Fronius MPP Hunting

[mradtke]

Hello,

I have 2 strings of 7 180 watt panels in a somewhat south southwest facing array and a matching array facing south southeast. These 4 strings feed a Fronius IG 5100 inverter. There are no data logging options on the inverter. Under some conditions, I see the power reported on the Fronius display oscillating about 400 watts with about a 42 second period. At other times, the oscillation is not nearly as evident, but it always seems to be present.

I also noticed that the display updates about every 2 seconds. However, after 21 updates, it does a double update. Is it a coincidence that the display period is the same as the power fluctuation period?

Both the installer and Fronius aren't showing much interest in my problem. Does anyone have an idea of what's going on?

Thanks,
Mike -- Phoenix, AZ

[Solar Guppy]

Well, a couple of thoughts,

First, 7 panels in series for a sting inverter in AZ seem to small, I checked out the data sheet

http://www.fronius-usa.com/worldwide/usa.solarelectronics/downloads/specifications_ig_4000_5000_4500lv_012008.pdf

So you should verify 7 panels works in the heat. if your panels are 24V panels ( typical vmp of 34V ) it might work, if they are 18V panels ( typical for 180 watts ), the vmp point would be below the minimum needed for the inverter which is 150V

Also, the Fronius inverters I tested had one very noticeable quirk, they change on demand the transformer windings "on-demand" depending on the input voltage. On the inverters I tested, its was @ 260V input that the switch would occur. If the Mppt is near this I could see some issues

I'd run your panel configurations thru the Xantrex string calculator ( to get the array operational voltage ) and compare to what the IG5100 is spec'ed for. http://www.xantrex.com/support/gtsizing/index.asp?lang=eng

[mradtke]

Hello Solar Guppy,

Thanks for your comments.

I have attached a text file which is really a dot.csv that you can load into about any spread sheet program. These data show the measurements that I took from the Fronius screen since I don't have the data logging option. From this you can see that the inverter is well above the 150 volt minimum during the oscillation.

The inverter feeds one phase of a delta connected three phase service. This is a relatively rare type of service that looks standard in that there is the usual 120-0-120 feed, but then includes a "stringer" which measures 240 volts to either of the other lines. Of course, all three wires are 60 degrees out of phase. I mention this in case there may be some special consideration for this circuit.

You'll notice from the data that the power pretty much follows a saw tooth with a period of 40+ seconds. A couple more things to note:

1) The display updates about every 2 seconds. Every 21 updates it does a quick double update. That would be about 42 seconds, or the same rate as the power oscillation. Coincidence?

2) It doesn't always oscillate. I thought that it was power or heat related, but for the last two days there have been no oscillations. Then today, it was already oscillating from the first time I observed it at about 08:00 and 1000 watts.

3) Today it oscillated most all of today. At 13:50 is was bouncing between 2100 and 2700 watts. However, when I checked at 14:40, the power was constant at 2700 watts. Some passing clouds may have quenched the oscillation, but the more interesting thing is that at 14:40 the inverter was reporting the same value as the peak power an hour earlier. It hasn't started oscillating again, but there are some clouds now.

Fronius is talking about doing some measurements, but it is over 10 days since I notified them of the problem.

Thanks for your interest,
Mike

[Solar Guppy]

unfortunately you will have to get much more accurate data before a manufacture would get some interest, or at least that has been my personal experience ... if your a home power subscriber ( Homepower issue 91 )

http://www.homepower.com/article/?file=HP91_pg46_Cutler

I tested the IG3000/4000 units in 2004 and found some quirks with them, which Fronius engineers admitted to, but hunting mppt was not one of the observations I measured

I looked at the file, The voltage current relationship seem valid but without external data loggers one can never be sure what the unit is reporting is accurate.

I'd continue pressing Fronius and see if the could hook-up and external logger OR swap out the unit, intermittent electronics can for sure make the Mppt track poorly.

For sure, its not optimum performance and this is a great example to explain why I strongly recommend the Xantrex GT series inverters. Built in RS-232 communications and either GT-View of SG-View on the PC gives 1 second resolution for full performance and free data logging.

If you can't get Fronius to own up to the issue, possibly you can get the install to install another manufactures unit

[mradtke]

Hello Solar Guppy,

Thanks for your additional comments and the link.

I will continue pressing the installer and Fronius to get a resolution.

The Fronius was chosen for the low voltage performance as you noted in your last reply. The physical constraints of the collectors make 28 the ideal number. According to the installer the choice was between a pair of SMAs or the Fronius.

Today the system came up without oscillation. So, I looked if I could start the oscillation. This is what I came up with:

Start the oscillation: Break the AC side and let the inverter cool for 15 minutes.
Restart the inverter by re-establishing the AC connection.

Stop the oscillation: Momentarily break the DC side.

By the way, the average power when the inverter is not oscillating is several hundred watts higher than the peak power during the oscillations.

I think that Fronius will take measurements tomorrow, but I think that this will only confirm what I already have reported. I'll follow up this post from time to time with progress reports. However, I am still open for advice.

Thanks,
Mike

[autoxsteve]

I've got a very similar system to yours.

I've noticed some 'dancing' with my inverter and called my installed (REC Solar) about it. I also spoke to an engineer from Fronius and the #s I had reported (I want to say around 200 watts or ~10%) at that time (back in March) were deemed 'normal'.

I've had my system operating for a little over 6 months (3/17 'go live') and have produced almost 4.9 MWh to date.

My thought on your sit is that the inverter is seeking the optimal point and it will dance a little. Have you had some high cloud / or overcast days to observe the behavior?

How many kWh are you getting each day with your system?

I'm getting about 23 kWh per day presently (over about 11.75 hours of operation).

[boB]

It looked to me as though there wasn't really a trend up or down in his average power level (from his data). Just the sweeping ?

But maybe I missed something.

boB

[mradtke]

Bob and Steve,

Thanks for your replies.

I don't understand your comment about a trend. My position was that since there was a peak power value and a lower power value in the 42 second oscillation, the MPP must be at least as high as the peak. I have learned to quench the oscillation by interrupting the DC (this doesn't always work the first time), I see that when the system is not oscillating, the inverter settles in at a stable MPP somewhat above the peak reported during the oscillation.

Discounting any cloudy days, the power has been about 21 kWh / day for the last 2 weeks and the system has been oscillating. Today was the first day that I stopped the oscillation early on and monitored the situation to be sure that it didn't recur. The system produced 24 kWh today. That would be empirical proof that the oscillation is reducing the energy production.

At the worst that I've observed, the difference between the maximum and minimum values that the system is oscillating between is over 1000 watts. That's not dancing. When the oscillation is quenched, the variation is a few 10s of watts. That's dancing.

I have been exchanging email with Dan Fortson of Fronius USA. He told me that no one else has reported this problem. Is he the person that you contacted?

Thanks,
Mike

[mradtke]

Hello,

The installer came to my home and observed the hunting that I had described. Fronius backed up the visit by phone.

One thing new that we learned is that the current, when measured with an external meter, appears to go to zero once per 42 second cycle. Fronius suggested the transformer tap switching might be a issue, but I was able to confirm that there was no audible click of the switch heard during the oscillation. Fronius has now suggested that we install a data logger on the system to gather more information ... something that I requested 2 weeks ago. It should be here in a couple of days.

If you have a Fronius, I suggest that you go and look if you have this problem as well.

I'll post again when I know more.

Thanks for listening,
Mike

[niel]

good to know and keep us posted as to any developements.

[autoxsteve]

I'll look for your update. You appear to have a different problem than I.
The jumping around that I am experiencing is only a few watts and I don't see any jitter or changes in current like you describe (I watched my meter and it's smooth).

[mradtke]

Hello,

I received and installed the data logger today. The system began oscillating on startup. However, there was some cloudiness so I think that the data will be meaningless for today.

The intent is to record at least one day of oscillations and then send the device back to Fronius for analysis.

Thanks for listening,
Mike

[mradtke]

Hello,

I am data logging today, but we have high cloudiness. The inverter is doing its 42 second oscillation though. The forecast looks like the next week will be cloudy.

This gives me time to think. Since I have lost confidence in Fronius, how can I be sure the repaired or replaced unit is working properly? Is there some acceptance test that I can use to verify that it is operating at maximum power? What do you folks do?

Thanks,
Mike

[boB]

I wonder what that Fronius would do if you were to power its PV input off of a suitable but steady power supply ?

boB

[autoxsteve]

If you wish, I can video record my fronius inverter output and meter output and email the files to you... let me know (pt or email)....

[mradtke]

Hello,

Thanks again for your comments.

The data logging is over. I had 2 completely cloudless days and the inverted hunted the entire day both days. So, I sent the logging equipment back.

Steve, I think that I know what the unit looks like when it is working properly, but thanks for your video offer. I used to be able to jolt the system into that state, Then, its output went up and it only hunted around a few 10s of watts. The hunting was random as well, not with the 42 second cycle.

boB, I've thought about running the inverter from a different power source as well. However, the trigger may be due to some characteristic of my array, so it was probably a good call to do the data logging on site. I don't have a lot of confidence that they logged the right things though since the Fronius engineer mentioned a 5 minute logging rate. That may not do a lot of good with a 42 second oscillation in output. But, I'm giving them the benefit of the doubt.

