Battery and Solar during an ice storm

[niveknow]

I learned this the hard way yesterday in the middle of the Texas ice storms where power was out everywhere. My system was fine all day until about noon then my inverter would turn off my panels. I thought it was inverter issues, so I flipped breakers, etc. Also went outside and noticed the inverter knob froze over so I couldn't do anything there. (spent a few mins researching cold weather operating range and ruled this from being the issue. will go negative-alot before it's an issue).

I did notice the inverters would occasionally bleep on for a split minute then off again, but wouldn't ever stay on long enough to charge. It effectively forced my home to power itself from the battery in the middle of a storm where I should be charging battery to 100% and powering my home from the sun.. .instead it was drawing from precious battery that should be reserved for sun down. Calling Telsa support (tier 1) was beyond frustrating because Tier 1 is clueless and gave me a wide range of non sense answers that just was illogical. My 4th call (yes... 4th! ) I finally found a person that seem to know what she was talking about.

Basically said that peak sun (11+ kwH for me) with my current home draw.. was too much for the batteries to charge.. so it would shut down the inverter. So I need to consume more so less is forced to the battery. She even gave an example where another customer ran his oven to increase house consumption. I immediately turned on my pool pump.. ran the DC as fast as I could and bam! That worked. Increasing my consumption to 5 kw left less available for the battery and turned on the inverter. I was charging again! By the time I worked this out, I had wasted 3 hours of peak battery charging time so got to sun down with a 80% full battery instead of 100%. Was tough trying to conserve battery overnight to keep the heater on during the ice storms, but we got through it.


In technical terms, I think the max charge rate per battery is 3.3. That means I needed to turn the consumption up leaving less than 6.6 going to the battery otherwise inverter would turn off.


Posting this now in the morning so others may be aware and learn from.

 

[jjrandorin]

This can happen if one has "too much PV, not enough powerwalls". You have a 12k solar system with only 2 powerwalls, and if your peak production can go as high as 11kW, in order to avoid this you either need another powerwall, or to increase your home loads if possible to prevent them being forced off because of too much power... as you found out.

 

[SMAlset]

@niveknow Glad you were able to have heat last night. Thanks for the info. How does cloud cover today look for you? I read that the utilities said outages could last longer than they thought.

 

[wjgjr]

This can happen if one has "too much PV, not enough powerwalls". You have a 12k solar system with only 2 powerwalls, and if your peak production can go as high as 11kW, in order to avoid this you either need another powerwall, or to increase your home loads if possible to prevent them being forced off because of too much power... as you found out.

I think the most interesting point is that this was apparently happening with production exceeding home load by 3.3 kW per powerwall, and not by 5.0 kW. If that is the behavior during an outage situation, it will affect far more customers.

I have commented before that this is a great example of Tesla doing a really poor job of communicating expectations to customers. Those of us who read most of the posts on this forum are probably aware of this issue, along with the issue of solar shutting down when the PWs start to approach full during an outage. But most customers would likely not be aware of these constraints or what to expect in an outage, and Tesla really should have a nice, one-page "what to expect and do during an outage" document that they provide customers to help understand and anticipate these kinds of issues.

 

[jjrandorin]

I think the most interesting point is that this was apparently happening with production exceeding home load by 3.3 kW per powerwall, and not by 5.0 kW. If that is the behavior during an outage situation, it will affect far more customers.

I have commented before that this is a great example of Tesla doing a really poor job of communicating expectations to customers. Those of us who read most of the posts on this forum are probably aware of this issue, along with the issue of solar shutting down when the PWs start to approach full during an outage. But most customers would likely not be aware of these constraints or what to expect in an outage, and Tesla really should have a nice, one-page "what to expect and do during an outage" document that they provide customers to help understand and anticipate these kinds of issues.

I think having some sort of 1 pager is a good idea in theory, the problem is, just like every house can have a different electrical setup, every install is a bit different. What might happen for me, is different than what might happen for you, or for this OP, based on amount of PV, etc.

What really needs to happen, though, is better vetting / explanation of a customers individual proposed system, and better advice from whoever the customer is going through, tesla or or otherwise.

