Outback FX-R Series Technical Note on Input Modes
Application Note
©2015OutBackPowerTechnologies,Arlington,WA98223MAM‐9/21/15Page7of10
Applications for full self-consumption include sites where the local utility does not allow
connection agreements with PV based inverters, or where the site owner wants to become
mostly off-grid, with the utility providing the occasional make-up power, acting like a backup
generator for when the PV array cannot satisfy all of the site’s load demand.
Grid Zero Mode
Grid Zero is designed to self-consume and utilize PV power at a controlled rate with load peaks
being supported using power from the grid. The grid never charges the battery, but will always
pull a minimum of 1 Aac from the grid to ensure no power from the inverter is “leaking” back
onto the grid input. The flow rate of PV power and/or battery power is determined by the DoD
Amps setting, in amps AC. By restricting the flow of DC power, the inverter is able to supply a
base amount of energy to the loads, while only blending grid power with DC power when load
demand is high or surging. Having a consistent discharge of the DC power provides a more
predictable load curve to match up to the available PV power.
Also, the battery acts as a buffer both for days of excess PV power as well as days with less,
and there is a DoD Volts setting to be sure the system always has the level of backup desired
by the site owner. Having a PV power based generation system will always have some level of
unpredictability, but the problem of having load variation coupled with PV power variations can
create a system with highly variable performance. Grid Zero solves this problem by helping
reduce the over/under performing system by bringing more balance to self-consumption.
Having a system with fewer highs and lows of performance is only one benefit of Grid Zero.
Some utilities have ended feed-in tariff (FIT) incentives, or have even disallowed battery-based
inverters that charge from the grid. Grid
Zero should therefore make it possible to
have a utility connection no matter what the
rules, as batteries are never charged from
the grid and the 1A minimum power draw
from the gird ensures that power is never
exported.
Here are some guidelines for Grid Zero to
optimize its operation in your application:
1. Use a battery that is designed for
daily cycling. Flooded lead acid
batteries are usually best, but
Lithium Ion (Li Ion) batteries also
have a high cycle life. OutBack
EnergyCell RE batteries can also be
used, but use a minimum C20
discharge rate (500 W or about 10
Adc per string), otherwise a slower
discharge rate could significantly reduce
3Aacfrom
32Adcto
loads
10Aacblendedcurrent
DoDAmps=7Aac
48Adcto
batteries
10ASurge
80Adc
Figure5 ‐ GridZeroCurrentPaths