SMA SUNNY DESIGN 3 - Manual (Page 34)

7 Glossary SMA Solar Technology AG
34 SD3-SDW-BA-en-20 User Manual
MPP Tracker
Readjustment of the power drawn so that a PV array is operated for as long as possible at the maximum power point
(MPP). This operating point varies with the solar irradiation and the temperature conditions of the PV modules.
MPP tracking optimizes 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 power-specific costs).
Nominal Power Ratio
The nominal power ratio indicates how high the maximum DC power of the inverter is compared to the peak power of
the PV array. In Central Europe, for example, the inverters in most PV systems are slightly undersized so that the nominal
power ratio is less than 100%.
The nominal power ratio is represented by the following formula:
With Sunny Design, the recommended lower limit of the nominal power ratio is calculated specific to the system.
The lower limit mainly depends on the location, the type and the orientation of the PV arrays as well as their circuitry with
the inverters. For a given configuration of the PV array(s) with an inverter, an individual lower limit is calculated.
This corresponds to an energy usability factor of 99.8%. Thus, PV arrays with an orientation that is not optimal,
e.g. east/west or facade systems, can be designed with optimal inverter dimensioning. If the lower limit defined for the
location, e.g. 90% for Central Europe, is below the calculated limit, the defined lower limit is used.
Peak Power
The peak power of a PV module is the electrical power supplied by the PV module if operated under standard test
conditions (STC) at the maximum power point (MPP). Peak power is also often called nominal power.
Performance Ratio
The performance ratio (PR) is the ratio between the nominal yield and the target yield of the PV system. It thus shows the
proportion of the energy that is actually available for feed-in operation after deducting the energy losses (e.g. due to
thermal losses and line losses) and the self-consumption. The closer the PR value determined for a PV system approaches
100%, the more efficiently this PV system is operating.
Polystring
Polystring operation is the parallel operation of two PV arrays with differing orientation that are of the same PV module
type and have the same number of PV modules at a joint inverter input. This operating mode enables two PV arrays with
differing orientation to be connected to just one MPP tracker.
Project
PV systems are created and edited in the form of projects in Sunny Design. The PV arrays and inverters in the PV system
are created and edited as subprojects.
Formula for calculating the nominal power ratio
Nominal power ratio =
Maximum DC power of the inverter
Peak power of the PV array