Discuss Non Con on Annual Assessemnt - Minimum Irradiance Levels on String Tests??? in the Solar PV Forum area at ElectriciansForums.net

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matt25

Hi, on our annual pv assesement we had a NC due to the irradiance level when testing the strings being recorded at 58 W/m2, so reasonably dull/overcast i guess but not exactly dark. I never knew that the minimum level has to be 200w/m2, does anyone know where this is documented please?? Our assessor couldnt point out where it was but assured us he was correct as he does this day in day out! he went on to state that the min levels were once set at 300w/m2! We now have to re visit site and re test, easy enough & no big deal but harder to predict a sunny day with the client at home! I wonder if this min level would this also apply to testing each panel as well?? This was with Elecsa, many thanks in advance if anyone can advise......
 

SolarCity

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I've heard something like this before - not sure where it is mentioned.

I know that a large portion of our tests have been carried out on levels less than 200w/m2. I would be very unhappy indeed if I am expected to return to these sites.
 
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matt25

The job we visited was installed in december last year, when i looked back at other jobs from nov & dec there were none above 200w/m2! It is so frustrating to see that MCS/Elecsa seem intent on closing down the trade rather than promoting growth, nothing gets easier, just more job related costs or unpracticle standards to meets. Rant over!
 

Gavin A

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Hi, on our annual pv assesement we had a NC due to the irradiance level when testing the strings being recorded at 58 W/m2, so reasonably dull/overcast i guess but not exactly dark. I never knew that the minimum level has to be 200w/m2, does anyone know where this is documented please?? Our assessor couldnt point out where it was but assured us he was correct as he does this day in day out! he went on to state that the min levels were once set at 300w/m2! We now have to re visit site and re test, easy enough & no big deal but harder to predict a sunny day with the client at home! I wonder if this min level would this also apply to testing each panel as well?? This was with Elecsa, many thanks in advance if anyone can advise......
absolute rubbish.

I'd email them and ask them to specifically point out exactly where this requirement is, then to pass you without the revisit, and retrain their assessors when they can't. As long as it's light enough to fire up the inverter, and to be able to assess the string voltage and ampage as being correct then there's no issue.
 

SolarCity

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I agreed with Gavin - But I did hear this somewhere before (perhaps on this forum?) so I am a little concerned about it.

If the assessor has always insisted on this (rightly or wrongly) then he must have picked up on almost every firm he has visited.
 
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matt25

Whilst with the assesor i checked on our previous assessment projects but they were above 200! he said thats why it wasnt flagged as an nc at the time, as gavin suggested i tempted to email for clarity but thought id ask here first, glad im not the only one who wasnt aware! thanks for your comments
 

Gavin A

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it's not about not being aware, it's about someone applying a regulation that doesn't exist.

I've just searched the DTI guide versions 2 & 3, and MIS3002 for '200' and there is definitely no mention of a 200W/m2 limit in either document, so they're making it up, and it can not be detailed as a non-conformity.
 
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matt25

thank you for checking Gavin, ive got our initial solar thermal assessment with the same assessor in the very near future, dont want to ruffle his feathers too much!
 

JulianC

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My assessment is coming up in October. If they play silly buggers like this, they can shove their non-conformities where the irradiance level never registers.

Seem to be hearing fairly frequently about assessors spouting utter nonsense on reassessments. Not encouraging.
 

Gavin A

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I had an elecsa rep on earlier trying to get me to switch to them..... I've just sent them an email about this to explain that I'll not be joining an organisation that has assessors issuing bogus non-conformities like this.
 
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Noshocks

Even in the south west with our Ibiza type climate..NOT, we regularly get below 200wm2 even in mid day, max i have recorded is 900 BTW, I have heard of DNO's bouncing back test forms as they have worked out the output from array against the w/m2 and concluded that readings were incorrect/made up, however no one has mentioned a minimum level required during testing.
 
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matt25

A bit of feedback...... I have spoken to the technical manager for MCS from elecsa this morning and it was explained to me why a minimum value was asked for. Basically we measured and recorded the results of the pv array test report at 30 W/m[SUP]2[/SUP] (not 58 as originally posted, wrong job!) and my Isc was 0.37A, it was explained that after multiplied up to give me my calculated output for 1000 W/m[SUP]2[/SUP] it would work out to be 12.3A. As it happens the modules used were rated at 8.63A so the values didn’t match up. They further explained that on many irradiance meters the actual sensor that takes the measurement is very small, the tester then multiplies the irradiance it receives in that small cell to match 1m[SUP]2[/SUP]. When the irradiance is low this can apparaently lead to results that aren’t always accurate, that’s why they had asked for a reading at above 200W/m[SUP]2[/SUP] where the irradiance is more stable.

Hope this helps, Im going to close out ther NC and move on, as usual many thanks to all that posted.

