Grid inverters, Contractual Array

The following parameters are often specified by inverter's manufacturers (see Grid inverter, Main parameters):

• Nominal PV power of the array. It may be understood as the recommended nominal STC power of the PV array.
• Maximum PV power is the recommended absolute maximal STC power of the PV array.
• Maximum PV current is the absolute maximal current admissible at the input of the inverter, usually the ISC current of the PV array at STC.

These values are sometimes presented as limit requirements, which may act on the warranty.

Nevertheless, we consider that these requirements do not have a real physical meaning, as they depend mainly on the plane orientation (please see the sizing tool). For example, in a facade system, you can use a Pnom ratio (Array / Inverter) of a factor of 2.

If the inverter is correctly designed, these limits normally present no danger to the device when operating in overload. The inverter will simply adjust the power drawn from the PV array by displacing the operating point along the I/V curve, so there is no additional power dissipation and therefore no accelerated aging.

In most cases, the inverter provider will propose oversized inverters, arguing that any power peak would otherwise be lost. This is a weak argument, as short-duration peaks represent very little energy. The cost of the oversized inverter must be weighed against this minor loss.

If the inverter's provider sets these limits as contractual (i.e. acting on the warranty), you should check these checkboxes. In this case the sizing tool will consider these as absolute limits, give warnings in red and prevent the simulation.

Otherwise this may produce an info message when defining the sub-array (in blue), that you can ignore.