Environmental effect (EE)

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five.five-six

Senior Member
Location
california
So, my understanding is that because if the EE, on residential systems, the highest VOC that can be calculated is 600VDC but has to be debated 20% due to EE

Do I have that right?
 
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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
five.five-six said:
So, my understanding is that because if the EE, on residential systems, the highest VOC that can be calculated is 600VDC but has to be debated 20% due to EE

Do I have that right?
Click to expand...

I'm not sure what you mean, but what you have to do is to use the voltage temperature coefficient specific to the modules you are using to adjust your module Voc to the coldest temperature it will be exposed to and multiply the corrected Voc by the number of modules in your string(s). For one and two family residences and for a lot of string inverters, that number must be less than 600V.
 
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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
five.five-six said:
so, the 290 watt modules I’m working with right now have a VOC of 38.8 times 1.2 = 46.56V

take 600V/46.56 and 12 modules is the most I can get on a string and stay under 600V?
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Yes, with the caveat that the 1.2 is only an approximation. Those numbers work out to nearly 12.9; it would certainly be worth doing the real calculation to see if it comes out over 13.0.

Go to http://www.solarabcs.org/about/publications/reports/expedited-permit/map/index.html, plug in the location of your installation, and you'll get the low temperature (Extreme Min). Use the Voltage Temperature Coefficient on your module data sheet to calculate your cold adjusted Voc.
 
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five.five-six

Senior Member
Location
california
ggunn said:
Yes, with the caveat that the 1.2 is only an approximation. Those numbers work out to nearly 12.9; it would certainly be worth doing the real calculation to see if it comes out over 13.0.

Go to http://www.solarabcs.org/about/publications/reports/expedited-permit/map/index.html, plug in the location of your installation, and you'll get the low temperature (Extreme Min). Use the Voltage Temperature Coefficient on your module data sheet to calculate your cold adjusted Voc.
Click to expand...


I’m going to need help on that. The temp extreme min is -1C the temp coefficient VOC is 0.30 and the VOC is 38.8.

edit:

I found this calculator that says I’m GTG
 
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G

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
five.five-six said:
I’m going to need help on that. The temp extreme min is -1C the temp coefficient VOC is 0.30 and the VOC is 38.8.

edit:

I found this calculator that says I’m GTG
Click to expand...

-1 deg C is 26 deg C below STC (25 deg C).

Assuming by 0.3 you mean -0.30%/deg C, the correction is (-26 deg C)(-0.30%/deg C) = 7.8%, a multiplier of 1.078.

(1.078)(38.8V) = 41.8V

600V/41.8V = 14.35. You are good for up to 14 modules/string.
 
F

five.five-six

Senior Member
Location
california
ggunn said:
-1 deg C is 26 deg C below STC.

Assuming by 0.3 you mean -0.30%/deg C, the correction is (-26 deg C)(-0.30%/deg C) = 7.8%, a multiplier of 1.078.

(1.078)(38.8V) = 41.8V

600V/41.8V = 14.35. You are good for up to 14 modules/string.
Click to expand...

thank you,

finding a calculator is good but understanding the calculations is better :)
 
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