Solar curtailment in Perth: what it is and what it means for your system

Perth's solar uptake is among the highest in the world per capita. On sunny weekend mornings, the SWIS (WA's main electricity grid) can receive more solar generation than it needs. To manage grid stability, Western Power has implemented solar curtailment mechanisms that can temporarily reduce or stop solar export from residential systems.

What is curtailment?

Curtailment is the deliberate reduction of solar generation or export to prevent grid instability. When the SWIS has more supply than demand, the grid frequency rises above its normal range (50Hz). To bring frequency back into range, some generation must be reduced or switched off.

In Perth, residential solar export can be curtailed when:

• Total solar generation on the SWIS exceeds demand by a sufficient margin
• Grid frequency rises above a threshold set by Western Power
• A specific feeder or zone is locally oversupplied

Curtailment is most likely on:

• Sunny spring and autumn mornings (high generation, low demand, before air conditioning loads ramp up)
• Weekends when commercial and industrial loads are lower
• Cool days with high irradiance

How curtailment is implemented in WA

Western Power uses two primary mechanisms:

1. Inverter frequency-watt response: When grid frequency rises above 50.25Hz (the threshold for the SWIS), modern inverters automatically reduce their output in proportion to the frequency excess. This is built into all compliant inverters installed in Australia. It's not Western Power actively switching off your system — it's an automatic safety response.

If you have monitoring that shows your generation dropping on a sunny day when frequency is elevated, you're seeing frequency-watt response. Generation typically recovers when frequency returns to normal (often within seconds to minutes).

2. Export limitation via network application: Western Power can limit export approval for new connections in constrained areas (feeder voltage concerns). In some Perth suburbs, new solar systems are approved with lower export limits (1–3kW instead of the standard 5kW) due to network constraints.

Demand management programs: Western Power operates a voluntary Demand Management program where enrolled customers can receive compensation for allowing remote curtailment of export. This is a trial/evolving program — check Western Power's website for current enrollment details.

Does curtailment affect self-consumption?

No. Curtailment only affects grid export. Your solar panels continue generating electricity. When the inverter curtails export, it reduces the power pushed out to the grid — but electricity generated and consumed within your home is unaffected.

This is why self-consumption is more valuable than export in Perth:

• Generation used in your home: zero risk of curtailment
• Generation exported to grid: subject to export limits and curtailment
• Generation stored in battery: zero curtailment risk; discharged later

A battery captures surplus generation before it reaches the export limit, converting what would be curtailed (or exported at 2c/kWh DEBS off-peak) into stored energy discharged at peak.

How to tell if your system is being curtailed

From your monitoring app:

• Unexplained generation drops on sunny days at peak generation times (typically 9am–12pm)
• Generation ramping down and up repeatedly within short periods
• Total daily generation noticeably below what clear-sky conditions would suggest

On the inverter display: Most inverters show the current power output. If you see output stepping down on a clear sunny day without any obvious cause (cloud, fault), frequency-watt response may be active.

From your electricity meter: If your smart meter shows zero export during periods when your system would normally export, export curtailment may be active. This is harder to detect without interval data access.

What can you do about curtailment?

Self-consumption first: Run high-draw appliances (dishwasher, washing machine, EV charging) during peak generation hours. Electricity used in your home isn't affected by curtailment.

Battery storage: A battery absorbs surplus before it reaches the export limit. Instead of exporting at 2c/kWh (DEBS off-peak) — or having that export curtailed to zero — the battery captures it and discharges at evening peak (55.33c/kWh on Midday Saver).

Hot water diverter: A solar diverter (like Catch Power) redirects surplus export to heat your hot water tank instead of exporting it. This is immune to curtailment — the electricity never leaves the property.

Export limiting: Some installers and inverter brands allow you to set your own export limit below the network's maximum. This doesn't help with curtailment per se, but it can prevent inverter performance issues from hitting export limits.

Is curtailment getting worse?

As Perth's solar uptake grows, grid management becomes more complex. Western Power has discussed dynamic operating envelopes (DOEs) — a system where each household's export limit would be adjusted in real-time based on network conditions, time of day, and local feeder capacity.

A dynamic operating envelope could mean your export limit is higher on some days (low solar saturation, high network capacity) and lower on others (high solar day, constrained feeder). This is a more sophisticated approach than blanket curtailment.

For Perth solar households, the direction of policy is toward:

• More dynamic export management (real-time limits rather than static limits)
• Greater value for battery storage that can respond to grid signals
• Compensation mechanisms for households who curtail export voluntarily

Stay informed via Western Power's distributed energy resources website.

Curtailment events and mechanisms are managed by Western Power. For questions about specific curtailment on your connection, contact Western Power.