BA_REFUSOL 008K-020K_V08.1_EN
Copyright REFU
sol
GmbH
17
If several PV connecting lines are available, the connections can be made as desired.
WARNING
When using the solar inverter without transformer, do not ground the
positive or negative pole of the PV generator!
3.6 Reverse Current through Defective Modules
Reverse currents are fault currents that only occur in PV systems comprising parallel strings. Given
short circuits of individual modules or cells in a module, or a double ground fault, the open circuit
voltage of the string in question can drop (e.g. due to defective modules or parts of modules) so far
that the intact parallel strings will drive a reverse current through the defective string. This may
result in strong heating and therefore to a destruction of the string.
What is more, the reverse current may cause secondary damage.
To prevent such damage to PV systems, appropriate precautionary measures should be taken.
There are the following two cases:
1. The PV system is designed such that the reverse current which is flowing in case of a
failure and consists of the sum of the short-circuit currents of all intact strings in the
worst case does not result in the destruction of the damaged string and therefore in sec-
ondary damage either. The decisive factor here is the current carrying capacity of the
system components (connectors, lines) and the reverse current carrying capacity of the
modules. The appropriate data can be found in the manufacturer's data sheet. In this
case, it is not necessary to take any further measures.
2. The PV system is designed such that the reverse current flowing in case of a failure ex-
ceeds the destruction limit. In this case, each string must be separately protected by a
string fuse connected in series with the other string fuses. In case of a failure, this iso-
lates the string from the intact strings so that destruction is prevented.
