Solar recharge calculator by city, with Bureau of Meteorology sun hours
Choose a city and month and it uses Bureau of Meteorology solar exposure averages to estimate what your panels put back each day, how long your battery runs a load, and whether solar keeps up.
Choose your city and month, put in your panel watts and your power station's battery size, and this tells you how many watt-hours the sun should put back on an average day, how long the battery runs your load, and whether solar can keep up. The sun hours come from Bureau of Meteorology long-term averages, so it's a typical day, not a forecast.
If you need to add up a list of appliances first, the runtime and watt-hour calculator does that. Bring its daily total or average watts back here.
The calculator
1. Where and when
2. Your power station and load
3. Your solar
Where the sun hours come from
The Bureau of Meteorology publishes mean daily solar exposure for its weather stations, in megajoules per square metre. It's the total sunlight landing on a flat surface over a day. The Bureau notes that 1 kWh per square metre is 3.6 MJ, so dividing by 3.6 gives kWh per square metre a day. That's the same thing as peak sun hours: the number of hours at a full 1,000W per square metre that would deliver the same energy.
Here's how much the season matters. Winter is the month that sizes your solar, not summer.
| City | Worst month | Sun hours then | Yearly average |
|---|---|---|---|
| Brisbane | June | 3.3 | 5.3 |
| Sydney | June | 2.4 | 4.6 |
| Melbourne | June | 1.8 | 4.2 |
| Perth | June | 2.6 | 5.3 |
| Hobart | June | 1.4 | 3.7 |
| Darwin | January | 5.2 | 5.9 |
The calculator also has Adelaide, Canberra, Cairns, Townsville and Alice Springs. Each figure comes from the airport or main weather station for that city, so a valley or a shaded campsite will see less. Darwin's worst month is January because of wet season cloud, which matters if you're relying on solar after a cyclone.
How the sums work
Daily solar harvest is panel watts × sun hours × the real-world percentage. A 200W panel in Brisbane in June gives 200 × 3.3 × 0.7, or about 470Wh. If your station caps solar input below the panel's rating, the calculator uses the lower figure.
Runtime is battery watt-hours × inverter efficiency ÷ load watts. A 1,024Wh station at 85% has about 870Wh to give, so a 60W average load runs for roughly 14.5 hours. The 85% is our working assumption, because makers don't all publish an efficiency figure and losses change with load. Running 12V devices straight from the DC outlets usually wastes less.
The daily balance compares the harvest with what the load uses in a day. If it's positive, solar keeps up on an average day in that month. If it's negative, the battery drains a bit each day and the calculator tells you roughly how many days it lasts from full.
Why 70% and not the full rating
Panel ratings are measured in lab conditions at 25°C cell temperature. SolarQuotes notes Australian panels commonly run 20°C or more above the air temperature, and output drops as they heat up. Add a less than perfect angle, a bit of dust and cable losses, and 70% is a fair starting point for a portable panel you move around. If you angle a folding panel towards the sun through the day, you'll often beat the flat-surface figure, especially in winter when the sun sits low. Our solar pairing basics cover the voltage and current limits to check, and how much solar to recharge a power station has worked examples by battery size.
What it can't tell you
Averages hide bad weeks. A run of cloudy days during a storm or a wet weekend at the campsite can cut harvest to a fraction of the average, so carry more battery than the sums say if you're relying on it for a fridge or medical gear. The calculator doesn't check your panel's voltage against the station's limits, and it says nothing about connecting anything to your house wiring. That needs a licensed electrician and a proper changeover switch. For camping setups, see the 4WD fridge weekend guide.
Sources (checked October 2026): Bureau of Meteorology: About daily solar exposure data (IDCJAC0003) · Bureau of Meteorology climate statistics for Brisbane Aero, Sydney Airport, Melbourne Airport, Adelaide Airport, Perth Airport, Hobart, Darwin Airport, Canberra Airport, Cairns Aero, Townsville Aero and Alice Springs Airport · SolarQuotes: Heat reduces solar panel output
Save this guide for later
Pin it to a storm-prep or camping board so it's there when the power goes.
Save to PinterestQuick questions
How many peak sun hours does Brisbane get in winter?
About 3.3 in June. The Bureau of Meteorology's long-term average for Brisbane Airport in June is 12.0 MJ per square metre a day, and dividing by 3.6 turns that into kWh per square metre, or peak sun hours.
Why use 70% of the panel's rating?
Panels are rated in lab conditions. Heat, angle, dust, cable losses and the charge controller all take a cut, so a portable panel rarely delivers its full rating. You can change the figure in the calculator.