Open-circuit Voltage

DFarid

Hello Community,

I'm encountering an issue with calculating the theoretical open-circuit voltage of my PV system. The formula I'm using results in discrepancies of over 5% specifically for low irradiance conditions (below 200 W/m²), where the calculated voltage is consistently lower than the measured one. Interestingly, for higher irradiance levels, the results are accurate.

The formula in question is : Vtheo = m * Vostc * [1+Beta * (Tcell-25)] + Ncell * m * 8,62 * 10^-5 * (Tcell + 273) * ln(G/Gstc)

m : NO. of Modules

I've already checked the units and ensured that all parameters are correctly inputted.

Do you have any suggestions on how to address this problem? Are there additional considerations or factors I should take into account?

Thank you in advance for your assistance

BB.

Another equation to look at:

https://www.pveducation.org/pvcdrom/solar-cell-operation/open-circuit-voltage

I am no expert--But it sounds like your low Voc calculation may be over estimating the diode junction leakage current under specific temperature conditions (i.e., real cell does not have as much leakage current). Also need to (possibly) take into account the loading of your volt meter (which does consume a small amount of current--But in theory, meter "excessive" current would reduce Voc-low-light voltage). Obviously, the size of the cells and array vs meter input current matters too.

I guess my question is "why" worry about Voc-low light conditions... For the most part, any solar array will go from zero to full sun every day--And you are worried about Voc-array (for your PV Array loads) under all conditions.

Unless you are trying to use a solar cell as a "solar sensor" of some sort???? Modeling cells/arrays for school project?

-Bill