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what I learned today - or why my powerwall doesn't fully charge from solar every day

Vostok

Active Member
Jul 1, 2017
2,624
3,045
Sydney
During the hours of 4-9pm I'd like to run my home off solar, send the excess to the grid, have my home run off the Powerwalls when there isn't enough solar, and NEVER draw power from the grid.

The only way to do that would be to set your PW2 to be in self-consumption mode with 0% reserve for outages during 4-9pm. Even then, whenever solar production is low and house has exhausted the battery, you will start using the grid. No way to avoid that.

During the hours of 9-4pm I'd like my home to run off solar if available, run off the grid if enough solar isn't available, use excess solar to recharge the Powerwalls, and NEVER run the home off the Powerwalls (unless there is an outage).

To do that, set the PW2 reserve for outages to 100% from 9-4pm.

If it looks like there isn't going to be enough solar to recharge the Powerwalls before 4pm then prioritize recharging the Powerwalls over the home. If that still can't recharge the Powerwalls in time then charge the Powerwalls from the grid.

There is no way to prioritise PW2 charging over home consumption via commands that I know of. Consumption is higher than charging in the hierarchy. TBC / stormwatch might do this occasionally, but that appears to be an internal algorithm in the PW2 software that is triggered, and is not triggered by API commands.

If anyone has figured out a way to do this it would be nice to know.

Assuming you don’t want to sit on the Tesla App and manually change PW2 settings at various times during the day like a human cron job, the only way is to learn the Tesla API and write a script to change the PW2 settings to whatever you want at whatever times of the day and run that script as a cron job.
 
The only way to do that would be to set your PW2 to be in self-consumption mode with 0% reserve for outages during 4-9pm. Even then, whenever solar production is low and house has exhausted the battery, you will start using the grid. No way to avoid that.



To do that, set the PW2 reserve for outages to 100% from 9-4pm.



There is no way to prioritise PW2 charging over home consumption via commands that I know of. Consumption is higher than charging in the hierarchy. TBC / stormwatch might do this occasionally, but that appears to be an internal algorithm in the PW2 software that is triggered, and is not triggered by API commands.



Assuming you don’t want to sit on the Tesla App and manually change PW2 settings at various times during the day like a human cron job, the only way is to learn the Tesla API and write a script to change the PW2 settings to whatever you want at whatever times of the day and run that script as a cron job.
Yea, I should have added that I want this to be automated and use the Tesla app settings. I live in an area of frequent outages so I want to keep my reserve at 50% - I'm OK with using the grid between the hours of 4-9pm if I've hit my reserve.

Using Time Based controls my Powerwals recharging are prioritized over home consumption during off peak. All solar goes to Powerwall recharging and the home runs off the grid. Once the Powerwalls are charged my home runs off solar and the excess is sent to the grid.
 
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Yea, I should have added that I want this to be automated and use the Tesla app settings. I live in an area of frequent outages so I want to keep my reserve at 50% - I'm OK with using the grid between the hours of 4-9pm if I've hit my reserve.

Using Time Based controls my Powerwals recharging are prioritized over home consumption during off peak. All solar goes to Powerwall recharging and the home runs off the grid. Once the Powerwalls are charged my home runs off solar and the excess is sent to the grid.
Is your goal maximizing house usage or minimizing grid export? You could try setting the sell price to a very low price so the Powerwalls minimize the export. This will also result in using more solar to power the house, but the Powerwalls will still charge from all solar if needed to fill up before peak starts.
 
Is your goal maximizing house usage or minimizing grid export? You could try setting the sell price to a very low price so the Powerwalls minimize the export. This will also result in using more solar to power the house, but the Powerwalls will still charge from all solar if needed to fill up before peak starts.
I'm a net producer so I want to minimize my NBCs and wear on my Powerwalls.

Prioritizing all solar to recharging the Powerwalls and running my home from the grid in the mornings unnecessarily increases my NBCs.

Sending all solar to the grid and completely running off the Powerwalls during peak hours causes my Powerwalls to discharge more than necessary. I could also reduce my peak hours in the app, or increase my reserve, and run my house off the grid some of the time during peak hours to accomplish a similar result but I would prefer to prioritize solar to the house. Discharging my Powerwalls more than necessarily also indirectly impacts my NBCs since I'm running longer from the grid in the mornings while my Powerwalls recharge.
 
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Gwgan

Almost a wagon
Aug 11, 2013
3,232
2,599
Maine
I want to minimize my NBCs and wear on my Powerwalls
Why not just use them for backup?

Sending all solar to the grid and completely running off the Powerwalls during peak hours causes my Powerwalls to discharge more than necessary.
Tesla’s goal is to maximize the financial value of the PW. Time based control does not seem to match your goals.
 

NikoV6

Member
Nov 13, 2018
37
24
Uk
From the support pages
“Some utilities allow Powerwall to send energy back to the grid and claim credits during peak times. When Powerwall is able to send energy to the grid, the following energy export options will be available…”
You should have the choice to export Solar (only) or Everything (solar + battery).

Is it financially beneficial to be exporting at that time?

I don't have the option in my app to export Solar (only) or Everything (solar + battery). My PowerWall is set to never export, I assume this is from the battery. This never export setting does not seem to stop it exporting solar for some reason!

I tried setting export tariff to £0:00 but the version of the app I have does not allow a zero value option. I am happy with Time Based mode, although I still think it can get caught out by the great British weather, which can often throw a dull day in after much sun and you end up with not enough energy in the battery. I just need it to never send solar back to the grid unless the excess is more than the max charge of the battery and the house load is being satisfied
 
Why not just use them for backup?


