Free Australian solar sizing calculator · No sign-up · Runs entirely in your browser
Work out how many solar panels you need for your daily energy use — using real Australian sun hours, and with system losses accounted for so the answer holds up in winter.
77% is a realistic Australian default covering heat, controller losses, soiling, cable and orientation. Lower it for a shaded or poorly oriented roof.
| Measure | Value |
|---|
| City | Annual | Winter |
|---|---|---|
| Darwin | 5.9 | 4.8 |
| Perth | 5.5 | 3.4 |
| Brisbane | 5.1 | 4.0 |
| Adelaide | 5.0 | 2.9 |
| Sydney | 4.9 | 3.4 |
| Canberra | 4.9 | 3.0 |
| Melbourne | 4.2 | 2.4 |
| Hobart | 3.8 | 1.9 |
Indicative daily averages. Check your own address against Bureau of Meteorology solar exposure data for a precise figure.
This is the number everything else depends on, and it is routinely misunderstood. A peak sun hour is not an hour of daylight. It is the amount of solar energy equivalent to one hour at 1,000 W per square metre — the intensity panels are rated against.
Sunlight arrives at varying intensity through the day: weak at dawn, strong at midday, weak again at dusk. Peak sun hours add all of that up into an equivalent number of full-intensity hours.
Latitude and climate produce very large differences. The last column shows the array you would need for 10 kWh a day, sized on winter sun at a 77% performance ratio.
| City | Annual average | Typical winter | Array for 10 kWh/day |
|---|---|---|---|
| Darwin | 5.9 | 4.8 | 2.7 kW |
| Perth | 5.5 | 3.4 | 3.8 kW |
| Brisbane | 5.1 | 4.0 | 3.2 kW |
| Adelaide | 5.0 | 2.9 | 4.5 kW |
| Sydney | 4.9 | 3.4 | 3.8 kW |
| Canberra | 4.9 | 3.0 | 4.3 kW |
| Melbourne | 4.2 | 2.4 | 5.4 kW |
| Hobart | 3.8 | 1.9 | 6.8 kW |
Panel ratings come from Standard Test Conditions: 1,000 W/m² irradiance, a 25 °C cell temperature, and a specified light spectrum. Those conditions occur in a laboratory. They do not occur on an Australian roof in February.
| Loss | Typical | Why |
|---|---|---|
| Cell temperature above 25 °C | −10% | Panels are rated at 25 °C; an Australian roof runs 55–70 °C |
| Inverter or MPPT controller | −5% | Conversion is never lossless |
| Soiling — dust, salt, bird droppings | −3% | Worse in dry inland and coastal areas |
| Cable and connection losses | −2% | DC run from array to controller |
| Panel mismatch and tolerance | −2% | No two panels are identical |
| Shading and orientation | −3% | Anything less than ideal tilt and true north |
| Term | What to use |
|---|---|
| Daily energy | Your actual consumption. A bill gives you kWh per quarter — divide by the days |
| Peak sun hours | Winter for off-grid reliability, annual average for grid-connected |
| Performance ratio | 0.77 is a realistic Australian default. Lower it for shading or poor orientation |
| Panel rating | Residential panels are commonly 400–450 W; portable and caravan panels 100–200 W |
Another way to think about sizing: how much array does it take to cover a particular load? Figures below use Sydney's annual average, where 1 kW installed produces about 3.77 kWh a day.
| Appliance | Daily energy | Solar to cover it | 400 W panels |
|---|---|---|---|
| Refrigerator (400 L) | 1.2 kWh | 0.32 kW | 1 |
| TV, 4 h/day | 0.5 kWh | 0.13 kW | 1 |
| Dishwasher, 1 cycle | 1.5 kWh | 0.40 kW | 1 |
| Washing machine (cold) | 0.5 kWh | 0.13 kW | 1 |
| Electric oven, 1 h | 2.5 kWh | 0.66 kW | 2 |
| Pool pump, 8 h | 8.8 kWh | 2.33 kW | 6 |
| Split-system A/C, 8 h | 16.0 kWh | 4.24 kW | 11 |
| Electric hot water | 10.8 kWh | 2.86 kW | 8 |
| EV, 40 km/day | 7.2 kWh | 1.91 kW | 5 |
This is why the practical advice for solar households is about timing rather than frugality. Running the pool pump, dishwasher and hot water in the middle of the day converts solar you would otherwise export at a few cents into electricity you would otherwise buy at 28–40 cents. Our electricity cost calculator puts a dollar figure on each appliance at your own tariff.