I am still concerned that even if Fronius makes a repair or replacement, how will I know that the system is operating at the maximum power point? I used to be primed to trust them that they got it right, but now that I see that they got it wrong, how can I verify that they get it right next time? What do you folks do the verify your systems are running at the maximum power possible?

Thanks,
Mike

[Solar Guppy]

If they don't come up with a resolution, get the installer to swap the Fronius with a Xantrex GT ... they are proven to work and Outsell the Fronuis 10 to 1 in the US last I knew the numbers

[mradtke]

Hi Solar Guppy,

Thanks for your comments, but the Fronius was chosen because of the panel configuration. I think that the Xantrex units don't match the panel configuration as well.

No one has commented on a method that might be used to verify that their inverter is operating at the maximum power point. Do you folks just trust the inverter manufacturer? That's what I did until I saw the oscillation. Now I see things differently.

I have devised a test that is pretty straight forward and should work with any system. The recipe is only about 4 or 5 steps long, but the theory is pretty complicated. I wouldn't ask anyone to trust the method until some experts have sorted through the theory with me. My point is that while the test is simple, the post to describe it would be pretty long.

What is the list protocol on sticking to the title of the chain? Should I start a new chain with the description of my test method and theory behind it?

By the way, I haven't heard anything more from Fronuis yet.

Thanks,
Mke

[BB.]

Since this is "your thread"--it would be fine to include your discussion here. Keeps everything together in one place--easier to find / follow for others later on.

If the detailed post is "long"--you might want to attach it as a file attachment.

-Bill

[boB]

One thing you can do as kind of a sanity check is to measure the open circuit voltage of the array. If there is NO shading of the array, the MPP voltage should be roughly 75% of that voltage. 75 to 80 % of Voc in full sun and no shading on the array.

boB

[mradtke]

B.B: Thanks for the advice.

boB: Good plan .. thanks.

OK, so here is my proposed method of determining whether an inverter is operating at the system's maximum power point. First the recipe:

1) On a sunny day record DC voltage and current measurements. Do this for at least long enough for the inverter to hunt around a few times for its MPP and for a few tens of measurements. There is no need to keep the measurements in pairs, but do have the same number of voltage and current measurements.

2) you may wish to use a spread sheet for the rest of this, but it's easy to do manually as well. Make columns of the measurements and sort the voltage measurements in ascending order and the current measurements in descending order.

3) Calculate a third column as the product of the adjacent voltage and current measurements. This is the power represented by each measurement pair.

4) Ignore the current column, and plot each power and voltage pair as a scatter diagram with power on the vertical axis.

5) Examine the results. Some possibilities:

a) Dots form some sort of a peak. The highest value is the MPP and the inverter is walking back and forth across it as expected. There may even be a heavy concentration of dots in the middle if the inverter is spending most of its time at the MPP.

b) Dots form some curve without a peak. The inverter is never finding the best spot. If the line looks very horizontal, perhaps the data isn't accurate enough, or the scale needs to be expanded to identify the peak.

I measured my malfunctioning Fronius for about 5 minutes and got 48 voltage and 48 current measurements. My plot was a diagonal line with no peak. The heaviest concentration of points was about 200 watts below the highest end of the line.

The theory starts with some assumptions:

a) The solar panels have consistent light during the test.

b) In the small range that the inverter hunts around for the MPP during the measurement period, the solar panels may be modeled to be a fixed voltage source in series with a fixed resistance.

c) The current and voltage measurements do not have to be especially accurate, but they must be repeatable. Therefore, the inverter's own display may be used to take the measurements.

Simultaneous current and voltage measurements would be perfect. However, those values are probably not possible to get. The measurements may be sorted, combined, and treated as simultaneous because of assumption #b. In other words, the highest voltage must be paired with the lowest current and so on.

The calculated power plotted against voltage should represent a sample of the inverter's attempts to maximize power by trying different voltages. Because of assumption #b, this may be considered equivalent to the inverter trying different currents. The plot could just as well be current versus power as well. The important thing is whether the plot shows a peak in power and whether the inverter spends most of its time at the peak.

So, what do you think?

Thanks,
Mike

[Solar Guppy]

You don't have the equipment to make measurements in the resolution necessary to have meaningful data for pin-pointing the vmp. You need a quality power analyzer that does simultaneous measurements and handles power factor as well ( both on the solar and AC sides )

Typical large inverters probably hunt in the 10-20 watt range

Instead, you should focus the effort in make Fronius get more involved

First, insist they change out the inverter as its hard to believe it needs a 200 watt perturb window to find the mppt value and stay on it, you just likely have a bum inverter. There are many ways internally a unit can have intermittent electronics that would cause the ( current sense transformer, faulty op-amps, for example )

Unless you want to spend a couple of grand renting the equipment needed ( Yokogawa WT2030 and a curve tracer ) its not a worth while for your time, spend that getting Fronius to resolve your issue

200 watt mppt perturb is not normal and not what I saw when I tested a IG2500/IG3000 in 2004.

Issues I don't like about this manufactures:

-> limited voltage range

-> active switching of the transformer primary for even the limited voltage range, very odd design

-> efficiency is different for each of the 3 ranges

-> Reported power is greater than 5% of actual power produced

-> Small heat sink that requires constant fan cooling ( about 1/20th the size of the Xantrex GT heat sink )

But in the month of testing I did, I never saw any large perturb issues like your seeing.

Again, get Fronius to swap out the unit as the next step

[mradtke]

Solar Guppy,

Thanks for your detailed response.

Since there is no way to get simultaneous measurements there is always the dependency of getting both the current and voltage measurements faster than the inverter can change them. That's why I cooked up my scheme which did not depend on simultaneity. The Fronius internal metering resolution is 1 volt and 0.1 amps which should be just good enough to verify a successful hunt over a few tens of watts. I think that if my proposed method shows a peak, it will be proof of finding the maximum power point. If it doesn't show a peak, not much can be concluded. On the other hand, I respect your experience in these matters and my hopes aren't very high for my proposed measurement. Which leaves us back at the point of trusting the inverter manufacturer unless some pretty sophisticated equipment is used.

You mentioned power factor and thus implied inverter efficiency verification as well. That is a whole new can of worms, isn't it?

So, do you ever see a partial inverter failure such as I have, or has your experience been with total failures? If you are seeing partial failures, how do you find them? I guess that I am back to some sort of system verification test.

Fronius has been dragging there feet on this. I am keeping the pressure up, but I am also trying to be cooperative so that they might learn something from this failure. Last week their excuse was the Solar show in San Diego. This week they say the their "brass" is in town and taking up their time.

Thanks,
Mike

[Solar Guppy]

I'm surprised Fronius is not being responsive ...

When I did my work and had questions, I literally got responses same day. I would think the same tactics that one would use for any company when not getting the support needed would apply, like getting the manager or directors email address and moving it up the chain.

You should be focusing on this, getting the proper person at Fronius to swap out your unit. unfortunately, my contacts from 2004 have moved onto other company's so I don't have emails to offer ... I'd call the Michigan office and not quit until I got a hold of the top person there and had there commitment to resolve the issue

I know where your at ... read my HP 91 article and my journey in inverter performance. Keep in mind, you need Fronius to step up here and better data collection is not a job if the customer.

You might want to bring this thread to there attention ... I suspect that would help in getting the support you need.

[crewzer]

Mike,

Perhaps I missed this info... Which 180 W modules (manufacturer and model) are you using?

Regards,
Jim / crewzer

[mradtke]

Jim: 28 Suntech 180 watt panels in 4 strings.

Solar Guppy: Thanks for your comments. I am dealing with Michigan.

Fronius got back to me about the data that I captured for them with their data logger. According to them, the collected data described a perfectly functioning inverter. I reminded them that I was concerned about that since before they sent me the logger, they told me that it logged at a 5 minute rate. My oscillation has a 42 second period.

Yesterday I did another measurement on my system with Fronius on the phone. We started out by my reading off current and voltage measurements to them for a while. They got lots of good data points on the hunting. Then they gave me the crack to enter a service mode on the inverter and had me change the inverter from MPP to fixed voltage mode. We chose a voltage inside the range that it had been hunting and the inverter ran fine this way and did not hunt. We then tried a voltage just below the lowest voltage seen during the hunt, but the inverter refused to accept this voltage setting. The error implied that the setting was too far below the current open circuit voltage value. I'm not sure that much was learned from this experiment, but Fronius has decided to send out a new inverter.

I still would like to know just what the failure is and I am a little concerned that a replacement inverter may fail in the same way. Some thoughts:

1) At first, constant voltage mode seemed like the ideal way to verify that MPP is being found. However, the fact that the fixed voltage could not be set low enough to overshoot or even reach the MPP makes it useless for this purpose. Or, is this a hint of what's wrong with this inverter?

