Help with string inverter problem

gazapc

Martyn1981 wrote: »

Go with the euro rating as I think(?) it's more comparable to other inverters.

FYI the two weighted efficiency values are typically European and Californian. The European is more relevant to the UK. Why are they different? The efficiency of an inverter varies depending on how sunny it is and hence how close to maximum (and generally optimum) capacity an inverter operates. Two identical inverters, one in a sunny location and one in a cloudy location, the sunny one will be more efficient. Hence when you give an efficiency figure it has to be based on an assumed operating condition. The European efficiency figure is typically marginally lower as it is based on a more European cloudy climate where as the other figure is based on a sunnier Californian climate.

Martyn1981

gazapc wrote: »

FYI the two weighted efficiency values are typically European and Californian. The European is more relevant to the UK. Why are they different? The efficiency of an inverter varies depending on how sunny it is and hence how close to maximum (and generally optimum) capacity an inverter operates. Two identical inverters, one in a sunny location and one in a cloudy location, the sunny one will be more efficient. Hence when you give an efficiency figure it has to be based on an assumed operating condition. The European efficiency figure is typically marginally lower as it is based on a more European cloudy climate where as the other figure is based on a sunnier Californian climate.

Thanks, I was wondering why. Can I ask, I've noticed that the efficiency curves rise rapidly, but are pretty low at low levels. Is that the (main) reason for the different ratings, as European inverters may sit in that poor spot more often? It would also explain why undersized inverters seem to do very well in the UK.

Mart.

gefnew

Hi PE
having had a quick look at the manual there is quite a lot you can check with a good electrician to determine where you are having your problems. Have your installer go through all the trouble shooting section to really identify where the problems stem from, before wasting money on inverter to find a bad connector within one of the strings.
link to manual files.sma.de/dl/16234/SB33-38-11-IA-en-62.pdf
Regards
gefnew

gazapc

Martyn1981 wrote: »

I've noticed that the efficiency curves rise rapidly, but are pretty low at low levels. Is that the (main) reason for the different ratings, as European inverters may sit in that poor spot more often? It would also explain why undersized inverters seem to do very well in the UK.

Mart.

First point, exactly, yes.

Rubidium

PotentialEnergy wrote: »

I'm not an electrician/electronics specialist. The firm sent a 3rd party electrician who deemed all the ins and outs were correct so I'm not touching things as it would be asking to invalidate things.

PotentialEnergy wrote: »

The system has a dual input DC Isolation Box(labelled IP66/IP67) with just one a single on/off so as the problem of halved energy existed before the electrician came, it presumably wouldn't be this unit.

But a few points and a question :

The SB3800 Single MPPT has 3 strings and the array is configured in 2*7 so 2 of the three strings were used to avoid overloading an individual string i.e. 7*285V is within range whereas 14*285V would exceed.

If just one string has gone defective couldn't the third string be used? After all, I’m still getting 50% generation which suggests one of the 2 used strings is fine and presumably the MPPT aspect is still functioning? A 3 string device can surely provide resilience in the event of just one string going defective.

If the third string doesn't work it rather suggests some open circuit issue exists on one of the arrays and in that case the SMA inverter is actually OK

Thanks for any more guidance/views. :idea:

Multi pole DC isolation switches are often used so that each of the input string arrays are isolated simultaneously when the switch is operated rather than a switch for each input string. A multi pole switch wins on cost and convenience when installing but a separate isolator for each string array makes testing easier without the need of a screwdriver/meter etc. and could be done by the end user.

Did you see exactly what this "3rd party electrician" did? Did he actually check the individual string array volts inside the DC isolation switch? - very easy with the cover removed and the switch in the off position, or simply do a basic in out check by reading the inverter display panel?

Your inverter does not have three strings, it has input connections to cater for up to three strings of panels or other DC generating devices. As I understand it, these inputs are simply connected in parallel in the inverter, although there may be a separate fuse/diode protecting each of the inputs. The panels are split into string arrays to achieve an acceptable input voltage to suit the particular inverter and the multiple input terminals are for connection convenience and load sharing the input current between the connectors.

If he simply did a quick check of volts in and volts out without checking the individual string array voltages after first isolating them, then one of the strings may not be providing any input to the inverter, resulting in half the normal input current and the reported drop in the generated mains output for July 16.

It could simply be an open circuit/high resistance connection anywhere on one string or an isolation switch problem, I have read about poor quality Chinese copy DC isolation switches that have caused problems and also in one of the SMA manuals it instructs the user to:

"Once a year, turn the rotary switch of the DC-Disconnect from the On position to the Off position 10 times in a row. This cleans the contacts of the rotary switch and extends the service life of the DC Disconnect"

I'm not convinced from what I have read in this thread that a new inverter is required yet. An independent competent tech who understands solar installations would be much better than this "3rd party guy" who may not have carried out a thorough enough investigation or who may actually stand to gain by simply confirming what you are expecting to hear that you need a new inverter and then getting the job of fitting it for you.