A setup consuming 3.35 kWh a day — a 12 V fridge, lights, water pump, laptop, Starlink and a little inverter use. Sized on winter sun at a 77% performance ratio, with 200 W panels.
| Location | Winter array needed | 200 W panels |
|---|---|---|
| Darwin | 0.91 kW | 5 panels |
| Sydney | 1.28 kW | 7 panels |
| Melbourne | 1.81 kW | 10 panels |
Ten 200 W panels will not fit on most caravan roofs, which is the real constraint. That is why touring rigs carry portable folding panels to supplement fixed ones, and why serious van builds either accept a generator, plan around driving days that charge from the alternator, or move south only in summer. Work out the battery side with our battery calculator.
A household using 20 kWh a day, on 400 W panels.
| Brisbane | Melbourne | |
|---|---|---|
| Sized on annual average | 5.09 kW | 6.18 kW |
| Sized on winter | 6.49 kW | 10.82 kW |
| Panels (annual basis) | 13 | 16 |
| Roof area (annual basis) | ~26 m² | ~32 m² |
For a grid-connected home the annual figure is the sensible basis — sizing a Melbourne system at 10.8 kW to cover winter would mean large summer exports at a low feed-in tariff. The economics favour matching annual production to annual consumption and importing during winter.
Useful as a sanity check against whatever the calculator gives you. If your result is wildly outside these, re-check your daily consumption figure first.
| Household | Typical system | 400 W panels | Roof area |
|---|---|---|---|
| Apartment or small unit | 2–3 kW | 5–8 | ~10–16 m² |
| Small home, 1–2 people | 5 kW | 13 | ~26 m² |
| Average family home | 6.6 kW | 17 | ~34 m² |
| Large home or pool | 10–13 kW | 25–33 | ~50–66 m² |
| Home with an EV | 13–15 kW | 33–38 | ~66–76 m² |
A 6.6 kW system in Sydney produces roughly 24.9 kWh on an average day — comfortably more than most households use, which is why self-consumption timing matters more than raw system size for most people.
For any system charging a battery, the controller between panel and battery matters more than most people expect.
| PWM | MPPT | |
|---|---|---|
| How it works | Connects the panel directly to the battery, pulling panel voltage down to battery voltage | Converts excess voltage into extra current |
| Typical efficiency | ~70–80% of available energy | ~93–98% |
| Cost | Low | Higher |
| Best with | Small panels matched to battery voltage | Higher-voltage panels, cold conditions, larger arrays |
| Worth it when | Very small systems, tight budget | Almost always above roughly 200 W |
A 6.6 kW system does not produce 6.6 kW, and it does not produce the same amount every day. Here is the realistic spread.
| Location | Summer day | Annual average | Winter day |
|---|---|---|---|
| Brisbane | 30.5 kWh | 25.9 kWh | 20.3 kWh |
| Sydney | 31.5 kWh | 24.9 kWh | 17.3 kWh |
| Melbourne | 30.0 kWh | 21.3 kWh | 12.2 kWh |
Melbourne's winter day is 41% of its summer day from identical hardware. Brisbane's is 67%. The further south you are, the more the seasons dominate your planning.
| Condition | Typical output | Notes |
|---|---|---|
| Clear summer day | 100% | The best case, though extreme heat trims the peak |
| Clear winter day | 40–70% | Lower sun angle and shorter day, not cloud |
| Light cloud | 50–80% | Diffuse light still generates usefully |
| Heavy overcast | 10–25% | The condition that sizes off-grid systems |
| Rain | 10–20% | Poor on the day, but it washes the panels |
| Extreme heat (40 °C+) | 85–90% of peak | Cell temperature costs more than the extra light gains |
| Factor | Effect |
|---|---|
| True north | Optimal in Australia. East or west facing typically costs 10–20% annually |
| Tilt angle | Roughly your latitude is best year-round. Steeper favours winter, flatter favours summer |
| Flat mounting | Common on caravans and flat roofs. Costs output and lets dirt accumulate rather than washing off |
| Partial shading | Disproportionate — one shaded panel in a string can drag down the whole string unless optimisers or microinverters are fitted |
| East–west split | Lower peak but a broader generation curve, which can suit self-consumption better than a single north array |
Shading deserves particular attention because its effect is non-linear. A single branch across one panel can cost far more than the fraction of area it covers, since panels wired in series are limited by their weakest member. If shading is unavoidable, panel-level optimisers or microinverters isolate the problem to the affected panel.
