SAJ

SAJ CHS2 series hybrid inverter integration within our EMS

Our EMS supports the SAJ CHS2 series of three-phase hybrid inverters.

SAJ is a manufacturer of solar and storage inverters. The CHS2 series is a hybrid inverter: a single unit that combines the battery power conversion system (PCS), the PV inverter, and an optional grid metering point in one device. Because everything lives behind one Modbus connection, our EMS exposes the inverter as several logical devices (battery, PV, grid meter) that are all served by the same integration.

Supported devices

We support the following SAJ CHS2 models:

Model	Rated AC power
CHS2-29.9K-T4-X	29.9 kW
CHS2-30K-T4-X	30 kW
CHS2-40K-T5-X	40 kW
CHS2-49.9K-T6-X	49.9 kW
CHS2-50K-T6-X	50 kW
CHS2-63K-T6-X	63 kW

All models use the same integration and communicate over Modbus TCP (default port 502, slave id 1).

How the integration works

A single CHS2 inverter is modelled in our EMS as one parent device with up to three child devices, all driven from the same Modbus connection:

• PCS (battery inverter) — the parent device. Receives the charge/discharge commands and reports battery power.

• BMS — reports state of charge, voltage, current and temperature of the connected battery.

• PV — reports the combined PV string production.

• Grid meter — the inverter's own CT measurement, exposed as a grid energy meter. Only active when a CT is physically installed and configured on the inverter (see below).

Battery capacity and the minimum/maximum state of charge are configured on the BMS child device; the rated power is configured on the PCS. There is no separate wiring or extra Modbus device to add — the children are created automatically from the parent.

Control approach

We steer the inverter through its EMS interface. Every control cycle (≈1 s) we refresh a keep-alive register so the inverter stays under EMS control, and we (re)assert the requested power command. Which command we send depends on whether a grid CT meter is present:

• With a CT meter → inverter-dispatch mode. We steer a net grid target: the inverter balances PV, battery and grid to hit that target. This enables self-consumption, grid charging and net-export limiting.

• Without a CT meter → battery-scheduling mode. We send a direct battery setpoint (charge/discharge power), because a grid-referenced target cannot be regulated without a meter to measure against.

The CHS2 protocol has no dedicated PV power-limit register. When PV curtailment is required, we achieve it indirectly by lowering the net grid target (inverter-dispatch mode only), so surplus PV is routed into the battery and the inverter curtails PV itself once the battery can no longer absorb it.

What is possible with which setup

The single most important factor is whether a grid CT meter is installed and enabled on the inverter (the inverter's MeterModeSet must be set to a grid-metering option in the SAJ installer app). This decides which EMS mode the inverter can run in, and therefore what is possible.

Setup A — With a grid CT meter (recommended)

This is the full-functionality setup. The inverter runs in inverter-dispatch mode and can regulate against the measured grid point.

• Full monitoring, including real grid import/export.

• Battery discharge to a setpoint.

• Battery charging from both PV and the grid.

• Solar self-consumption (the inverter balances the grid to zero on its own meter).

• PV curtailment (indirect, via the net grid target).

• Grid import/export limiting.

Setup B — Without a grid CT meter

Without a CT the inverter runs in battery-scheduling mode with direct battery setpoints. This is meter-independent and works out of the box, but with important limits.

• Monitoring of battery and PV. No grid measurement (the grid-meter device reads zero, since there is nothing to measure).

• Battery discharge to a setpoint — works fully.

• Battery charging from PV surplus — works.

• Battery charging from the grid — not possible. The inverter firmware will not import from the grid to charge the battery without a CT; charge power is effectively capped at the available PV.

• No self-consumption mode and no PV curtailment.

Capability matrix

Capability	Setup A (with CT)	Setup B (without CT)
Battery / PV monitoring	✅	✅
Grid import/export monitoring	✅	❌
Discharge to setpoint	✅	✅
Charge from PV	✅	✅
Charge from grid	✅	❌
Self-consumption (net-zero)	✅	❌
PV curtailment	✅	❌
Grid limit (import/export)	✅	Discharge side

Key takeaway: to charge the battery from the grid, a CT meter is required. Without one, the inverter only charges from solar. Discharging does not need a meter and works in both setups.

Configuration parameters

Beyond the standard battery parameters (capacity, min/max state of charge), the SAJ CHS2 PCS exposes:

• Rated power (kW) — the inverter's nominal AC power. Pre-filled from the selected model.

• Allow self-consumption mode — controls whether the inverter is allowed to use its own self-consumption (net-zero) balancing when the strategy asks for it:

  • automatic (default) — use self-consumption when a CT is present and no PV curtailment is active.

  • yes — same behaviour; self-consumption is allowed whenever the control mode requests it.

  • no — never hand balancing to the inverter; the EMS always steers an explicit grid target.

  This setting only has an effect in Setup A (with a CT). Without a CT the inverter runs in battery-scheduling mode, where this setting does not apply.

Validation status

Direct battery control in battery-scheduling mode (Setup B) has been validated on hardware: a 5 kW discharge command is followed accurately, and the integration correctly falls back to battery-scheduling mode when no CT is configured. Grid-referenced control (Setup A) requires a CT to be present and is validated as part of a CT-equipped commissioning.

Additional functionality may be added over time as integration capabilities evolve.