In large PV installations (i.e. in the MWp range), the transformer is not part of the inverter, but is instead an external device directly connected to the grid.
The main losses associated with the transformer are:
- The iron losses (mostly due to hysteresis and eddy currents in the core) are proportional to the square of the core flux, i.e. to the square of the voltage. As the grid has a constant voltage, the iron loss is considered as a constant loss. A typical default value is 0.1% of the nominal power. It should be noted that iron loss remains active and constant during connection, and may represent a significant energy loss. Therefore, it may be economically advantageous to install a switch that can disconnect the transformer from the grid at night.
- The ohmic losses in either the primary and in the secondary windings (coils that draw energy in one side and deliver it in its transformed state back out the other side) can be approximately 0.6%.
Total transformer loss is typically around 1.5%.