How Much Backup Power Do You Need for a 72-Hour Blackout?
A battery that keeps your phone charged for a long weekend may run out quickly once you plug in the fridge. For a 72-hour blackout, start with the appliances you want to keep on, not the biggest wattage printed on the box. An Australian household planning for storms, bushfire-related outages or a hot spell needs to answer two questions: how much energy will those appliances use over three days, and can the backup supply run them together? Once you have those numbers, battery sizes are much easier to compare.
The numbers that matter
Watt-hours (Wh) describe stored energy. Watts (W) describe the power needed at a particular moment.
Estimate a full day’s essential use, then multiply by three.
A 2 kWh station is not a promise of three days’ power; the appliances determine runtime.
If stored energy will not cover the plan, arrange dependable recharging or additional capacity.
What changes the amount of backup power you need?
Start with the essentials
Picture a day at home without mains power. You may need a charged mobile, some lighting and a fridge, but not the television or dishwasher. Write down how long each essential device needs to operate. Count every phone you plan to charge. If you rely on an electric pump for tank water, add that too; it is an easy load to miss on a regional property.
Handle powered medical equipment separately. Ask the treating clinician and equipment supplier for an approved backup plan, including tested runtime and when to relocate. Where applicable, arrange life-support registration with your electricity retailer or distributor. Unexpected outages can still happen, so registration does not replace that plan.
A fridge does not draw the same power all day
A router usually draws power for as long as you leave it on. A fridge works differently: the compressor cycles, so its running wattage does not tell you the full day’s consumption. Measure it over a representative day with a suitable energy meter. Allow for conditions as well. A fridge in a hot kitchen, with the door opening frequently, may use more than your quiet-day test suggests.
Some appliances need an extra kick to start
A station might have plenty of stored energy yet fail to start a fridge or pump. Motors can briefly need more power at start-up than while running. Check that requirement alongside the combined running watts of appliances you will use together. The manufacturer’s surge figure is a separate limit, not extra power you can use continuously.
Rated capacity is not all available at the socket
A battery labelled 2,048 Wh stores a rated amount of energy, but the inverter and the station’s own electronics use some of it. Connection method, load and operating conditions affect what reaches your appliances. Give the plan some spare capacity instead of matching the battery label exactly to your estimated demand.
Calculate your 72-hour energy requirement
Use these calculations for a steady load. For a cycling appliance, use measured daily energy where possible:
Daily energy (Wh) = power (W) × hours used each day
Three-day appliance energy (Wh) = total daily energy (Wh) × 3; allow separately for losses and reserve
Here is a worked example, with every load powered from the backup supply. The fridge’s 30 W is an assumed average over the whole day, including its cycling, rather than its compressor rating. These are illustrative figures. Replace them with measurements from your own equipment before buying a battery.
Device | Rated or Assumed Power | Daily Runtime | Daily Energy Use | 72-Hour Energy Use | Priority Level |
Phone charging | 10W | 2 hours | 20Wh | 60Wh | High |
Router | 15W | 8 hours | 120Wh | 360Wh | High if the network operates |
LED light | 8W | 6 hours | 48Wh | 144Wh | High |
Refrigerator | 30W average | 24 hours | 720Wh | 2,160Wh | High when refrigeration is essential |
Fan | 40W | 8 hours | 320Wh | 960Wh | Depends on heat and household needs |
Choose realistic running times
Suppose your router uses a steady 15 W and you need it for eight hours a day. It requires 120 Wh daily, or 360 Wh over three days. Check whether your nbn service also has a mains-powered connection box and add its consumption separately. Powering the equipment at home will not guarantee service if the wider network is affected.
Add the daily energy, then multiply by three
The phone, router and light in this example total 188 Wh a day: 564 Wh for three days. Include the fridge and that rises to 2,724 Wh. Add the fan for eight hours a day and it reaches 3,684 Wh. Those totals exclude conversion losses and any separate nbn box. EcoFlow AU’s portable power station sizing guide gives more detail on working through an appliance list.
Check output after checking capacity
Now look at the loads that overlap. Their combined running watts must fit within the station’s continuous output, and motor start-up must also stay within its limits. Where practical, avoid starting several demanding devices together. This check is separate from the Wh calculation: spreading loads out may reduce peak demand, but it does not remove the energy they use.
Treat a margin as an estimate, then test
For a rough first comparison, adding 20% takes the 564 Wh light-load example to about 677 Wh. That is a planning allowance, not a measured efficiency figure or a guarantee of runtime. Low loads left on for long periods can make the station’s own consumption matter. Refine the estimate with the manufacturer’s guidance and a trial of your setup, and leave charge for delays or extra use.
How different households change the calculation
These profiles use the example above. The figures describe appliance energy over three days, before losses and reserve. They are not battery-size recommendations. Your actual fridge, daily routine and local conditions can change the result substantially.
Load Profile | Essential Devices | Estimated Daily Demand | 72-Hour Demand Before Margin | Recharging Requirement |
Light | Phone, router, LED light | 188Wh | 564Wh | Depends on battery size and losses |
Moderate | Light loads plus refrigerator | 908Wh | 2,724Wh | Likely needed with a 1.5–2kWh station |
Higher | Moderate loads plus fan | 1,228Wh | 3,684Wh | Plan dependable recharging or more storage |
Medical needs | Depends on prescribed equipment | Device-specific | Calculate individually | Follow the clinical backup plan |
Phones, internet and lighting
A modest kit may be enough if you mainly need charged mobiles and light after dark. The router becomes a larger share of the budget if left on all day. Check nbn’s power-blackout advice for your connection type, and keep a battery radio and charged mobile as alternatives. Add the radio’s energy to the total if you intend to power it from the station rather than separate batteries.