2) Doing these measurements yet again caused me to notice that the lowest indicated voltage was always 232 volts, and just before the current dropped to zero. So, yesterday afternoon, when the power output was much lower than it had been when I made all of my other measurements, I watched the voltage again. Just like before, as the system oscillated. The voltage slowly dropped to 232 volts, then the current dropped to zero, the voltage shot up to the open circuit value, and the cycle repeated. Is the 232 volts another hint about the cause of the failure?

I'll post again when the new inverter gets installed. You know that I'll be running measurements again.

Mike

[BB.]

What is the minimum Solar Panel input voltage rating of the inverter?

-Bill

[mradtke]

Bill,

Thanks for your question.

From the manual: MPP-voltage range: 150-400 V.

This inverter was chosen specifically for its low operating voltage.

Mike

[BB.]

Well--there went my guess...

-Bill

[Solar Guppy]

I'm pretty sure 232VDC is very close to the transformer primary switch voltage trigger for their units .. I seem to recall it was a 230 - 260V window, its probably a bit different for the 5kw unit but close.

Fronius has a very odd way to extend the voltage range, they have the isolation/ step up transformer ( between the DC-DC and DC-AC converters ) with three taps. The unit via relays under software control will switch the tap to keep the secondary voltages down, a really big issue with 2 stage units.

They are the only manufacture to do this. The unit in theory has enough hysteresis to not oscillate but in your case I have a hunch why your seeing this and other sites don't

If the new unit performs the same, my educated guess is the root cause is you vmp is to close to the software trigger switch combined with you have split facing arrays, the vmp between the SE and SW arrays is probably make a very flat and even possibly double hump vmp point .. so the unit keeps swinging between the voltages and keeps triggering the hysteresis algorithm which requires the unit momentarily stop generating power

You can prove this by disconnecting one of the arrays ( just run on the SE or SW arrays ) and see if the hunting stops. If this is the case one fix would to be rewire the arrays so half come from each SE/SW ( 7 from SE string then would goto 7 of the SW panels ).

Its unfortunate that you probably have found a condition there units are not able to work well with .. I'll keep my fingers crossed that I'm wrong

By the way, the Xantrex GT5.0 works fine with split arrays as does the Sunnyboys ... and if you gave up one panel you could have had three strings of 9 panels for either a GT5.0 or a SB5000U both are much better units.

Again, if the new Fronius does the same thing, get the installer to give you either a GT5.0 or SB5000U, its not YOUR fault the inveter doesn't function correctly. Oh and if you haven't done so, get Michigan to read this post and send of to Austria ... I bet once the real engineers read this you'll be having visitors with lots of test equipment

Oh one last thing, since you can put the unit into fixed vmp mode, it would be simple to start at the top of the range and keep setting lower voltages, I'm sure you can find the vmp this way and if the unit refuses to run a a commanded voltage, its may be below the transformer switching point or there 2 stage design can't operate below the vmp point, common for two stage units .. try 5 volt steps and then smaller are you hone in on the vmp .. should take more than a minute to do

[BB.]

Another possible experiment/fix to try (for your installer, if you have room)--try adding a panel or two to each string and raise the working voltage (even if temporally) out of the "instability zone".

-Bill

[mike95490]

Actually, once you "discover" the peak power point for a specific array/combo, how much would one loose, if you "constrained" the inverter to that point. Sure it will change a bit over temperature, but overall, once you set it close, (maybe a warm weather setting and a cold weather setpoint) you might be ahead on your harvest, if the hunting stops.

[Solar Guppy]

Quite a bit Mike .... Even in the same day between the morning to afternoon, the vmp will move 10%. And Being off more the 10% on the vmp can be 30%+ on harvest lost of your wrong on the high side of the curve.

A VI curve from VOC->VMP is very steep , in @20% of the total array voltage the power goes from zero to maximum. As the voltage is pulled down from the VMP point to zero, its pretty linear, hence that's why pwm controllers work as well as they do, they are always below the arrays vmp point

[mradtke]

Hello,

Thanks for all of the discussion.

I really would like to know exactly what's failing in my Fronuis, but it is unlikely that I'll ever know if the replacement unit works. It seems unproductive to wish for that one to fail as well just to better analyze the problem.

A few additional comments:

I don't think that the Fronius is at a tap switch point. I base that on the fact that on the fact that I can hear a relay when the tap switches. Fronius verified that there is always a click. I don't hear a click at the 232 volts, nor at any time during the oscillation.

The 4 arrays are all wired in parallel. So, there is no possibility to rewire them crosswise.

Setting a fixed voltage would only deliver maximum power for one time of day. Besides, I found that, at least at mid day, I couldn't set the fixed voltage low enough to reach the MPP because of the weird limitation on settable voltage range.

I hear you about switching to another brand of inverter. Hindsight is 20/20. I will see this through with Fronius. If the new ivnerter works, we're done. If not, I'll find an email address for someone at headquarters in Austria and try that route.

Continuing their high level of customer support, Fronius has not told me when to expect the new inverter.

Phooey!
Mike

[mike95490]

> Continuing their high level of customer support, Fronius has not told me when to expect the new inverter.

You can expect a letter of "Declined", a week after the warrenty expires.

[Solar Guppy]

You can cross wire, but it will require your installer to do that on the roof as sub-arrays to be split half& half ... not that big of a change a day at most

[mradtke]

Solar Guppy,

I understand now. What is a lot less clear to me is what effect that that would have.

I remember that I explored that subject with my installer some time ago when he was thinking about installing 2 inverters instead of the single Fronius. I read a white paper from Fronius about parallel strings and shading as well. I have a palm tree that will cause some shading in the winter months. I don't remember all the reasoning, but it turned out that under most of the partial shading conditions that I expect, wiring the strings in a simple stripe pattern is better than any other scheme. In only one shading condition was other wiring better, and then only marginally.

I'll wait for the new inverter and hope that it solves my problems.

Thanks,
Mike

[Solar Guppy]

Your installer is not considering the irradiance and temperature difference of the two array. They are on different roofs and face different directions. This will cause the vmp of the two groups to be different and depending on the gap very well be beyond what the Fronius can handle for Mppt tracking

If they are split so each string is half from one roof and half from the other, all four strings will have similar vmp point which is the important consideration.

Shading will kill production, having as you do now, it will only take 2 panels shaded to knock out 1 of the 4 stings production wise, so regardless, your going to get a big hit by the palm when it starts shading things

[mradtke]

Solar Guppy,

Thanks once more for taking the time to respond.

According to the Fronius specification, it should find the MPP at anything over an input of 150 volts. The drop out at 232 volts is far above that, so either the unit is bad or Fronius lied. The new one is scheduled for installation Friday, so we should know soon.

Thanks,
Mike

[mradtke]

Hello,

Today the replacement inverter was installed. It has the same problem.

I found out another thing which annoys me. My installer went out to check another site that has the same type and number of panels with the same inverter. It was hunting as well.

The measurements were taken by a relatively unskilled person so it is not clear whether the problem exactly matches mine. It was reported back to Fronius. That was 2 weeks ago and they didn't follow up by getting better measurements. Fronius elected to waste everyone's time by having a replacement installed.

I made it clear to Fronius that I need to work on this problem with the Austrian engineers at the home office and they have agreed. I made it clear to the installer that I consider this a system problem and that I hold him responsible.

Mike

[mike95490]

Today the replacement inverter was installed. It has the same problem.


Damm ! Sorry about that. Sounds like it's the Software department. Software says Hardware. Hardware says Installer or it's Software. Is the tide high or low when it hunts ?

Does the installer carry any other brand (like Xantrex GT series) that he could swap in as a replacement? Sweeten the deal, offer to pay the price difference and/or labor.

[Solar Guppy]

Your going to have to decide if you want to be a unpaid testbed for Fronius or do you just want a properly working PV system.

If its the later, you can simply have the installer put in a pair of Xantrex GT2.8's. They have a 193-600V voltage range and would work perfectly with the arrays you have now. no wiring changes

Cost wise a pair of GT2.8's are similar to the Fronius 5100 you now have but IMHO you would come out much further ahead as you would have an inverter for each of the arrays ( SE/SW ), fully data-logging and web abilities and MUCH better thermal and efficiency performance and its convection, not fan cooled.

If you stick with Fronius, you have at best an uncertain path ahead. I been down this path and at least I have found, even with a lab full of equipment, hard data showing the issues its very difficult to get the proper people involved. It is a huge amount of time invested to at BEST, just get what it should always have been, a properly functioning product. You don't have to do this, there are many other manufactures that have products that DO work.

[mradtke]

Hello,

Thanks for your comments.

I have set some rules with Fronius on what level of support I will tolerate from this point on. If they won't agree to it, I have asked my installer to replace the inverter. Unfortunately, replacing a single inverter with a pair will be a pain for him. As far as I know, the Fronius 5200 IG is the only single inverter which will match my collectors with any spare voltage tolerance under the Phoenix high summer heat conditions.