People can, in general, understand what having more solar panels gives them. They then look at "the budget" and say "I only need to run my system for a few hours, 1 battery is fine" or I know I have 15kW of PV but 2 batteries is fine, they are too expensive to get more". The company they are going with should absolutely push back, if they are not getting "enough" batteries, but we know that tesla absolutely does not do that.

They just "make it work" with whatever the customer is asking for. I did my own research and came to the conclusion I needed 2 batteries for my 8.7kW PV. If I had 12kW of PV, I would have 3. Tesla (I think) says you can have "up to" 7kW of PV per powerwall, from a recommendation standpoint... although I cant remember where I saw that. Thats not nearly enough IMO.

I suspect if one went with a company like the one @Vines works with, or went with a construction company like @wwhitney, who are familiar with PV, batteries, etc, they would provide real advice on what a customer needs to consider. We know tesla doesnt do that.

TL ; DR. There should be some more education "somewhere" by tesla on this, but no idea what that would look like, because everyones install is different.

 

[MorrisonHiker]

We had a similar problem during a 48 hour outage back in 2019 but our issue was due to the Powerwall SoC being too low. We had a perfect sunny day right after a big snowstorm but our Powerwalls were drained down to 5% and were raising the frequency to warm up. I tried turning the inverters off throughout the day. Sometimes they would stay up for 5 minutes, sometimes for up to an hour but they kept cycling off due to the high frequency from the Powerwalls. We had 3 inverters at the time and I tried various combinations but nothing worked to keep things up. It was frustrating talking with tier 1 tech support at the time since they said a "grid-tied solar system" goes down when the grid goes down. I had to explain that's what the Powerwalls were for...to allow my solar to continue working when the grid was down! Tesla came out a day or two later and found our inverters needed the firmware updated and to have the frequency shutoff value adjusted. Since then, we had another 48 hour outage in warmer temperatures and did a 200 hour off-grid test during a week with a decent snow storm and didn't have any problems.

It looks like Tesla has also updated the Powerwall/gateway firmware since then and when the battery level gets low, the Powerwalls will go into standby but still try to start solar back up:

 

[Electrph]

so to be clear .. this is behavior while the OP's utility power was out correct ? (i know OP stated power out everywhere.. does that include their home?)
otherwise system would send excess pv gen to grid and continue to keep powerwalls topped off ?
so if "off grid" this is similar issue to powerwalls nearing full just now rate of charge "too high" for powerwalls to handle no where to send excess?

 

[MorrisonHiker]

so to be clear .. this is behavior while the OP's utility power was out correct ? (i know OP stated power out everywhere.. does that include their home?)
otherwise system would send excess pv gen to grid and continue to keep powerwalls topped off ?

Yes

 

[gpez]

I learned this the hard way yesterday in the middle of the Texas ice storms where power was out everywhere. My system was fine all day until about noon then my inverter would turn off my panels. I thought it was inverter issues, so I flipped breakers, etc. Also went outside and noticed the inverter knob froze over so I couldn't do anything there. (spent a few mins researching cold weather operating range and ruled this from being the issue. will go negative-alot before it's an issue).

I did notice the inverters would occasionally bleep on for a split minute then off again, but wouldn't ever stay on long enough to charge. It effectively forced my home to power itself from the battery in the middle of a storm where I should be charging battery to 100% and powering my home from the sun.. .instead it was drawing from precious battery that should be reserved for sun down. Calling Telsa support (tier 1) was beyond frustrating because Tier 1 is clueless and gave me a wide range of non sense answers that just was illogical. My 4th call (yes... 4th! ) I finally found a person that seem to know what she was talking about.

Basically said that peak sun (11+ kwH for me) with my current home draw.. was too much for the batteries to charge.. so it would shut down the inverter. So I need to consume more so less is forced to the battery. She even gave an example where another customer ran his oven to increase house consumption. I immediately turned on my pool pump.. ran the DC as fast as I could and bam! That worked. Increasing my consumption to 5 kw left less available for the battery and turned on the inverter. I was charging again! By the time I worked this out, I had wasted 3 hours of peak battery charging time so got to sun down with a 80% full battery instead of 100%. Was tough trying to conserve battery overnight to keep the heater on during the ice storms, but we got through it.


In technical terms, I think the max charge rate per battery is 3.3. That means I needed to turn the consumption up leaving less than 6.6 going to the battery otherwise inverter would turn off.


