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Are these the same? VOC Temperature Coefficient C° and Temperature coefficient of PMAX

WYtreasure

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Are these two different ways of saying the the same thing?

VOC Temperature Coefficient C° and Temperature coefficient of PMAX

I am trying to figure out which numbers to plug into the MidNite Solar Classic sizing tool.

Thanks
 
Some panels specify all three:

Voltage vs Temperature
Current vs Temperature
Power vs Temperature

as a percentage per unit degree, with a specified value at a specified reference temperature

Voc often goes up with colder temperature. So if you’re checking for max safe volts to charger, perhaps use historic all time low temperature for where the system will be used and use the resultant re-rated Voc for charger selection.

Good luck!
 
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Are these two different ways of saying the the same thing?

VOC Temperature Coefficient C° and Temperature coefficient of PMAX

I am trying to figure out which numbers to plug into the MidNite Solar Classic sizing tool.

Thanks
these are distinct concepts to me

VOC temp coefficient is volts vs degrees while
PMAX temp coefficient is watts vs degrees

some hardware can handle the watts but not the volts, so to speak
 
PV MPPT voltage is the dominate parameter (other than sun illumination level) that changes versus temp. Silicon diode conduction voltage has about -0.35% per degree C temp coefficient so Vmp will drop as temp of panel rises due to sun heating.

Vmp rises as weather gets cold. For SCC there is a maximum input voltage limit for their electronics so you have to be careful of cold temps pushing panel voltage above this limit. Cold mornings is most vunerable time for high Voc as panels are cold and have yet to be warmed up from sun heating. Many MPPT controllers will check Voc maximum voltage before turning on as a self protection scheme.

PV current has a minor temp coefficient, about +0.04% per degree C.

Poly-crystaline panels can have some variance on mono-crystaline cells so their Vmp temp coefficient may be different than -0.35% per degree C. Usually the farther poly panel's Vmp temp coefficient is from -0.35% degs C, the more 'wood chip' the surface appearence of the poly panel and the worse the watts per PV area performance.

Since Pout at MPPT is Vmp x Imp, and Imp current temp coefficient is minor, Pout temp coefficient will be close to Vmp temp coefficient.
 
Okay

Appreciate the replies. I will be attempting to process the information for a while.

I am trying to avoid over voltage at extreme cold temps.
These are the numbers I will use: -45.0 degrees F (-42.8 degrees C)
 
Okay

Appreciate the replies. I will be attempting to process the information for a while.

I am trying to avoid over voltage at extreme cold temps.
These are the numbers I will use: -45.0 degrees F (-42.8 degrees C)
So take your Voc temperature coefficient and multiply by 67.8 (25C - -42.8C) to get your adjustment %. Add that % to 100% and multiply the result by Voc to get your worst-case open circuit voltage at -45F.
 
My brain is working in low gear.
I just need to be sure which numbers go where?

On the left MidNite solar tool, On the right numbers for a solar panel.
MN REC.JPG
 
yes

except I thought it got colder than -22°F
Thank you my good man. (y)

Yes we do, -40 f will be my numbers. The only numbers I changed on the sizing tool were the temp Coefficient nos.

Now I can plug the proper numbers into the tool and find out if I want the REC panels recommended by Northern AZ Wind & Sun, REC365NP2.
 
Can I get a Yes on this?

I am only looking at Temperature Coefficient numbers.
View attachment 75875
If Voc is 37.6V @ 25C and the coldest ambient temps you are planning for are -45F or -42.8C, then you will be as much as 67.8C below operating conditions of 25C meaning your Voc will increase by 67.8 x 0.26% = 17.62%.

Voc_max = 117.62% x 37.6V = 44.226V.

But -45F is awfully cold, are you sure you will have your MPPT controller switched on if / when temps drop to that extreme?
 
If Voc is 37.6V @ 25C and the coldest ambient temps you are planning for are -45F or -42.8C, then you will be as much as 67.8C below operating conditions of 25C meaning your Voc will increase by 67.8 x 0.26% = 17.62%.

Voc_max = 117.62% x 37.6V = 44.226V.

But -45F is awfully cold, are you sure you will have your MPPT controller switched on if / when temps drop to that extreme?
Great question. The thought never crossed my mind to simply flip a switch and not worry about it.

I can assure you I will shut any and all equipment at any time such issues will be forecast.
Excellent food for thought.
 
Great question. The thought never crossed my mind to simply flip a switch and not worry about it.

I can assure you I will shut any and all equipment at any time such issues will be forecast.
Excellent food for thought.
Yeah, so a long as you are certain you will remember to disconnect the MPPT from the string by opening a breaker anytime temps are forecasted to drop below whatever threshold you decide to use, that’s an Avenue that gives you lot’s of headroom if needed.

For example, if your MPPT charger has an absolute maximum voltage rating of 40V, that means you can handle a maximum of 40V / 37.6V = 106.4% of Voc.

Since your temperature coefficient for Voc is -0.26% / degC, you can handle a maximum of 6.4% / 0.26% = 24.62 degC below 25C or 0.38 deg C before needing to shut off.

0.38C = 32.7F so unless you live in Florida, you probably need an SCC that is rated for at least 50V.
 
Great question. The thought never crossed my mind to simply flip a switch and not worry about it.

I can assure you I will shut any and all equipment at any time such issues will be forecast.
Excellent food for thought.

What happens the ONE time you forget or aren't able to?

If you're going with a Midnite controller, they have a degree of over-voltage protection, so you won't have to worry about it as long as you're over the protected amount.

IMHO, when you design a system to rely on human intervention when other solutions are readily available, you're designing a failure point into the system.
 
I was misunderstood. I have no intention to create a "Manual operations needed" system.

If there's a massive thunderstorm, or severe sub-zero temps with sunlight, or a neighbor working near my panels with a backhoe; I will shut it all down for safety reasons.

The MidNight controller seems to build in some nice degrees of protection, but why should I knowingly allow those limits to be approached.
The Combiner box will be fitted with 150vdc breakers and surge protection, so I am probably beating a dead horse anyway.

Input and questions are greatly appreciated. I'm still in the realm of knowing enough to be dangerous.
 
My brain is working in low gear.
I just need to be sure which numbers go where?

On the left MidNite solar tool, On the right numbers for a solar panel.
View attachment 75872
You clipped this picture right in the middle of the ‘Number of Modules in Series’ field, but it looks like a ‘2’.

If you are using no more than 2 or even 3 of those panels with equipment rated for 150V, you should have nothing to worry about (with or without worrying about shutting anything down).

So yes, unless you’re tying to push your string to 4 panels in series or you are looking at equipment rated for less than 120V rather than 150V, sounds like you are beating a dead horse…
 
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