Perth solar panel output by month: what to expect from January to December

Perth has one of the best solar resources of any major Australian city, but generation varies significantly by month. Summer (December–February) can generate 2–3 times more than winter (June–August). Understanding the monthly pattern helps with energy planning, battery sizing, and evaluating whether your system is performing correctly.

Perth solar irradiance by month

Perth's solar resource is driven by daily sunshine hours and cloud cover. The Bureau of Meteorology's Perth Airport station provides long-term average data:

| Month | Average daily sunshine hours | Average daily irradiance (kWh/m²) | |---|---|---| | January | 10.5 | 7.2 | | February | 9.8 | 6.5 | | March | 8.5 | 5.4 | | April | 7.0 | 4.2 | | May | 5.8 | 3.2 | | June | 5.0 | 2.7 | | July | 5.3 | 2.9 | | August | 6.5 | 3.8 | | September | 7.8 | 5.0 | | October | 9.0 | 6.1 | | November | 10.0 | 7.0 | | December | 10.5 | 7.3 |

Source: BOM long-term Perth Airport averages. Figures are approximate guides only — your location, shading, and panel orientation will vary.

Perth's annual average is approximately 5.0 peak sun hours (PSH) per day — one of the highest in Australia. But the June minimum (2.7 PSH) vs the December maximum (7.3 PSH) is a nearly 3:1 ratio.

Typical monthly generation for a 6.6kW Perth system

For a north-facing 6.6kW system with a modern TOPCon panel and string inverter (12–15% system losses assumed):

| Month | Daily PSH | Daily generation (kWh) | Monthly generation (kWh) | |---|---|---|---| | January | 7.2 | 41.0 | 1,271 | | February | 6.5 | 37.0 | 1,036 | | March | 5.4 | 30.7 | 952 | | April | 4.2 | 23.9 | 717 | | May | 3.2 | 18.2 | 564 | | June | 2.7 | 15.4 | 462 | | July | 2.9 | 16.5 | 511 | | August | 3.8 | 21.6 | 670 | | September | 5.0 | 28.5 | 855 | | October | 6.1 | 34.7 | 1,076 | | November | 7.0 | 39.8 | 1,194 | | December | 7.3 | 41.5 | 1,287 | | Full year | | 348 kWh/day avg | 10,595 kWh |

Notes:

• These are typical values for a north-facing, unshaded, optimally tilted system
• West or east-facing panels generate 10–20% less annually
• Shading from trees, aerials, or adjacent structures reduces generation further
• Newer TOPCon panels at lower system losses may generate 5–10% above this; older PERC panels with higher losses may generate 5–10% below

The summer/winter difference explained

Why summer generates so much more

Longer days: Summer solstice (late December) gives Perth 14+ hours of daylight vs just under 10 hours at winter solstice (late June). Longer days mean more generating hours.

Higher sun angle: In summer, Perth's sun is near-overhead at solar noon (80–85° elevation). Panels face the sun almost directly, maximising irradiance. In winter, the sun's maximum elevation is only about 30°, reducing the effective irradiance on panels.

Less cloud cover: Perth summer is reliably sunny (Mediterranean climate). Winter brings Perth's rain season — cloud cover reduces irradiance on many winter days.

January vs June: the extreme contrast

A 6.6kW Perth system generates approximately:

• January: ~1,271 kWh (the best month)
• June: ~462 kWh (the worst month)

Ratio: January generates approximately 2.75× more than June. A household that exports surplus in summer will import from the grid in winter — solar doesn't eliminate grid use year-round unless the system is very generously sized and/or paired with a battery.

What this means for your energy planning

Self-consumption in summer vs winter

In summer, Perth systems typically generate far more than a household can self-consume during the day. Surplus export at DEBS rates (2c/kWh for most A1 households) is less valuable than self-consumption (33.26c/kWh avoided). In winter, a smaller system may not even fully cover daytime loads.

High self-consumption strategies for winter:

• Run dishwasher and washing machine during the middle of the day (11am–2pm)
• Pre-heat or pre-cool the home before peak sun drops off
• Schedule pool pump to run during daylight (10am–2pm)
• Heat pump hot water cylinder should already be scheduled for midday

Summer surplus management:

• Battery captures surplus that would otherwise export at 2c/kWh
• EV charging during midday solar surplus (Zappi or smart charger in ECO+ mode)
• Shift flexible loads (ironing, clothes dryer) to the middle of the day

Battery sizing and winter performance

A 10kWh battery sized for summer will often cycle twice daily in summer (fill from solar, discharge in evening, refill overnight). In winter, solar generation may not fully charge the battery by mid-afternoon — leading to partial cycles or overnight grid charging.

Battery value is higher in winter on Midday Saver (overnight grid charge at 24.34c to discharge at 55.33c peak) but lower on A1 (only 33.26c value per kWh discharged, vs charge cost of 33.26c/kWh — no arbitrage benefit without solar charging).

Checking your system against these benchmarks

If your system is significantly underperforming the figures above, possible causes include:

Under-generation by 10–20%:

• Panels dirty or dusty (Perth summer dust storms + pollen can reduce output; annual cleaning recommended)
• Partial shading (trees grown taller, new structures nearby)
• Inverter running at reduced power (thermal derating on very hot summer afternoons — normal, not a fault)

Under-generation by 20–40%:

• One string or MPPT disconnected (check inverter error codes)
• Panel failure (one or more panels significantly underperforming — visible via Enphase or SolarEdge panel-level monitoring)
• Inverter fault (check inverter display for error codes; iSolarCloud or Solar.web will flag alerts)

Under-generation by >40%:

• Multiple panels or strings offline
• Inverter failed or disconnected
• External issue (Western Power disconnect, main isolator tripped)

Use your monitoring platform to compare daily generation against these benchmarks. Most platforms (Fronius Solar.web, Sungrow iSolarCloud) allow year-on-year comparison which is the easiest diagnostic tool.

Seasonal planning summary

| Season | What to expect | What to do | |---|---|---| | Summer (Dec–Feb) | Peak generation, large surplus | Maximise self-consumption; consider battery if exporting significant amounts at 2c DEBS | | Autumn (Mar–May) | Declining generation | Shift loads to midday; start monitoring for any performance drop | | Winter (Jun–Aug) | Lowest generation; may not meet daytime loads | Overnight charging valuable for battery owners; schedule high-use appliances for midday | | Spring (Sep–Nov) | Rapidly increasing generation | Best months for cleaning panels; self-consumption rises |

Perth's annual average of 5.0 peak sun hours gives it excellent solar economics, but the 2.75:1 summer-to-winter ratio means households need to plan for winter shortfalls. A correctly sized battery and smart appliance scheduling close the winter gap significantly. Use your monitoring platform's monthly comparison feature to verify your system against these benchmarks each month.