KEY POINTS
- You will need a special backup battery to keep the lights on during a blackout. This is because standard batteries need grid power to operate.
- Backup batteries work on a separate circuit that is only connected to your essential appliances.
- To decide if a backup battery is worth it for you, consider both the upfront cost and the lifespan of the battery.
When it comes to blackouts, you can never be too prepared. For customers with rooftop solar, a solar battery with a backup system allows access to their stored electricity during grid uncertainty and blackouts.
This Canstar Blue article will discuss what a solar PV battery backup system is, how they work, how they differ from other old solar batteries on the market and whether it is worth the investment.
On this page:
- What is a solar battery backup system?
- How does solar battery backup work?
- How does a battery with backup differ from a regular solar battery?
- How much does solar battery backup cost?
- How do I know how much backup power I need?
- How do I access battery backup power?
- What is the lifespan of a solar battery backup system?
- Is solar battery backup worth it?
- Compare solar plans and prices
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What is a solar battery backup system?
A solar battery backup system is a solar battery designed to store electricity in order to power essential appliances during a blackout. A solar battery without backup won’t work during a blackout because it still relies on the electricity grid to work.
A quality solar system can also continue collecting energy from the solar panels during a power outage, so that the battery is not instantly depleted, though this will depend on the weather.
There are a few different levels of backup for solar panels — partial or full.
To determine which one you need, it might be worth considering:
- How often your neighbourhood experiences power outages
- How long they last
- Is your neighborhood situated in a bushfire or storm-prone region
- Which critical appliances do you need to continue running (e.g. fridges or internet modems).
While a solar battery backup system won’t mean that you can live off the grid forever, it could help power your essential appliances during a blackout.
How does solar battery backup work?
Solar batteries with backup capabilities will kick in during a blackout as long as there’s enough energy stored prior to the power outage.
The set-up is fairly simple: a cable is run from the battery and solar inverter to a select number of circuits in the switchboard, protected by a main battery circuit breaker and one changeover switch for protection.
This divides your home into three circuits: critical loads, essential loads and non-essential loads:
- Critical loads: Appliances such as life-sustaining equipment that must remain operational and cannot be turned off.
- Essential loads: Your fridge and lights may be put in the essential category.
- Non-essential: Creature comforts such as a coffee machine or gaming system might not be deemed essential and excluded.
If your power does fail, your battery should detect an outage and switch to blackout mode. These appliances would then draw electricity directly from the battery, meaning that your solar power can keep essential and critical appliances running.
How does a battery with backup differ from a regular solar battery?
The main difference between a regular solar battery and those with backup capabilities is that a regular battery can’t be used during a blackout.
Generally, rooftop solar systems, with or without a solar battery, are automatically switched off during blackouts to protect themselves from power surges.
It can, however, still be used at night or on cloudy days when your solar panels aren’t generating enough energy for your household. In contrast, a solar battery with backup capabilities can provide power both at night and during a blackout.
Depending on the model, a backup battery can also allow the solar panels to continue to generate power while in use – for the house and to recharge the battery.
You will need to speak with your solar installer and specify that you want solar backup included in your installation, as well as what level of backup you require.
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How much does solar battery backup cost?
Not all battery systems offer backup capabilities because they’re more expensive to buy and install. Prices can also vary significantly between partial and full backup functionalities.
Here are some factors influencing the final cost of a solar battery backup system:
Size of solar battery
A regular solar battery storage system without backup can cost between $1,000 and $2,000 per kilowatt hours (kWh) of storage capacity. If you’re interested in getting backup capabilities, expect to pay an additional $1,500 to $3,500.
A solar battery system with partial backup capabilities will require a smaller battery and inverter, which attracts a lower upfront cost.
Conversely, a solar battery with full backup functionality requires a larger battery and a larger inverter. Expect to spend more if you opt for the full backup option.
Energy needs
Evaluate and organise your appliances into the critical, essential and non-essential categories in the event of a power outage.
If powering critical and essential appliances is your utmost priority, partial backup capabilities should be more than sufficient to keep you going.
However, if you are averse to interrupted power and enjoy peace of mind, full backup functionality may be more suited to your lifestyle.
How do I know how much backup power I need?
How much power you’ll need during a blackout is contingent on how much energy you consume (or intend to consume during an outage).
Below is a simple example illustrating how you can measure the amount of backup power you may need for a 10-hour blackout.
Step 1: Assess which appliances you’d like to keep running in the event of a blackout. In this example, we’ll be using Appliance 1 and Appliance 2 as our essential appliances.
Step 2: Identify their power ratings. Their power ratings — denoted in watts or W — can be found on their respective labels. Make sure that their power ratings are converted into kilowatts (kW) by dividing them each by 1000.
