SMA Sunny Island 4248U, Installation & Operating Instructions Manual

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Installation SI4248U Manual
18
System Configuration
The system installer and the user or owner of the system should discuss the various
configurations that are possible with the Sunny Island 4248U and decide which options will
be installed and connected. The system configuration will significantly affect how the inverter
is connected and set up to work harmoniously with the other components in the system.
Off-Grid / Stand Alone Systems
By definition, off-grid or stand alone systems are systems where electrical power is generated
and stored without assistance from the utility grid. These systems typically consist of one or
more power generation sources such as a PV array, a wind generator, a hydro-electric
generator or a gas powered generator.
Typically, there is a need to store the power that is generated. Without a storage method,
power would only be available when one or more of the generating devices were active (i.e.
when the sun was shining for a PV array, or when the wind was blowing for a wind generator).
Batteries are the most common device used for power storage. The size and type of batteries
used depends greatly on the system power requirements.
Because many of the loads that will be powered by the system require AC power as opposed
to DC power, an inverter is needed to change the DC voltage to an AC voltage that can be
used by the AC loads. This is exactly what the Sunny Island 4248U was designed to do.
The Sunny Island 4248U can also function as a battery charger for charging the battery bank.
This mode operates by connecting an AC power source to the inverter’s AC power input. The
AC power source could be a gas powered generator or even the utility grid, if available at the
system’s location. The power generated by the external source can be used to power AC loads
via the Sunny Island 4248U while the batteries are being charged at the same time. The Sunny
Island 4248U watches the battery voltage and only applies the amount of power necessary to
bring the batteries up to a full state of charge after all power required by the loads is supplied.
Frequency Shift Power Control (FSPC) for Off-Grid Applications Only
When the Sunny Island 4248U is coupled to Sunny Boy inverters on the AC output, it requires
a method in which to control the power output of the Sunny Boys. To do this, it employs a type
of control referred to as Frequency Shift Power Control (FSPC). Using the FSPC feature, the
Sunny Island 4248U is able to increase the frequency of its AC output. This increase in
frequency causes the Sunny Boys to decrease their power output.
Although the Sunny Island 4248U increases its output frequency during these periods, it keeps
track of how much frequency shifting has taken place. Shortly afterwards, the inverter will
automatically compensate for the frequency shifting and bring any appliances such as electric
clocks back to normal. In this way, users don’t have to worry about any inaccuracies in their
electronic equipment.
The activation of the FSPC feature is controlled by the “SunnyBoys” parameter in the Sunny
Island 4248U. When this parameter is set to “Yes”, the FSPC feature is enabled.