9 Glossary SMA Solar Technology AG
86 SDesign-BA-BEN120432 User Manual
Maximum PV voltage
The maximum PV voltage occurs if the PV cells are very cold and the PV array is in no-load operation.
A common design point for maximum PV voltage is therefore the open-circuit voltage at a cell
temperature of − 10°C.
Maximum short-circuit current
It can make sense in certain situations to short-circuit the PV array to protect the PV modules or the
inverter. SMA inverters with Optiprotect offer this option. However, the PV array can only be short-
circuited if the short-circuit current resulting from the short-circuit does not exceed a certain maximum
value. The PV plant must therefore be designed in such a manner that the short-circuit current of the
connected PV array does not exceed the maximum short-circuit current of the inverter inputs.
Minimum DC voltage
The minimum DC voltage must exceed a minimum value in order for the inverter to feed into the power
distribution grid. Depending on the inverter's working principle, the minimum DC voltage is either
preset or varies with the current line voltage. When designing a PV plant, the minimum DC voltage for
operation at high PV cell temperatures and for the time at which the inverters start feeding in the
morning must be observed.
Minimum PV voltage
When operating a PV plant, the minimum PV voltage only occurs if the cell temperature of the
PV modules is high and the PV modules are operated at their maximum power point (MPP). Therefore,
the MPP voltage at a cell temperature of +70°C is a common design point for minimum PV voltage.
MPP tracker
Regulation of the power drawn so that a PV array is operated for as long as possible at the MPP. This
working point varies with the solar irradiation and the temperature conditions of the modules. MPP
tracking optimises the extraction of electrical power and is a feature of inverters and charge
controllers.
Multi-string inverter
An inverter which, to a great extent, combines the advantages of several string inverters (separate
MPP tracking of individual strings) and a central inverter (low output-specific costs).
Nominal power ratio
The nominal power ratio indicates how high the inverter's maximum DC power is compared to the
PV array's peak power. In Central Europe, for example, the inverters in most PV plants are slightly
undersized to make the nominal power ratio less than 100%.
