[RE-wrenches] Temperature coefficient versus Power

[George McClellan]

Good Morning;

Excellent update Rebekah (someone is up early).  Module voltage stays pretty linear as irradiance varies and temp stays constant.  Currently the industry calls this linear, but as the whitepaper Rebekah posted shows, it is not truly linear.
[cid:image001.png at 01DA534A.1D15BC60]

George McClellan | Senior Technical Sales Manager | REC Americas LLC
330 James Way Ste 150 | Pismo Beach, CA 93449 | USA
Cell phone +1 805 704 3226 | Fax +1 805 357 6104
www.recgroup.com<http://www.recgroup.com/> | george.mcclellan at recgroup.com<mailto:shannon.kent at recgroup.com>



From: RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> On Behalf Of Rebekah Hren via RE-wrenches
Sent: Tuesday, January 30, 2024 6:26 AM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Cc: Rebekah Hren <rebekah.hren at gmail.com>
Subject: Re: [RE-wrenches] Temperature coefficient versus Power

Hi Jason,
That's an interesting question, as typically it is stated that temperature coefficients are linear, however the "linearity" is with respect to the temperature variable, not power (irradiance) I have always assumed that tkPmp is fairly linear with respect to power, but now that you mention it I don't have much basis for that assumption!

However, this article <https://www.sciencedirect.com/science/article/pii/S0038092X21004837> seems  helpful: https://www.sciencedirect.com/science/article/pii/S0038092X21004837
Scroll all the way down to section 4.3, and it appears that there are only very minor variations in tkPMP with low to high irradiance (power).

As that chart shows, tkVoc varies more significantly with irradiance, but I do think the industry realizes that and factors it in with the allowance in NEC 690.7 to calculate maximum voltage based on SAND 2004-3535, Photovoltaic Array Performance Model, which takes into account the effect that low irradiance has on voltage - you can see the lower tkVOC at lower irradiances.
Cheers,
Rebekah




Licensed Electrical Contractor
NABCEP Certified Solar PV Installation Professional™ 091209-85
Tel: 336.266.8800


On Tue, Jan 30, 2024 at 9:04 AM Jason Szumlanski via RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto:re-wrenches at lists.re-wrenches.org>> wrote:
I'm having a hard time finding concrete information on the relationship of temperature coefficient and power output. Solar panel temperature coefficients are determined at Pmax.

My question is, at lower irradiance levels, say where power output would be 50% of Pmax at 25C, would the temperature coefficient be greater, less, or the same?

Jason Szumlanski
Florida Solar Design Group
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