Preconditions for the oversizing of the PV system power
Oversizing the PV system power compared to the inverter's nominal power can be beneficial under certain conditions. The following conditions must be taken into consideration:
The maximum permissible input voltage of the inverter must never be exceeded.
The maximum short-circuit current of the PV modules (ISCPV) must not be exceeded.
Power loss of the inverter in the form of heat generation.
Inverters and their constituent components are designed and rated for certain voltage levels. If these specifications are exceeded, it will almost certainly result in loss of warranty and in the inverter's immediate failure. Furthermore, it must be ensured that the specified voltage range for the maximum power point tracker (MPP tracking) is adhered to. When the DC input voltage is outside an MPP voltage range, the inverter is not able to maximize the performance of the system.
Adhering to this threshold is crucial for the maximum short-circuit current of the PV modules for the electrical safety of the inverter and warranty compliance. The maximum short-circuit current is indicated on the inverter type label as well as on the datasheet and in the technical data in the product manuals. In this context, the maximum input current (IDCmax) is often mistakenly used as a relevant limit for connecting the PV modules. The maximum input current refers to the maximum electric current that the inverter can capture, i.e. the maximum usable input current. Exceeding this value is possible with SMA inverters and usually only results in negligible yield losses. Information on the maximum usable input current can be found on the inverter's datasheet and in the technical data in the product manuals at www.SMA-Solar.com.
The power loss of the inverter must also be taken into account. Broadly speaking, the efficiency loss from an inverter is realised as heat generation. An inverter has a different efficiency at different output powers. Thus, at 100% AC output power, the heat generation is higher than at 60% or 80% AC output power. When oversizing a PV system, an inverter will be more often operated at or close to its rated AC output power. Thus, the higher heat generation from the inverter may create an issue for the installation site, especially if inverters are installed in a system room or similar where air flow and heat dissipation might be limited ( > Installation site and heat dissipation). You can find more information under the following links:
"Technical Information Efficiency and Derating"
"Technical Information Temperature Derating" at www.SMA-Solar.com.
Maximum permissible DC input power
The datasheets of the SMA inverters indicate the maximum DC input power for the inverter. Observing this limit is a condition for the warranty services by SMA. The maximum DC input power may be exceeded for some SMA inverters if the full load hours (determined from the energy fed in yearly and the nominal AC power of the inverter) to be expected at the system location remain within a defined threshold. When using our Sunny Design software for planning a system, you can determine the full load hours for our inverters depending on the system location.
Additional information is available under the following link: Manufacturer's Declaration "Nominal Power of the PV System" and at www.SMA-Solar.com.
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