Anatomy of a Balanced Time-Based Control Setup

[dandrewk]

I recently installed three PWs with an 8 kW solar array. I've been experimenting with the various charge profiles available via the Tesla app. The one for balanced time-based control looks really pretty:

The rate schedule times summer weekdays for E-6 via PG&E/MCE:

Peak: 1-7 PM
Partial Peak: 10 AM to 1 PM and 7 PM to 9 PM
Off Peak: All other hours.

We have two EVs, a Bolt and Leaf (sorry, no Model Y yet...). No central A/C, the spikes are for the EV charging, several PCs (we have three sons...), dishwashers etc.

Starting at 12 AM, we are running on grid until the Bolt starts charging around 4:30 AM. Those little spikes (horns) are from the central fan circulating the air for 15 mins every hour during the night.

The goal seems to be having the PW fully charged by peak time, using our calculated energy needs leveraged with typical solar output. So 2/3 through the Bolt charge, the app seemlessly switches the output from grid to PW. The household starts waking up around 6:30 AM, and solar starts to kick in around 8 AM. During this time, the household is powered by the grid and later solar/grid until solar produces more than we need and sends excess to PW.

At 10 AM when partial peak starts, all grid usage stops. At 1 PM, peak time, home is entirely powered from PW and all solar energy goes to grid. From 7-9 PM the home is powered from the little solar power remaining and PW. After 9 PM the home is 100% powered from grid.

BTW, at 1 PM the battery has been at 99-100% SOC. It totally works. Tesla gets a lot of grief over perceived shortcomings of the app, but this is something that works great.

 

[miimura]

I have also used TBC Balanced for most of my time with the Powerwalls. However, I did give Cost Saving a try during most of June and July. I've switched back to Balanced now. Cost Saving works, but it hugs the bottom end of the SOC range during the week and then fills up on Off-Peak energy on the weekend. I prefer the mostly Self-Powered like operation of Balanced but without Off-Peak discharge. This is my chart from Yesterday.

However, I think that if you had enrolled in EV-A before July 1, you would save money versus E-6. The Off-Peak EV charging on E-6 is expensive. However, if you're close to net zero kWh for the year, it probably doesn't matter.

 

[dandrewk]

However, I think that if you had enrolled in EV-A before July 1, you would save money versus E-6. The Off-Peak EV charging on E-6 is expensive. However, if you're close to net zero kWh for the year, it probably doesn't matter.

I didn't have the option really, as the PWs are only about a month old. EV-A was attractive mainly because of peak charge rates that are similar to EV-6, but are available year-round. EV-6 is basically a higher off-peak rate 24/7 during winter months.

One big advantage of cost saving choice is having the EVs charge overnight off the grid instead of PW. I don't want to move the EVSE circuit breakers off the PW gateway, and even the balanced choice will use PW for overnight charging.

I don't know what system I will settle on long term. Most likely it will be cost savings/balanced during summer rates, and then anything during winter.

 

[Ampster]

I didn't have the option really, as the PWs are only about a month old.

EV-A was available to EV owners, It had nothing to do with the PW install date. Not trying to make you feel bad but trying to inform other readers. EV2-A is still available and offers a $0.16 per kWh rate off peak rate when charging EVs. I don't know how that compares to your current grandfathered E-6 rate.

 

[miimura]

EV-A was available to EV owners, It had nothing to do with the PW install date. Not trying to make you feel bad but trying to inform other readers. EV2-A is still available and offers a $0.16 per kWh rate off peak rate when charging EVs. I don't know how that compares to your current grandfathered E-6 rate.

Without knowing his exact usage pattern, I suspect he will be better off staying on E-6 than EV2-A. The Generation Credits on EV2 are terrible because Off-Peak goes all the way to 3pm. It really depends on how big the solar is relative to how much EV charging he has.

 

[dandrewk]

EV-A was available to EV owners, It had nothing to do with the PW install date. Not trying to make you feel bad but trying to inform other readers. EV2-A is still available and offers a $0.16 per kWh rate off peak rate when charging EVs. I don't know how that compares to your current grandfathered E-6 rate.

It actually has everything to do with PW install date, because prior to that time I would have had no reason to switch to EV-A. I did the numbers and found EV-6 was slightly better for our usage. Even now, there are some things I like better on EV-6.