The logical explanation for approx half generation is that there is a failure somewhere on one string array, not that the inverter has failed. The LED's and display panel will give sufficient info to those who those knowledgeable enough i.e. a real engineer (not your average electrician) to understand what the various parameters displayed mean, so more investigation required.

PotentialEnergy

Thankyou for the very informative addition to the thread explaining the slight misnomer calling inverters string devices when it is more string input devices. That is something no techie I've liaised with has corrected me on.
I contacted three solar firms and only one made contact. The gentleman was adamant like you (and my gut feel has come to feel too) that it is probably some input or solar panel array issue as opposed to needing a replacement inverter. He referred me to a local Electrical firm who are 9.8/10 on Checkatrade and they're coming Thu.
I certainly don't want to replace the inverter. That isn't what I want to hear is necessary for sure. And with technical steers from this board I have become ever more convinced that it is the case of a fault elsewhere, not the inverter itself as a whole needing replacing. If the Electrician the Installer employed did an incomplete job(20mins max was spent there) the installer will come to know about it. As will the Which? board that has the installer recommended by well over a dozen people. I'd have trusted him but not for the moment. I could be proved wrong of course

I'll let people know what transpires for sure but if anyone reading the thread has more technical advice/input please add to it. Especially knowledge of a SMA Sunny Boy 3800 or others behaving this way due to an internal fault.

Rubidium

PotentialEnergy wrote: »

I'll let people know what transpires for sure...................

Why no update one month on?

PotentialEnergy

I had to have second thoughts on letting the third party do much as it invalidates the MCS cover unless they are an MCS approved firm. The MCS approved firm I had made contact with went away til 5th Sep.

At present, a replacement Sunny Boy 3800 has been installed and the fault still exists.
My installer took a fortnight off before sending his electrician subcontractor. A few days later with wall to wall sunshine it was quite clear the replacement had the same defect or - what I suspect - is that there is a fault with a string. The electrician has other work on and so I don't know when he will come. It may be late this week or even the following! He apparently has the DC amp tester and the installer is saying they cost £690. Not that I believe him! He was saying in July that it was the first time an SMA Inverter had failed. Yet, by the time the inverter was being replaced on 8th Sep, he said there'd been a spate of them failing cos Southern Electric changed some parameters!

So, I'm no further forward hence the general lack of an update.

I feel utterly disgusted with the original installer but have to bide my time and thoughts in case it is actually a general fault with legacy SMA inverters. If it isn't he'll be in a pickle cos I'll ask him to re-install my original and return the replacement. He can sort out the mess with SMA in that eventuality. Whatever the outcome he'll need to pay me a hefty sum not to take him through the RECC complaint process. To conclude on 11th July that cos the voltages were apparently OK, that meant the strings were OK and it was an inverter that had gone faulty is poor and surely incompetent. Now, maybe his subco electrician was instructed to check voltages which he did or made that silly conclusion. Maybe the subco electrician lied about the voltage levels. Whichever, the installer is responsible.

So, does anyone know if Southern Electric did change parameters or is that as I suspect another yarn to try and point the finger of blame elsewhere?

Rubidium

PotentialEnergy wrote: »

So, I'm no further forward hence the general lack of an update.

Thanks.

I can understand why you "feel utterly disgusted with the original installer" as they and their subcontractors seem to be completely incompetent cowboys, looking to make some money out of your situation.

The "Southern Electric changed some parameters" is pure bovine excreta as you rightly suspect.

I really hope that you have not paid them a penny for their pathetic incorrect diagnosis, replacing a working inverter with another working inverter.

Presumably they are in some trade body that you can get involved as obviously you are now in an awkward situation and they are simply extracting the urine!

PotentialEnergy

Thanks for the sympathy. So far, the only money I've paid was to SMA for a retrospective warranty extension that I didn't need. But, it was a third of the price of a new inverter! But, time passed getting it out of SMA of course during which I lost FiT payments. I see my originally installer as liable for all lost FiT payments since 11th July. The RECC I mentioned is Renewable Energy Consumer Code. He advertises with RECC amongst a set of logos. The Micro Certification Scheme is another body. The annoying thing is that they don't allow people to claim for lost time, distress and inconvenience. Therefore, I may go to the Small Claims Court instead.
https://www.recc.org.uk/scheme/consumer-code