Powerwall 2 + UPS Connundrum - and solution

[power.saver]

It's fine for Tesla and other hybrid inverter manufacturers to use frequency shifting if they just want to shutdown grid tied inverters just like the utilities would do. However, it's not fine to use frequency shifting to shutdown grid tied inverters AND expect other electronic devices in general to function with frequency shifting. Utilities have no expectation for electronic devices in general to function properly with frequency shifting.

That's right. Tesla took this too far when they changed the default to 65Hz so every inverter made would shutdown. Originally, they did not do this, and the frequency shift was much less. Now, new installations have to learn the hard way that things don't work, and it takes calling Tesla to request a change, which doesn't seem to be consistently applied. They really should rethink the default, and incorporate testing into the commissioning of PW to prevent all this grief.

 

[aesculus]

I'll let @power.saver weigh in here but this whole frequency thing with controlling the inverters with the powerwalls is a hack IMHO.

The purpose of regulating the frequency for generation sources comes from the fact that the frequency of the grid needs to be fairly constant. When a generation source comes on it needs to match the frequency within tolerances otherwise it could cause damage to nearby generation sources if it was too high or low (I am talking about rotational generations sources here). Plus there is a lot of equipment tuned to run at the frequency and having it fluctuate can cause extra wear and tear too. And then there are protection devices and there were (are?) devices that use the grid frequency to do certain things (VCRs, TV's, even some old clocks).

Anyway the point is that the frequency is important to non premise devices. Solar inverters are on premise devices but they are injecting energy across the boundary and therefore have to behave properly with that regard. They need to match the grid frequency when on and connected, so they sense that and act accordingly. No voltage or frequency and they turn off and monitor until they see an environment that makes sense (the range they are set to work within).

When the utility terminates the power your system would still be grid connected but Tesla terminates that. Therefore your inverters are now not part of the utility system. Prior to the powerwalls they still would be. The powerwall is fooling the inverters to think they are grid connected by supplying power that "looks" like the grid. Up until the point that the PWs cannot handle the power that the inverters are putting out, so they change the frequency to something that is unacceptable, which is what the inverters were designed for when grid connected. They will then shut themselves down. The primary purpose here is safety (so they don't inject power into the grid which everyone thinks is dead). Also you would be powering others with non sufficient power etc. Lots of issues here to be avoided.

But this is the problem. The grid NEVER gets this far away from 60Hz when it is active. It's really very binary. Tesla is putting in a frequency that you would never see in the real world unless there was some serious problem somewhere when they force a shutdown of the inverters. As was pointed out this causes havoc with all sorts of premise devices. The other rub I have with this is if you have multiple inverters. Again inverters act binary on the frequency. If you have all of the same inverters or same range of frequency tolerance, then when the PWs go to an abnormal state all the inverters would terminate. A better solution would be to terminate them in units so perhaps you could use some of the power.

Perhaps if Tesla incremented the frequency a bit at a time it would be better. They could monitor the output of the inverters and keep increasing the frequency until they shut off. This could help in the frequency tolerance issue but would not solve the incremental inverter opportunity.

A better solution IMHO would be some sort of isolation device per inverter, but I am not aware of standards in the industry that would support this. Without this you could potentially damage the inverters. Most (all?) the inverters where never really designed to be operated behind a super intelligent battery system.

So I think we are early adopters in this game and this whole environment is going to have to be thought through in the long run to be more efficient. Tesla is sort of stuck with what they have (the hack).

 

[power.saver]

Where to begin...

I don't think it's a hack, and as @gpez stated, it's a standard. But I do believe Tesla's implementation of that standard is not well done.

There are a few problems that Tesla faced. They built a system, the PW, to integrate into any existing grid-tied inverter. Lots of older inverters, mine included, don't support Frequency Shift Power Control (FSPC) that gradually ramp down the output as frequency rises. So I have the "binary" inverters that just shutoff at 60.5Hz. Okay, that works for me, but I had to get Tesla to change the max frequency from 65Hz to 61Hz so it doesn't cause other problems.

Newer inverters, and that should include your recent install, support FSPC and will reduce output as the frequency rises. This allows some generation during off-grid operation without constantly switching the inverters off and on. This part Tesla did well. If you are off-grid, and your PW approach 100%, the frequency shift is gradual in an attempt to curtail power. If your FPSC inverters respond properly, you will find a balance at a frequency not to far above 60Hz.

But where the problem arises is when your PW are already at 100%, your solar is generating a lot of power, and the grid goes down. In this case, the inverters must all shutdown immediately, and the way they do this is to set the frequency above the shutoff threshold. It is this shutoff threshold that Tesla got wrong, IMO, because they used an abnormally high 65Hz which is above what any grid-tied inverter needs.