Tesla’s goal is to maximize the financial value of the PW. Time based control does not seem to match your goals.
If I use the Powerwalls for backup only I will become a net consumer and my annual costs will increase significantly.

The problem is Tesla's algorithm doesn't take Non-Bypassable Costs (NBCs) nor powerwall throughput degradation into account so it doesn't maximize the financial value for a net producer. And Time of Use is the only reasonable option for me since it only makes sense to run off the powerwalls during peak rates.
 

Gwgan

Almost a wagon
Aug 11, 2013
3,232
2,599
Maine
What are your rates? Is there any form of net metering? We have 1:1 net metering so when I lost my afternoon off-peak period it took me a bit to appreciate that it made more sense to export solar during the day. My batteries only charge on the weekends and during stormwatch.
 
What are your rates? Is there any form of net metering? We have 1:1 net metering so when I lost my afternoon off-peak period it took me a bit to appreciate that it made more sense to export solar during the day. My batteries only charge on the weekends and during stormwatch.
I'm under PG&E's EV2A rates which are currently $.25/kWw off-peak (12am-3pm), $.45/kWh part-peak (3-4pm & 9pm-12am), and $.56/kWh (peak 4-9pm).

I'm under NEM2 which effectively means I'm charged an additional ~$.03/kWh for every kWh I draw from the grid that I have previously "banked" to the grid. So, when I'm running my house off the grid in the mornings while all solar goes to my powerwalls I'm being charged an additional $.03/kWh that I wouldn't be charged if solar was prioritized to my home and the residual was used to recharge the powerwalls.

I'm a net producer which effectively means compensated ~$.05/kWh at the end of the year for any residual kWh's that I haven't used.
At this point every kWh I overproduce is is a kWh drawn from the powerwall. To me, $0.05/kWh isn't worth the wear and tear on my powerwalls.

This is only going to get worse when California transitions to NEM3.
 

Vostok

Active Member
Jul 1, 2017
2,624
3,045
Sydney
The problem is Tesla's algorithm doesn't take Non-Bypassable Costs (NBCs) nor powerwall throughput degradation into account so it doesn't maximize the financial value for a net producer.

I’m in Australia and have no idea what an NBC is, but I don’t care much about my PW2’s degradation, because it’s been so fast that I am locked in to get a warranty replacement. I won’t even pounce as soon as it is eligible, I’ll probably wait until year 7 or 8 when its capacity loss is starting to cost me significant dollars (the majority of the value is in the first 7kWh of capacity, not the second 7 kWh).

And who knows, by then the warranty replacement might be an entirely new system with new battery chemistry and new gateway because they no longer have replacements for the original kit I have. So it actually might pay to wait.
 

aesculus

Still Trying to Figure This All Out
May 31, 2015
4,967
2,892
Northern California
I'm under PG&E's EV2A rates which are currently $.25/kWw off-peak (12am-3pm), $.45/kWh part-peak (3-4pm & 9pm-12am), and $.56/kWh (peak 4-9pm).

I'm under NEM2 which effectively means I'm charged an additional ~$.03/kWh for every kWh I draw from the grid that I have previously "banked" to the grid. So, when I'm running my house off the grid in the mornings while all solar goes to my powerwalls I'm being charged an additional $.03/kWh that I wouldn't be charged if solar was prioritized to my home and the residual was used to recharge the powerwalls.

I'm a net producer which effectively means compensated ~$.05/kWh at the end of the year for any residual kWh's that I haven't used.
At this point every kWh I overproduce is is a kWh drawn from the powerwall. To me, $0.05/kWh isn't worth the wear and tear on my powerwalls.

This is only going to get worse when California transitions to NEM3.
What is the difference between your minimum monthly charge and the NBCs you are paying monthly?
 

Gwgan

Almost a wagon
Aug 11, 2013
3,232
2,599
Maine
~$.03/kWh for every kWh I draw from the grid
That is the Non-Bypasable Charge on every delivered kWh regardless if that energy is being offset by your banked export, or essentially the difference between your sell and buy prices. Perhaps if you modified your TOU plan in the app to increase that difference to 15 cents during the times you want to be sure not to be importing then the algorithm would work more like you would like. Just a guess.
 
That is the Non-Bypasable Charge on every delivered kWh regardless if that energy is being offset by your banked export, or essentially the difference between your sell and buy prices. Perhaps if you modified your TOU plan in the app to increase that difference to 15 cents during the times you want to be sure not to be importing then the algorithm would work more like you would like. Just a guess.
I tried playing with the settings a while ago and would up drawing power during peak periods. Before I play around again I'd like to see if anyone else has been successful with using Time Based control and get the system to prioritize solar to the home with the residual recharging the powerwalls during off-peak.
 
I'm under PG&E's EV2A rates which are currently $.25/kWw off-peak (12am-3pm), $.45/kWh part-peak (3-4pm & 9pm-12am), and $.56/kWh (peak 4-9pm).
It probably doesn't matter to this discussion, but I believe EV2A is already on the winter schedule, so the rates should be $.25, $.42 and $.43. The one difference I noticed is that my Powerwalls will no longer charge during partial peak to export during peak (with "export everything"). I'm assuming this is because with round-trip losses this no longer is profitable with the small difference between peak and partial-peak.
 
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Gwgan

Almost a wagon
Aug 11, 2013
3,232
2,599
Maine
Seems this has been discussed before but the difference here is trying to minimize PW cycling which any internal algorithm is going to think is ok.
 

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