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| Appliance name | Power rating |
|---|---|
| Appliance 1 | 100W (0.1kW) |
| Appliance 2 | 150W (0.15kW) |
Step 3: Measure their respective hours of operation over the blackout period you’d like to cover. In this example, we’ll assume a blackout window of 10 hours and four hours of operation for Appliance 1 and Appliance 2 respectively.
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| Appliance name | Power rating | Hours of operation |
|---|---|---|
| Appliance 1 | 100W (0.1kW) | 4 hours |
| Appliance 2 | 150W (0.15kW) | 4 hours |
Step 4: Multiply the kW power rating of each appliance by its hours of operation — these figures (in kWh) represent the total amount of energy each appliance consumes over a 24-hour window.
← Mobile/tablet users, scroll sideways to view full table →
| Appliance name | Power rating | Hours of use | Energy consumption (kWh) |
|---|---|---|---|
| Appliance 1 | 100W (0.1kW) | 4h | 0.4kWh |
| Appliance 2 | 150W (0.15kW) | 4h | 0.6 kWh |
Step 5: Add the total energy consumption of each appliance from step 4 — the final sum represents the total backup power you need to keep Appliance 1 and 2 running over a 10-hour blackout.
Total backup power required over 24 hours: 0.4kWh + 0.6 kWh = 1.0kWh
By assessing your essential or critical energy appliances, you can purchase or install an appropriately sized solar battery to meet your needs in the event of a blackout, be it with partial or full backup.
How do I access solar battery backup power?
When your solar system with backup is installed, your installer will configure the solar system and inverter in order for the system to work during a blackout. If a blackout were to take place, the switchover period should only take seconds.
Installing an extra inverter and the separation of essential vs nonessential circuits may incur additional installation charges.
What is the lifespan of a solar battery backup system?
The lifespan of a solar battery backup system is typically 10 to 15 years. Most solar panels, however, have a lifespan of 20 to 30 years, which means you may have to replace the battery system during this time.
According to SolarQuotes, however, an ageing, grid-connected solar battery can still serve as a full/partial backup as long as it has the minimum capacity to power your essential or critical loads during a blackout.
Your solar installer will give you information regarding the expected lifespan of your solar system, along with the warranty you’ll receive with your purchase.
Is solar battery backup worth it?
Solar batteries are a huge investment. Unless you’ve got a high-end model, you might find that not enough power is stored to last you through a blackout.
That being said, they can still be a great addition to a home solar system, depending on your circumstances. With the added benefit of accessing your solar energy at all times of the day, you can rest assured that you have at least enabled your system to operate at its best in all conditions.
More importantly, a solar battery is much more than its backup functions — purchasing a solar battery can possibly help you reduce your power bill, depending on your energy plan’s tariff structure.
If you’d like to learn more about all things solar batteries, visit Canstar Blue’s comprehensive guide to solar batteries.
Compare solar plans and prices
Here are some of the cheapest solar-specific deals from the retailers on our database. These costs are based on the Ausgrid network in Sydney but prices will vary depending on your circumstances. We show one product per retailer, listed in order of lowest price first. Annual price estimates assume general energy usage of 3900kWh/year for a residential customer on a single rate tariff. Price estimates exclude solar feed-in tariff credits. These are products from referral partners†. Our database may not cover all deals in your area, and please check retailer websites for up to date information. Here are some of the cheapest solar-specific deals from the retailers on our database. These costs are based on the Citipower network in Melbourne but prices will vary depending on your circumstances. We show one product per retailer, listed in order of lowest price first. Annual price estimates assume general energy usage of 4000kWh/year for a residential customer on a single rate tariff. Price estimates exclude solar feed-in tariff credits. These are products from referral partners†. Our database may not cover all deals in your area, and please check retailer websites for up to date information. Here are some of the cheapest solar-specific deals from the retailers on our database. These costs are based on the Energex network in Brisbane but prices will vary depending on your circumstances. We show one product per retailer, listed in order of lowest price first. Annual price estimates assume general energy usage of 4600kWh/year for a residential customer on a single rate tariff. Price estimates exclude solar feed-in tariff credits. These are products from referral partners†. Our database may not cover all deals in your area, and please check retailer websites for up to date information. Here are some of the cheapest solar-specific deals from the retailers on our database. These costs are based on SA Power network in Adelaide but prices will vary depending on your circumstances. We show one product per retailer, listed in order of lowest price first. Annual price estimates assume general energy usage of 4000kWh/year for a residential customer on a single rate tariff. Price estimates exclude solar feed-in tariff credits. These are products from referral partners†. Our database may not cover all deals in your area, and please check retailer websites for up to date information.
If you are on the hunt for the right solar battery system for your home, then be sure to check out some of the top contenders currently available in Australia below. These models have been broken into best for price, size, backup capabilities and more.
See the best home solar battery storage
Original reporting by Kelseigh Wrigley
Image Source: New Africa/Shutterstock.com
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