 

PvNewbie

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This has probably come about due to the fact that if irradiance levels are low, then it's difficult to ascertain the output from the panels 'accurately' and someone's made some 'rule' up about it. There's no 'rules' about this as far as I know and I can't remember for sure but think most of the installs during the December 'rush' had irradiance levels well below the 200 mark.

Perhaps they will next say we must not install in November - February when it's cloudy!!!

I think your regulatory body need regulating! I would have thought OFGEM would be regulating them, I wouldn't be surprised if next year they won't spout on about it.

Was it an actual NC, or just 'advice'? My NIC inspector gave me loads of helpful hints and tips, with no NC's so I felt pretty good after my inspection because he helped me make my organisation better, even though I was actually doing nothing 'wrong'.
 
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matt25

It was an NC (1 of 6) but hey im just gonna put it right and move on, I'll live, learn and definitly remember it for next year!
 

Gavin A

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I've just had a really interesting chat about this that's led on to all sorts of other relevant topics.

Suffice to say, that there definitely isn't a 200W/m2 limit specified anywhere, and Elecsa think this probably got a bit lost in translation somewhere, although it's true that the instruments and calculations will all be more accurate at those sort of levels.

They did point to BS62446 guidance for inspection and testing of solar PV systems, which apparently contains a reference to the measurement of the irradiance levels being taken at the same time as the DC test readings, and being to within a 5% tolerance. If we all worked to that though, unless you've got one of the all in one test units, it'd make it virtually impossible to actually test the circuits from the internal DC isolator - unless you've got a second person taking the light levels at the exact same time.

Also as the accuracy of the light meters is relatively low at low light levels, and no record is kept of the actual temperature of the cells, it's just not possible to calculate the figures backwards as accurately as they've tried to do here... a point that was taken on board and both agreed with and disagreed with, so I'm not sure what the final outcome was there, other than that rigid adherence to guidance that assumes accuracy where no accuracy should ever be assumed isn't particularly sensible, and that the point of the tests is mainly to check if the figures are in the right ball park for the correct number of panels being connected, and ideally all the strings within the panels being operational.... though I personally can't see how this can be done without any reference to panel temperature.
 
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matt25

LOL "rigid adherence to guidance that assumes accuracy where no accuracy should ever be assumed isn't particularly sensible"

I think its worthwhile me stating that elecsa have generally been first class with us, I couldnt knock them for any support we have ever asked for and wouldnt hesitate in recommending them to another installer.
 

JD6400

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Matt25 , i will take a bit of a punt here and guess that your inspector was a chap called Steve and was Scottish !?
 

JD6400

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This was when we first registered with elecsa nearly 2 years ago .
We were told to make sure that there was a reasonable level of irradiance when taking a reading but when we pushed to find the minimum amount he would not tell us !
He was generally unhelpful and arrogant for most of the day , we only spent around 6 minutes on site looking at the installation ( well more like just if the stickers were the right way around !) and he annoyed my client so much she wanted to put a official complaint in about him !!!!
 

moggy1968

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Gavins comments above fit very much with my view of this. There is no requirement for the temperature of the panels to be measured and without taking this into account the figures are really just to look at wether you are in the right ballpark. Thats not to say they should introduce temperatures as part of the testing, just that the figures should be taken for what they are.

There is no logical need for figures accurate to within 5%.
 
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PeteC

from 62446:
...5.4.5.2 PV string- short circuit test
...test is to verify that there are no major faults within the PV array wiring
~ low irradiance testing cannot verify this as Elecsa explain
...these tests are not to be taken as a measure of module/array performance.
~ results will not be accurate enough for performance testing without taking other things into account ie cell temp./string cable resistance.
...For non-stable irradiance conditions, the following methods can be adopted:
* testing can be delayed
* tests can be done using multiple meters with one meter on a reference string
* an irradiance meter reading may be used to adjust the current readings
~there is no mention of min. irradiance levels but below 200W it is less likely to see current proportional to irradiance (as comments show) and City and Guilds 2399 have included this "200W" threshold level in their corricullum (from what I remember) which is far more relevent when fault finding.
...62446 also has PV string operational tests (5.4.5.3) conducted under normal operation (mpp) conditions, although no reporting of results is included in the model test form.
I also agree that temp. readings are important to performance testing, but here again more so if you are fault finding and need more accurate analysis.
C&G include cell temp.recording and "expected" values for Isc & Voc to be calculated and all shown on their test form, which goes beyond 62446 requirements: although they are covering faultfinding in the course.
~the 5% diversity of string outputs is to verify the design requirements have been met which is more about damage limitation to modules and inverters and was far more relevent when module outputs were more diverse within a batch; on multiple string systems, less so now, modules were moved arround the arrays to different strings to meet the 5% tolerance during commissioning.
 
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