The fix is simple (use a lower max frequency) but the process to get there is not. That's why I think Tesla should make this part of their commissioning routine.

 

[aesculus]

The fix is simple (use a lower max frequency) but the process to get there is not. That's why I think Tesla should make this part of their commissioning routine.

Well at least three of us in the last week have fought Tesla to lower it below 63 Hz. I was successful to get them to set it to 62 Hz but others were not.

I have an 18 month old inverter that does not support FSPC so I am not sure you widespread it is to date but it sounds promising in the long run.

 

[power.saver]

I have an 18 month old inverter that does not support FSPC so I am not sure you widespread it is to date but it sounds promising in the long run.

What make and model inverter do you have?

 

[aesculus]

What make and model inverter do you have?

Fronius Galvo 2.5.

I have one that is 4 years old and one that is 18 months old. Both have frequency range of 59.5 to 60.5 according to Fronius but I can find no evdience of either supporting FSPC.

 

[power.saver]

Thanks. I'm not familiar with Fronius inverters, so can't offer much other that it seems odd that the one only 18 month old would not have the capability.

 

[gpez]

I've seen newer inverters that don't support FSPC (or whatever name the company has for it) and older ones that do. Think of it as a feature on a car like heated seats - some companies have them as standard options and others you need to purchase the upgraded model.

@aesculus it seems the Fronius Galvos do actually curtail power during out-of-spec grid operations, check out page 46 under error code
650: "The status code is displayed with excessive grid frequency. The inverter reduces the power." from https://www.fronius.com/~/downloads/Solar Energy/Operating Instructions/42,0410,1934.pdf

They also seem to be configurable as to what frequency range it operates under, the spec sheet on page 50 says 45-65hz (!) with the ability to set the minimum (FILmin) and maximum (FILmaw) on page 34 at 0.05hz increments.

Interestingly the Galvo does support voltage based power reduction called "AC Voltage Derating" on page 35. There's also a Dynamic Power Reduction feature but that seems to be for export scenarios where you're feeding to the grid but the grid doesn't want to take it.

 

[gpez]

Looking further, it seems perhaps the Fronius Primo line does support "AC Frequency Derating" with a firmware update. Can't confirm that on their tech docs though as they only list voltage derating. http://download.selectronic.com.au/..._01 Fronius Firmware Update Configuration.pdf​

 

[aesculus]

@aesculus it seems the Fronius Galvos do actually curtail power during out-of-spec grid operations, check out page 46 under error code
650: "The status code is displayed with excessive grid frequency.

Yes. They do this. Factory range setting is low 59.5 Hz and high is 60.5 Hz. But they don't seem to support the scalable feature that @power.saver refers to as FSPC, which would allow them to sort of operate incrementally. That seems to be pretty specialized.

I have verified that when my power walls are full the PWG sets the frequency to 62 Hz and they trip off. I have not tried the incremental test from say 90% to full disconnected yet. Has not been enough sun until recently to try that but I think I am in the clear now until October.

 

[aesculus]

Looking further, it seems perhaps the Fronius Primo line does support "AC Frequency Derating" with a firmware update. Can't confirm that on their tech docs though as they only list voltage derating. http://download.selectronic.com.au/documents/TechNotes/TN0072_01 Fronius Firmware Update Configuration.pdf​

I have Galvo's

 

[gpez]

I have Galvo's

Yup - was more just showing that different models from the same maker can have different features.

 

[cali8484]

Well at least three of us in the last week have fought Tesla to lower it below 63 Hz. I was successful to get them to set it to 62 Hz but others were not.

I have an 18 month old inverter that does not support FSPC so I am not sure you widespread it is to date but it sounds promising in the long run.

Does Tesla explain why they are so reluctant to change? In any case, I agree with you that it's a hack. There is no requirement for electronic devices in general to work properly outside of normal grid frequency range.

 

[aesculus]

Does Tesla explain why they are so reluctant to change?

Just that they are uncormfortable with going too low the inverters won't power down. Maybe after they have more experience they may relax this a bit. Who knows. I kind of had to make a stink.

 

[cali8484]

Where to begin...

I don't think it's a hack, and as @gpez stated, it's a standard. But I do believe Tesla's implementation of that standard is not well done.

There are a few problems that Tesla faced. They built a system, the PW, to integrate into any existing grid-tied inverter. Lots of older inverters, mine included, don't support Frequency Shift Power Control (FSPC) that gradually ramp down the output as frequency rises. So I have the "binary" inverters that just shutoff at 60.5Hz. Okay, that works for me, but I had to get Tesla to change the max frequency from 65Hz to 61Hz so it doesn't cause other problems.

