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A typical 10kWh solar battery can power essential appliances like a fridge, lights, and modem for 10 to 20 hours during a blackout. However, this duration depends entirely on your battery's size, which specific appliances you run, and whether your solar panels can recharge the battery during the day. With careful management and sunny weather, a well-designed system can keep you powered for several days.
How long can a solar battery keep the lights on during a blackout?
One of the main reasons Australian homeowners invest in a solar battery is for peace of mind during a power outage. Knowing you can keep the fridge cold and the lights on when the grid goes down is a powerful motivator. But the answer to how long your battery will last isn’t a simple number; it’s a dynamic calculation based on three key factors:
- Your battery’s storage capacity: How much energy it can hold.
- Your home’s energy consumption: What you choose to power during the outage.
- Solar recharging: Whether your solar panels can top up the battery during a blackout.
Understanding these elements is the first step to replacing uncertainty with clarity about your energy security.
Understanding battery capacity (kWh) vs. power output (kW)
To get a clear picture of battery performance, it’s crucial to understand two key terms: kilowatt-hours (kWh) and kilowatts (kW).
Think of capacity (kWh) as the size of your battery’s fuel tank. It’s the total amount of energy your battery can store. A 10kWh battery, for example, holds 10 kilowatt-hours of energy.
Think of power output (kW) as the size of the pipe coming out of that tank. It determines how many appliances you can run simultaneously. A battery might have a 5kW continuous power rating, meaning it can deliver up to 5 kilowatts of power at any given moment. If you try to run more appliances than the kW rating allows, the system may overload and shut down.
It’s also important to know the difference between ‘nominal’ and ‘usable’ capacity. Due to how batteries work, you can’t always use 100% of the stored energy without affecting the battery’s lifespan. The ‘usable capacity’ is the actual amount you can draw. Modern lithium-ion batteries, like those from Sungrow and Sigenergy, offer a high depth of discharge (DoD), meaning their usable capacity is very close to their nominal capacity, often 95% or more.
What can you realistically power during an outage?
A common misconception is that a battery will power your entire home as if nothing has changed. While whole-home backup is possible, it drains the battery very quickly. The smarter approach is to back up only your “essential loads.”
During the installation of a battery system with blackout protection, your accredited electrician will help you decide which circuits to connect to the backup system. This is a critical conversation to have.
Essential loads typically include:
- Refrigerator and freezer
- LED lights in key areas
- Internet modem and router
- A few power points for charging phones and laptops
- Medical devices, if applicable
High-drain, non-essential loads to avoid running are:
- Air conditioners and electric heaters
- Ovens and cooktops
- Washing machines and dryers
- Pool pumps and electric hot water systems
By focusing only on the essentials, you can dramatically extend your battery’s runtime.
Let’s do the maths: A real-world example
So, how does this translate into hours and days? Let’s imagine you have a fully charged battery with 10kWh of usable capacity and you’re only running the essentials during a blackout.
- Modern Fridge/Freezer: Cycles on and off, using about 1.5 kWh over a 24-hour period.
- LED Lights: A few lights on will consume around 0.05 kW (or 50 watts).
- Internet Modem: Uses about 0.015 kW (15 watts).
- Device Charging & Standby: Another 0.02 kW (20 watts).
Your continuous load at any one time might be between 200–300 watts. If we take an average load of 400 watts per hour (0.4kW) to be conservative, the calculation is simple:
10 kWh (battery capacity) ÷ 0.4 kW (your load) = 25 hours of runtime.
This is a simplified estimate, but it shows that a typical 10kWh battery can comfortably get you through a full day and night without any solar input.
The Game-Changer: Recharging your battery from the sun
Here’s where a properly configured solar and battery system truly shines. Unlike a diesel generator, your system can use the sun to replenish what you use. If your solar and battery system is set up with blackout protection, your solar panels can continue to safely generate power and recharge your battery even when the grid is down.
On a sunny day, your panels can power your essential loads directly while also fully recharging your 10kWh battery. This means you could potentially stay powered indefinitely, or at least through a multi-day outage. On overcast days, your solar generation will be lower, but it will still help to slow the battery’s depletion and extend its runtime.
How to make your battery last longer in a blackout
When an outage hits, a few simple habits can make a big difference to your battery’s endurance:
- Be ruthless with your usage: Turn off every non-essential appliance at the wall to avoid “phantom loads” from devices on standby.
- Minimise fridge use: Avoid standing with the refrigerator door open. Grab what you need and close it quickly to conserve energy.
- Monitor your system: Use your battery’s mobile app. Modern systems from brands like Sigenergy, Sungrow, and Tesla offer sophisticated apps that provide real-time data on your battery’s charge level and your home’s consumption. This allows you to see exactly what’s using power and make informed decisions to preserve it.
- Use smart features: Some systems have intelligent functions to prepare for outages. For example, Tesla’s “Storm Watch” feature uses weather forecasts to automatically charge the Powerwall to full capacity before a storm is predicted to hit.
Conclusion: It’s about preparation and peace of mind
Ultimately, a solar battery’s purpose during a blackout isn’t to let you live without limits, but to provide you with safety, comfort, and connection. The runtime isn’t fixed—it’s a flexible resource that you control.
The key is preparation. By understanding your own energy needs and discussing your goals for blackout protection with an accredited installer, you can design a system that gives you genuine confidence. A correctly sized battery, combined with defined essential loads and the ability to recharge from the sun, is the formula for true energy resilience.
If you’re considering a battery and want to ensure it meets your expectations for blackout protection, connecting with an experienced installer is the most important next step. They can help you analyse your usage and design a system that delivers peace of mind when you need it most.