Hindsight is always 20-20. If I had installed the PWs earlier, I probably would have grabbed EV-A while available.

These conversations happen pretty regularly here. The thread is about the difference between the charge profiles offered by the Tesla app. It's a bit hard to understand until you actually see it in action.

 

[Ulmo]

How do these settings handle the higher priced times between peak and off peak? The thing seems to be using grid during the partial-peak times! That's not a good idea!

 

[troptop]

Is it possible to discharge the powerwall into the grid during on-peak?

 

[power.saver]

No. You can only discharge to offset house load, thus sending all solar to the grid during peak.

 

[Ulmo]

I posted this yesterday, but for some reason, I cannot find the post:

How do these settings handle the higher priced times between peak and off peak? The thing seems to be using grid during the partial-peak times! That's not a good idea!

I'm seeing the grid used in partial-peak rates, which are expensive, so I went ahead and moved the peak setting to cover the rateplan's nighttime partial-peak rate.

That is, on weekdays, the rate is off-peak 11pm-7am, medium 7am-2pm, peak 2pm-9pm, then medium 9pm-11pm. I set that last medium to be considered peak by PowerWall, so that it will pull from battery at that time rather than grid.

Now, I saw this today:

This is my first time seeing a really true full day on Time Based Control. At noon, the home batteries (PowerWalls) were full (light blue line %), so only EXCESS solar was sent to grid. At 2pm (14:00 above), Peak Rate started, so to maximize that, the PowerWalls supplied ALL HOME use, and ALL solar was sent to grid rather than just excess. Right now, it looks like about half my batteries are still available, and I got to be 100% battery since 2PM, all of which time I sold solar back to the grid.

This is the first time I'm selling solar to the grid in these quantities in years, since without this, the PowerWall would soak up 100% of my solar, and the grid was nothing but an expense for me.

By me setting the peak time all the way through the PG&E partial-peak time to the beginning of off-peak (11PM), I will use batteries all the way til then, and not draw any grid in the evening. I used to use so much PowerWall during the day when the sun was shining that I wouldn't have any left for late evening, when PG&E still has its highest usage period, but now with Time Based Control active, I will finally make money off my solar installation. I lost somewhere between a thousand and thousands of dollars not having this option available, with the net effect that I could not always keep battery use during PG&E's peak net demand times (evening). This is WAY better.

I'm curious if I picked Time Based Control "Balanced" or "Savings". I think in winter when I turn on the electric heater and have the least sunlight available, I'm going to have to go to "Savings" to reduce my costs even further. Checking: I'm on Cost Savings mode. I like this mode. I need the money, and this is better for the grid and better for the environment. Win win win! Why didn't we have this available years ago?!

 

[Ulmo]

Following up, looks like the PowerWall is not doing a deep discharge in Cost Savings mode, only going down to around 50% by 8:45PM, which means I had to purchase more electricity until 2PM. Right now use is almost 3kW.

I wonder if I should either pick "Balanced" or move the "Peak" rate an hour earlier to 1PM or both. I'm trying both. Scratch that -- both seems like overkill; I'll switch to straight up Balanced and move the peak rate start point back to 2PM.

 

[Ulmo]

For the PowerWall Time Based Control software variables, I wish we had more insight and fine-grain control. Maybe expose those in a Super Advanced tab.

 

[NuShrike]

For the PowerWall Time Based Control software variables, I wish we had more insight and fine-grain control. Maybe expose those in a Super Advanced tab.

Well, since you wrote your own monitor and graphing, why not just advance it a little more and talk to the PW API for more control?

 

[Ulmo]

This looks funny. This is the first time I've seen anything like this.

Well, since you wrote your own monitor and graphing, why not just advance it a little more and talk to the PW API for more control?

I've been trying for years and so far it has failed. Is that available yet? Maybe I can try again. For instance, I was trying to get on what they call Time Based Control every year as well, and this year I finally succeeded. Maybe the API works better now?

 

[miimura]

This looks funny. This is the first time I've seen anything like this.

View attachment 452361

That is totally normal for both Cost Saving and Balanced modes during the Peak period. The Powerwalls supply the household loads and the solar generates maximum NEM credits.