User Guide

AC Coupling System Design
There are several important considerations when designing an AC coupled system with the
XW+/SW inverter:
n PV Inverter Compatibility
n Battery Inverter/PV Inverter Sizing
n Lithium Ion (Li-ion) Battery Compatibility
n AC Coupling in Generator-Based Systems
PV Inverter Compatibility
NOTICE
RISK OF INCOMPATIBLE EQUIPMENT
n Ensure that the PV inverter warranty covers off-grid applications, specifically AC coupling
with a battery-based inverter.
n Ensure that the PV inverter is capable of operating when it is AC-Coupled with the battery-
based inverter which forms the local grid. PV inverters with an impedance sensing anti-
islanding scheme are not compatible with the inverter/charger.
Failure to follow these instructions can result in equipment damage.
Anti-Islanding
PV inverters feature protection mechanisms that detect when a grid fails so that the inverter
can cease generating power. This feature helps to protect against unintentionally supplying
power to a dead grid that might be under service. Some legacy implementations of anti-
islanding protection on PV inverters use a grid impedance check as a mechanism to detect
a failed grid. Battery inverters typically have higher output impedance compared to the grid,
and this impedance might render the system incompatible.
Always check with the PV Inverter manufacturer to verify that the anti-islanding mechanism
is compatible with AC-coupled systems using battery-based inverters.
Frequency-Watt
The Conext XW+/SW inverters use Frequency Shift to regulate battery charge current
coming from AC coupled PV. PV inverters used in AC coupled systems are recommended
to have frequency-Watt controls. Legacy inverters without frequency-Watt controls can be
used with some limitations. See Battery Charge Control Using Frequency Shift on page 10
for more information about the required features and configurations.
976-0240-01-01 Revision G This document is intended for use by qualified personnel 7
Conext XW+/SW Battery Inverters and PV Solutions Guide