Outback FX-R Series Technical Note on Input Modes

Application Note
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and blending it with 10A from the AC grid-side of the inverter to meet the 30A demand from the
load panel. Note that some amount of charging current will always be diverted to the batteries
before going to the inverter as even a “full” battery draws about 2% of its amp hour rating when
a charging voltage is applied. More details on the Offset function can be found in the Offset
Functionality application note on the OutBackPower.com website.
SELLING EXCESS POWER TO THE UTILITY GRID
The vast majority of DC to AC
grid tied inverters move excess
DC power from photovoltaic (PV)
arrays to the utility power grid
once the site’s local power
demand has been met, as
illustrated in Figure 2.
Historically, battery-based
inverters were mostly for off-grid
or battery backup applications.
Battery-based inverters from OutBack have since evolved into a
grid/hybrid design that can sell excess power to the grid, as well as provide backup power when
the power grid is down. The components and energy flow in a grid/hybrid inverter system are
shown in Figure 3.
When the grid is active, DC current
flows from the PV array to a DC to
DC converter called a charge
controller, then to the battery bank.
Once the battery bank is charged,
the DC power is converted to AC.
The AC power is consumed by the
critical loads connected to the
output of the grid/hybrid inverter,
then passed to the input side of
the inverter where it is consumed
by loads connected to the main
panel. If the PV production should
fall short of the critical load
demand, whatever PV power is
available is blended with grid
power (Offset function) to satisfy
load demand. If there is excess PV power, then it is passed on to the grid which effectively spins
the meter backwards and provides what is known as net metering, or reduction in the metered
utility charges. Some utilities provide additional renewable energy production credits in some
Figure2 ‐ GridTiedInverterCurrentFlow
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Figure3 ‐ GridHybridInverterCurrentFlow