Non Con on Annual Assessemnt - Minimum Irradiance Levels on String Tests???

[Gavin A]

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.

 

[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]

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

 

[matt25]

Have you been picked up on this aswell then?

 

[JD6400]

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]

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%.

 

[moggy1968]

Mizanci, you trying to get your number of posts up for some reason?

 

[alberthot]

Go with someone else.....

 

[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.