How much solar to recharge a 1kWh, 2kWh or 3kWh power station

Take your station's watt-hours, divide by the number of sun hours your city gets, then divide by 0.75 to cover heat and other losses. That's the panel wattage that puts a full charge back in one average day. For a 1kWh station in Brisbane it works out to about 410W of panels in June and about 200W in December. Hobart in June needs about 1,000W for the same job, which most 1kWh stations can't even take.

We haven't used any of these setups ourselves. The sun figures are Bureau of Meteorology long-term averages, the station limits come from the makers' Australian pages and manuals, and the rest is our arithmetic. All of it is linked at the bottom.

What a sun hour is

The Bureau of Meteorology publishes a figure called daily global solar exposure, which is the total sunlight reaching the ground in a day, in megajoules per square metre. Divide it by 3.6 and you get kilowatt-hours per square metre. Panel makers rate their panels at 1,000W of sunlight per square metre, so one kilowatt-hour per square metre is the same as one hour of the sun a panel's label assumes. That's a sun hour.

Brisbane's June average is 11.9 megajoules, so 11.9 / 3.6 = about 3.3 sun hours. Its December average is 24.0, which is about 6.7 sun hours. The sun doesn't actually shine at full strength for 3.3 hours and then stop. It's the whole day's weaker morning and afternoon light added up into the equivalent of full sun.

Why we use 0.75

A 400W panel doesn't give you 400W for each of those sun hours. EcoFlow's manual for its 220W panel says output drops 0.30% for every degree the panel sits above 25°C, so a panel at 55°C on a warm day loses about 9%. Add a bit for dust, a panel that isn't pointed straight at the sun all day, cable losses and the station's own charging losses, and 75% of the label is a fair working figure. It's our allowance, not a maker's number, so treat the results as a starting point.

The sum is: panel watts = battery Wh / (sun hours x 0.75).

Sun hours and panel size by city

The panel column uses 1,024Wh, the size of an EcoFlow DELTA 3 Plus or Bluetti Elite 100 V2. For Brisbane that's 1,024 / (3.3 x 0.75) = about 410W. In December every city on the list lands between about 160W and 240W, because summer days are long right down the country.

Darwin is the odd one out. Its dry season winter is its sunny time, and its lowest month is January, in the wet, at about 5.3 sun hours. Townsville and Brisbane get a gentler winter dip than the southern cities, while Melbourne and Hobart in June get less than a third of their December sun.

Scaling up to 2kWh and 3kWh

Double the battery and you double the panels. A 2,048Wh setup, such as a DELTA 3 Plus with a DELTA 3 Smart Extra Battery, needs 2,048 / (3.3 x 0.75) = about 830W to refill in a Brisbane June day and about 410W in December. A 3,072Wh setup needs about 1,240W in a Brisbane June and about 610W in December.

In Melbourne the same 3,072Wh needs about 2,300W of panels in June. That's a lot of roof, and more than the station can take anyway.

The station's solar limit

The station caps how much solar it will accept, and adding an extra battery doesn't raise that cap. The DELTA 3 Plus takes two inputs of up to 500W each at 11 to 60V, so 1,000W in total. The Bluetti Elite 100 V2 also takes up to 1,000W. The Anker SOLIX C1000 takes up to 600W at 11 to 60V, and the Jackery Explorer 1000 v2 has two DC8020 ports, each for a 100W or 200W panel, for 400W in total.

So flip the sum around and see what a day gives you. A Jackery with its full 400W of panels in Brisbane in June puts back about 400 x 3.3 x 0.75 = 990Wh, close to a full charge. The same setup in Hobart in June gives 400 x 1.4 x 0.75 = about 420Wh. A DELTA 3 Plus with 1,000W of panels in a Brisbane June gives about 2,480Wh, which covers a 2kWh setup but not 3kWh. A 3kWh battery in winter takes two sunny days to refill from empty on that station, in most cities.

You can connect more panel watts than the cap as long as you stay inside the voltage and current limits, and the station just takes what it can. That helps in the morning and on hazy days. Our solar pairing basics explain how to check those limits before you wire panels in series or parallel.

Cloudy days and storm blackouts

These are long-term averages, so they already include the cloudy days. They don't tell you about a run of grey days after a storm, when a heavy overcast can bring far less than the average. If you're buying solar for blackouts, size it on June and expect to be short in a storm. It's usually easier to start an outage with a full battery and treat the panels as a top-up. Our cyclone season guide covers the rest of a storm plan, and the runtime calculator helps you work out how much you'll use in the first place.

Angle matters most in winter. The BOM figure is sunlight on the ground, and a panel tilted up toward the low northern sun around midday catches more than one lying flat. Turning a folding panel to follow the sun two or three times a day is free power.

If you're working out a whole camping or caravan setup, our caravan sizing guide goes through the daily watt-hours first.

Where to buy in Australia

Buying from the brand's Australian store means 230V AU outlets, the local warranty and local support. Prices move around a lot, so check on the day.

• EcoFlow DELTA 3 PlusEcoFlow AustraliaSee it at EcoFlow Australia
• Bluetti Elite 100 V2Bluetti AustraliaSee it at Bluetti Australia
• Bluetti solar panelsBluetti AustraliaSee panels at Bluetti Australia