I think that a pair of Xantrex GT2.8's is just marginal for my conditions. I think that a better choice would be two KACO 2901xi's. Even better would be a single KACO 4501xi, but they don't seem to sell it in the USA. Any comments on the KACO inverters?

Still, the best outcome would be good cooperation from Fronius. That way I get my problem fixed and they get a better product.

I'll report again when something changes.

Thanks for listening and commenting,
Mike

[mike95490]

KACO ? never heard of them, if you think Fronius has good support, try KACO. Xantrex are a known Good Company.
If I understand your initial post right, you have 2520W of panels, in 2 different arrays @ different angles. 1260W of solar is duck soup for a Xantrex 2.8 Heck - both could feed a single 2.8, as you only realize about 80% of label output. But 2 different directions would play heck with the MPPT - the inverter might hunt around, trying to figure out where the sweet spot is.
The inverter rewire is all at ground level (or should be) the installers flunky should be able to handle that.

[Solar Guppy]

your reported vmp was 232vdc , the GT2.8 works down to 193vdc

Having a pair of inverters side-by-side is simple, all connections can come in one unit and transition to the second inverter thru the side holes. If your installer can't handle this you have other issues

Going with yet another unproven manufacture isn't the best choice. Xantrex is number one in the US for a reason

Here is my home system, 12kW of pv, 2 GT5.0's and a GT3.3 ... all the wiring comes into the BOS ( balance of system ) from behind for a super clean install
Also the BOS can be raceways, for example, The AC for all the Units comes into the left most unit and thru the side goes to the other two units, similar for the PV

[mradtke]

Mike and Solar Guppy,

Thanks for your advice.

The panels are 5,040 total. Sorry if my original explanation was fuzzy.

From what I've heard from you folks, the Xantrex is an excellent choice from all aspects except one: it is marginal for my array. I used the Xantrex calculator and see that rewiring to 2 strings of 14 modules would work for the Xantrex GT5.0. Is that a better choice?

Thanks,
Mike

[Solar Guppy]

For a single inverter and mixed orientations the GT5.0 should perform well, its been vetted in these configurations and proven to work. You can hookup a PC with SG-View and log to your hearts content ... after the Fronius issues you, more than most will appreciate this feature!

The ideal setup is a pair of inverters, each for the two orientations ... but I don't see any reason the GT5.0 won't work for you setup , the mppt will be a compromise of the two arrays, but you shouldn't have helpless hunting with the Xantrex unit

One of my GT5.0's has two stings of 15 panels ( 30 total ) of the Evergreen 190's, Outstanding performance from the Array and Inverter

[mradtke]

Hello,

This is an update on what's happening with Fronius.

Their last response to me was "As far as I know, there are no plans to for an internal fix in the immediate future."

I asked Fronius USA to consult with their home office (Austria). I asked them several times since then whether they have done that and they have not answered my question. For USA customers, I think that this closes the chapter on Fronius support.

Do we have any readers of this forum from outside the USA? If so, I am willing to try to contact Austria directly and take this one step further.

Thanks for reading this.
Mike

[mradtke]

Hello,

My installer and I did one more pass of useless measurements for Fronius today. I say useless, because the usual Fronius contacts weren't available when we called them, and we got to talk to a guy that we didn't know. He asked for some system information. With that information, he was able to reply that the Fronius 5100 IG wouldn't work. No kidding!

So in spite of the Fronius position up to now, there is a known set of conditions that are within the Fronius specifications that the unit fails with. My installer pressured Fronius to publish this information and they have refused. As noted before, they have also refused to fix the problem.

What I do know is that the keys to determine whether the Fronius will work or not are the DC open circuit voltage, and the AC mains voltage. But I cannot give you the formula since Fronius isn't sharing.

Fronius has now offered to buy me an autoformer to reduce my line voltage and move out of the failure window. I have refused.

I would recommend that anyone who owns or is responsible for a Fronius IG series inverter contact Fronius with the AC line voltage and DC open circuit voltage and ask them whether the combination falls into the design flaw. If you are considering a Fronius inverter, you could do the same thing, but you might save a lot of time and energy just to specify a competitive brand.

This is the end of the line for me and Fronius and I don't intend to post anything else. So, I'll say thanks to all of you who offered technical advice and moral support. You are a great group and I very much appreciate the time and efort that you spent on me.

Please feel free to share my experience as you wish.

Thanks again,
Mike

[niel]

sorry to hear of all of your trouble with this inverter and with fronius. thanks for sharing this info with us that others may not fall prey to the same thing.

[Solar Guppy]

Please update this thread when you install a working inverter, which sounds like it will be another manufacture

[niel]

i'm glad to hear that there is at least a conclusion to your dilema and it's a shame that bad publicity motivated them rather than owning up to their own product short-comings or care for their customers. this gives other companies and the industry in general a bad rap when this happens.

speaking of a bad rap, i even saw in that off the grid in tennessee thread in another forum that outback had gotten a bad rap by somebody that said they were prone to breakdown and i think that to be unfair to outback as he is giving the impression it is commonplace. for the record, all electronics is prone to breakdown and the feedback i've seen and heard is that outback has excellent service to their customers for those rare instances of breakdown.

[mradtke]

Hello,

I deleted an angry and inappropriate post that I made yesterday. I apologize to those who read it.

Fronius finally struck a deal with my installer to replace my Fronius IG 5100 with two PVPowered 2800 IX inverters and to pay for all of his expenses, including his diagnostic time. Fronius did not agree to publicize the details of the defect. However, Fronius did agree to work some sort of similar deal for another customer of my installer that has the same problem. They haven't told the customer that he even has a problem yet.

The deal made me angry because I am pretty sure that I spent more time on the issue than any other individual and all I got was a solution that I should have had months ago. And, Fronius is off the hook for any public disclosure, so the solar community gets no benefit.

I'll post a follow up when the inverters are installed.

Thanks,
Mike

[mradtke]

Niel,

Thanks for your comments.

As you can see, I deleted my post because I wrote it when I was angry and it was a rant. It made me feel a lot better to write it though.

Situations like the Outback story happen all the time. You can't trust it just because you read it on the internet. I'm guessing that's why Fronius isn't worried about me spreading the word. Which frustrates me, because my story is reliable.

Mike

[niel]

understandable. yes, i understand how your problem has truth to it and the other i mentioned, well maybe one person's misguided opinion.

[mradtke]

Hello,

Executive summary: No progress.

OK, so I'm paranoid after my Fronius experience.

Last time that I posted, I said that the final solution was a pair of PVPowered 2800 XV inverters paid for by Fronius. Well, I got a little uncomfortable with that since these inverters are no longer in production. So, I decided to test the PVP support by asking them for a copy of their inverter monitoring software. Their reply was that they no longer supported that software and if I wanted to monitor my inverter, I should buy a current model instead and they would "sell" me software for it. I would have expected that software that was included with the product, or so the manual says, would be available for at least the 10 year warranty life. I understand that they might not wish to their software to new versions of the operating system, but it still should be supported for the OS that it was designed for. And, why should I expect better support on a current inverter? PVPowered failed my support test.

I looked around some more for an alternative solution. The problem is that I need to track an MPP of 190 volts or lower. A pair KACO 2900 inverters would do, but they introduce another problem with the code and AC wiring that make them an expensive solution.

I also found a Power-One PVI-5000-OUTD-US single inverter with dual MPP tracking inputs that looks like the ideal solution. Its problem is that it is a "transformerless" design which requires a bunch of changes to my system to meet code. I don't mind this one bit, but my installer is not comfortable with it.

Both KACO and Power-One seem to have good customer support.

So, here I am being pushed into using poorly supported inverters and making a mess of my carport wall with additional disconnects, inverters and combiners. Every day, I lose about 10% of the power that I could have generated. All because Fronius refuses to fix their product.

I'll post again when something changes.

Thanks for listening,
Mike

[Solar Guppy]

A pair of Xantrex GT2.5's is the best solution.

The GT2.8 is good to 195V for the VMP, your panels are in the 230V range from your postings, so unless there is something missing, they will be the best option for your installation. Street price is in the 1700 price range ( each )

I would NOT recommend PVpowered, especially the older units, lots of issues and performance quirks

[mradtke]

Solar Guppy,

Thanks for you reply.

I have concluded the same as you about PVPowered. I too want to use Xantrex, but it just doesn't quite make it. My panels are SunTech STP180-24/Ab-1. They are not included in the Xantrex string calculator. Using other string calculators, I see my low MPP to be at 190 volts. It gets very hot in Phoenix. I would expect to see power limiting for at least 4 months per year with the Xantrex. At this point, I don't see that as a good solution.

Thanks for your thoughts,
Mike

[Solar Guppy]

I think your way off on your calculations

using the data sheet here http://www.solarshop-europe.net/solar-components/solarmodules/suntech_stp180-24-ac_m_744.html

The vmp at standard conditions is 36.2V

The reduction in voltage is 0.34%/C or .12V/C over standard conditions ( per panel ) , your configuration is 7 in a series string , so the vmp at 25C is 253V and for every degree C over standard its a reduction of 0.84V

You state the VMP can get down to 190V ... that would imply a temperature of 75C over standard or the panels being 100C.