Solar is close to maintenance-free, but "close to" is not "entirely", and a system quietly underperforming for years is a common and expensive outcome.
| Check | Why | How often |
|---|---|---|
| Monitor your inverter output | The single most valuable habit. A failed panel, tripped string or dying inverter shows up as a gradual decline you will never notice on a bill | Monthly glance |
| Watch for new shading | Trees grow, neighbours build. A system commissioned unshaded may not stay that way, and one shaded panel can drag a whole string | Seasonally |
| Trim overhanging branches | Removes shading and reduces leaf and bird-dropping soiling at the source | Annually |
| Clean panels if needed | Rain handles most of it on tilted panels. Dry inland, coastal salt and flat-mounted panels need attention. Soiling can cost 5%+ | Annually, or after dust events |
| Inspect mounting and cables | Australian sun and wind degrade cable insulation and loosen fixings over time. Best done by a professional on the roof | Every few years |
| Compare your bills year on year | Same quarter, previous year, is the simplest performance check available. A step change means something has failed | Quarterly |
How many solar panels do I need?
Divide your daily energy use in kWh by peak sun hours multiplied by the system performance ratio, then divide by your panel rating. For 20 kWh a day in Sydney with 400 W panels at 77%: 20,000 ÷ (4.9 × 0.77) = 5,300 W, which is 14 panels. Use winter sun hours instead of the annual average if the system has to work year-round.
What is a peak sun hour?
A peak sun hour is solar energy equivalent to one hour at 1,000 watts per square metre — the intensity panels are rated against. It is not an hour of daylight. Sydney can have fourteen hours of daylight in summer while averaging under five peak sun hours across the year, because early and late sunlight is much weaker.
How much power does a 400 W solar panel actually produce?
Around 309 W under real Australian conditions, once you allow for cell temperature above 25 °C, controller losses, soiling, cable losses, panel mismatch and imperfect orientation. Over a day in Sydney at 4.9 peak sun hours, a single 400 W panel produces roughly 1.5 kWh.
Why do panels produce less than their rating?
Panels are rated at Standard Test Conditions — 1,000 W/m² and a 25 °C cell temperature. Australian roofs commonly run 55–70 °C, and silicon loses roughly 0.3–0.4% of output per degree above 25 °C. Add controller, soiling, cable and orientation losses and a realistic performance ratio is about 77%.
Should I size my system for winter or the annual average?
Off-grid and caravan systems should be sized on winter, because there is no fallback when generation drops. Grid-connected homes are usually better sized on the annual average, since the grid covers shortfalls and oversizing for winter means exporting heavily in summer at a low feed-in tariff.
How much roof space do I need?
A typical 400 W residential panel occupies roughly 2 square metres, so a 6.6 kW system of sixteen panels needs about 32 m² of usable, unshaded, ideally north-facing roof. Allow extra for edge setbacks and access requirements, which vary with roof type and local rules.
What is the difference between MPPT and PWM?
A PWM controller connects the panel almost directly to the battery, pulling panel voltage down to battery voltage and losing the difference. An MPPT controller converts that surplus voltage into extra charging current, typically recovering 20–30% more energy. MPPT is worth the extra cost on almost any array above roughly 200 W.
Which direction should solar panels face in Australia?
True north is optimal for total annual generation. East or west facing typically costs 10–20% a year, though a west-facing array can suit households that use most electricity in the late afternoon. An east–west split produces a lower peak but a broader curve, which often improves self-consumption.
Does shading really matter that much?
More than the shaded area suggests. Panels wired in series are limited by their weakest member, so one shaded panel can reduce output across the whole string. Panel-level optimisers or microinverters confine the loss to the affected panel and are worth considering wherever shading is unavoidable.
How much solar do I need for a caravan?
It depends on consumption and where you travel. A rig using 3.35 kWh a day needs roughly 0.9 kW of panels in Darwin winter but 1.8 kW in Melbourne winter. Since few caravan roofs fit that much, most touring setups combine fixed panels with portable folding panels, alternator charging while driving, or seasonal travel patterns.
Do I need an accredited installer in Australia?
For grid-connected solar, yes — installation must be carried out by a Clean Energy Council accredited installer, which is also the condition for accessing federal small-scale technology certificates. Standalone extra-low-voltage systems such as caravan and camping setups are generally not restricted, but anything connecting to mains wiring is licensed electrical work.
Is it worth oversizing my solar array?
Modest oversizing relative to the inverter is common practice and improves output in weak light and winter. Beyond that it depends on your export limit, your feed-in tariff and how much you can self-consume. Since exported energy earns far less than the retail rate you avoid paying, a system matched to consumption usually beats one built for maximum export.
Two numbers decide almost everything: your daily consumption, and the peak sun hours where you actually are. Get those right, apply a realistic performance ratio rather than the panel's sticker, and decide honestly whether you are designing for the average day or the worst one.
From here, size the storage side with the battery calculator, check cable losses on the DC run with the voltage drop calculator, and work out what you currently pay with the electricity cost calculator.