Off-grid frequency shifting

[bdarav]

Hi, first-time poster, long-time reader. I might have missed another thread explaining this issue, sorry if I have.

PV system is an 11.9kW system with IQ7+ microinverters and 1 Powerwall 2 with gateway 2.

The grid went down yesterday because of Hurricane Lee around 7pm with battery at 100% (with reserve set at 100%). The batter supplied the house overnight with about 40% remaining by sunrise. We had also lost internet overnight so I had to monitor the battery status by direct connection. I could see the PV system recharging the batteries around 8am with a good amount of sun.

Strangely when I checked the system at 10am, the battery had charged to 66% but the solar had stopped producing all together with plenty of sunshine. From 10am to 12pm, the PV system produced basically nothing, and the battery dropped from 66% to about 56%. The powerwall installer (different to the PV system installer) suggested restarting the system which I did but still no PV production.

When I asked the PV installer, they checked the logs which had a number of events saying frequency and voltage were high so the microinverters were shutting down. I can only assume that the gateway/powerwall increased frequency to shut down PV production but why would it do so at a 66% SOC? House consumption remained pretty steady between 0.7 and 0.9kW.

I've had the powerwall for about 8 months and this is the longest period of being off grid. Any ideas why this happened? Coincidentally, grid power came back at 12pm and PV production went to 100% capacity which you can see in the enphase image.

Any help is really appreciated!

Some screenshots below

 

[jjrandorin]

You probably want to contact Tesla powerwall support to ask them that question. The frequency shift should not be in effect with battery capacity that low, but I remember seeing a few other people talk about such a thing too.

IMO you want Tesla to look at the logs and see whats going on, so try giving them a call for powerwall support (actual, physical phonecall, to powerwall support, not chat, email, or app ticket).

 

[Tazzman]

I'm no expert but it looks to me that you have more solar then 1 battery can handle. It should be able to be setup to work with frequency shifting but will probably require Tesla to set a proper frequency stepping unless one of your installers can set the frequency shift.

 

[jjrandorin]

I didnt catch that, but 11kW solar and one powerwall, it makes perfect sense to me now why it wouldnt charge when off grid. As @Tazzman said, its probably too much solar for 1 powerwall. Anything more than 5kW of power production for one powerwall is too much, and OP I bet you will find that your power production during the time specified, if on grid, is likely over 5kW.

 

[bdarav]

Thanks @jjrandorin and @Tazzman. I'm on hold with Tesla support now while they look at the data and will report back if they find anything. You're correct, by 10am with clear skies the PV system would be producing about 7kW and peaks at 8/9kW by noon. We purchased the PW2 a year after the PV install and the installer never mentioned we might right into this problem with the size of the system.

If we bought another PW2, would we run into this problem off grid if 1 PW2 is fully charged with the 2nd partially discharged and the solar is at peak production?

I also wonder if there are some kind of workarounds - for example, we could increase the house consumption to 3 kWs during daytime.

 

[jjrandorin]

If we bought another PW2, would we run into this problem off grid if 1 PW2 is fully charged with the 2nd partially discharged and the solar is at peak production?

With 2 powerwalls and your current system you would likely be fine, since the limit of intake would be 10kW of power (5kW each). "The system" charges and discharges the batteries together, so you wont hit a time "when one battery is full and one is partially discharged"***, because they charge and discharge together.


***unless there is a technical issue with cells in your powerwall battery or something.

I also wonder if there are some kind of workarounds - for example, we could increase the house consumption to 3 kWs during daytime.

If you had a way to force consumption higher, the powerwall might have let the solar come on, but I dont know that for a fact. You could also theoretically get your solar wired in such a way as only part of it produces during a power outage to somewhat work around this issue, however since your solar and PV installer sound like different companies, working that angle will be "difficult" to say the least.

The approach I would take, were I in your shoes, would be to talk to "powerwall install vendor" and politely explain they did not tell you this would happen with your amount of solar and 1 powerwall, and see if they will work with you on it. You might be able to get them to eat part of the cost of installing another one, or otherwise work with you on it.

You should be able to demonstrate this issue clearly to your powerwall installer by throwing your main breaker and taking yourself off grid, when production is over 5kW.