You have reported VMP's in the 220V range, which what I would expect .. ( 39C over standard )

With the GT's VMP good down to 195V, that would allow panel temperatures about 95C ... hard to beleive even in phoniex you would get stuff that hot, you have other issues like wire ratings that can't run in those temperature if indeed thats true. Do your self a favor and get an IR point and shoot meter if you need exact numbers, I'll hazard a guess and say, even in 110 degree days, the panels will be @75C

The Xantrex GT2.8's are your best choice and should work fine in your configuration.

[mradtke]

Solar Guppy,

Thanks for your calculations. However, there are two errors. First, you used the specification for the STP180-24/Ac, not the STP180-24/Ab-1. The difference is that the correct Vmp is 35.6, not 36.2.

Second, you used the temperature coefficient for Voc, not Vmp. The correct value should be -0.47, not -0.34.

Using the correct figures, I calculate the Vmpp for the system is 190 volts at a panel temperature of 75 degrees C.

I think that the only thing left to argue is the 75 degrees C. If I use the Xantrex string calculator with the STP180S-24/Ab-1, and 110 degrees as the average high (which is appropriate for June), both the GT2.5 and GT2.8 come out as non-optimal. In comparing the STP180S-24/Ab-1, with the STP180-24/Ab-1, I find that the panel used in the Xantrex calculation is the same except for having a lower temperature coefficient. That means that the result would even be worse for my panels.

Please correct me if I have missed something.

Thanks,
Mike

[Solar Guppy]

OK, got the data sheet http://www.suntech-power.com/products/docs/STP175_24_Ab-1_E01.01%20Sept10%202008EN.pdf

And I now do see the coefficients are different for VOC and VMP, I didn't realize they had specs for both, but the .047% is similar to other panels and makes sense

The GT 2.8 runs mppt down to 195V, so that would allow about 47C of temperature rise above standard 25C ... so these numbers agree with your calculations

So now the interesting questions is just how hot do the panels run above the ambient temperature? ... I bought a nice IR point and shoot Extech brand off ebay for about 50 bucks .. that is the only way to answer what you need.

The Xantrex calculator ( or any other ) can't take into consideration your stand offs, mounts, roof surface underneath the panels or wind flow, all effect what the temperature rise could be. I also believe as the ambient temperature rise the panels temperatures do not follow in a linear fashion, I don't have a reference on this, but something along the lines that thermal energy is more efficiently radiated at higher temperatures ( from memory )

Also, if your that far down in voltage, then it would seem you might be able to run 14 panels in a single string?. I have run here in florida a GT3.3 with a similar VOC for 3 years without issue ( 20 18V panels in a single string ). You will have to check the VOC at cold temperatures for your area.

Before you purchase anything, I'd recommend you make actual measurements, with that data, then you can see what your options are.

FYI, the Xantrex GT series has the widest operational range of any Grid Tie inverter, if that won't work, you may need to make other adjustments

[mradtke]

Hi Solar Guppy,

Thanks again for you comments.

Of course IR measurement would be best, but I'll have a long wait until summer for the test. I think that I should trust the various string calculators but stay away from the boundary conditions. On the other hand, I was well within the Fronius specifications and look where it got me.

Neither of us is very happy with PVPowered. Do you (or anyone else) have opinions of KACO or Power-One?

Thanks,
Mike

[mradtke]

Hello,

With the holidays, little has happened. However, yesterday all parties came to a tentative agreement to install a Power One PVI-5000-OUTD-US. This is a transformerless inverter so my installer is having to make a number of electrical modifications to my system in order to support it. I chose this inverter because it has dual MPP tracking inputs which matches my system requirements, is sized correctly, and will at least match the expected efficiency of the flawed Fronius.

If anyone has reservations about using this inverter, or transformerless inverters in general, please reply to this post as soon as possible.

Thanks,
Mike

[Solar Guppy]

full power requires a listed a 200VDC minimum input, no better than the Xantrex inverter

http://www.power-one.com/resources/products/appnote/AlternativeEnergy/safety_certification_pvi-5000-outd.pdf

Section 8.5 discusses voltage and current derating ... Fig 27 in the link below showes the maximum current is decreased as the volts falls ... from a technical aspect, I would expect this. The UL minimum is listed as 200V, the manual showes 180V ... I would trust the UL listed value

http://www.power-one.com/resources/products/appnote/AlternativeEnergy/manual_instruction_pvi-6000-outd.pdf

As far as transformerless, you will be the first install I have heard of, only the most recent NEC2008 allows this , better check that your power company and your local building department both recognize and allow installs to NEC2008

Your going with a manufacture that at a minimum is brand new to the US market, that's a risk in both support and unproven operation

[mike95490]

If anyone has reservations about using this inverter, or transformerless inverters in general, please reply to this post as soon as possible.


Without a transformer, your power output stage is sitting right on the AC feed. Any spikes or glitches will have a straight shot at the transistor junctions. If someone on your block generates "noise" with a backyard welder, or a hairdryer with nasty brushes, you may find how well noise rejection works in the inverter. Sure, the stuff can be filtered, but the transformer simplifies that filtering.

I'm not even sure how they do it without a transformer, but I guess they have a way.

[Solar Guppy]

To do an inverter without a transformer, one uses inductors, still magnetic's but slightly better efficiency, and probably a SEPIC converter ( can boost or buck )

Current multi-stage inverters are no different than transformer less units on the AC side, its a PWM H-Bridge driving the AC from a DC rail ( 430 VDC ), the transformer is used to step up the DC input side and the isolation is before the AC inverter stuff. So I don't see and difference in regards to Mikes comments

[mike95490]

Ah, SG, thanks for that. I just could not see how to not fry stuff w/out coils somewhere.

[boB]

Actually, I don't think there was anything specifically in UL1741 that kept a manufacturer from listing a non-transformer isolated inverter.
Some may have "thought" they weren't supposed to for one reason or another. And there has always been requirements for things such as DC-Injection limits, etc.

There was at least one utility that said it was fine to have a non-isolated grid tie inverter as long as you used one of their huge transformers between that inverter and their grid.
There went all your efficiency gains down the toilet.

boB :D

[Solar Guppy]

Hi boB,

I was told in 2004 it was not allowed in the US by Xantrex as they were in the middle of the GT program and I specifically asked about the typology. UL1741 isn't free, so I can't scan to give the exact text/section for reference but I seem to remember it was the most recent UL/NEC changes that allowed what has been done in Europe for years

This is a link to a white paper discussing the benefits of going transformer less and specifically calls out UL1741 and the galvanic isolation requirement. Also, GFD is much harder without the isolation as one can't just bond a PV leg to ground for sensing

http://74.125.77.132/search?q=cache:OIScv7NQ4wYJ:www.elkraft.ntnu.no/eno/Papers2008/Schimpf-norpie08.pdf+UL1741+galvanic+isolation&hl=en&ct=clnk&cd=12&gl=us&client=firefox-a

[boB]

Thanks Guppy. I will look again for this.
I don't remember looking for the word "galvanic" so maybe that word is/was in there. However, just because someone (even someone at Xantrex), said it isn't allowed, doesn't necessarily mean it isn't allowed. I've gone over UL1741 many times, but it IS a large document and I could certainly have missed it somehow.

And, thanks for that link.

boB :D

[boB]

"At the
moment this is the case in countries where the safety standards
for PV-systems do not yet cover transformerless topologies.
One example is the UL-standard UL1741 [11] which is valid in
the USA."

This paper tends to agree with my findings... "Transformerless" PV inverters are not covered or mentioned in UL1741.

I will still look again in the spec for galvanic.
Thanks again for the link to that paper. I can't get enough of those it seems. (even though I have a bunch that are fairly worthless).

boB

[mradtke]

Hello,

Thank you all for the replies. And thanks for the link to the interesting paper.

I'll try to address the issues.

Unknown company: My answer to that is that Fronius is well known and well respected and look where it got me.

UL1741: The inverter is newly compliant although I would expect that as experience grows with this type of inverter, there may be some changes. The code complications mostly deal with having 240 VAC on the array and my installer has addressed them. Because the array is floating, when the disconnects are opened it is much safer to work on.

200 volts: This CSA statement seems to point out what should be obvious. But since the CSA flagged it, it had me going for a while too. But, here is the math for the PVI-5000

Maximum Utility Backfeed Current (AC) = 30 A @ 240 V, or 7200 peak AC watts
Maximum Input Current (DC) = 2 x 18 A = 36 A

Therefore (7200 peak watts)/( 36 peak A) = 200 minimum DC input volts.

Using a similar calculation, 138 DC volts is necessary to run at the continuous 5000 watt rating. The MPP tracking is from 90-580 volts.

Derating: As far as I know, the 200 volt issue was as stated above and applies to derating from the peak power, not the continuous power and is just a re-statement of the peak specifications. I believe that the 180 volts on the graph applies to continuous duty and is well below my array voltage.

