Can I define a system with highly undersized inverter ?

[André Mermoud]

In PVsyst, the criteria for the sizing of the inverter with respect to the array nominal power is to evaluate the foreseen yearly overload loss.

Losses up to 3% are considered acceptable (warning "The inverter is slightly undersized in orange).

Higher annual losses prevent performing the simulation (warning "The inverter is strongly undersized in red).

Array sizing limitation

For some special uses (for example output nominal power constraints for tariff, Grid power limitation, economical optimization, etc), you can modify this limitation.

In the version 5: in the main menu, please choose "Preferences" / "Edit hidden parameters" / topic "Detailed Simulation Verification Conditions".

Here you can increase the value "Limit Overload loss for design", which is fixed at 3% by default.

in the version 6, the definition of this limitation has been moved in the Project's definitions, (so that it is valid for the project, not for the full software). When you are in the Project's definition, please press the button "Project settings"

Be careful !!! When defining highly oversized arrays, the voltage displacement on the P/V curve of the array may overcome the VmppMax of the inverter, and in this case the system has to stop and the loss may become catastrophic ! With such systems you have to work at rather low voltage.

Inverter limitation

It is also possible that you get the error message: "The array maximum power is greater than the specified Inverter maximum power (or current)".

Some Inverter manufacturers specify a maximun Nominal Power of the array connected to their inverter, or a maximum current (ISC value of the array).

To my mind this is not really meaningful, as the operating power is controlled by the inverter input circuit, which will manage for not overcoming the limit values (power limitation by moving along the I/V curve). These values are not used during the simulation.

If this messages appears in blue, no problem, it is just an information.

If this message is in red, with the mention (contractual condition), it means that the manufacturer submits the warranty of his product to this condition (i.e. overcoming these values will cancel the warranty). Therefore PVsyst will prevent defining such a configuration.

Now this "warranty" information is specified in the inverter's specifications, by a checkbox "Required" for the "Maximum PV Power (or current)". If desired, you can uncheck this checkbox, and save the inverter (under another filename). In practice, this is under your own responsibility.