Safety
SMA America, LLC
12
SB50US-80US-eng-IUS112633
Installation Guide
2 Safety
2.1 Appropriate Usage
The Sunny Boy is a PV inverter which converts the DC current of the PV array to AC current and feeds
it into the power distribution grid. The Sunny Boy is suitable for use with fuel cells, small wind power
plants and other DC current sources. The Sunny Boy takes the current from a DC source and converts
it into AC power for the power distribution grid. This power is then supplied to the local consumers
(C). Surplus energy is fed into the power distribution grid (E). Due to the power that is consumed by
the local devices, the amount of power required from the power distribution grid is reduced. An
energy surplus may even result in the energy meter (D) of your plant running backward. This power
may also be recorded as power credits by the electric utility company depending on the
interconnection agreement.
Principle of a PV Plant with a Sunny Boy
Anti-Islanding Protection
A stand-alone grid is a status. It occurs when the power distribution grid is switched off and the Sunny
Boy is in operation. For this to happen, the remaining load must be resonant at 60 Hz and exactly
match the power of the Sunny Boy. Although the appearance of these conditions is extremely unlikely,
the Sunny Boy has an active safety algorithm to protect against islanding. The effect of this is that, in
the event of the power distribution grid being switched off, the PV plant does not supply any power
to a symmetrical load that is resonant at 60 Hz. In addition, the Sunny Boy regularly feeds leading
and lagging reactive currents into the power distribution grid. This procedure is checked by the
certification body, in order to destabilize and switch off stand-alone grid status.
Item
Description
A
PV array
B
Sunny Boy with SMA DC Disconnect
C
Local consumers
D
Energy meter
E
Power distribution grid
