Max PowerWall Charge when below Backup Reserve

[Tim-in-CA]

Now that I'm getting less charge from PV as the days shorten, I find that I'm running out of Battery in the middle of the night and the house is switching to grid. During the day, by the time PV stops producing I'm at approximately 50% of battery SOC. I'm on TOU4-9PM SCE plan and in winter the charge from 9PM to 8AM is slightly higher than 8AM to 4PM. To help compensate for this, I tried setting my reserve to 75% at 8AM to charge the system from PV and then set reserve back lower (5-10%) at 4PM to both raise the SOC of the batteries and utilize stored power overnight. The issue I'm seeing is that the battery will max out at 3.3kW charge rate from PV and begin to dump any excess PV greater than 3.3 into the home (the rest comes from the grid). Is the normal behavior that others have seen? My goal is two fold : reduce/eliminate grid use overnight and let the PWs charge to a higher level SOC. Any insight on other's experience is appreciated. Thanks

 

[Redhill_qik]

Now that I'm getting less charge from PV as the days shorten, I find that I'm running out of Battery in the middle of the night and the house is switching to grid. During the day, by the time PV stops producing I'm at approximately 50% of battery SOC. I'm on TOU4-9PM SCE plan and in winter the charge from 9PM to 8AM is slightly higher than 8AM to 4PM. To help compensate for this, I tried setting my reserve to 75% at 8AM to charge the system from PV and then set reserve back lower (5-10%) at 4PM to both raise the SOC of the batteries and utilize stored power overnight. The issue I'm seeing is that the battery will max out at 3.3kW charge rate from PV and begin to dump any excess PV greater than 3.3 into the home (the rest comes from the grid). Is the normal behavior that others have seen? My goal is two fold : reduce/eliminate grid use overnight and let the PWs charge to a higher level SOC. Any insight on other's experience is appreciated. Thanks

Looking at the detailed SCE Tariff rates for your TOU-D-4-9PM the rates are:

Summer On-Peak (4:00pm-9:00pm)	$0.47431​
Summer Mid-Peak (9:00pm-8:00am)	$0.38487​
Summer Off-Peak (8:00am-4:00pm)	$0.29679​
Winter Mid-Peak (4:00pm-9:00pm)	$0.41437​
Winter Off-Peak (9:00pm-8:00am)	$0.31421​
Winter Super-Off-Peak (8:00am-4:00pm)	$0.28539​

Since the Powerwall charging is only 90% efficient, it really doesn't make sense to discharge the Powerwalls during the Winter Off-Peak (9:00pm-8:00am) time. As an example of you discharge 10 kWh to save $0.31421/kWh you will save a total of $3.1421. The next day during Off-Peak (8:00am-4:00pm) it will take 11.1 kWh of solar to recharge the Powerwalls at $0.28539 which is Powerwall which is $3.1678, so you have lost $0.0257 on your NEM balance.

I would continue to discharge due the more expense Mid-Peak (4:00pm-9:00pm) period, but not at any other time to maximize your savings.

 

[Tim-in-CA]

Looking at the detailed SCE Tariff rates for your TOU-D-4-9PM the rates are:

Summer On-Peak (4:00pm-9:00pm)	$0.47431​
Summer Mid-Peak (9:00pm-8:00am)	$0.38487​
Summer Off-Peak (8:00am-4:00pm)	$0.29679​
Winter Mid-Peak (4:00pm-9:00pm)	$0.41437​
Winter Off-Peak (9:00pm-8:00am)	$0.31421​
Winter Super-Off-Peak (8:00am-4:00pm)	$0.28539​

Since the Powerwall charging is only 90% efficient, it really doesn't make sense to discharge the Powerwalls during the Winter Off-Peak (9:00pm-8:00am) time. As an example of you discharge 10 kWh to save $0.31421/kWh you will save a total of $3.1421. The next day during Off-Peak (8:00am-4:00pm) it will take 11.1 kWh of solar to recharge the Powerwalls at $0.28539 which is Powerwall which is $3.1678, so you have lost $0.0257 on your NEM balance.

I would continue to discharge due the more expense Mid-Peak (4:00pm-9:00pm) period, but not at any other time to maximize your savings.

Thanks. My current consumption results in the battery running out at about 2AM or so With reserve set very low (5%) So I’m at full battery use durin most expensive TOU period. My question was around max charge rate limitation on 3.3kW while charging when battery is less than reserve. What’s interesting is my system went into storm watch as I was typing this response and the batteries are charging at 6.7kW rate from the grid. So charge rate doesn’t seem to be a system limitation.

 

[sk00]

I posted about the same issue here earlier in the month. I don't believe this has anything to do with the TOU settings as I have the same problem in self-powered mode.

I'm currently stuck in tier-2 customer service hell. They did push firmware 21.39.1 7759c368 this morning so they and I will be monitoring. Will see if that fixes it but pretty sure it's a software issue.

 

[Tim-in-CA]

I posted about the same issue here earlier in the month. I don't believe this has anything to do with the TOU settings as I have the same problem in self-powered mode.

I'm currently stuck in tier-2 customer service hell. They did push firmware 21.39.1 7759c368 this morning so they and I will be monitoring. Will see if that fixes it but pretty sure it's a software issue.

Thanks. Seems similar. I’ll have to monitor.

 

[sk00]

Thanks. Seems similar. I’ll have to monitor.

