How Temp. coefficient value affect modules string sizing

Assumption Temp ∝ 1/Voltage [ Temp ↑ Voltage↓] or [Temp↓ Voltage ↑]

Above assumption is always followed mostly but that is wrong. It depends upon the temp. of location.

Why we need to consider record low temperature for the project location

Example:?Let consider a module with 2 different locations then see how much value has changed.

Module Panasonic Ever Bolt EVPV 370W

Voc: ?44.1V ???????Isc:?10.55A????????Voc Coef: -0.24 %/?C (all value referred from data sheet)

Now we can calculate the maximum number of modules that we can have in our system by doing a very similar type of calculation.

Vmax = Voc X [1+ (TLow - TStc) x (Voc Coef in %)]

Where Voc: ?44.1V(from data sheet)

??????????????Isc:?10.55A (from data sheet)

??????????????Tlow: ?Form ASHARE Meteo

??????????????TStc 25 ?C

Example location 1. Fremont, CA 94538

From ASHARE Min: ?0.6?????????????????Max: 35.4

Then Vmax= 44.1 X [1+(0.6-25) X (-0.24%)

??????????????????=44.1 X [1+(-24.4) X -.0024]

??????????????= 44.1 X [1+ 0.05856]

??????????????= 44.1 X 1.058

??????????????= 46.68 V

Example location 2. Chennai, India

From ASHARE Min:?18.1????????????????Max:?41.4

Then Vmax= 44.1 X [1+(18.1-25) X (-0.24%)

??????????????????=44.1 X [1+(-6.9) X -.0024]

??????????????= 44.1 X [1+ 0.01656]

??????????????= 44.1 X 1.016

??????????????= 44.80 V

Conclusion- we have now seen that the corrected VOC value has changed in above two locations by 2 volts per module. If we are working on 1500VDC system and around 28 modules per string than there will be a total of 56 volts of delta. Hence to calculate accurate max string length we must follow the temp. coefficient and calculate the results based on site’s record low temperature.