TBC-Balanced Springtime Behavior

[miimura]

I have been a little frustrated with Time Based Control now that the sun is actually shining in Northern California. The Powerwalls have been discharging early before the Peak rate period starts. This is exacerbated by the fact that there is an offset of the rate periods now that Daylight Saving Time has taken effect but the PG&E is not shifting the rate periods until April. Through the Winter the system has been doing exactly what I expect, managing the best it can with the limited generation and hitting the Reserve each day.

Thursday:

Friday:

In both of these images the Powerwalls are reaching about 90% when they start discharging, well before the start of the Peak period.

I called Powerwall Support on Wednesday afternoon and complained about the early discharge and the first level support guy told me that nothing was wrong and the system thought it was saving me money doing it this way. I disagree. To my way of thinking, the Powerwalls should keep charging until they're full and then they should go into Standby and let the Surplus Solar go to the grid. When the Peak period starts, it should start discharging the Powerwalls to match my household consumption and let All Solar go to the grid to earn Peak period credits.
However, the Friday behavior is kind of brilliant in its own way. The Off-Peak period started at midnight and the Powerwalls ended the day at almost exactly the Reserve level. Weekends are Off-Peak except 4pm-8pm, so all the extra discharge on Friday is actually OK because all that energy will be replaced with Off-Peak solar generation. The only problem is that it has battery charge-discharge losses during Part-Peak on Friday morning. If it had just stopped charging at 85% or something and went to Standby at noon before starting to discharge, the round-trip losses could have been avoided and more solar credits generated.

 

[power.saver]

Are you on Cost Savings or Balanced? I use Balanced and have no part-peak programmed, just to prevent this kind of nonsense. Try making all your part-peak as off-peak.

 

[NinjaVece]

I have been a little frustrated with Time Based Control now that the sun is actually shining in Northern California. The Powerwalls have been discharging early before the Peak rate period starts. This is exacerbated by the fact that there is an offset of the rate periods now that Daylight Saving Time has taken effect but the PG&E is not shifting the rate periods until April. Through the Winter the system has been doing exactly what I expect, managing the best it can with the limited generation and hitting the Reserve each day.

Thursday:
View attachment 387168

Friday:
View attachment 387169

In both of these images the Powerwalls are reaching about 90% when they start discharging, well before the start of the Peak period.

I called Powerwall Support on Wednesday afternoon and complained about the early discharge and the first level support guy told me that nothing was wrong and the system thought it was saving me money doing it this way. I disagree. To my way of thinking, the Powerwalls should keep charging until they're full and then they should go into Standby and let the Surplus Solar go to the grid. When the Peak period starts, it should start discharging the Powerwalls to match my household consumption and let All Solar go to the grid to earn Peak period credits.
However, the Friday behavior is kind of brilliant in its own way. The Off-Peak period started at midnight and the Powerwalls ended the day at almost exactly the Reserve level. Weekends are Off-Peak except 4pm-8pm, so all the extra discharge on Friday is actually OK because all that energy will be replaced with Off-Peak solar generation. The only problem is that it has battery charge-discharge losses during Part-Peak on Friday morning. If it had just stopped charging at 85% or something and went to Standby at noon before starting to discharge, the round-trip losses could have been avoided and more solar credits generated.

Miimura, what firmware release are you on? I've been updated to 1.34.2 (I have a separate thread created about it) and on Cost Savings and all hell is breaking loose with it. It doesn't follow my settings at all and it seems to be in Stormwatch mode as best as I understand the icon. Let me know what release you are using at the moment to see if your problems are related at all to mine.

 

[miimura]

Miimura, what firmware release are you on? I've been updated to 1.34.2 (I have a separate thread created about it) and on Cost Savings and all hell is breaking loose with it. It doesn't follow my settings at all and it seems to be in Stormwatch mode as best as I understand the icon. Let me know what release you are using at the moment to see if your problems are related at all to mine.

I am still on 1.32.0 and have been for quite a while. This weekend it has done exactly what I expect, probably because there is no Part-Peak period. Only Peak and Off-Peak on weekends here.

 

[zanary]

I am still on 1.32.0 and have been for quite a while. This weekend it has done exactly what I expect, probably because there is no Part-Peak period. Only Peak and Off-Peak on weekends here.

I’m also on 1.32 and it’s been very stable. I use the cost saving setting.

 

[MorrisonHiker]

I've been on TBC-Balanced for months and it has always discharged long before the peak period actually starts. While my peak period starts at 2 pm, today it started sending everything back to the grid once the Powerwalls were charged to only 70% or so, around 10:30 am. I wonder if it is trying to estimate my daily usage and only charge up as much as it thinks it will need. On most days, the Powerwalls do power the house all through the part-peak period until the scheduled start of my off-peak period (which I've purposely set to 4 am). I wonder if they are just trying not to charge them to 100% if that much charge isn't needed. We had a long outage(nearly 46 hours) last week and once the grid was back online, the Powerwalls were charged to 100% for three days straigh before returning to the "random" maximum charge that I'm seeing again today. Mine are still on 1.32.0.

