SI4548-US-10 Manual

14 Connecting External Sources SMA America, LLC
136 SI4548_6048-US-TB_en-13 Technical description
14.2.10 Operation Together with PV Inverters and
Wind Power Inverters
Energy of the PV inverter or wind power inverter not being consumed in the off-grid system, is fed-in
by the Sunny Island via the internal transfer relay into the utility grid in order to avoid an overload of
the transfer relay. For this reason, reverse power monitoring is used that, if required, disconnects the
connection to the utility grid if the reverse power limit is exceeded or if the relay is subjected to too
high load.
If the battery is fully charged, the frequency limits the power output of the AC feeding-in generators
(PV inverter) in the stand-alone grid. If the grid is now reconnected, the frequency would be lowered,
if required, as the Sunny Island is synchronized with the grid. The AC feed-in generators would then
feed additional energy into the system and possibly overload the batteries. In order to prevent this, in
this case the stand-alone grid frequency is temporarily increased, in line with the synchronization, until
the AC feed-in generators are disconnected from the stand-alone grid as a result of the grid limits
being exceeded.
Overload of the Sunny Island through high currents. Destruction of the Sunny Island.
If the current via the relay exceeds the maximum permissible current, the Sunny Island disconnects
from the grid (relay protection).
• The quantity of PV power installed in the stand-alone grid must never exceed the maximum
quantity allowed by the AC input (see Section 22 "Technical Data", page 225).
• The maximum AC power of the connected PV inverters and the connected wind power
inverters may not exceed 7 kW in grid-connected plants.
• Observe the following:
P
AC max
of the wind power inverter = P
AC nom
of the Sunny Island