Thanks again for all of your comments.

Mike

[Solar Guppy]

A 6kW inverter is rated for 6000 watts continuous output, UL doesn't test or list peak values, what the DC voltage deals with is the maximum input current. Like most GT units, they power limited on the DC power, not the AC power

The maximum input current as the graph shows in figure 28 is the unit is DC current limited from 90 to 200 VDC ( notice the 90 and 200 have been added to the graph to meet the update listing changes )

Whatever the DC power is ( each channel on the 6Kw unit ) is listed as 18 amps DC

90VDC * 18 amps = 1620 watts DC
200VDC * 18 amps = 3200 watts DC

as a guess for 5KW unit ( 0.83 of the 6K )

90VDC * 15 amps = 1350 watts DC
200VDC * 15 amps = 3000 watts DC

So as your hot panels drop, lets say to 180V , the maximum the inverter can harvest is 180V * 15 = 2700 watts per channel or 5400 watts DC ... If the inverter is efficient as it claims, then even at 180V it will be full power, maybe that's the difference between the 5k and 6K units, but certainly not 135VDC, that would be only 4Kw of DC power

[mradtke]

Solar Guppy,

First, I owe you an apology, because I noticed this and forgot to correct you. The manual that you are referencing is not correct. The correct one is:

http://www.power-one.com/resources/products/appnote/AlternativeEnergy/pvi-6000-outd-us.pdf

Please note that it is 100 pages long and includes the certificates.

I agree that the calculation that the CSA did is not correct because it apparently mixed AC and DC and ignored the efficiency of the unit. My reference to 138 volts was built on that incorrect calculation, not to support it, but to show that even this incorrect calculation supported my application. I think that we are justified in ignoring the whole thing and using the graph in the manual for derating. You may note that the "correct" manual does not have a reference to the 200 volts outside of the CSA certificate.

I appreciate your calculation for the 5000 watt maximum input current. It is not listed in the manual as it should be, but the included CSA certificate for the 5000 lists it as 18 A. But then, I have lost confidence in the CSA certificate.

In the end, I think that you are saying that other than being "bleeding edge" technology, the unit is a good match for my arrays. Please take a look at the referenced new manual and let me know if you spot anything else.

Thanks for your careful and thoughtful effort.

Mike

[Solar Guppy]

All sorts of errors in that document

Search for UL1741 and it gives 50hz and 230VAC for the parameters, which is wrong, the 5Kw unit has the same input current specs, which it shouldn't

Its also CSA , not UL listed ... this is SUPPOSE to be the same I have been told CSA is no where near UL in checking things out ... the errors in this document and the listing signoffs seem to back this up

I wouldn't use it ( Aurora unit ), I would ( and do ) use Xantrex GT's, 4+ years of proven performance and similar efficiency, but that's just one guys opinion.

You might have to start you own testing service ...

[mradtke]

Hi Solar Guppy,

Thanks again for your thoughts.

You are certainly correct about the errors, and as I have said before, the Xantrex GT's would be an excellent choice if they would work on my low voltage.

Besides the P1 documentation and the CSA certificates, I looked at the CEC testing of the unit. I think that everything is OK, but not at all proven when compared to the Xantrex. That doesn't mean that it's a bad choice though. It means that it is not the safest choice.

I think that I am about 1 week away from installation now. I'll report back as current begins to flow.

Meanwhile, the well documented and popular Fronius IG 5000 continues to hunt down to 232 volts for the MPP and then resets ... over and over and over.

Please stay tuned,
Mike

[mradtke]

Hello,

No long after my last post, my installer contacted me and said that Fronius had contacted him with a fix for the problem that I have been whining about. I quit talking directly with Fronius some time ago, so this information is second hand. I was told that the fix was coming from Austria and would arrive in a few weeks. I was caught completely off guard by this information. My installer asked me to wait for and evaluate the fix, rather than going ahead with the Power-One inverter installation.

It took me a few hours before it dawned on me that this might well just be another delay in getting to a final solution. I had no way of knowing whether the Fronius fix was real or not. The earlier Fronius behavior documented in this chain was enough evidence for me not to change my plans. So, I asked my installer to continue with the Power-One inverter installation.

If I become aware that there really is a demonstrated fix, I will post that information here so that everyone may benefit.

The Power-One inverter was installed yesterday. Everything went smoothly and I find it interesting, but perhaps not all that useful, to look at the energy being harvested by each of my two arrays separately. It will take a few days to know about how much more energy I am capturing with the inverter not oscillating, and I'll post again when I can better quantify that.

The inverter looks to have good workmanship, even if its manual is not all that great. It is convection cooled and during our 75 degree afternoon, the heat sync is just barely warm. The Fronius was not noisy with its forced air cooling, but it could be heard most of the day. By afternoon this time of year the exhaust air was a lot warmer than the Power-One heat sync.

Thanks for listening,
Mike

[niel]

heat is the enemy of electronic components and your saying it's cooler even without a fan is a very good sign it may outlast the other and be quieter too.

[mike95490]

HEAT. That's a new clue.

Perhaps the inverter was overheating, and throttling back, and as it cools, throttles up. Oscillation !

[niel]

i don't think it was heating and cooling quite far and fast enough to have been the cause, but good thought.

[mradtke]

Hello,

Thanks for your comments.

There is no evidence that heat had anything to do with the problem. I was just commenting that the Power-One seems to run a lot cooler and quieter without the fan noise of the Fronius. At some point a Fronius engineer talked about the performance hole being related to an MPP in the area of 230 volts with a high AC line voltage of around 250 volts.

I haven't heard anything more from Fronius on their recently promised fix.

The Power-One inverter seems to be working just fine. I took some temperature measurements of the array back side and calculated the MPP for that array. My calculations were within 1 volt of what the inverter had tracked.

I also looked at my personal method of seeing whether the MPP tracking was working by looking at the changing voltages and currents. I think it was SolarGuppy that predicted that I would fail at this and he was right. The Fronius walked around a lot, and that's what I based my method on. The Power-One stays very stable with essentially constant voltage and current values unless a cloud passes by.

I figured that the Fronius was oscillating about 1/2 the day this time of year. I also made a rough calculation of the losses while oscillating as about 10%. On the sunny day just before the new inverter was installed the Fronius was collecting 18 kWh. Under the same conditions, the Power-One is harvesting 20 kWh.

From the above, I conclude that everything is working as it should and I am pleased with the replacement (upgrade?) so far.

Thanks,
Mike

[autoxsteve]

glad you're getting output from your system. I find it disheartening that Fronius has not bellied up to the bar and altered their specs or fixed this.

Power One - I believe that they are a Camarillo, CA HQ'd company....

[mradtke]

Hello,

The Power-One is silently inverting power just as it's supposed to.

As was discussed in this chain, the Power-One is a transformerless inverter, so the arrays are floating. This makes them much safer to work on when the disconnect is open, but also much more sensitive to a ground fault than the type of inverter that is usually installed. Besides the GFCI protection that is always present, the inverter checks the array resistance to ground and leakage current to ground during startup. This has been 18 megohms an 0 milliamps consistently, which probably means off scale. I live in the desert, but there was a driving rain one day during the startup last week. That presented a good test of the array isolation. The resistance reading that day dropped to 6 megohms, and the current stayed at zero. My feeling is that those are pretty good readings for the conditions, so I can stop worrying about the isolation.

I am very pleased with my choice of Power-One. I guess it's because of all of my earlier difficulties with the Fronius, but I just can't get over how this inverter just quietly sits there doing what it's supposed to do. I keep stopping to scroll through all of the information on it looking for some sign of trouble, but everything always looks great.

No further word from Fronius.

Thanks,
Mike

[mradtke]

Hello All,

The Power One inverter is still working just fine. I look for trouble every day and can't find a thing to complain about. I am harvesting more than 25kWh per sunny day now which seems more than satisfactory for a 5kW system this time of year in Phoenix. Since I didn't have the Fronius last February, I can't do a direct comparison. I'll be sure to talk about that in June.

No word from Fronius about their fix.

Thanks,
Mike

[autoxsteve]

excellent you're getting good production from the replacement inverters.

[mradtke]

Hello,

The Power One inverter is still doing just fine and it is now harvesting more than 30 kWh per sunny day. According to my installer, the best harvest should be in May for my installation. I still can't do a direct comparison to the Fronius since it wasn't operational until June of last year. However, the best ever for the Fronius was 29 kWh in a day and it only did that once.

My installer says that Fronius has still not provided the fix that they unexpectedly offered two months ago. He says that Fronius has reverted to an earlier claim that any fix would require re-certification before it could be used in a customer system. Fronius now says that when a fix is available, it will be only for beta testing. I have no further word about whether Fronius has changed their mind about keeping the fault secret. Please draw your own conclusions.