Posting this now in the morning so others may be aware and learn from.

One automatic solution to this is to have your PV scale it's output based on the local grid frequency. When the grid is down and your battery fills up it will raise the local frequency which the inverters will react to by lowering production. Configured properly this will keep your PV on throughout the day at reduced capacity to meet demand but keeping your battery fully charged.

SolarEdge inverters all it "P(F) Power Frequency" (https://www.solaredge.com/sites/default/files/application_note_power_control_configuration.pdf, page 6) and Enphase calls it "curtailment" or "ramp down" (https://enphase.com/sites/default/f...Considerations-AC-Coupling-Micros-Battery.pdf, page 6). Since the Powerwall will increase the power frequency during off grid operations to instruct the inverters how to behave you can match the Powerwall's frequency profile with your inverters to ensure that you never exceed the Powerwall limits. This is what I do for my 8.6kW PV system which just barely reaches the PV inverter rating of 6.6kW during the sunniest of days. If your system supports it this is probably the best way to go.

 

[jboy210]

Does anyone know if the new Tesla Inverters are "smarter" about this. Such as being able to shut down strings to control the amount of solar energy generated when there is no place for the power to go. They say it is integrated with Powerwalls, which would imply TEG integration, but I have not seen any details on what this means.

 

[gpez]

Does anyone know if the new Tesla Inverters are "smarter" about this. Such as being able to shut down strings to control the amount of solar energy generated when there is no place for the power to go. They say it is integrated with Powerwalls, which would imply TEG integration, but I have not seen any details on what this means.

There's a ton of opportunity for them to be smarter for sure, though the "dumb" automatic version should work fine and all the major inverters have supported it for years now...

 

[wjgjr]

TL ; DR. There should be some more education "somewhere" by tesla on this, but no idea what that would look like, because everyones install is different.

They are, but I feel like it should be possible to pull in a few variables (size of array, type of inverter, number of PWs, full-home vs. partial) to cover those, and then address other basic questions about an outage. Things like the OP posted about and the issue of PWs charging to 100% don't really change by install - just the exact math on where the cuttoffs are.

I don't think they could perfectly cover all situations, but I think it could help with a number, while also hopefully improving customer satisfaction and reducing call center volume. And having a local PDF (or even a sheet of paper) is also potentially helpful in cases where there is a loss of internet associated with an outage.

I do agree this is not the level of service we tend to expect from Tesla, but I think it is an area where relatively little effort could provide a lot of benefit.

 

[wwhitney]

a construction company like @wwhitney

Not following this thread, but I just wanted to be clear that I don't have a construction company. I'm a full time owner-builder-designer-etc primarily working on my own projects.

Cheers, Wayne

 

[jjrandorin]

Not following this thread, but I just wanted to be clear that I don't have a construction company. I'm a full time owner-builder-designer-etc primarily working on my own projects.

Cheers, Wayne

Ahh thanks for the clarification. You are just such a fountain of knowledge I keep assuming you are doing it professionally. Sorry about that

 

[shs1]

Solar overproduction can certainly be a problem during a power outage and if unmanaged, will lead to no solar production. You need a place to dump excess power, such as heating water, or better yet, charging a Tesla. Recent Tesla cars, e.g. my Model 3, coordinate their charging with the state of the Powerwall(s) and solar so that they won't charge, e.g. at night during a power failure, but will charge during the day to take up excess solar power. A few years ago, I had to do this manually, e.g. sit in the car and adjust charing speed to take up excess solar generation without the inverters shutting down. With the current Tesla app, you set a limit, e.g. 90% battery SOC, and if the Powerwall(s) are above that the car's rate of charging is automatically adjusted in realtime to assure the batteries stay charged during the daytime and no potential solar energy is wasted! Worked great during CA's recent high wind and heavy snow event. Only problem is getting the snow off of the solar panels, but that is a story for another day.

