Perth solar in summer vs winter: what to expect month by month

Perth gets more annual sunshine than almost any major city in the world, but solar generation is still highly seasonal. Your 6.6kW system generating 35–43 kWh on a clear December day drops to around 18–24 kWh on a typical July day.

Understanding the seasonal pattern helps you set realistic expectations, plan appliance use, and avoid thinking something is wrong with your system in winter.

Perth's solar seasons

Perth's solar resource follows the sun's altitude above the horizon:

• Summer (December–February): Longest days, sun highest in sky, least cloud cover. Peak solar output. Days 13–14 hours long.
• Autumn (March–May): Declining output as days shorten and rain events increase. Still strong production — April averages 5.2 PSH.
• Winter (June–August): Shortest days (10–11 hours), sun lowest in sky, most cloud cover. Lowest solar output. June–July are the trough months.
• Spring (September–November): Rapidly recovering output, often with excellent sunshine. October is typically the second-best solar month after December.

Monthly generation estimates for a 6.6kW north-facing system (Perth)

Based on Perth's long-term BOM radiation data and a 6.6kW system on a north-facing 22° pitch:

| Month | Daily PSH (avg) | Monthly output | Bill impact | |---|---|---|---| | January | 6.8 | 1,180 kWh | Very high surplus, bill often near zero | | February | 6.4 | 1,060 kWh | Still strong; late-month cloud possible | | March | 5.8 | 1,010 kWh | Good output; autumn transition | | April | 5.2 | 880 kWh | Noticeable drop; rainfall picks up | | May | 4.2 | 730 kWh | Clear shift into cooler-season mode | | June | 3.5 | 600 kWh | Winter trough; expect higher bills | | July | 3.5 | 610 kWh | Lowest output month | | August | 4.0 | 695 kWh | Recovery begins | | September | 5.0 | 870 kWh | Spring jump — often pleasantly surprising | | October | 6.0 | 1,040 kWh | Near-summer output | | November | 6.5 | 1,090 kWh | Approaching summer peak | | December | 7.0 | 1,210 kWh | Best month of year | | Annual total | 5.0 avg | ~10,975 kWh | |

Estimates use Perth's 5.0 PSH annual average. Monthly variation is typical; individual years differ based on cloud cover, dust, and weather events.

What happens to your electricity bill in winter

In summer, a 6.6kW solar system typically covers most or all of a household's electricity needs, and the electricity bill may be minimal or even credit-positive. In winter, the same system generates roughly half as much, and electricity bills rise — sometimes substantially.

Typical winter bill increase for a solar household:

• A household with a summer electricity bill of $50–100/quarter
• Can expect a winter electricity bill of $200–400/quarter (June–August billing period)
• The difference comes from: less solar generation, more heating consumption, and shorter days that push more consumption outside solar hours

This is normal and expected — the system's annual savings don't change just because winter bills are higher. The $600 kWh/month you generate in winter still saves you approximately 33c per kWh in avoided electricity.

Winter-specific strategies for solar households

Shift loads to the reduced solar window: In winter, the usable solar window is roughly 10am–2pm. The 8am–10am and 3pm–5pm shoulder periods that are useful in summer produce significantly less in winter. Focus washing machine, dishwasher, and heat pump operation to 10am–2pm.

Heating on Midday Saver: On Midday Saver, heating with reverse-cycle AC costs 8.85c/kWh between 9am–3pm. Pre-warming the home from 11am–2pm on solar (near-zero cost) and letting it coast into the afternoon is the most efficient winter heating strategy.

Heat pump hot water: If your heat pump is timer-controlled, shift it to 11am–1pm in winter (instead of the broader 9am–3pm summer window) to catch the solar peak more precisely.

Monitor your system more closely: Soiling accumulates through autumn and winter (dust, bird droppings, pollution). A clean 6.6kW system generating 18 kWh on a clear July day is normal. The same system generating only 12 kWh on a clear day in July suggests soiling or a fault — worth investigating.

Avoid the Monday-after-ANZAC-Day trap: Perth solar households sometimes report system faults in May–June when in reality the system is working correctly and winter has just begun. Compare your winter output to last year's winter output (visible in inverter app history), not to summer output.

Summer-specific strategies for solar households

Run energy-intensive tasks 9am–3pm: Air conditioning in summer runs during peak sun hours. This is ideal — you're running AC directly off solar. Schedule it to pre-cool the home from 10am–1pm, then coast into the afternoon on residual thermal mass.

Hot water on shortest possible run: In summer, your heat pump may heat a full 315L tank in 2 hours rather than 4. If your timer is set for a 4-hour window, you're running the heat pump into the late afternoon (higher tariff or DEBS period) unnecessarily. Trim the timer to match actual heating time in summer.

Pool timing: Longer daylight hours mean more solar is available. Pool filters can run 8 hours/day in peak summer — schedule all of it inside solar hours if possible.

Export limit impact: If your suburb has a 1.5kW export limit, summer's 6–7 kW peak production hours generate the most curtailment. The financial impact of curtailment is still modest ($2c/kWh), but it reinforces the value of shifting loads to midday to absorb generation rather than waste it.

Annual bill expectations for solar households

Over the full year, a typical Perth household using 20–25 kWh/day with a 6.6kW solar system can expect:

• Summer quarter (Dec–Feb): $0–$150 bill, sometimes a small credit
• Autumn quarter (Mar–May): $100–$250 bill
• Winter quarter (Jun–Aug): $200–$450 bill
• Spring quarter (Sep–Nov): $80–$200 bill
• Annual total: $380–$1,050, down from approximately $1,800–$2,600 without solar

The winter quarter almost always generates the highest bill even for solar households — this is universal across Perth and not a sign of a system problem.

Monthly PSH estimates based on Bureau of Meteorology global solar exposure data for Perth. System output estimates assume a 6.6kW system with 79% system efficiency, no shading, north-facing at 22° pitch. Actual output varies by year, roof orientation, and soiling.