How Long Can a Solar Battery Power a House?

Australia’s uptake of rooftop solar has made us world leaders in distributed renewable energy.  Many households are now looking beyond panels to solar battery installations to increase self‑sufficiency, reduce bills and improve resilience during blackouts.  Yet the simple question “how long can a solar battery power a house?” has no one‑size‑fits‑all answer. Runtime depends on battery size, household consumption, how you use your system and whether solar panels are available to recharge the battery. This article draws on independent research and government guidance to explain the factors that determine battery runtime and to help you choose the proper storage solution.

Understanding battery capacity and household consumption

The ability of a battery to keep your lights on is governed by its capacity, measured in kilowatt‑hours (kWh). One kWh represents the amount of energy required to run a 1 kW appliance for one hour. An article on battery sizing notes that a battery labelled 10 kWh powering a home that uses about 2 kWh per hour during a blackout would theoretically provide around five hours of backup.  In practice, real‑world performance is less neat: manufacturers build in a safety buffer so the battery isn’t completely drained, meaning usable capacity is typically 5–10 % lower than the rated capacity.  The Australian government’s energy guide echoes this, explaining that household batteries usually range from 4 kWh to 14 kWh and that the usable capacity of a lithium‑ion battery is slightly smaller than the total capacity because some charge must remain to protect battery health.

Your daily electricity usage is just as important.  According to an energy consumption survey, the nationwide average for a three‑person household is 18.71 kWh per day, a four‑person home uses 21.355 kWh, and households with five or more people consume about 25.43 kWh per day.  In Sydney, the daily average for a four‑person home is roughly 20 kWh, climbing to more than 23 kWh in winter and falling below 18 kWh in spring. Climate and lifestyle matter – homes in cooler regions like Hobart use considerably more energy than those in milder Melbourne. You should also consider high‑demand appliances: an energy‑use breakdown lists a refrigerator using 1.5–2 kWh per day, a few lights and a Wi‑Fi router about 0.5–1 kWh per day, but an air‑conditioner drawing 3–5 kWh per hour, an electric oven 2–3 kWh per use, and an EV charger 7 kWh or more per hour.  These large loads can drain a battery rapidly.

How long can a solar battery power a house?

In typical conditions a 10 kWh solar battery powering only essential appliances – lights, a fridge and maybe a fan – can run for about 24 hours.  Researchers at the Lawrence Berkeley National Laboratory found that a small solar‑plus‑storage system with 10 kWh of battery could meet critical backup needs through a three‑day outage in most counties in the United States, though this assumes careful energy management and adequate sunlight for recharging.  Without a solar array to replenish it, that same 10 kWh battery delivering around 2 kWh per hour will be exhausted after roughly five hours.  The big takeaway: runtime depends on what you plug in.  Turning off energy‑hungry heaters or air‑conditioners during an outage dramatically extends backup time.  Adding solar panels improves the picture because the battery can recharge during the day, effectively providing “limitless” backup as long as sunlight and careful usage continue.

How long can a solar battery power a house?

For essential loads like a refrigerator, lights and a few low‑watt appliances, a 10 kWh solar battery can typically power a home for about 24 hours.  If air‑conditioning, electric cooking or EV charging are involved, runtime falls to a few hours.  When combined with solar panels, the battery can recharge during the day and provide backup for several days, particularly if consumption is managed carefully.

What determines how long a battery lasts?

Every home uses power differently.  An EcoFlow guide identifies several factors that influence how long batteries can run: battery capacity, household energy use, inverter efficiency, sunlight availability and smart energy controls.  Let’s break these down.

Battery capacity and usable energy

Larger batteries hold more energy. Household units typically range from 4 kWh to 14 kWh.  Premium systems are modular; you can start with 10 kWh and expand to 40–80 kWh to cover an entire home.  Remember, you can’t drain a battery completely.  Manufacturers restrict the depth of discharge to preserve lifespan. For a 10 kWh battery, the usable capacity might be around 9 kWh after accounting for a 10 % buffer. Deeper discharges accelerate wear and shorten the battery’s life.

Household consumption and load management

Your load profile dictates how quickly stored energy disappears.  A home using 2 kWh per hour during an outage will drain a 10 kWh battery in five hours, whereas running only essential circuits might stretch backup to 24 hours.  The energy guide lists typical consumption: refrigerators use about 2 kWh per day, but air‑conditioners use 3–5 kWh per hour and EV chargers 7 kWh per hour.  Reducing demand by turning off high‑draw appliances or using efficient devices extends runtime.

