Whole-Home Backup vs Essential-Load Backup: Which Blackout Protection Suits You?

A home battery does not automatically keep your lights on in a blackout. Backup has to be designed in, and there are two main approaches. Essential-load backup moves selected circuits, such as the fridge, lights and internet, onto a backup sub-board. Whole-home backup keeps the entire switchboard running, as far as the battery and inverter power rating allow. For most Sydney homes, a well-chosen set of essential circuits gives the best balance of cost, battery runtime and reliability, while whole-home backup suits homes with larger systems and a genuine need to run more during outages.

Power and energy: the two limits that decide what runs

Every backup system has two separate limits, and confusing them is the most common source of disappointment.

• Power (kW) is how much the inverter can supply at any one moment. Exceed it, for example by running the oven, kettle and air-conditioner together, and the backup supply can shut down to protect itself.
• Energy (kWh) is how much is stored in the battery. It decides how long your loads can keep running before the battery is empty.

Appliances with motors or compressors, such as fridges and pumps, also draw a short surge when they start, so the inverter's surge rating matters too. The table below shows typical ranges; check the labels on your own appliances.

Essential-load backup

With essential-load backup, a licensed electrician moves your chosen circuits from the main switchboard to a separate backup sub-board. During a blackout, only those circuits stay powered. Common choices are the fridge and freezer circuit, lights, the kitchen and living area power points, the internet, a home office and sometimes a garage door or water pump.

Because large loads are left off, a modest battery lasts much longer and the inverter is unlikely to be overloaded. The trade-off is planning: circuits in older homes often mix loads, so a fridge may share a circuit with the kitchen power points, and some rewiring may be needed to separate what you want from what you do not. Our market lists an Essential-Load Backup Circuit from $990, added to a battery installation.

Whole-home backup

Whole-home backup connects the entire switchboard to the backup side of the system, so you do not need to decide in advance which circuits matter. That convenience comes with conditions. The inverter's backup power rating must realistically cover the way your household uses power during an outage, and the battery drains faster because nothing is excluded. You may still need to avoid running several large appliances at once. In three-phase homes, check whether the system backs up all three phases or only some circuits. Whole-Home Backup is listed from $2,490, added to a battery installation, where the battery and inverter power rating allow.

Sizing the battery for the backup you want

A simple way to test whether a battery will carry you through an evening outage is to add up what you want running and for how long. As an illustration, a fridge averaging 150 W, a modem and router at 20 W, and around 130 W of lighting and a television come to roughly 300 W together. Over ten hours, that is about 3 kWh, which a typical home battery can supply comfortably with plenty left over. Add a split-system air-conditioner running at 1.5 kW for four hours and you need another 6 kWh, which changes the picture quickly.

Remember that the battery may not be full when the grid fails, particularly on a winter evening after a cloudy day. That is why we size backup around the loads you truly need, rather than around the best-case scenario. The exercise is also useful for another reason: it shows most households that a focused essential-load design meets their needs at a lower cost.

Changeover and solar during a blackout

Backup-capable systems switch over automatically when the grid fails. Depending on the equipment, the changeover ranges from almost unnoticeable to a brief interruption, so clocks may reset and desktop computers may restart. If a device cannot tolerate any break, a small uninterruptible power supply for that device is still worthwhile.

A standard grid-connected solar system shuts down in a blackout for the safety of line workers. With a backup-capable battery system, the panels can keep running on the backup side and recharge the battery during daylight, which makes a real difference in longer outages. Confirm this capability for any system you are considering.

Which option suits your home?

Here is how the choice typically plays out across Sydney and surrounding regions:

• Occasional short outages in suburban Sydney: essential-load backup covering the fridge, lights and internet is usually enough.
• Working from home: essential circuits that include the office, modem and router keep you online.
• Regular storm outages in areas such as the Blue Mountains or Southern Highlands: a larger battery and either whole-home backup or a generous essential set, including any water pumps. Properties that want to go further can read about off-grid and hybrid systems.
• Homes relying heavily on ducted air-conditioning: essential backup, since large air-conditioning loads would drain most batteries within a few hours anyway.
• Larger homes with a big battery and a high-power inverter: whole-home backup becomes practical and convenient.

Our solar and battery calculator helps estimate battery size, and our home battery page explains the batteries we install.

Next steps

Our published indicative price for a 10 kWh battery in Sydney is $8,000-$11,000 after the federal battery discount. If you want the battery and backup organised together, the Blackout Protection Package in our energy market starts from $10,490, including a backup-capable inverter, essential circuits and automatic changeover. Prices are indicative and confirmed after a site assessment. Request a quote and tell us what you need running during a blackout.

Frequently asked questions

Can I charge my electric vehicle from the battery during a blackout?

Technically it may be possible on some systems, but it is rarely a good idea. A home EV charger draws several kW, which can exceed the backup power rating or empty the battery in a short time, leaving nothing for the fridge and lights. For that reason, most backup designs leave the EV charger off the backup circuits. If you need some charging during outages, discuss it at the design stage.

How do I make sure the battery has charge left when a blackout hits?

Most batteries let you set a backup reserve, a portion of capacity the battery will not use for everyday savings. A higher reserve gives more blackout protection but reduces daily bill savings. A common approach is to keep a modest reserve most of the year and raise it before forecast storms or bushfire weather. We set the reserve at commissioning and show you how to adjust it in the app.

Does backup still work if the battery is added to an older solar system?

The battery can usually supply backup circuits if its own system is backup-capable, but whether your existing solar inverter keeps generating during the outage depends on how the equipment is connected and whether the components are compatible. If it cannot, the battery will not recharge from the panels until the grid returns. We check this during the assessment and explain the result before you decide.