I am reasonably sure the issue you experienced was due to "too much solar for the powerwall" thus it shut down your system, which is exactly what you DONT want during an outage.

One of our other regular members @zƬesla had exactly this issue, and I think their third party installer actually stepped up and provided another powerwall after a bunch of discussion. Thats exceptional (and not expected) but you should expect your powerwall installer to "do something" to help you.

 

[cali8484]

Getting a second PW should solve the problem but it's rather expensive fix. Not sure how often you have outages but one free alternative is just turn off the breaker for one microinverter branch when the problem happens.

 

[arnolddeleon]

Getting a second PW should solve the problem but it's rather expensive fix. Not sure how often you have outages but one free alternative is just turn off the breaker for one microinverter branch when the problem happens.

I was just about to suggest the same, if you have multiple circuits for your PV then you can turn one off.

Another possible option to check what firmware versions are supported by your Enphase. There is a version for some of the hardware that support frequency shifting to control their output so it is not binary on or off. Your Powerwall will need to be configured to ramp the frequency shift and obviously the inverters need to respond. If they don't respond then will simply shutoff so no downside.

 

[arnolddeleon]

It looks like you need to configure a grid profile like the California one. So most likely you need help from your PV installer.

At what frequency shift does the frequency ride-through operate on the IQ7+? According to the data sheet: "Complies with advanced grid support, voltage and frequency ride-through requirements" but I do not see which requirements are referred to. - Community | Enphase

 

[bdarav]

Thanks everyone, this is very helpful. Just as an FYI, after 40 minutes of looking at the data, Tesla support sort of gave the same but slightly different reason. The rep I spoke with said the house draw was low (below 1kW) so once the battery's SOC goes > 50%, it will shut off PV production because the excess electricity has nowhere to go. I didn't quite follow the logic but I think the missing piece is what was picked up here - the size of the PV system. Looking at the enphase data, the last peak production off-grid was 4.7kW and then the system throttled down.

@arnolddeleon , @cali8484 , this is a really useful point. The panels are in a 4 array setup - 2 arrays are 2.45kW, 1 array is 3.15kW and 1 is 3.85kW so if it's as easy as turning off the circuits in the combiner box, I can scale it up and down accordingly. I will also take a look at the grid profile configuration post.

We're looking to add a PW within the next year or two but at least now we have options to consider and something to talk to our PW installer about.

 

[jjrandorin]

We're looking to add a PW within the next year or two but at least now we have options to consider and something to talk to our PW installer about.

That makes sense. Just keep in mind that the farther you get from the install date, the less leverage you will have with the powerwall installer to do anything to help you.

I dont work in the PV / solar industry or anything, but as I have mentioned previously here (and regular members likely remember), I have worked in customer service my entire working career, either directly providing support or managing people who do. Even the best intentioned company is not going to be very interested in hearing "you installed this powerwall a year and half ago, and I just noticed that my system doesnt function properly because its only 1 powerwall, can you split the cost with me on that?".

At a minimum, if it were me, I would (politely) bring it up to "powerwall vendor" and demonstrate it to them, and and ask for their input on a resolution. Even if you decide to self manage by turning off breakers, you would want to have that be a collaborative thing with powerwall vendor, so IF you decide that isnt working, you have a next step, and the appearance of a "reasonable customer who has tried to work with them" vs someone who is bringing something up after a couple of years that you likely noticed before.

Not like I have any skin in this game of course, just putting forth my own opinion on how I would proceed. Good luck with whatever you decide.

 

[cali8484]

In case you care, one thing to remember about Enphase grid profiles is that technically your local power company may only allow certain ones as part of their interconnection agreement. So, a CA Rule 21 profile may or may not be compliant with your interconnection agreement. Your installer should know for sure.

 

[zƬesla]

We were in process of getting PV when we decided to also get 2 PWs. The PV installer couldn't get Tesla to answer his calls so I got a Tesla certified installer involved. We were looking at 15.4kW in inverter capacity, and at the time the Tesla installer said 2 PWs were limited to 15.2kW (7.6kW/each), so we switched to 14.7kW in inverter capacity. After install, the system would shutdown completely because the certified Tesla installer didn't know the limit was 5kW/each. Skipping ahead, we got a third PW at no cost to us as they did not engineer the original system properly, and the system has been humming along for a few years.

