User Guide

Operation with Smart PV Inverters
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.
With smart PV inverters, surplus power is regulated using Frequency Shift according to the
battery charge settings. When the battery reaches the bulk charge voltage, the battery-
inverter frequency is ramped up linearly and the PV inverter responds by curtailing power
according to its frequency-Watt settings. Depending on the grid code requirements of the
installation and the settings of the PV inverter, power curtailment down to zero may not be
possible. As a result, PV inverters may trip off during the final stages of the charge cycle,
especially if there is significant surplus PV power. After a reconnect delay (typically 5
minutes), the PV inverter reconnects. This mode of operation is acceptable for grid-tied
applications with less frequent outages.
Optimal charge management can be achieved by adjusting PV inverter settings to allow
power curtailment to zero, which is a capability of many smart PV inverters. This allows
improved charging in the Constant Voltage Absorption stage where the charge current
continues to reduce towards zero. In grid-tied applications, follow the grid code
requirements for all PV inverter settings unless approval is obtained from the utility. Contact
the manufacturer for information on the available settings for AC coupling with battery-
based inverters.
Note: Frequency-Watt power curtailment to zero may require special settings that are
typically used in off-grid applications, where compliance with grid code requirements is not
required.
Operation with Legacy PV Inverters
When AC coupling with legacy PV inverters without frequency-Watt capability, the battery-
based inverter will have reduced ability to regulate the battery charge. When surplus power
charges the batteries and the battery voltage reaches the bulk charge voltage, the battery-
based inverter frequency is ramped up and the PV inverter will cease producing power and
disconnect. When battery voltage drops below the charging voltage due to loss of PV back-
feed power, its output frequency returns to normal (50 or 60 Hz). This return to normal
frequency causes the PV Inverter to initiate its reconnect delay timer (usually 5 minutes),
and come online. Depending on the available array power and loads, any surplus power will
be used to charge the batteries and the cycle will repeat. It is recommended to set the
Absorb Time limit to the minimum value to help reduce cycling.
976-0240-01-01 Revision G This document is intended for use by qualified personnel 11
Conext XW+/SW Battery Inverters and PV Solutions Guide