Add the fridge and the budget changes
In this example, the fridge alone uses 2,160 Wh over three days. That is more than a nominal 2 kWh battery can store, even before losses. A laptop or extra phones add further demand. Either plan more storage or work out how you will recharge reliably. Do not stretch runtime by switching the fridge off for long periods without considering food safety; keep its doors closed and follow your state or territory food authority’s guidance.
Cooling and medical needs deserve their own plan
A 40 W fan for eight hours a day adds 960 Wh across three days. That is a significant extra load during an Australian summer outage, and it still does not mean the home will remain safe in extreme heat. If someone depends on cooling or powered medical equipment, plan a suitable alternative location and how to get there. Follow local emergency advice rather than waiting for the battery to run flat.
What about the kettle or air conditioner?
An appliance can be within the output limit and still use more energy than you want to spare. A 2,000 W kettle running for three minutes uses about 100 Wh before losses; repeat that throughout the day and it adds up. Air conditioning can be much more demanding over several hours. Check the label and likely runtime before adding these loads. Never bring an outdoor barbecue or camping stove inside as a substitute.
Match the power station to the load plan
The Australian EcoFlow models below illustrate the difference between storage and output. Capacity is rated base storage; usable energy will be lower. The continuous AC ratings are shown separately from short-duration surge ratings, so do not treat the surge number as an everyday operating limit.
Product | Capacity | Continuous AC Output | Surge Output | Suitable Load Profile | Main Limitation |
EcoFlow DELTA 3 (1500) | 1,536Wh | 1,800W | 3,600W | Selected essentials with lower simultaneous demand | Needs load management or recharging for higher three-day demand |
EcoFlow DELTA 3 Max Plus | 2,048Wh | 3,000W | 6,000W | More simultaneous devices or higher start-up demand | Still insufficient for some 72-hour plans without recharging |
DELTA 3 (1500): assess it against a smaller load plan
The EcoFlow DELTA 3 (1500) Portable Power Station has 1,536 Wh rated capacity, 1,800 W continuous AC output and a 3,600 W surge rating. Compare that with the 564 Wh light-load example, then allow for losses and test your actual devices. The fridge-inclusive example needs 2,724 Wh, so that plan already exceeds the station’s base storage. It would require recharging or more capacity. A higher output rating cannot make up that energy shortfall.
DELTA 3 Max Plus: more output, but still a finite battery
The EcoFlow DELTA 3 Max Plus Portable Power Station increases rated storage to 2,048 Wh, with 3,000 W continuous AC output and a 6,000 W surge rating. That gives more scope for compatible loads running together. It still falls short of the example fridge, phone, router and light demand of 2,724 Wh before losses. For that three-day plan, arrange reliable recharging or suitable extra storage rather than assuming the larger unit will last. EcoFlow AU’s portable power station range lets you compare other capacities.
Be realistic about recharging
Portable solar panels may help on a clear day, but a storm outage can come with poor sunlight. Shade, panel angle, smoke and cloud can reduce generation. Check the station’s input limits and panel compatibility, then plan for the energy you can realistically collect rather than the panel’s peak rating multiplied by daylight hours. Vehicle charging also depends on the charger and time available; never run an engine in a garage or enclosed space. EcoFlow AU’s home-backup guide to generator and solar power covers charging options.
Use Australian-compatible equipment and safe connections
Check the Australian model and manual for suitable outlets, output and charging connections. Plug compatible appliances into the station using sound leads within their ratings. A connection to fixed home wiring needs appropriate equipment and a licensed electrician; a lead plugged into a household power point is not an alternative. Queensland’s electrical-safety guidance explains why backfeeding can endanger people working on the network as well as those at home.
Choose against your own appliance list
For this example, three-day demand starts at 564 Wh for the light loads, rises to 2,724 Wh with the fridge and reaches 3,684 Wh with the fan. Your numbers will differ. Use them to shortlist a battery, check start-up and simultaneous output, then test the setup before an outage. If the figures only work with perfect sunshine or no spare charge, revise the plan while you still have time.
Common questions about three-day backup power
Does a 72-hour plan mean the power will be back by then?
No. It is a useful planning period, not a forecast from your electricity distributor. Check local outage information and emergency warnings, and have a plan for a longer disruption. Restoring power to a damaged regional line may involve different challenges from a short suburban fault.
How much capacity does an average household need?
An average is not much help when deciding which appliances you will back up. In this worked example, the light loads need 564 Wh over three days, while adding the fridge takes demand to 2,724 Wh. Neither figure includes losses. Start with your own appliances and running times rather than assuming a single advertised battery size suits every household.
Will my rooftop solar keep working?
Usually not if it is a standard grid-connected solar-only installation. Backup depends on how the inverter, battery and circuits are configured. Ask your installer which circuits will work during an outage and whether the battery can recharge from the panels while the grid is down. Australian Government guidance explains the role of backup-capable systems.
Can a portable station power the home switchboard?
Only through a suitable approved arrangement installed by a licensed electrician for that equipment. For ordinary portable use, connect compatible appliances directly to the station. Never plug it into a household power point to energise the wiring.
Will a 2 kWh battery last three days?
It can for some carefully measured, low-energy setups. It cannot cover every household. The example fridge alone uses 2,160 Wh over three days, already above 2 kWh before losses. If refrigeration is essential, plan enough usable storage or reliable recharging. Do not compromise safe food storage simply to reach the 72-hour mark.
What if the blackout lasts longer?
Review the remaining charge, the latest local advice and the needs of everyone at home. Cut optional loads and use a safe charging source if available. If you cannot maintain medical support, safe temperatures or other essential needs, use your planned alternative location. Make that decision while you still have enough power and time to organise the move.