Inverter and system efficiency

Solar batteries rely on inverters to convert between direct current (DC) and alternating current (AC).  This conversion isn’t perfect; there is typically around 10 % efficiency loss when charging and discharging a lithium‑ion battery.  Choosing a high‑quality inverter and matching it to your battery reduces these losses.

Sunlight and solar recharging

A battery paired with solar panels can recharge during the day. A 5 kW solar array in Sydney receiving about 4.5 hours of peak sun and performing at 75 % efficiency produces roughly 16.875 kWh of electricity per day. This energy can run the home and recharge the battery, enabling multi‑day independence during outages. Without solar, the battery can only provide what’s stored.

Smart energy controls

Modern battery systems incorporate smart controls that prioritise critical loads, schedule charging and discharging based on electricity tariffs, and can even participate in virtual power plants (VPPs).  Smart management extends runtime by shifting consumption to times of high solar production and turning off low‑priority devices during peak demand.  In regions with time‑of‑use tariffs, storing cheap daytime electricity and discharging it during the evening peak reduces bills and payback time.

What factors determine how long a solar battery can power a house?

A battery’s runtime is influenced by its capacity, the household’s power use, the efficiency of the inverter, sunlight for recharging, and whether smart controls manage loads. Larger batteries and lower consumption extend backup.  Pairing a battery with solar panels allows recharging during the day, while smart management shuts down non‑essential devices and stretches each kilowatt‑hour.

How long does a 10 kWh battery last?

Let’s apply the numbers. Suppose your home uses about 2 kWh per hour during a blackout (covering refrigeration, lighting and internet). A 10 kWh battery would be empty after around five hours. If you instead power only a refrigerator and a few lights, your hourly use might fall to 0.4 kWh, allowing the same battery to run for roughly 24 hours. Real‑world capacity is slightly lower due to the safety buffer, so plan for 9 kWh of usable storage. Adding solar panels changes the game – a 5 kW array producing 16.875 kWh per day can recharge the battery, potentially sustaining critical loads indefinitely.

How long will a 10 kWh battery last during a power outage?

A 10 kWh battery provides about 9 kWh of usable energy once you account for a safety buffer.  If your home draws 2 kWh per hour, that battery will power your house for roughly five hours.  By limiting use to essential circuits like the fridge and lights (around 0.4 kWh per hour), the same battery can supply backup for about 24 hours.  Pairing with solar panels extends runtime because the battery can recharge during the day.

Sizing a solar battery for your home

Proper sizing ensures you invest in the right amount of storage. The EcoFlow guide suggests a simple method: check your daily energy use, decide how many days of backup you need, and add a buffer.  For example, a home using 25 kWh per day that wants two days of backup would require 50 kWh, plus a 20 % buffer to cover cloudy weather, resulting in 60 kWh of storage.  For many Australian households, a 10 kWh system provides overnight backup for essential loads, while 40–80 kWh is needed to run an entire home for several days. Also consider whether you plan to add electric vehicles, heat pumps or pools, as these dramatically increase demand.

How do I size a solar battery for my home?

Start by checking your daily electricity usage (in kWh) on your bill. Multiply it by the number of days of backup you want and add a 10–20 % buffer for bad weather. If you need to power the whole house through multiple days of blackout, you may require 40–80 kWh of storage. For overnight backup of essential circuits, a single 10 kWh battery often suffices.

Beyond runtime: safety, lifespan and policy

A battery’s runtime is only part of the story.  Australian government guidance emphasises that lithium‑ion batteries now dominate the market because of their high performance, long lifetimes and low maintenance requirements.  Battery lifespan is typically 10–15 years, though it varies with usage and technology.  Safety is crucial: batteries should be installed by Clean Energy Council–accredited professionals, meet Australian standards, and be located according to building regulations.  Some states offer incentives, such as the Australian Government’s Cheaper Home Batteries Program, which discounts the cost of small‑scale battery systems from July 2025.

Not every solar‑plus‑battery system automatically provides backup during outages.  Solar Victoria warns that standard grid‑connected systems often shut down for safety, and only multimode systems designed for islanding can supply power when the grid is down.  Even then, the duration of backup depends on battery size, system design and the circuits selected.  If backup power is critical, discuss your needs with a professional installer and ensure your system is configured accordingly.

Conclusion

Solar batteries are revolutionising home energy in Australia.  How long they power your house depends on the balance between capacity and consumption, the presence of solar panels for recharging, and smart management.  A typical 10 kWh battery can keep essential appliances running for about a day, while bigger systems and careful load management extend independence to multiple days. Knowing your daily energy use and prioritising critical circuits are key to sizing a system that meets your needs. For expert advice and customised solar battery installations, contact Solar National. Our experienced team will design a storage solution tailored to your home, ensuring reliable backup, lower bills and a sustainable future.