Powerwall Time Of Use Charging

[jesseasi]

Just had my powerwalls installed two weeks ago.

I am still trying to find the sweet spot to maximize savings by time of use and still minimize my NBCs.

Right now I am running on self powered mode.

This seems like a good option for me because the powerwall charges from any excess solar (and I have a lot with 23kw solar system).

However my powerwalls only make it till about 2-3am each night. At which point I run off the grid.

The next morning I am on shoulder rates from 8am to 2pm. I don’t have excess solar till about 9am. And if it is cloudy it could be even later in the day.

So here is my question.

Could I run on time of use and just get rid of all peak time. Making all shoulder and peak time into just shoulder.

If I do this, would the power wall only charge when there is excess solar and power the house when there is not enough solar but in shoulder time?

I don’t think I need to power the house with the powerwall when I am in the lowest rate times.


Anyone figure this out?

 

[miimura]

The best way is to just try different settings for a week at a time and see what it does. My solar is really small compared to yours, so my system would behave differently than yours.

 

[NuShrike]

Just had my powerwalls installed two weeks ago.

I am still trying to find the sweet spot to maximize savings by time of use and still minimize my NBCs.

Right now I am running on self powered mode.

This seems like a good option for me because the powerwall charges from any excess solar (and I have a lot with 23kw solar system).

However my powerwalls only make it till about 2-3am each night. At which point I run off the grid.

The next morning I am on shoulder rates from 8am to 2pm. I don’t have excess solar till about 9am. And if it is cloudy it could be even later in the day.

So here is my question.

Could I run on time of use and just get rid of all peak time. Making all shoulder and peak time into just shoulder.

If I do this, would the power wall only charge when there is excess solar and power the house when there is not enough solar but in shoulder time?

I don’t think I need to power the house with the powerwall when I am in the lowest rate times.


Anyone figure this out?

Is your consumption near-constant? That would make it easier and harder to come up with strategies.

The best strategy I see is to use the PWs to just power through peak-consumption times, prioritized. You can run Excel/etc simulations to balance how deep to drain vs recharge (if TBC worked perfectly) to find what minimizes the most NBCs.

I used NREL's System Advisor Model (SAM) | to do battery/power simulations. I could support hour-by-hour customized simulation, but I haven't done that yet. Reminds me that SCE's new TOU rates need new analysis with this.

 

[cwied]

Do you actually have to pay anything at your annual true-up? If not, extra credits are just going to be wasted (unless you are in a CCA that pays out for them). If you do generally pay, then it's likely that TOU credits are worth more to you than the NBC's, since the NBC's are generally less than 3 cents per kWh, where depending on the rate you're on, TOU credits could be as much as 20 cents per kWh.

 

[PBBear]

However my powerwalls only make it till about 2-3am each night. At which point I run off the grid.

I'm wondering what sort of overnight loads you're powering if multiple powerwalls are drained from full to empty by 2-3am??
Anyway, what do you have the 'Reserve %' set to? Perhaps setting 'reserve %' lower might allow you to get through to the next day.

 

[jesseasi]

I'm wondering what sort of overnight loads you're powering if multiple powerwalls are drained from full to empty by 2-3am??
Anyway, what do you have the 'Reserve %' set to? Perhaps setting 'reserve %' lower might allow you to get through to the next day.

I have my reserve set to 5% on my app. But when I look at the powerwall from its IP address in my network - it charges down to 10%.

Either way we seem to use a lot of electricity. We have a 5000 sq foot house - two hybrid head pump water heaters, fish tanks, computer server that runs 24/7 and 8 Fridges! Normally we run at about 1.5-2.5kWh. But our community does not have natural gas - so our heat comes via propane - which is super expensive. So when it is cold out - we have little electric heaters around the house. We turn on of those on and that is 800-1000 watts of electricity. We also have a Tesla Model S that we charge at night. I try not to charge at home.

One of the draw backs of our setup. When we charge our car - it pulls from the powerwall. Tesla told me there was really no way around this. Even though the EV circuits are outside my whole house backup- power still comes from the powerwall. Only if the power were to go out - would I not be able to charge my car.

 

[cwied]

You pay the same NBC's on the car charging as you would on the other use, so I don't think it's that big a deal if you discharge into the car instead of offsetting house load. I would just make sure to set the backup reserve so the Powerwalls aren't completely drained when the car charges.

 

[MorrisonHiker]

One of the draw backs of our setup. When we charge our car - it pulls from the powerwall. Tesla told me there was really no way around this. Even though the EV circuits are outside my whole house backup- power still comes from the powerwall. Only if the power were to go out - would I not be able to charge my car.

Since there is no current "scheduled self-powered mode", you can use TBC to schedule when you want your Powerwalls to shut off. We've been using this trick since last September. I had to extend my part-peak period to pretend it ends at 4 am instead of 9 pm. Then we have the cars start charging between 4 am and 7 am.

People have also requested better communication between the cars and the Powerwalls. While there really isn't any communication now, they could easily have the cars check the servers and have them delay, limit or stop charging entirely if the Powerwalls are powering the house. Elon said that there will be more communication between cars and Powerwalls (via Tesla's servers) but we don't have an ETA.