 

[wwhitney]

Another possible option to check what firmware versions are supported by your Enphase. There is a version for some of the hardware that support frequency shifting to control their output so it is not binary on or off. Your Powerwall will need to be configured to ramp the frequency shift and obviously the inverters need to respond. If they don't respond then will simply shutoff so no downside.

Do you know if anyone has actually gotten this to work properly? It should work in theory, but requires both the PW and the PV inverter to be configured properly so they will play nicely with each other.

Cheers, Wayne

 

[Tazzman]

Do you know if anyone has actually gotten this to work properly? It should work in theory, but requires both the PW and the PV inverter to be configured properly so they will play nicely with each other.

Cheers, Wayne

And from my conversation with someone at Enphase they are not interested in working with the customer since the Powerwall is not supported in their eyes.

 

[cali8484]

And from my conversation with someone at Enphase they are not interested in working with the customer since the Powerwall is not supported in their eyes.

Enphase drastically changed their MO and attitude about third-party home batteries after they came out with their own. I have seen reports of customers calling Enphase support about problems with third-party home battery systems being told that Enphase batteries are the solution and get passed to the battery sales people. It's a really a bad trend for the industry and consumers. If the home solar market ever gets big enough there will likely be anti-trust issues with the intentional proprietary mechanisms these companies are creating to prevent cross-vendor interoperability. What's missing is an open standard for interfacing and control of home batteries and PV inverters. I hope there will be regulatory requirements for interoperability like the EV industry at some point.

 

[h2ofun]

Enphase drastically changed their MO and attitude about third-party home batteries after they came out with their own. I have seen reports of customers calling Enphase support about problems with third-party home battery systems being told that Enphase batteries are the solution and get passed to the battery sales people. It's a really a bad trend for the industry and consumers. If the home solar market ever gets big enough there will likely be anti-trust issues with the intentional proprietary mechanisms these companies are creating to prevent cross-vendor interoperability. What's missing is an open standard for interfacing and control of home batteries and PV inverters. I hope there will be regulatory requirements for interoperability like the EV industry at some point.

Regulatory requirements? The cars do not even have one standard connector. Can you image having to find a gas station with a noozle that fit into your car.

 

[cali8484]

Regulatory requirements? The cars do not even have one standard connector. Can you image having to find a gas station with a noozle that fit into your car.

A single standard is not the point but rather open standards. Any given EV will likely only have one connector type but open standards make it possible to have adapters that allow one connector type to interoperate with other connector types. The IRA regulations require open standards based charging stations to qualify for incentives. It helped force/incentivize Tesla to open up its charging interface and make it an open standard. So, similarly, regulations could/should change to require open standards based interface/protocols for solar inverters/converters and home batteries in order to qualify for the federal tax credits.

 

[arnolddeleon]

Do you know if anyone has actually gotten this to work properly? It should work in theory, but requires both the PW and the PV inverter to be configured properly so they will play nicely with each other.

Cheers, Wayne

I don't know anyone personally. If my reading is correct, a new install CA should work correctly by default because the current requires that new inverters respond to grid curtailment signals. I think main barrier to have it work "out of the box in CA" is if Enphase islanding detection needs to be tweaked.

The OP certainly has the disadvantage of not being in CA. I would think they just need a cooperative installer (not necessarily Enphase).

I'll probably get to face this in future since I have a property with both a Tesla (SolarEdge) and Enphase PV system with no batteries. Which ever battery I add in the future will have to deal with another party.

 

[Will792]

And from my conversation with someone at Enphase they are not interested in working with the customer since the Powerwall is not supported in their eyes.

Enphase has a white paper specifically for PowerWalls. I think all interaction between IQs and PWs should be controlled by profile, not firmware itself. Enphase has plenty of standard profiles with different curves and delays for frequency shifts. It is also possible to create custom profile but I did not figure our procedure for it.

I am surprised that 1 PW was approved for this size PV system. PW has a clear stated charge limit and unless PV branches can be split I do not see how PW can protect itself from taking too much charging current fast enough.