Maximum Voc voltage test

[Ahmad Elghobashy]

I have two questions

In the configuration limits options screen

the part for the parameters to calculate PV module working point for voltage test

in the maximum open circuit voltage test, the temperature that I insert

1) is it the ambient or cell temperature?

2) if it is the ambient temperature, should it be the absolute lower temperature during the year, or the lowest temperature during the sunshine hours, i.e. night temperature or morning temperature?

 

[developer_mh]

Hi Ahmad,

thanks for your question! This temperature refers to the cell temperature. In STC (Standard Test Conditions, for measuring the nominal power, voltage and current), you'll have 25°C for cell temperature at 1000 W/m². But when configuring a system, you also want to make sure that a certain voltage is never exceeded by your PV array, so you'll calculate with lower cell temperatures.

So you have to estimate the lowest ambient temperature at the given location (at daytime of course). For Europe, you normally just use -10°C at 1000 W/m² and you are on the safe side.

Does that answer your question? If not, do not hesitate to ask!

Cheers, Martin

[Ahmad Elghobashy]

how can I calculate the cell temprature? and what would be the recommendation for central west of Tunisia?

[developer_mh]

I really don't know what a recommended temperature for West Tunisia would be. In PV*SOL, I had a look at the climate data from Tozeur/Nafta, and the temperature looks like this:

Minimum ambient temperature seems to be around 4°C. The cell temperature usually is higher, due to the irradiance, so I think if you go with 0°C cell temperature, you should be safe, even for worst case scenarios. But perhaps there are local guidelines you could follow?

Kind regards,

Martin

 

[Ahmad Elghobashy]

but at the time where the temperature is low -during the day- the radiation is also low around 200-400 only

so can I calculate Voc at 6°C and 400 radiation? would that be correct?

[developer_mh]

Hi Ahmad,

In the end it is all about safety and warranty. It is right of course that an irradiance of 1000 W/m² is very improbable to occur when the temperature is 6°C, it is just that you want to make sure that these voltages are the absolute minimum that can occur. You can also just input higher tolerance values in PV*SOL if the standard values are too strict:

But I am not going to suggest any standard planning or system design values to you. In the end you will have to clarify these questions with the people you are working for, or ask the inverter manufacturer for recommended voltage limits.

Beste wishes,

Martin