Thanks,
Mike

[rsl360]

I also have a system with a Fronius inverter, the IG-5100. It also hunts and fails to find the MPP. This has been going on for a while. I contacted my installer and Fronius and everyone agreed that the system is hunting and Fronius agreed to replace the inverter. 11 days ago the inverter was replaced. It's still hunting. Tomorrow I will contact my installer and Fronius with the bad news, not sure what Fronius will do this time. This would appear to be a problem that Fronius does not want to fix, or is incapable of doing so.

I held off on posting anything until the new inverter was installed and tested, hoping that I could say Fronius had the problem solved. Obviously they have not. Or, Fronius could issue a bulletin, stating that the inverter was inappropriate for certain installations, (assuming it can be defined), such as ones with high line voltage. (which seems to have been suggested as a possible problem.)

More info as I get it.

[solarvic]

I have 2 Fronius inverters and don,t have the problems you all seem to have. ! is an Ig-2000 and other is Ig 3000 Due to 2 different brand of solar panels. I am running them at a lot higher voltage than indicated here and I am thinking that might be your problem. Your voltages aren,t ideal because of your high temperature. Don,t know how hot it gets in Phoenix but Idid a string chart @ 110 f at highest temp and 32F at lowest temp and my results is :
strings of 7 = 203 v
strings of 8 =232 v
strings of 9 = 261 v
strings of 10 =290 v. According to string chart you can run 3 strings of 10 on that inverter. operating voltage is 150 to 450 v with a buffer to 500 v. So my theory is you should have either run 3 strings of 9 panels or bought 2 more so you could run 3 strings of 10. Or got 2 smaller inverters since your panels are aimed in 2 different directions. I am running a lot higher voltage at my location where the record low is -26f and the normal high never gets above 97f. With a total of 16 Kyocero KC- 158 g ans 12 Sharp 167 sharp ND 167 ndu3a I have benn getting 25 to 29 KW on sunny days in Western pa. which has plenty of cloudy weather.
S:Dlarvic

[Windsun]

I also have a system with a Fronius inverter, the IG-5100. It also hunts and fails to find the MPP. This has been going on for a while. I contacted my installer and Fronius and everyone agreed that the system is hunting and Fronius agreed to replace the inverter. 11 days ago the inverter was replaced. It's still hunting. Tomorrow I will contact my installer and Fronius with the bad news, not sure what Fronius will do this time. This would appear to be a problem that Fronius does not want to fix, or is incapable of doing so.

I held off on posting anything until the new inverter was installed and tested, hoping that I could say Fronius had the problem solved. Obviously they have not. Or, Fronius could issue a bulletin, stating that the inverter was inappropriate for certain installations, (assuming it can be defined), such as ones with high line voltage. (which seems to have been suggested as a possible problem.)

More info as I get it.

Or it could be something wrong with your panel installation. Since this is your 2nd inverter, that seems more likely. If you have mismatched strings it will cause hunting in any inverter.

[rsl360]

Hmm, maybe I should have started a new thread. I posted on this thread because I have the same problem as the original poster and wanted to continue the discussion of what seems to be a flaw in at least one model of Fronius inverter. I'd like to be able to say that Fronius fixed it, but that does not seem to be the case.


To solarvic: I'm not in Phoenix, that's the original poster. And it any case, it's not a hot weather issue, the hunting occurs in very cold or moderate weather. Not sure about hot weather. The problem is not very obvious unless one is logging at a fairly rapid interval. Logging at a one minute interval will show the problem, but what shows up on a graph is actually an alias of the hunting. The hunting takes place on about a 45 second interval. Recording data at a two second interval shows this well.

My System: Two strings of 12 Evergreen ES-A-205 panels (total 24 panels) and Fronius IG-5100 inverter.

To Windsun: I suppose until the problem is solved, I won't know for sure what the problem is. As to it being mismatched panels- When I sent the data to Fronius, there response was that we needed to swap the inverter. While I'm pleased that Fronius has been responsive to the problem, I'm not sure why they would swap out the inverter if the problem is in the strings. Having the problem recur just makes Fronius look bad.

What is your authority for "If you have mismatched strings it will cause hunting in any inverter." This is not obvious to me. Even if strings are mismatched, there still exists an MPP. Neither string will be at it's MPP, but the system overall will be, given the restraint of having to pick the same voltage for both strings.

rsl

[Windsun]

What is your authority for "If you have mismatched strings it will cause hunting in any inverter." This is not obvious to me. Even if strings are mismatched, there still exists an MPP. Neither string will be at it's MPP, but the system overall will be, given the restraint of having to pick the same voltage for both strings.

rsl
My "authority" is the simple fact that if you have two or more strings, you can have two different MPP's if the strings are not matched. In some cases the inverter will try to pick the best overall point, but some will settle on the highest peak.

But I suspect that Guppy's analysis is probably more correct - panels can be anywhere from 5 to 40 degrees hotter than air temperature on a roof, so you may be getting too low.

[a0128958]

... Recording data at a two second interval shows this well....

Can you show us this in chart or graph form?

Best regards,

Bill

[solarvic]

Hmm, maybe I should have started a new thread. I posted on this thread because I have the same problem as the original poster and wanted to continue the discussion of what seems to be a flaw in at least one model of Fronius inverter. I'd like to be able to say that Fronius fixed it, but that does not seem to be the case.

To solarvic: I'm not in Phoenix, that's the original poster. And it any case, it's not a hot weather issue, the hunting occurs in very cold or moderate weather. Not sure about hot weather.
I think both of you guys have the same problem of running too low of voltage. It would be nice if you said whar part of the country you are inso we could try to figure tempatures, But in my area I wouldn, run that small of a string of panels. Voltage is too low. AT 110F you only get 15.3 v per panel. That is only 183.6 at 100 sun. All 24 panels in 1 string would only be 367.2 v.
In my area @-26f I could still run 18 modules and would. I would think Fronuis would catch it that them inverters don,t work well at such a low voltage you guys want to run them at. S:Dlarvic

[rsl360]

My location is on Cape Cod, Massachusetts. The hottest weather we are going to see is about 100f, coldest is about -15f

The setup of 2x12 panels is within the recommendations of Evergreen for the Fronius inverter. It is also within the recommendations of Fronius with for the Evergreen panels. I don't see that low voltage is an issue. And it's neither hot nor cold here at this time, so I don't see what it would have to do with hunting.

I'll put some images in, but I see that I have to have them hosted somewhere.

Originally posted by windsun
My "authority" is the simple fact that if you have two or more strings, you can have two different MPP's if the strings are not matched. In some cases the inverter will try to pick the best overall point, but some will settle on the highest peak.
Yes, absolutely true. The inverter might pick the wrong peak, yes. But that's not hunting.

Before we get too far off track: My issue is that the system was/is hunting. Fronius agreed that this was the case, there was no dispute. They did not say I have too few panels, or that it's too hot or too cold. The new inverter does the same thing. So, is the Fronius MPP algorithm faulty? Perhaps there is nothing wrong with the inverter, but Fronius is unable to diagnose a system problem properly? (I say that facetiously, as it seems unlikely)

rsl

[Windsun]

I have to admit that given your conditions and setup, it is something I have not seen before. The few instances I have heard of it you have eliminated.

There are not many possibilities left, aside from a 2nd bad inverter - I assume you checked the Fronius site for any software upgrades?

What is left to look for might be out in left field - birds sitting on the panels, a loose wire connection, voodoo.... :confused:

One more remote possible is wind - which would cool the panels temporarily, but I have never seen that happen anyplace but hot zones.

[Solar Guppy]

Your correct, 12 panels is fine, for some reason I thought I read 10, but can see that's not the case.

If this system was installed by a contractor, I'd insist they install different manufactures inverter. Xantrex and SMA are both well vetted designs

[Windsun]

Not sure I would recommend the Xantrex right now - they are backordered 8-16 weeks for most models.

[rsl360]

Lets see if I can get some pictures of my system performance up here.

This is a day of normal performance from the "new" (replacement) inverter. The green line is voltage*10 and the red line is the AC output of the system, in watts. The numbers on the bottom are a form of decimal date and time. (makes plotting easier) (click on the image for a larger view. I think you will then have to click on it again to get the full view)
http://i202.photobucket.com/albums/aa247/rsl360/solar/th_solar-normal.jpg (http://s202.photobucket.com/albums/aa247/rsl360/solar/?action=view&current=solar-normal.jpg)

This image is the system hunting for the first part of the day, then it stops on it's own. This is also from the replacement inverter. Again, green is array voltage*10, red is AC output in watts. I'd estimate that I'm losing over 10% of my output when this is happening.
http://i202.photobucket.com/albums/aa247/rsl360/solar/th_solar-hunting.jpg (http://s202.photobucket.com/albums/aa247/rsl360/solar/?action=view&current=solar-hunting.jpg)

This is a detail of the prior image. The tick marks are at about 2 second intervals. Thus you can see that the hunting period is about 45 seconds.
http://i202.photobucket.com/albums/aa247/rsl360/solar/th_solar-hunting-detail.jpg (http://s202.photobucket.com/albums/aa247/rsl360/solar/?action=view&current=solar-hunting-detail.jpg)

[Solar Guppy]

Thanks for the graphs ...

