Power Rating of PV Array

PZhou

Dear Support,

In the KU265 datasheet, I see three power rating numbers:
There is Pmax, under STC section; there are another two, Pmax and PTC, under NOCT section.

I think I understand the first and the last, but what about the Pmax in the NOCT section? How is this number obtained and should it be used in determining the number of panels or should PTC be used?

Not sure if I can attached the datasheet successfully, but here is link just in case http://www.kyocerasolar.com/assets/001/5740.pdf

Regards
Peter

Vic

Hi Peter,

Personally,  I would not use PTC (believe that this used to be referred to Pacific Test  Conditions).   Many PVs seem to not have this rating these days.

This was stolen from the following document:
http://www.gosolarcalifornia.ca.gov/equipment/pv_modules.php

   "   ...   PTC are 1,000 Watts per square meter solar irradiance, 20 degrees C air temperature, and wind speed of 1 meter per second at 10 meters above ground level. PV manufacturers use Standard Test Conditions, or STC, to rate their PV products. STC are 1,000 Watts per square meter solar irradiance, 25 degrees C cell temperature, air mass equal to 1.5, and ASTM G173-03 standard spectrum. The PTC rating, which is lower than the STC rating, is generally recognized as a more realistic measure of PV output because the test conditions better reflect "real-world" solar and climatic conditions, compared to the STC rating. All ratings in the list are DC (direct current) watts.   ...   "

NOCT Ratings are much more meaningful,  so would use those to estimate approximate PV module output.

Vic

vtmaps

When you are designing a system use the STC numbers in the formulas that calculate the minimum size of your cables and circuit breakers.  In the winter I occasionally achieve STC power levels for sustained periods of time.... my cables and breakers are sized for that.

When you are designing a system use the NOCT numbers in the formulas that determine the size of your battery (off grid) or the amount of energy that you will produce.

--vtMaps

PZhou

Hi Vic,

Thank you for your comment!

What is confusing is that in the datasheet, both Pmax and PTC are listed under the same NOCT condition, it makes me wonder which one should be used. Over/under design aside, I want to understand the story behind the Pmax number. Kyocera must have a reason to put both two numbers there. The data sheet is not much help, it would be a lot better with some graphs/explanation in there. 

Regards
Peter

PZhou

Hi VtMaps,

Thank you! and Yes, agree with you. The worst condition should be considered for each component of the entire system.

Regards
Peter

Vic

PZhou said:

Hi Vic,

Thank you for your comment!

What is confusing is that in the datasheet, both Pmax and PTC are listed under the same NOCT condition, it makes me wonder which one should be used. Over/under design aside, I want to understand the story behind the Pmax number. Kyocera must have a reason to put both two numbers there. The data sheet is not much help, it would be a lot better with some graphs/explanation in there. 

Regards
Peter

Hi Peter,

In my opinion,  the PTC rating is essentially useless.   In the OLD days,  IIRC,  a PTC Rating was required for any PV modules that were installed in California,  in order to qualify for the CA Grid-Tied PV system Rebates.

Believe that this rating gave way to NOCT.   Even NOCT can be a bit of an optimistic rating,  as it is specified at 20 degree C Ambient temperature,   and 1.5 MPS air motion.

Frequently,  many of those here,  multiply the STC Pmax rating by 0.77 for most systems,  and by perhaps 0.80  for systems at higher altitudes,  in order to approximate PV typical PV Production.

If you use a PV String Design Tool from the manufacturer of your Grid Tie (GT) inverter,  for from the manufacturer of any CCs that you plan to use,  you can find a nominally-ideal string configuration for your system and its environment,  and determine the approximate PV production  with varying conditions.

That Kyocera Data Sheet that  you linked to,  has at least one error,  IMO  --  the Parent part number for that PV module series seems to be missing one digit in the model number,  a leading number 2,  in front of the 60  (reads KU-60) in the graphics at the top.   Kyo seems to be one of the few companies that still shows PTC ratings,  and I do agree that the PTC rating does not belong in with the NOCT ratings,  without a note that PTC is rated under different Cell temperature than is NOCT.

I would forget about PTC,  it is a hold-over from times long-past.

FWIW,   Vic

PZhou

Thank you Vic for the thorough explanation!

Regards
Peter