Here's an example from when we had the part-peak set to end at 5 am. You can see how the Powerwalls power the house until 5 am and then shut off and the first car starts charging. You can also see how we had 3 cars charge that day. At the time, I would work from home a lot and would manually start charging one of the cars during the day...but I forgot to adjust the maximum amps initially and used a little grid power. I was going for maximum self-consumption vs. maximizing bill savings. Now, we typically just start charging that car in the same 4 am to 7 am period and then send more back to the grid during the day.

 

[zanary]

Elon said that there will be more communication between cars and Powerwalls (via Tesla's servers) but we don't have an ETA.

I asked Elon a few months ago regarding his original statement that this is coming. I think we all need to put more pressure on this topic.

Zubin Anary on Twitter

 

[jesseasi]

Since there is no current "scheduled self-powered mode", you can use TBC to schedule when you want your Powerwalls to shut off. We've been using this trick since last September. I had to extend my part-peak period to pretend it ends at 4 am instead of 9 pm. Then we have the cars start charging between 4 am and 7 am.

People have also requested better communication between the cars and the Powerwalls. While there really isn't any communication now, they could easily have the cars check the servers and have them delay, limit or stop charging entirely if the Powerwalls are powering the house. Elon said that there will be more communication between cars and Powerwalls (via Tesla's servers) but we don't have an ETA.

Here's an example from when we had the part-peak set to end at 5 am. You can see how the Powerwalls power the house until 5 am and then shut off and the first car starts charging. You can also see how we had 3 cars charge that day. At the time, I would work from home a lot and would manually start charging one of the cars during the day...but I forgot to adjust the maximum amps initially and used a little grid power. I was going for maximum self-consumption vs. maximizing bill savings. Now, we typically just start charging that car in the same 4 am to 7 am period and then send more back to the grid during the day.

Your picture did not seem to come through. For the Time Based Control - I think ideally I want to charge the powerwall any time there is excess solar over my house consumption. I would then like to power the house any time there isn't enough solar till about midnight then shut off. I would then charge my car from midnight to about 6am. Then repeat - from 6am to Midnight power the house from the battery any time there is not enough solar and recharge the battery any time there is excess solar.

Hope that makes sense. Not sure how exactly to set that up.

I think.. I got to Time Based Controls - Balanced. Then adjust the cost structure to be all shoulder from 6am to midnight. Removing all peak times. Then off peak from Midnight to 6am. I just don't know if it will charge and discharge like I hope.

 

[EV-by-the-Sea]

Your picture did not seem to come through. For the Time Based Control - I think ideally I want to charge the powerwall any time there is excess solar over my house consumption. I would then like to power the house any time there isn't enough solar till about midnight then shut off. I would then charge my car from midnight to about 6am. Then repeat - from 6am to Midnight power the house from the battery any time there is not enough solar and recharge the battery any time there is excess solar.

Hope that makes sense. Not sure how exactly to set that up.

I think.. I got to Time Based Controls - Balanced. Then adjust the cost structure to be all shoulder from 6am to midnight. Removing all peak times. Then off peak from Midnight to 6am. I just don't know if it will charge and discharge like I hope.

Did you ever figure this out? Like you, I was told that the EV charging circuit wasn't backed up by the powerwall but I've found that overnight when the car starts charging it pulls power from the powerwall (draining it pretty quickly). I think I'm seeking to do exactly what you explained.

 

[miimura]

Did you ever figure this out? Like you, I was told that the EV charging circuit wasn't backed up by the powerwall but I've found that overnight when the car starts charging it pulls power from the powerwall (draining it pretty quickly). I think I'm seeking to do exactly what you explained.

What Powerwall settings are you using? Either of the Time Based Control settings should not drain the Powerwall during Off-Peak. However, if you are set up for Self-Powered and your EV usage is measured by the Powerwall system, it will discharge to match that usage. It doesn't matter if it's backed up or not. The only time it matters if the EV circuit is backed up or not is whether or not it will drain the Powerwall(s) during a grid outage.

 

[MorrisonHiker]

What Powerwall settings are you using? Either of the Time Based Control settings should not drain the Powerwall during Off-Peak. However, if you are set up for Self-Powered and your EV usage is measured by the Powerwall system, it will discharge to match that usage. It doesn't matter if it's backed up or not. The only time it matters if the EV circuit is backed up or not is whether or not it will drain the Powerwall(s) during a grid outage.

We've had 1.37.1 since May and the TBC setting changed how our Powerwalls were charged and discharged, even during off-peak. During the day, they now charge to 100% instead of only charging up to the estimated SOC that will get them through peak and part-peak. Ours power the house during peak and part-peak. They stop once off-peak starts but if there's still a large SOC during off-peak, they will start powering the house again around 4 or 5 am.

Our off-peak period is from 9 pm until 9 am but we have it scheduled from 2 am until 9 am so that the Powerwalls and solar can power the house until we start charging the first Tesla at 2 am. In the past, the Powerwalls wouldn't discharge between 2 am and 9 am but now they will kick in and help charge the other Teslas around 4 am and 5 am. In the image above, you'll see we really only used grid power from 2 am until about 3:30 am and then a few more quick spikes of grid usage later in the day.