Is your solar system underperforming? How to check in Perth

Most Perth solar owners never check whether their system is generating what it should. They see solar credits on their bill, assume it's working, and move on. But a system running at 70% of expected output — due to a shaded string, a failing inverter, or a meter configuration issue — can go undetected for years.

Here's how to establish whether your system is generating what Perth's sun should deliver.

Step 1: Calculate your expected annual generation

Perth receives approximately 5.0 peak sun hours (PSH) per day as a year-round average. A solar system's annual output can be estimated as:

Annual generation = System kW × PSH × 365 days × system efficiency factor

Using a 79% system efficiency factor (accounting for inverter conversion losses, temperature derating, soiling, cable losses, and orientation):

| System size | Expected annual generation (Perth) | |---|---| | 3kW | 4,300–4,800 kWh | | 5kW | 7,200–8,000 kWh | | 6.6kW | 9,500–10,600 kWh | | 10kW | 14,600–16,000 kWh | | 13.3kW | 19,000–21,000 kWh |

These ranges reflect north-facing panels at 15–30° pitch. West or east-facing panels produce approximately 85% of these figures.

Where to find your actual generation:

1. Your inverter monitoring app (Fronius Solar.web, SolarEdge monitoring, Sungrow iSolarCloud, Tesla app)
2. Your Synergy smart meter data (via MyAccount — shows imported and exported kWh by billing period, from which you can back-calculate total generation)
3. Your quarterly electricity statement (shows DEBS export credits in kWh)

Step 2: Interpret the comparison

Within 10% of expected: Normal performance variation. Perth generation varies 15–20% between good and poor solar years. No action needed.

10–20% below expected: Worth investigating. Could be a minor shading issue, one underperforming string, or a meter configuration problem.

More than 20% below expected: Likely a real fault or significant shading issue. Commission an inspection.

Step 3: Common causes of underperformance

New shading since installation

Trees grow. Additions to neighbouring properties appear. A tree that cast no shade in 2015 may now shade two panels from 2pm onwards in winter. Even one shaded panel can drag down an entire string's output in a conventional string inverter.

How to identify: Check generation on clear days in winter (when the sun is lower) vs summer. Significant winter/summer ratio deviation compared to expected seasonal pattern can indicate winter shading that didn't exist at installation.

Inverter running in reduced output mode

Some inverters throttle output when internal temperatures reach safety limits. A unit in full afternoon sun on a west-facing wall in Perth summer (wall surface temperature 60°C+) may clamp output. This isn't a fault — it's self-protection — but it reduces afternoon generation.

How to identify: Monitoring logs showing output plateauing below inverter rated output on hot afternoons.

DC isolator fault or string disconnection

DC isolators (the red switches on the roof next to each panel array) can fail, particularly the earlier generation of red button isolators that were subject to recalls. A tripped or failed isolator disconnects a panel string entirely.

How to identify: Monitoring showing one MPPT input at zero while another is normal; visible error code on inverter display.

Clipping losses

If your system has significantly more panel capacity than inverter capacity (e.g., 10kW of panels on a 5kW inverter), the inverter clips output at its rated capacity during peak generation hours. This is by design — the inverter is sized intentionally — but can cause confusion if expected generation was calculated on panel capacity rather than inverter capacity.

How to identify: Monitoring showing output flatlined exactly at inverter rated output for several hours mid-day on clear summer days.

Soiling (dust, bird droppings)

Perth is dusty, particularly through winter and dry spring. Heavy soiling can reduce output by 5–15%. A system that hasn't been cleaned in 3+ years in a dusty outer suburb may be underperforming for this reason.

How to identify: Perth's autumn rains typically self-clean panels. A system that improves significantly in output after the first good rain event was likely soiling-affected.

Panel fault or micro-crack

Individual panel failures are rare but do occur. A cracked or delaminated panel generates less than its rating.

How to identify: Thermal imaging during a solar inspection can identify failed or partially failed panels. Per-panel monitoring (SolarEdge or Enphase systems) shows individual panel output.

Step 4: When to call someone

Call your installer if:

• Generation is more than 20% below the expected range after accounting for orientation
• Your monitoring shows a string at zero or significantly below the other string
• There's an error code on the inverter display that hasn't cleared after a restart

Commission an independent inspection if:

• The installer is no longer in business (common with early-boom companies)
• You want an objective assessment for insurance purposes or a property sale
• The system is more than 7 years old and you've never had it checked

Solar inspections in Perth: approximately $200–$400 for a qualified CEC-accredited inspector.

Expected generation ranges based on 5.0 PSH Perth average, 79% system efficiency, north-facing panels at 20° pitch. Actual generation varies with orientation, shading, panel brand, and inverter efficiency.