What is your reserve percentage set to and why?

[Lloyd]

Off Grid as in you have no electrical service or put the Powerwall in "off grid" mode?
Or Off Grid as in you have negligible draw from the electrical service?

Software limited now to "off Grid" until we decide to cut the cord with PGE! To date there have been no issues with not using grid power at all.

 

[Oobflyer]

The Tesla app hides 5% of the charge - 0% reading in the app is actually 5% of charge in the PowerWalls. The TEG's web interface shows the actual charge level - 5% in the TEG is 5% actual charge.

Since the Power Reserve % is set in the app, that means you can't set it below 5% of the actual charge level, evidently providing the reserve power needed to keep the PowerWalls and TEG operating.

We've settled on 30% as our Power Reserve level, providing us enough stored energy to operate our house for several hours during an unplanned power outage (when we may not be at home, and the pool pumps/air conditioners could be running).

We have a Free Nights electric plan - providing free power between 9PM to 9AM, so our goal is to use the solar/PowerWalls to minimize grid power usage during the day (when we're charged about 2X the fixed price rate for electricity). During the summer with high temperatures outside, we don't generate enough solar power to fully power the house between 9AM to 9PM, so we end up at 30% of charge for overnight power outages. Now that it's cooler out, we are fully charging the PowerWalls during the day, and have 60-80% of charge at 9PM.

Under the Advanced Time-Based Control settings, the TEG will try to guess how much solar charging will happen the next day and will provide power from the PowerWalls over night to bring that charge level down before the sun starts recharging the PowerWalls. Because our electricity is free overnight, I wish there was a setting that would turn this feature off - because we'd prefer to store as much excess energy as possible in our PowerWalls, to provide power during very cloudy days, when there isn't much solar energy generated.

This is the info I was looking for. Good to know that there is a 5% reserve below the 0% settings on the app. Assuming that the same safety recommendations regarding charging/discharging Li-ion batteries (for longevity) hold true for the PowerWall battery pack, a 15% minimum setting should keep the battery healthy for years to come - yes?
Does anyone know if the same is true at the top end? Since we don't charge our cars to 100% every day, is there a way to stop the PowerWall battery from charging beyond 80% (or is that already happening automatically in the background?...)

 

[Redhill_qik]

There is an interesting Reddit post from someone that has disassembled and claims that there are 1,050 battery cells inside that are the Panasonic 21700 (21x70) variant that has 17.1 Wh capacity each for a total of 17.96 kWh for the array. Since we are only getting 13.5 kWh for each Powerwall that would imply that a 100% SOC is really only 75.2%.

 

[yblaser]

There is an interesting Reddit post from someone that has disassembled and claims that there are 1,050 battery cells inside that are the Panasonic 21700 (21x70) variant that has 17.1 Wh capacity each for a total of 17.96 kWh for the array. Since we are only getting 13.5 kWh for each Powerwall that would imply that a 100% SOC is really only 75.2%.

Do you think they would put all the buffer on the top of the SOC and none on the bottom? Might make sense since the PWs very rarely hit the bottom and stay at the top a long time.

 

[Redhill_qik]

Do you think they would put all the buffer on the top of the SOC and none on the bottom? Might make sense since the PWs very rarely hit the bottom and stay at the top a long time.

Well the Reddit poster claims that the installer bricked the 4 Powerwall because they let them run down to 0%, so that would indicate that it is all on the top end.

I don't really believe that the numbers are right and that there is something different about the battery cells or the way that they are used because having 25% headroom is too much margin.

One possibility is that there is a lot of variation in the cell capacity and Tesla is building the Powerwalls with cells at the lower end of the curve that don't meet the higher specs for a car.

 

[cwied]

Well the Reddit poster claims that the installer bricked the 4 Powerwall because they let them run down to 0%, so that would indicate that it is all on the top end.

The term used actually is "past 0% SOC," so that would seem to imply a buffer at the bottom as well.

 

[Redhill_qik]

The term used actually is "past 0% SOC," so that would seem to imply a buffer at the bottom as well.

The Tesla app percentage is scaled so that it displays some margin at the low end (0% = 10% I think) and none at the top end (100%=100%). I ignore what the app is telling me and use the REST API to know how much each Powerwall can hold and it's real SOC.

 

[cwied]

The Tesla app percentage is scaled so that it displays some margin at the low end (0% = 10% I think) and none at the top end (100%=100%). I ignore what the app is telling me and use the REST API to know how much each Powerwall can hold and it's real SOC.

I don't think it's a given that the REST API shows the actual 0% and 100%. It would not be surprising if there's a buffer beyond these numbers on both ends. I think they added the extra 5% buffer to the app because of the trouble the system had restarting from low SOE states. It hasn't always been that way. When I first got my Powerwalls, the app SOE matched the SOE returned from the local API.

 

[Redhill_qik]

I don't think it's a given that the REST API shows the actual 0% and 100%. It would not be surprising if there's a buffer beyond these numbers on both ends. I think they added the extra 5% buffer to the app because of the trouble the system had restarting from low SOE states. It hasn't always been that way. When I first got my Powerwalls, the app SOE matched the SOE returned from the local API.

Musk doesn't seem to be one to put a lot of margin into his products, SpaceX being the exception. There is some as most new units report having 13.7-14.0 kWh of nominal capacity, but shipping with 17+ kWh (+25%) seems excessive. Tesla has replaced some units that have dropped below 70% (9.45 kWh) before the 10 year mark, so if they had a lot of extra margin I wouldn't expect that to happen unless the entire margin was eaten up first forcing the warranty repair or maybe the hardware team never told the software team about this and they are maintaining a fixed buffer at the top end.

My Powerwalls are alternating between 100% and 80-85% on most days as they discharge during peak. I've only lost 198 Wh (0.72%) between the two units over the last year and both are reporting higher than 13,500 kWh after 19 months, so I am happy with the performance so far.