid. Spend a couple of hours exploring the house to make sure every single switch, appliance, device and whatever plugs in still work and work properly (they will). Stay off grid and see how long it takes to get to 75%, 50% and 25% capacity on the battery (realizing that the battery will recharge from solar when the sun comes up). If your battery gets down to 10% at any time…reset the breaker and reconnect to the grid. With your usage and production, you should easily make it for several days, even in the winter…I easily did 32 hours (in the summer) when we had a real outage - while still running air conditioning and lending power to a neighbor.

Then - once you have confidence in your system, your stated actual goal is some equivalent of off-grid, so set to self powered and set the reserve to get you a minimum of 12 hours of pure battery (based on your 75%, 50%, 25% test) in case of a real failure. I am guessing your reserve should be about 20%. At that point, you will be fully self powered, but will have the grid available in case the sun don't shine.

bcmusik | 24 December, 2019

Excellent post Jones !!!!

Patrick | 25 December, 2019

Great explanation and good advice Jones. Agree with your recommendation - we figure a 20-30% reserve setting will be about right for our self-powered use case as well.

Passion2Fly | 25 December, 2019

When you set your schedule, only peak and off peak can be set. The rest is automatically supposed to be shoulder. I have my battery set to advanced/cost-saving all year long because of the huge difference between peak and super off peak rates, even in winter. I live in San Diego and my night rates are $0.09/kWh versus summer peak $0.58 and winter peak at $0.28/kWh... However, during the weekends and in March and April my super off peak times extends from 12AM to 2PM... that’s a 3:1 price ratio that you definitely want to capture with the PowerWall! My reserves are usually very low, around 10%. SDGE has a very robust and high quality distribution network. I usually get an outage every 1-2 years and never lasts more than 2-3 hours. So, backup mode is not necessary for me... I know that PG&E is much worse...

Watch out for the Storm Watch. It doesn’t work very well for me... I don’t know why...

Passion2Fly | 25 December, 2019

Sometimes Storm Watch turns on on a beautiful and sunny day and stays off during huge storms... don’t know why...

jrweiss98020 | 25 December, 2019

I am in the Seattle area, and have not yet (since Aug 2019 install) seen Storm Watch activate, even during the big rainstorms & flooding last week. Anyone else around Seattle see it activate?

18R | 27 December, 2019

@Jones, you say: "am a net consumer of electrons, PG&E still sends me a check"

How does this work ... AFAIK you have to have a net surplus (NSG = Net Surplus Generation in PGE speak) to get a check at true up?

18R | 27 December, 2019

*** NSC = Net Surplus Compensation

Jones | 28 December, 2019

PG&E is the utility - we have a community provider called MCE (operates in several Bay Area counties). Basically, they execute the arbitrage of the differential rate schedules. I get my check based on "selling" my peak production and buying bulk at off-peak. Since I have driven electric cars since 2013 (Leaf, then Bolt, then Model 3) - I charge them at night using grid power and then daytime recharge my powerwalls in the morning and discharge them in the evening. Virtually all of my peak time solar is sold to the utility. The rules for MCE may be a little less onerous than PG&E since MCE is a green provider - they are always looking for green generation.
The $ value will change this year because as I said in my original post - the pencil pushers at PG&E are not stupid - they have moved the peak time to a non-solar period and have compressed the differential rates. Since I have recently retired - my vehicle charging has subsided considerably and I will in fact become a net surplus generator this year.

gregbrew | 29 December, 2019

Check with your utility, and determine how they carry excess production during the year, and pay for surplus at True-Up.

Some utilities will carry excess production during the year as an accumulating dollar amount based on average *retail e-rates*. At the end of the True-Up year, they will pay out for excess production at the *wholesale e-rate*. The result is that you may think you're getting a check for several hundred dollars, only to receive a check for 15% of what you expected. Look carefully at your net-metering agreement and bills to avoid an unpleasant surprise.

Joshea8500 | 2 January, 2020

I am just outside San Francisco with 35 panels and three tesla batteries. My winter solar production is poor due to shading from San Bruno mountain. I am interested in exploring a wind turbine that would be compatable with the tesla batteries to help recharge especially at night. I have not contacted Tesla to see if a wind turbine would mesh with their software. Any thoughts?

Patrick | 3 January, 2020

I’m not familiar with typical wind turbine controllers but would guess they operate much like solar inverters in terms of providing relatively stable 240 VAC output power during periods of sufficient wind.

If so, seems like one could connect the controller output to the same “generation” breaker panel used with multi-Powerwall installations. This would bridge the wind power into the same circuit that couples the solar inverter output with the Powerwalls. When operating with sun, the solar inverter provides power to this panel. The wind controller would do the same thing.

While this connection would bridge the wind power into the home microgrid, the TEG would not be aware of the new power source without some kind of Tesla software “driver” for the wind controller and another set of CTs on the controller output. Something like this could certainly be in the works but I haven’t seen any public info on the topic.

Without formal Tesla product integration for this use case I guess one of the first questions would be - will the PWs take a charge from the new wind power generator at night when the solar output is zero? Maybe so. But maybe not as the TEG and battery management software control all the Powerwall behavior.

Might be worth a test - shouldn’t blow anything up...

Patrick | 3 January, 2020

Might be worth a formal new PW/TEG feature request to Tesla as well.

Jones | 6 January, 2020

I agree with @Patrick and have had similar thoughts in terms of going true off-grid. The actual connection in your panel is not difficult and the system should handle it without incident. However, if you are connecting to the grid, you have a contract with PG&E (the PTO) that defines the exact size and type of generation you have in place. If you install wind, you are violating that contract, so I would only do it with the intent to disconnect and put PG&E in the rear view mirror.