OND File - Main parameters clarification

[Mechiboue]

Hi Andre,

I as checking several data sheet with respect to .OND files, and I found some discrepancies in the way each manufacture understand the parameters.

My main question is regarding the differences between the operation voltage range and the MPPT voltage range.

In the case that the operation voltage of an inverter is between 240-950V, and the MPPT voltage range is between 540-800V (I have attached the derating curve)

* Minimum MPP Voltage: Is it 240 or 540?

* Min Voltage for Pnom: 540

* Maximum MPP Voltage: Is it 800 or 950?

My confusion is because in the definition "Maximum MPP voltage is the voltage window in which the inverter is able to search for the MPP" Generaly the inverter is able to search in all the range, so I think that the Minimun-maximun MPP Voltage range is between 240-950V.

Can you help me with this clarification?

Thanks a lot,

Best regards

[André Mermoud]

PVsyst doesn't treat this behavior in the present time. I have not seen much inverters with these characteristics up to now.

During the simulation, PVsyst clips the voltage at the limit value, and therefore displaces the operating point on the I/V curve, leading to losses with respect to the Pmpp array possibility.

So that the efficiency limiting is related to the PV module's properties rather than a special inverter behavior. The results should not be very different.

For the lower voltage, the "Minimum voltage for PNom" represents indeed an input current limit. The limit current is indeed Pnom / VMinPnom.

When the array MPP voltage is below this limit, the inverter works at this fixed input current on the P/V curve.

[Mechiboue]

Thanks Andre for the quick response.

Unfortunately all the string inverters that we work with have this type behavior.

I understood PVSysyt can model two zones: where you have full power (540-800 V constant), and where the inverter cannot deliver full nominal voltage when the input voltage is too low (this is the zone between 240-540).

For this particular case, we were thinking about model the parameters like stated below.

Minimum MPP Voltage 240 V

Min. Voltage for PNom 540 V

Nominal MPP Voltage N/A

Maximum MPP Voltage 800 V

Absolute max. PV Voltage 1000 V

We interpreted that doing this, we are estimating the lower voltage behavior and the maximum power mpp window (540-800 V) and we are not taking into consideration the higher voltage behavior (from 800-950V).

If we assume that 'Maximun MPP Voltage is 950V, we will be overestimating the production for higher voltages (800-950V).

Do you think our thought process is correct? Do you recommend to have a different approach in order to do the most accurate modelling?

Thanks a lot for your help,

Best regards

Mercedes