 

[miimura]

Monday update: Powerwalls charged to 100% by 11:45am. As soon as the solar was greater than the household load, it charged with only surplus solar. They remained in Standby until 1:45pm when they started discharging to partially offset household load, then started offsetting 100% of the household load at 2:00pm. Peak does not start until 3:00pm. The weekend behavior was as expected, charge to 100% during Off-Peak, discharge to satisfy household loads during Peak, then Standby during Off-Peak.

I want to reiterate my opinion about how it SHOULD be working. I have pure Net Metering (PG&E NEM 1.0 w/o NBCs) so anything that happens within the same time period has the same value. So, what I say below is shaped by that context.
1. I do not have ANY Off-Peak generation on weekdays, so it makes no sense to discharge in the Part-Peak period Monday through Thursday. Once the batteries are full, just go to Standby and wait for the Peak period. Any extra discharge is just incurring round trip energy losses for no good reason.
2. If the starting SOC is relatively high and the solar is ramping up smoothly, which indicates a nice sunny day, then there is no need to charge with All Solar, just charge with Surplus Solar.
3. On a Friday with good solar production it may not be necessary to charge to 100%. It may make sense to go into Standby at 80% or 90% and coast through the early afternoon Part-Peak earning solar credits before Discharging during the Peak and evening Part-Peak. The reason Friday is different is that the discharged energy can be replaced by Weekend generation during the low priced Off-Peak that runs most of the day, usually until 3pm.

Anyone that has Non-Bypassable Charges or a feed-in tariff that credits less $/kWh for grid feed-in than consumption would clearly want something different. In that case, it might make sense to discharge in the morning before the solar generation exceeds household consumption. The assumption here is that the financial difference is greater than the round trip charging losses. However, in order for Tesla to accurately make that decision for you, they would have to know the per kWh prices of consumption and grid feed-in for every time period. This is one area that I want to see them implement a more detailed setup. Until they have that data, their algorithm is just being arbitrary.

 

[Frankman60]

I agree with your statements about how the PW2 should charge and discharge in your environment miimura. I know that you have been using TBC Balanced since TBC was activated by Tesla, and have posted positive comments about it. Do you have an idea of why the TBC Balanced is now behaving differently? Because your gateway is still running the same firmware version, it can’t be that. Is it possible for Tesla to change the PW2 behavior without updating the FW? You mentioned that your area is getting more sun as Spring gets closer, but in the past didn’t you have sunny days once in a while that mimic a Spring day? It seems that something else changed the behavior of TBC Balanced. Have you tried using the other TBC mode to see what happens?

 

[miimura]

I agree with your statements about how the PW2 should charge and discharge in your environment miimura. I know that you have been using TBC Balanced since TBC was activated by Tesla, and have posted positive comments about it. Do you have an idea of why the TBC Balanced is now behaving differently? Because your gateway is still running the same firmware version, it can’t be that. Is it possible for Tesla to change the PW2 behavior without updating the FW? You mentioned that your area is getting more sun as Spring gets closer, but in the past didn’t you have sunny days once in a while that mimic a Spring day? It seems that something else changed the behavior of TBC Balanced. Have you tried using the other TBC mode to see what happens?

It must be the weather combined with the relatively small size of my solar array. We literally didn't have two back to back completely sunny days in 2019 until last week. My system was previously bouncing off the Reserve every day through the whole winter. In the Winter I set the Reserve on my two Powerwall system to 50% or 75% depending on the solar production. On a completely sunny day in December my solar only generates 5kWh, so there's no point setting the Reserve any lower because there's never enough generation to bring the SOC back up to the top.

On the other hand, today is a partly cloudy day with very peaky solar generation and it looks like the Powerwalls only reached about 84% before they started discharging, 45 minutes early. Sigh.

I really don't want to force the system to do what I want with exaggerated settings. I'm sure that if I took away the Part-Peak in the settings it would eliminate the early discharge. However, it would always charge with All Solar and that's not really what I want either. I guess what I really want is to control the actual rule engine.

 

[Shygar]

Do you think it's maybe accounting for a bit of vampire loss if it sits with a higher battery % overnight? I would assume that would be less than the loss of charging the battery and using the battery, but not certain.

@NinjaVece if you are in stormwatch mode, you will definitely know. It shows up on your main graph (the part of the app that shows the direction of travel for all of your solar, powerwall and home/grid usage). It also puts like an orange box around the border on that same screen.