Peter.W Posted February 2 Share Posted February 2 I wanted to get a little clarity on muVoc mV/°C vs %/°C. We have often done string sizing calculations by hand by using the %/C value on the data sheet but when using the same temperature values we receive a close but slightly different maximum Voc value. For example: STC 25°C with an absolute low of -14°C. VOC Coef = -.0026V/C string size of 18 Starting Voc of 49.8 (-14 - 25)(-.00265)(49.8)+49.8=54.95VocMax 54.95*18=989V a -14°C system with a Voc Coef would indicate a max voltage of 983.33 for a string of 18 with an VOC of 49.8 and a VOC Coef of -.265% for a 25°C STC system. The pan file indicate a muVoc of -150mV/°C. When I use the Pan defined MuVoc value It indicates the max Voc at 994V, if I use the one diode model we see a max Voc of 999V. This isn't a problem with this solution as both methods are in are inverter range, but we have run into being a large enough discrepancy. Essentially, PVsyst indicates we should lower our string size, but the datasheet calc indicates we are in an acceptable range. I have tried to read the Module parameters section of the help section and it indicated the one diode can no longer be edited because its an R shunt and R series calc. Values which I wouldn't know where to start with. Any advice on this subject would be greatly appreciated on why these values aren't inline and if its a problem to proceed with the one calculation over the other would be greatly appreciated. Pan defined MuVoc Pan File One Diode model Link to comment Share on other sites More sharing options...
André Mermoud Posted February 8 Share Posted February 8 The muVoc as result of the one-diode model is indeed not equal to the muVoc (beta parameter) of the datasheets. When establishing the one-diode model, it is indeed impossible to specify simulatneously the muPmpp and the muVoc temperature coefficient. By default, PVsyst uses the muVoc result of the one-diode model for the sizing voltage limit. However in the PV module definitions, you can specify the muVoc of the datasheets (page "Additional data => Secondary parameters", item "Specified mVoc). And for using this value during the sizing process, you have to choose this in the project's settings, page "Design conditions => muVoc values" Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now