Newer inverters, and that should include your recent install, support FSPC and will reduce output as the frequency rises. This allows some generation during off-grid operation without constantly switching the inverters off and on. This part Tesla did well. If you are off-grid, and your PW approach 100%, the frequency shift is gradual in an attempt to curtail power. If your FPSC inverters respond properly, you will find a balance at a frequency not to far above 60Hz.

But where the problem arises is when your PW are already at 100%, your solar is generating a lot of power, and the grid goes down. In this case, the inverters must all shutdown immediately, and the way they do this is to set the frequency above the shutoff threshold. It is this shutoff threshold that Tesla got wrong, IMO, because they used an abnormally high 65Hz which is above what any grid-tied inverter needs.

The fix is simple (use a lower max frequency) but the process to get there is not. That's why I think Tesla should make this part of their commissioning routine.

Tesla's implementation of IEEE 1547 to shutoff grid tied inverters is really not qualitatively better or worse than other hybrid inverter manufacturers. However, the problem is that Tesla, like other hybrid inverter manufacturers, is intentionally providing frequency shifted power to devices and expecting them work properly in general. Powerwall is essentially an UPS for the entire home so it should provide proper power voltage and frequency like UPS. I doubt many people would accept an UPS that puts out frequency shifted power that needs to be tweeked and may or may not work with devices you already have and devices that you add in the future.

Standards are good for their intended purposes. For those in interested standards for backup power systems, you can look at IEEE 446 (https://pdfs.semanticscholar.org/c72f/efd3fc4270c365dc945bc35a294ce7e04c52.pdf). Section 5.5 on battery/inverter systems clearly states power should have frequency of 60Hz+/-0.5% for 60Hz systems.

 

[bob_p]

Tesla is likely being very conservative on the frequency setting, because they want to make sure the solar power is cutoff when operating off grid and the PowerWalls are full, because they want to avoid excess solar power with nowhere to go - which could be a safety issue.

Our system was installed by a 3rd party Tesla approved installer. Tesla requested (over the phone) the specific microinverters we had installed and the specified cutoff frequency - and that was enough to get them to adjust the frequency to 61.5 Hz.

Because we have microinverters, if Tesla sent someone out to our house to check the microinverters, they would have had to get up to our 2nd story roof and walk along the concrete spanish tile roof to do a visual verification of the microinverters - something I would have been hesitant to approve (prefer not to have anyone on the roof, unless absolutely necessary...).

It's possible they changed the policy after adjusting our frequency and now want someone to be at the location when they adjust the frequency, so they can verify everything is working properly, and they haven't created a safety hazard.

 

[Thibaultmol]

I might not be the most informed person about this..
But why isn't possible for (micro)inverters to just communicate via a Canbus or something with the powerwall/backupgateway.
So that when they need to shutdown they can just send such a message via the can instead of increasing the frequency and causing all kinds of problems?

 

[mspohr]

I might not be the most informed person about this..
But why isn't possible for (micro)inverters to just communicate via a Canbus or something with the powerwall/backupgateway.
So that when they need to shutdown they can just send such a message via the can instead of increasing the frequency and causing all kinds of problems?

The Enphase IQ series of microinverters do just that.

 

[GenSao]

The Enphase IQ series of microinverters do just that.

Thibaultmol,

Welcome to the TMC. Enjoy your stay.

It is possible for (micro)inverters to communicate via a Canbus or wifi to a third party device. But, it is more universal, simpler, and cheaper to use an existing standard. No additional hardware or wiring required.

For safety reasons, all grid tied (solar) inverters are required to shut off in the event of the grid going down. This is to protect the linemen working at repairing the grid form electrocution. Grid Support Inverters complaint with UL 1741 and IEEE 1547 standard can be controlled by the condition of the AC power (such as frequency in Hz with 50 or 60 Hz nominal). If the frequency is too low or high, then the inverter shuts off. Newer "smart" inverters (under UL 1741 SA) can scale production based on small difference in frequency.

In the event of a grid outage, the Powerwall can replicate the grid and make adjustments to the frequency to directly control inverters in the micro-grid.

 

[Krash]

I might not be the most informed person about this..
But why isn't possible for (micro)inverters to just communicate via a Canbus or something with the powerwall/backupgateway.
So that when they need to shutdown they can just send such a message via the can instead of increasing the frequency and causing all kinds of problems?

The Enphase IQ series of microinverters do just that.

The Enphase IQ series microinverters communicate over powerline. CANBus is a wired standard but not power line. Whatever protocol they use is almost certainly not something that a Powerwall speaks. I don't think a Powerwall uses any power line communication. Anyone know what protocols either use, or if proprietary, on what either are based?