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rgormley
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Joined: 22/02/2006
Location: Australia
Posts: 245

Posted: 02:44am 15 Mar 2012

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tell me if i have this correct...

panel: Sharp Nu185A1H

http://www.sharp.net.au/product-catalogue/products/NU185A1H/

VOc = 30.2volt (@25 Deg)
temp coefficient of Voc -0.104 V/DEG,c

SO....

if the VOc at 25 deg is 30.2v
then at 0deg the voc would be 25x.104 =2.6 volts increase
30.2v + 2.6v
thus VOc at0 deg would be 32.8V (open cct)

(assuming 1kw/M2 irradance)<<---perfect conditions...)

all this so i can work out a cold sunniy morning max open cct voltage)

Cheers

Tinker

Guru

Joined: 07/11/2007
Location: Australia
Posts: 1904

Posted: 01:58pm 15 Mar 2012

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So... what is the reason for this precise knowledge of the open cct voltage?

Somehow a gut feeling tells me that you won't get 1Kw/sqm when its that cold in the morning.

Klaus

rgormley
Senior Member

Joined: 22/02/2006
Location: Australia
Posts: 245

Posted: 07:29pm 15 Mar 2012

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hi tinker, thanks for the reply, you are correct not ever reaching these max values.
just would like to know if my "theory" maths is correct...

AND I will be running close to my 500Vdc max input on my string and i want to add one more panel.

so am looking at possible worse case voltage spike.

early morning cold, edge effect, grid goes of etc etc then the inverter gets hit with a high voltage from cold panels.

panels will be (QTY X 16) at 25Deg-c (30.2Vdc x 11 = 483Vdc)

my inverter is max 500Vdc input.

I could go 2 strings but inverter only has one string input.

So i would have to parallel the panels and it`s a lot of work to get to the cabling. SO i`m doing it all in series. (one string) hence the higher voltage

(PS my area`s record low in 2.7 deg-c,)

Tinker

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Joined: 07/11/2007
Location: Australia
Posts: 1904

Posted: 01:40pm 16 Mar 2012

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Fair enough, that explains it perfectly now that I know that you are aiming for a rather high DC max voltage.
BTW, your record low temp suggests you live in Perth - correct

Klaus

rgormley
Senior Member

Joined: 22/02/2006
Location: Australia
Posts: 245

Posted: 08:14pm 16 Mar 2012

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Altona Meadows (Melbourne)

The Melbourne radar is about 2-3 k`s from where i live

from the weather zone web

***************************
lowest on record
2.7�C
26th 2005

*****************************

don't think i`l have an issue as these low temps are early in the morning and the sun prolly has not risen as yet. so not much light on the panels....

Georgen
Guru

Joined: 13/09/2011
Location: Australia
Posts: 462

Posted: 12:42am 19 Mar 2012

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Could probably have thermometer coupled with some shading device that could also keep an eye on strength of solar output.

Or another device to protect solar PV system should this rare event to occur.

George

VK4AYQ
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Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 01:04pm 19 Mar 2012

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Checked mine on a cold clear morning 15 C open circuit volts 36.2 open circuit no load ,by 10 am 28 C OCV 34.

it is a different brand of panels to yours.

Bob

Foolin Around

daveames
Newbie

Joined: 19/09/2009
Location: United States
Posts: 30

Posted: 09:49am 20 Mar 2012

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I'd be worried about all the over voltage flags stored to memory every time the temp goes below 15*C..I believe this will still happen with VERY little sun light.

Should we need any warranty work with the inverter in the future there may be some splannin' to do.

Dave

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