 

[gpez]

Solar overproduction can certainly be a problem during a power outage and if unmanaged, will lead to no solar production. You need a place to dump excess power, such as heating water, or better yet, charging a Tesla. Recent Tesla cars, e.g. my Model 3, coordinate their charging with the state of the Powerwall(s) and solar so that they won't charge, e.g. at night during a power failure, but will charge during the day to take up excess solar power. A few years ago, I had to do this manually, e.g. sit in the car and adjust charing speed to take up excess solar generation without the inverters shutting down. With the current Tesla app, you set a limit, e.g. 90% battery SOC, and if the Powerwall(s) are above that the car's rate of charging is automatically adjusted in realtime to assure the batteries stay charged during the daytime and no potential solar energy is wasted! Worked great during CA's recent high wind and heavy snow event. Only problem is getting the snow off of the solar panels, but that is a story for another day.

You don't have to do this Modern inverters have the ability to scale their production.

Now if you have a car to charge then that's great too but no need to "dump" excess power if you have your system configured to simply adjust production.

 

[MorrisonHiker]

Solar overproduction can certainly be a problem during a power outage and if unmanaged, will lead to no solar production. You need a place to dump excess power, such as heating water, or better yet, charging a Tesla. Recent Tesla cars, e.g. my Model 3, coordinate their charging with the state of the Powerwall(s) and solar so that they won't charge, e.g. at night during a power failure, but will charge during the day to take up excess solar power. A few years ago, I had to do this manually, e.g. sit in the car and adjust charing speed to take up excess solar generation without the inverters shutting down. With the current Tesla app, you set a limit, e.g. 90% battery SOC, and if the Powerwall(s) are above that the car's rate of charging is automatically adjusted in realtime to assure the batteries stay charged during the daytime and no potential solar energy is wasted! Worked great during CA's recent high wind and heavy snow event. Only problem is getting the snow off of the solar panels, but that is a story for another day.

Back during our extended outage in 2019, we tweeted to Elon about the possibility that our Powerwalls could be drained by our charging cars. He replied within minutes that the ability to address that issue would be "Coming soon..." and it eventually showed up in a software release. At first, it was only for the 3 and Y but eventually they added it to the S and X as well. We can confirm that it works great and allows our cars to charge while still maintaining a reserve in our Powerwalls.

 

[shs1]

I had suggested coordinated car charging to solve the solar overproduction problem on this forum some time ago, but was told it was not practical because the car might not be on the same panel that was backed up by solar. How would the app know, it was said? Fortunately it is practical and this ability is a good reason to have your EV on a panel that is backed up. Unfortunately my 8-year old Model S won't play nice with the Powerwalls, I believe.

 

[shs1]

You don't have to do this Modern inverters have the ability to scale their production.

Now if you have a car to charge then that's great too but no need to "dump" excess power if you have your system configured to simply adjust production.

Unfortunately, I suspect most inverters already in place don't scale back their production using FSPC, but just shutdown for a bit and then try again, and I am sure you know that! That is certainly my situation. As to dumping solar energy, the object is not to "waste" that energy but to use every precious bit of it during a power failure. In my case I have a resistance heater in one of my water tanks, that are normally heated by my geothermal system. I typically turn off the geo during a power failure, although, given the installed soft start device, it will run off of the Powerwalls, just not for long. The resistance heater allows my to use excess solar energy more gently, e.g. at 5 kW rather than 8-10 kW. Heating domestic hot water is not wasted energy, but even 5 kW is too granular for managing solar over production. The Tesla coordinated charging scheme is perfect for keeping the batteries at 90 or 95% as long as the sun is shining and not allowing solar energy to be wasted or not used. Of course when the car hits 100% SOC that is another matter.

 

[Kodemonkey]

I ran a simulated outage for 2 days and had the "vehicle charging during power outage" set to 90%. I am only using the wall plug charger, but it worked as it was designed. Once the batteries hit 90%, the charger started pulling 3 amps, the PW SOC went to 91% and it started pulling the full 12A. Unfortunately, the wall charger was not enough and when they got to 96% the solar shut down and I had a "see saw" effect of the solar shutting down until 94% and then turning back on. Once I have the HPWC installed I should be not running into that problem. What is nice is that it appears the TEG can vary the charging consumption to balance everything. Not what I was expecting, but that is even better if it proactively load balances.

I have a model Y with 2 PW and 9.5KW PV with 10KW SE inverter (tesla "upgraded" me to the 10KW SE inverter because they couldn't find a 7.6KW SE inverter).