If you haven't already, I suggest reporting to Tesla customer service and get a case number assigned. Customer service at this company is pretty terrible in general and most people on the other end of the line are completely incompetent. But, if enough customers report the same issue, I do think things get escalated/accelerated internally to the engineers who are actually working on resolving software bugs.

 

[Vines]

Now that I'm getting less charge from PV as the days shorten, I find that I'm running out of Battery in the middle of the night and the house is switching to grid. During the day, by the time PV stops producing I'm at approximately 50% of battery SOC. I'm on TOU4-9PM SCE plan and in winter the charge from 9PM to 8AM is slightly higher than 8AM to 4PM. To help compensate for this, I tried setting my reserve to 75% at 8AM to charge the system from PV and then set reserve back lower (5-10%) at 4PM to both raise the SOC of the batteries and utilize stored power overnight. The issue I'm seeing is that the battery will max out at 3.3kW charge rate from PV and begin to dump any excess PV greater than 3.3 into the home (the rest comes from the grid). Is the normal behavior that others have seen? My goal is two fold : reduce/eliminate grid use overnight and let the PWs charge to a higher level SOC. Any insight on other's experience is appreciated. Thanks

The powerwall should charge at 5 kW unless it is too cold or too full to accept the full charge rate.

Are your batteries located outside? Does this happen with warm batteries as well as cold ones?

 

[yblaser]

The powerwall should charge at 5 kW unless it is too cold or too full to accept the full charge rate.

Are your batteries located outside? Does this happen with warm batteries as well as cold ones?

I see this same behavior. It does not seem to be a hardware limitation, just how Tesla programmed the behavior. If the PW SOC is under your reserve and your solar production is less or equal to your home load plus 3.3 kW then it will only charge the powerwall at 3.3 kW and send the rest of the power to your house taking the remaining if any from the grid. If your solar production exceeds the above value it will power the house and send all the excess production (>3.3 kW) to the PW.

 

[Vines]

Hmm good to

I see this same behavior. It does not seem to be a hardware limitation, just how Tesla programmed the behavior. If the PW SOC is under your reserve and your solar production is less or equal to your home load plus 3.3 kW then it will only charge the powerwall at 3.3 kW and send the rest of the power to your house taking the remaining if any from the grid. If your solar production exceeds the above value it will power the house and send all the excess production (>3.3 kW) to the PW.

Good to know, thanks for the explanation. Soon enough I will be getting to the next stage of my install, PGE just approved the 400A service upgrade and is only charging us like $1800

 

[yblaser]

Hmm good to

Good to know, thanks for the explanation. Soon enough I will be getting to the next stage of my install, PGE just approved the 400A service upgrade and is only charging us like $1800

Cool. I've never had anything over 200A. What is the scope of work for PGE to do the upgrade? When upgrading our house to 200A, SCE only had to put the security band back on the meter and reattach the aerial. I don't think they charged anything for that.

 

[Vines]

It looks like they are just replacing the aerial. We have a few different homes attached to the same service so 200A was just not cutting it.

 

[sk00]

I see this same behavior. It does not seem to be a hardware limitation, just how Tesla programmed the behavior. If the PW SOC is under your reserve and your solar production is less or equal to your home load plus 3.3 kW then it will only charge the powerwall at 3.3 kW and send the rest of the power to your house taking the remaining if any from the grid. If your solar production exceeds the above value it will power the house and send all the excess production (>3.3 kW) to the PW.

I'm not sure this is the behavior we're describing. Take a look at this screenshot (first pic) of my system this morning. I'm in self-powered mode, which means any excess solar should be used to charge the Powerwalls to 100pct before exporting to the grid. But you see that at 84pct Powerwall SOC, all the excess solar is going to the grid, and none is used to charge the Powerwalls. It feels like the software is randomly limiting the charge rate -- sometimes Powerwalls do charge but also a portion is exported to the grid when there should be zero going to the grid (second pic).

This started to happen in early November and I suspect this behavior was driven by a new firmware. My system was functioning perfectly fine until then.

 

[yblaser]

I'm not sure this is the behavior we're describing. Take a look at this screenshot (first pic) of my system this morning. I'm in self-powered mode, which means any excess solar should be used to charge the Powerwalls to 100pct before exporting to the grid. But you see that at 84pct Powerwall SOC, all the excess solar is going to the grid, and none is used to charge the Powerwalls. It feels like the software is randomly limiting the charge rate -- sometimes Powerwalls do charge but also a portion is exported to the grid when there should be zero going to the grid (second pic).

This started to happen in early November and I suspect this behavior was driven by a new firmware. My system was functioning perfectly fine until then.View attachment 735466
View attachment 735467

This behavior seems to be different than what the OP was describing. Regardless I agree your system shouldn't be doing that in Self Powered mode.

 

[Tim-in-CA]

I see this same behavior. It does not seem to be a hardware limitation, just how Tesla programmed the behavior. If the PW SOC is under your reserve and your solar production is less or equal to your home load plus 3.3 kW then it will only charge the powerwall at 3.3 kW and send the rest of the power to your house taking the remaining if any from the grid. If your solar production exceeds the above value it will power the house and send all the excess production (>3.3 kW) to the PW.

Thanks for confirming. I’ll have to monitor once production kicks up in the spring and try the same test.

 

[sk00]

This behavior seems to be different than what the OP was describing. Regardless I agree your system shouldn't be doing that in Self Powered mode.

Upon re-reading the original post, you're right that I'm describing a different issue. Apologies for the confusion. Still trying to get Tesla to address my problem.