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How Long Would a Home Battery Run My House in a Blackout? Calculator
Checked and updated by our licensed electricians: October 2026
How long would a home battery actually run your house when the power goes out? Pick the battery, how charged it is, tick what you want to keep running and say how much solar is on the roof. In about a minute you get an honest estimate in hours or days, with and without sun, and a check on whether your list can all run at once, with no details asked for. If you want it, you can then ask us to text you the estimate with our Northern Rivers Battery Buyer’s Guide. Built for Northern Rivers homes, where storms, floods and fallen trees take the power out for hours and sometimes days.
How the estimate is worked out
Two numbers decide a blackout. Battery energy (kWh) is how long you can run. Inverter output (kW) is how much you can run at once. The calculator uses these assumptions, so you can see exactly what sits behind the result:
- About 90 per cent of the battery nameplate is counted as usable, allowing for round-trip losses and a small reserve.
- Typical appliance draws while running: fridge and freezer 0.15 kW, lights, phones, wifi and modem 0.1 kW, TV and a laptop 0.12 kW, ceiling fans 0.1 kW, a tank or bore water pump 0.2 kW (it cycles), one split-system air conditioner 1.0 kW, electric storage hot water 0.7 kW, a pool pump 0.9 kW, electric cooking 0.3 kW averaged over a day of meals, an EV on a 7 kW charger 7 kW, and a whole house running as normal about 1 kW (around 24 kWh a day). Yours may be higher or lower; the peak figures used for the at-once check are higher.
- Solar on an average Northern Rivers day: about 3.8 kWh for every kW of panels (the Clean Energy Regulator rates our zone at 1.382 MWh per kW a year). A stormy day is counted as a quarter of that, because the outages that matter usually come with weather.
Running time = usable kWh at the charge you chose, divided by the kW your list draws. Read more in whole-home vs essential-circuits backup and blackout backup batteries for Northern Rivers homes.
Why Northern Rivers homes ask this first
In March 2025, ex-Tropical Cyclone Alfred left tens of thousands of homes and businesses across the region without power, some for days, mostly from fallen trees and branches. The 2022 floods cut power to many homes too. When the grid goes down, solar panels on their own go down with it. A battery system set up for backup separates your home from the grid, keeps the fridge, lights, water pump and internet going, and on a sunny day the panels recharge the battery while the house runs.
A typical install from us gives full home backup, running all circuits unless you ask us to leave some out, such as an EV charger or a pool pump. On the site visit before install day we look at where the battery and inverter can go, including your property’s flood history, and agree what stays on. See where a home battery can be installed.
Batteries we install for backup
- Sigenergy (premium): 9 kWh modules, so 9, 18, 27, 36 or 45 kWh, with an optional EV charger that works with the battery. Sigenergy batteries.
- GoodWe ESA (mid-tier, very high quality): 8 kWh modules, so 8, 16, 24, 32 or 40 kWh. GoodWe batteries.
We also install Sungrow, SolaX and Tesla batteries. Not sure which size suits you? Take the 60-second battery quiz, see what one costs with the solar and battery price calculator, and check the federal rebate with the battery rebate calculator. All our free calculators are on one page.
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Backup is one chapter of the home battery buyer’s guide; already have solar? See whether it is battery-ready with the battery-ready checker.
Weighing a generator against the battery? Our generator vs home battery guide for Northern Rivers blackouts compares fuel, noise, switch-over and safety, and turns your outage plan into litres of petrol or kWh of battery.
Air conditioning is the load that decides most blackout plans: our air conditioning on solar and a battery guide shows what splits and ducted systems really draw and how to pre-cool on solar.
A pool pump should be the first thing left off the battery in a blackout: our pool on solar guide explains why and how to time it instead.
Questions we get asked
How long will a home battery run my house in a blackout?
It depends on two things: how much energy is stored (kWh) and how much your appliances draw (kW). A 16 kWh GoodWe or 18 kWh Sigenergy battery running the fridge, lights, wifi, fans and a water pump (about half a kilowatt together) lasts well over a day. Add a split-system air conditioner and that drops to around 8 to 10 hours. The calculator on this page works it out for your own list of appliances.
Does solar keep working in a blackout?
Only with a battery system set up for backup. Plain grid-connected solar switches off when the grid goes down, for the safety of the people fixing the lines. A backup-capable battery system separates your home from the grid and keeps the solar running, so on a sunny day the panels recharge the battery while the house runs. That is why a long outage in summer is far easier than one in a week of storms.
Can I run the air conditioner and the oven at the same time on battery?
Sometimes. Battery size decides how long you can run; the inverter output decides how much you can run at once. A single-phase home battery system typically supplies about 5 to 10 kW at once, depending on the model. Several heavy appliances together can go past that and the system will trip, so during an outage run the big items one at a time. We size the inverter to your home and explain what it can carry at the site visit.
Which appliances use the most battery in a blackout?
Electric storage hot water, air conditioning, pool pumps, ovens and EV chargers. A fridge, lights, phones, wifi, fans and a water pump are small. Most of our customers keep the EV charger off during an outage and let the hot water wait, and the battery lasts far longer.
Do you set up whole-home backup or just essential circuits?
A typical Sun Connect Solar install gives full home backup, running all circuits, unless you ask us to leave some out, such as an EV charger or a pool pump. Essential-circuits backup, which powers only the circuits you choose, is also possible. We agree what stays on at the site visit before install day.
Do I have to give my details to see the result?
No. The estimate shows on the screen as soon as you have answered the four questions, with nothing to fill in. Under the result there is an optional box: add your first name, mobile and postcode and we text you the estimate with a link to our Northern Rivers Battery Buyer’s Guide, plus two times for a free 15-minute phone call about what you want kept running, which you can take or leave.
Is this calculator a promise of how long my battery will last?
No. It is an estimate from typical appliance draws, about 90 per cent of the battery nameplate counted as usable, and an average Northern Rivers solar day. Your appliances, the season and the weather all change the answer. We size the real system from your power bills and what you want kept running, and we visit your home before install day.
How much does a backup battery cost in the Northern Rivers?
Use our solar and battery price calculator for a range after the federal rebate. Prices depend on the size, the brand (Sigenergy premium, GoodWe mid-tier) and your switchboard. We build the federal Cheaper Home Batteries rebate into every quote and handle the paperwork.