Looks to me like your problem days are when its colder and the vmp is higher, its right at or just above the switch point in the inverter. Fronius has a very odd design that in order to get a larger operational range they have internally a multi-tap transformer and switch it based on the input voltage. On the IG2000/3000 is recall it was about ~200V and ~250V ( this is from memory of testing 6 years ago )

On the day you have a good harvest, notice the voltage is about 20-30V lower than the problem day. I would say the inverter on the colder day, switches to a different tap in the early morning and as the temperature rises, then unit is either switch the tap causing efficiency changes confusing the tracking or the software is struggling between the hysteresis or vmp ( mppt ) algorithms.

This is definitely the inverter and has been seen before. Likely as the temperatures warm up towards summer you will not see this issue.

Two things you can do for proof,

First when its ramping / mis-tracking, listen for audible clicks ( relays switching the transformer winding )

Second, pull one panel out of each string ( lower the voltage of the string ), the unit will not be near a transition point, which is likely the root cause of the hunting

[solarvic]

Looks to me like your problem days are when its colder and the vmp is higher, its right at or just above the switch point in the inverter. Fronius has a very odd design that in order to get a larger operational range they have internally a multi-tap transformer and switch it based on the input voltage. On the IG2000/3000 is recall it was about ~230V and ~330V ( this is from memory of testing 6 years ago.

Did you mean that the switching voltage is 230 v for the IG 2000 and 330 v for the
IG 3000? If this is right I shouldn,t have any problems with the IG-2000. Might have a problem with the IG 3000 as I estimate about 325 v at STC VMP. Really can,t tell for sure as It has a mixed array. 12 sharp 167 u3a and 2 Kyocera KC 158g and some panels are aged and some not aged. Glad to know these switching voltages. So far I am not having the problems the guys with the IG-5100 inverters are having and I am just guessing, but have a hunch that they are operating at the switching voltages and agree that they should try changeing the number of panels in thier string to see if inverter stops the searching. S:Dlarvic

[Solar Guppy]

I had to do some digging around, here is what Fronius sent me back in 2004


The voltage ranges for the different taps are 150V-200V, 200V-270V, and 270V-450V. This is for both the IG2000 & IG3000, they both have three ranges ajustable by software and relays inside the units

Now keep in mind, the unit doesn't switch at 200V/270V , that's the operational limit of the inverter and software has a threshold window of about ~20V as I recall so its likely 180-200V 250-270V are the transition windows to the next tap.

In the posted logs, its pretty clear something is happening near 250V that's causing the issue.

For the record I found a couple of issue with the IG2000 & IG3000, I had DOA units, lose screws, over poor build quality, optimistic reported watts and grid disconnects that I proved was their software. Fronius was very open and helpful and I had communication to their engineers in Austria ( through US sales ) and verified improvements they made, so I know more than most about how these units work.

I'm sure issue with the IG5100 could easily be replicated and I'm disappointed that multiple users are not getting through to Austria its a real problem. The other OP had the installer replace the Fronius with a Power one inverter ... and no issues since

My contact at Fronius left and went to Xantrex a few years ago, so I have no inside name to recommend for help.

[rsl360]

I've checked to see if the inverter is switching transformer taps when it's hunting and it's not. (and I do know what the clicks sound like.) I was pretty sure this was not the case, but I wanted to double check before posting anything.

What I see when I look at the inverter's behavior is that it lowers the array voltage, the power goes up, but before the power maxs out (and maybe starts to drop), it gives up, raises the voltage, and starts over again. Another strange thing, seen occasionally, is the average array voltage will suddenly drop about 5% (215v to 203) with no significant change in the output. All I can make from this is that the inverter was running on the "higher" end of the MPP voltage, and then it switches to the lower end. Not that this makes much sense.

rsl

[mradtke]

rsl,

I am the originator of this chain and you can see that there is a lot of information in it, most of which I have forgotten now that my system is performing flawlessly.

I read your posts through a couple of times and looked at your graphs. I believe that you have exactly the same problem that I had with my IG5100 and Fronius has treated you in a similar fashion. There are probably a range of conditions that cause the problem, but in my case the two key things were a low panel voltage of about 230 volts and a high AC ;ine voltage of about 240 volts. I don't know the exact numbers, but one Fronius engineer that I accidentally spoke to readily confirmed that my voltages triggered the error, and that it indeed was a known error.

When Fronius finally admitted the problem, my installer checked another local Fronius IG5100 installation that used a low panel voltage against the typical Phoenix high line voltage. Although the customer wasn't aware of it, this system was hunting as well.

I agree that the issue is with the transformer taps, but my inverter was not switching taps either. I am only guessing this, but I think that the software loads the panels while searching for the MPP until it triggers the algorithm that says it's time to switch taps. The software then shuts down the inverter to prepare for a zero current change of the transformer tap. Another software routine is then run to choose the tap. However, during this instant, the panels are open circuit and the software is probably using a different algorithm. Instead of choosing an adjacent tap, the software chooses the same tap again. The inverter is restarted, and the cycle repeats.

While Fronius declined to fix the problem with their inverter, they did work with my installer to fix the problem. In the case of the other local system with the problem, Fronius bought the customer an additional panel per string to move the DC voltage out of the problem area. I had no room for extra panels, but they bought me a competitive inverter from Power One to replace the IG5100.

Now, more than a year later, I am very pleased with the Power One inverter. It is a "transformerless" design which improves the efficiency 2-3% over the Fronius. In addition, the Power One has dual independent MPP seeking inputs. I have two arrays with different orientations, so I picked up a little more efficiency with this feature as well. And lastly, the Power One is convection cooled and thus is very quiet compared to the Fronius.

My advice to you is remind Fronius of this chain. Have them read it again and ask them to either add panels to your system, or buy you a competitive inverter that actually meets its published specifications.

If you think that I can be of assistance in resolving this, please just ask.

Thanks,
Mike

[rsl360]

Hello mradtke. Thanks for the interest. I thought from the start that you and I had exactly the same problem. Fronius is now sending me the equipment to log more data, which is also similar to your tale. (Although I think you did some logging, then they sent the new inverter?) Fronius seem interested in solving the problem, not sure why it's so difficult. The new inverter seems to have a different algorithm than the previous one, although as I said, it still has issues. But I believe that fronius is doing their best to solve this, and I think they are entitled to keep trying to do so, at least for now.

rsl

[mradtke]

Hello rsl,

Yes, I agree that Fronius should have their chance to sort this out..

Both I, and my installer spent a lot of time doing measurements at Fronius's request. I was happy to do this because I expected that Fronius would use these data to find and resolve the problem. This all changed when Fronius inadvertently revealed that the problem was already well known. I was further disillusioned when Fronius refused to either fix the problem or update their specifications to reflect the performance gap.

Have you referred Fronius to this forum chain?

Thanks,
Mike

[rsl360]

Well, here it is almost a year later. It's cold again and the hunting has returned. When the system is hunting, I'm loosing about 10% of my output. I've heard nothing from Fronius in regards to the measurement that were taken on my inverter, nor have I heard anything as to how to resolve the hunting issue. I've emailed Fronius three times recently, I've heard noting back. This is very disapointing. Fronius KNOWS that there is an issue. I'm willing to work with Fronius on this, but they no longer seem interested. So at this point, I'd have to say that Fronius IG5100 inverters have a problem that Fronius can not, or will not, resolve. It's probably not an issue in all installations, but it's definitely an issue for some. That is, it's not just me.

[autoxsteve]

Bummer.

I have had almost 3 trouble free years with my Fronius inverter. I did have one day where things acted up a bit, and my installer was all over providing a replacement unit but the odd performance only occurred on one day and has not returned in over 6 months.

Good luck on your situation - your installer should be standing behind the product - and I'd be all over them if they didn't.

[rsl360]

Well, you probably would not see this problem in Southern California. Overall, the inverter seems to be pretty good, except when I'm losing 20% of my power from hunting.

I did manage to contact someone new at Fronius, and to their credit, they are still interested in fixing this. And they still have the information about the first inverter swap, and seem to have some idea as to how to get in touch with the guy who was working on the problem. So the potential to do the right thing is still there.

And my installer is standing behind the product. I'm pretty technically oriented, so I've been dealing direct with the factory, but the installer is well aware of what's happening. I've got my own data collection system, so it's easier for me to get the information to the factory.

[tampasolar]

Fronius IS hiding this from new purchasers. I asked their sales rep UP FRONT whether I should buy the newest IG Plus model or the older IG5100. They did not divulge this hunting concern at all.

Now that I got the system built, I now have this very hunting issue and would never have bought Fronius if they were a honest company.

Do they care -- doubtful.

[Macaw]

Here it is is another year later-- And I noticed the same problem with my Fronius IG3000 and a high AC line voltage. I'm in the process of debugging the solar.access software so I can formally document the problem but in the meantime can watch the built in display and see the massive power fluctuations on a cloudless day.