AS 4777.2:2020 defines what Australian grid-connected solar inverters must do — not just in terms of electrical connection, but in terms of active grid support. The volt-watt and volt-VAR response functions now built into every compliant inverter exist because Australia’s distribution networks experience voltage problems caused by the scale of rooftop solar.
For installers, the practical implications are: inverter selection must be from the CEC-approved list, settings must be configured correctly before commissioning, and DNSPs may specify non-default settings that require documentation and implementation.
What AS 4777.2 Requires
AS 4777.2:2020 covers the following key inverter capabilities and settings:
| Function | What It Does | Default Setting |
|---|---|---|
| Volt-watt response | Curtails active power when voltage is high | Active above ~250 V (single-phase) |
| Volt-VAR response | Provides reactive power to regulate voltage | Default curve per standard |
| Frequency response | Trips or curtails at out-of-range frequency | 47–52 Hz operating range |
| Voltage ride-through | Stays connected during brief voltage disturbances | Per ride-through curves |
| Frequency ride-through | Stays connected during brief frequency disturbances | Per ride-through curves |
| Anti-islanding | Disconnects when grid power is lost | Detection within 2 seconds |
| Reconnection delay | Wait period before reconnecting after disconnect | Minimum 60 seconds |
| Soft-start | Ramps output gradually on reconnection | Per standard ramp rate |
| Reactive power capability | Operates at non-unity power factor | Rated reactive capability |
Volt-Watt Response
Volt-watt response is one of the most commercially significant requirements in AS 4777.2:2020, because it can affect how much energy a solar system exports at times of high grid voltage.
How it works: When grid voltage rises above a defined threshold, the inverter reduces its active power output proportionally. The curtailment is automatic and continuous — the inverter constantly monitors grid voltage and adjusts output.
Default volt-watt curve (single-phase, at nominal 230 V):
| Grid Voltage | Active Power Output |
|---|---|
| Below 235 V | 100% of available |
| 235–255 V | Linear reduction from 100% to 20% |
| Above 255 V | 20% minimum |
| Above 258 V | Disconnect (overvoltage trip) |
Note: These values are indicative defaults — verify against the current published standard and your DNSP’s requirements.
Impact on generation: In areas with high solar penetration (much of SA, WA coastal, parts of QLD), volt-watt curtailment can reduce generation by 5–15% in some systems. SA Power Networks’ network — with the highest solar penetration in Australia — sees significant volt-watt curtailment during peak solar periods.
Designing to reduce curtailment: Larger conductor sizes (lower cable resistance = less voltage rise), placing the inverter close to the switchboard, and choosing a lower export limit can all reduce volt-watt curtailment. Battery storage that absorbs curtailed energy is another approach.
Volt-VAR Response
Volt-VAR response provides reactive power support to the local network:
How it works: The inverter adjusts its reactive power (Q) based on the measured grid voltage. At high voltage, the inverter absorbs reactive power (lagging power factor — appears capacitive from the grid’s perspective, which tends to reduce voltage). At low voltage, it injects reactive power (leading power factor).
Default volt-VAR curve: At nominal voltage, the inverter operates at unity power factor. As voltage deviates, reactive power response is proportional to the deviation.
Impact on inverter rating: Operating at non-unity power factor slightly reduces the available active power output (since the inverter’s apparent power capacity is shared between active and reactive). In practice, the impact on a well-functioning system in normal voltage range is minimal.
Frequency Response
AS 4777.2:2020 defines the frequency range within which inverters must operate and how they should respond to frequency deviations:
| Frequency Range | Required Action |
|---|---|
| 47.0–47.5 Hz | Trip permitted, reconnect after frequency returns to normal |
| 47.5–52.0 Hz | Normal operating range — must remain connected |
| 52.0–52.5 Hz | Trip permitted |
| Above 52.5 Hz | Must trip |
Australian grid frequency is nominally 50 Hz. Frequency deviations outside the normal range are unusual in the National Electricity Market (NEM) but can occur in network disturbances or islanding events.
Anti-Islanding Protection
Anti-islanding ensures that a solar inverter disconnects from the grid when grid power is lost. This is a safety requirement — it prevents the solar system from energising a de-energised line, which could endanger network workers.
Detection time: The inverter must detect loss of grid supply and disconnect within 2 seconds under standard conditions. In practice, most modern inverters detect islanding within fractions of a second.
Methods: AS 4777.2:2020 accepts active or passive anti-islanding methods. Active methods (where the inverter deliberately perturbs the grid to detect islanding) are more reliable. Type-testing verifies the anti-islanding method meets the standard requirements.
Reconnection Delay
After disconnecting for any reason (overvoltage, undervoltage, frequency, anti-islanding), the inverter must wait at least 60 seconds before attempting to reconnect to the grid. This prevents repeated connection/disconnection cycling during grid disturbances.
During the reconnection delay, the inverter output is zero. This is not configurable — it is a fixed requirement. Some DNSPs specify longer reconnection delays.
DNSP-Specific Settings
Some DNSPs specify settings that differ from AS 4777.2 defaults:
SA Power Networks: Has historically required specific volt-watt response settings (sometimes more aggressive curtailment starting at lower voltages than the standard default) due to SA’s high solar penetration and network voltage management challenges. Check SAPN’s current published technical requirements before commissioning any SA installation.
Ausgrid: Generally applies AS 4777.2 default settings. Specific requirements apply to larger commercial systems.
Energy Queensland (Ergon/Energex): Follows AS 4777.2 defaults with some specific requirements for systems above 5 kW in certain network areas.
Western Power: Follows AS 4777.2 with specific requirements for export-limited systems and systems connecting in network-constrained areas.
Always Check the DNSP’s Current Technical Requirements
DNSP requirements for inverter settings are periodically updated as networks change. What was correct for SA Power Networks 12 months ago may have been updated. Download the DNSP’s current connection requirements document (not just the generic application guide) and check the specific inverter settings required for the connection address’s network zone before commissioning.
CEC Approved Inverter List
The Clean Energy Council maintains the list of inverters approved under AS 4777.2 for Australian grid connection. Key points:
- Approval is model-specific and firmware-version-specific
- New models are added periodically as manufacturers complete type testing
- Approval can be suspended if an inverter is found to not meet the standard in service
- Check the current CEC list before specifying any inverter — lists are updated regularly
Where an inverter is not on the CEC list, it cannot be used for STC-eligible installations. Some DNSPs may allow non-listed inverters via the specific approval pathway, but this requires individual DNSP approval and is uncommon for standard residential/commercial installations.
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Frequently Asked Questions
What is AS 4777.2?
The Australian standard for grid connection of energy systems via inverters. It defines volt-watt response, volt-VAR response, frequency ride-through, anti-islanding, and reconnection requirements for solar inverters.
What is volt-watt response?
An inverter function that automatically reduces power output when grid voltage rises above a threshold. It prevents rooftop solar from causing network voltage problems in high-penetration areas.
Do I need to configure inverter settings?
Yes. The volt-watt, volt-VAR, and frequency response settings must be correctly configured before commissioning. Some DNSPs require non-default settings — check the DNSP’s published technical requirements.
Where is the list of approved inverters?
The Clean Energy Council maintains the approved inverter list at cleanenergycouncil.org.au. Check the specific model before specifying — approval is model and firmware-version specific.
Can DNSPs override the standard settings?
Yes. DNSPs can specify settings different from the AS 4777.2 defaults for their network. SA Power Networks is the most notable example. Always check the DNSP’s current technical requirements document.
