A battery suits some households and not others

By Oliver Hill

The question is shape, not price

A battery mainly does one thing. It moves power you generated earlier to a time you need it later. Some can also be set to charge from the grid on a cheap rate, which changes the sums, but your own surplus is the core case. Everything about whether it suits you follows from how much power you need later, and when.

That is why two houses with the same bill, the same roof and the same quote can get genuinely different answers.

When does your house actually use power?

This is worth thinking about before anything else, and you can do it without any data. Run through a normal weekday. Who is home, and when. When the heating or cooling runs. When the washing, the dishwasher, the hot water and the car charging happen. What is still drawing power after everyone has gone to bed.

A household that is busy from five until ten at night has the shape a battery fits. A household whose consumption is mostly in daylight does not, because that power is already being used as it is made.

The evening-heavy household

Family homes through Caroline Springs, Hillside and Taylors Hill often fall here. Several people home after school and work, climate control running into the evening, and a meaningful load after dark. These households export a lot of what they generate during the day and buy it back at night, which is precisely the gap a battery closes.

The empty-all-day household

Smaller homes through Seddon and Yarraville, where people are out on weekdays, can look like good candidates because they export so much. Often they are, but the evening load has to be big enough to be worth storing for. A two-person household whose evening consists of lights, a television and a dishwasher may find the battery larger than the load it is covering.

Ducted heating is a point in favour

Ducted heating tends to run in the evening and early morning, on the shoulders of the solar day and heaviest in the months when generation is lowest. If it is your main heating, it is one of the strongest arguments for storage, because it is a large load that consistently falls outside your generation.

Ducted cooling usually argues the other way. It tends to run hardest in the afternoon when the array is producing, so more of it is covered directly and less of it needs storing.

A pool mostly argues against

A pool pump is a large load, but it is one you can move. Running it in the middle of the day turns it into daytime consumption, which is exactly what you want and what a battery is not needed for. If your pump currently runs overnight, changing the timer is free and does some of what a battery would do.

An EV competes with the battery

This one catches people out. An electric car is a large, flexible load, and if it can be charged during the day it is a better use of surplus generation than storing that surplus in a home battery would be. If the car is usually away during daylight and charges overnight, the picture changes, and the two can work together. Either way, an EV is a reason to think about the whole picture rather than to add a battery reflexively.

How big is your existing solar?

If you already have panels, the surplus available to charge a battery is capped by what that array produces beyond what you use. A modest system on a household with high daytime use may leave very little over. The first question there is often whether to add panels rather than storage. Adding a battery to solar you already have goes through what a retrofit involves.

When a battery would be oversized

The most common mistake is buying storage sized to the household you imagine rather than the one you have. A battery that is routinely part-charged, or that routinely still has charge left in the morning, is larger than it needed to be. Size it to the evening load you actually have.

When solar only still makes more sense

Plenty of households in the west are better served by more panels than by storage, at least for now: daytime occupancy, a shiftable pool pump, modest evening consumption, or an existing array too small to fill a battery. That is not a permanent verdict. It is the right answer for the household as it is today, and households change.

Homes in Werribee and Point Cook span both patterns, which is why the answer is worth working out for your own house rather than taking from a neighbour.

Backup is a separate reason

Some people want a battery so the house keeps running in an outage. That is a legitimate reason to buy one, and it is worth being clear with yourself that it is the reason. Backup is worth something real, but it is not a saving, and it should not be presented as one.

And the money

Once you know your household is the right shape, the cost question is a separate one with real numbers attached. Is a home battery worth it in Victoria has what storage costs in Victoria after rebates and how it compares with panels alone. Time of use or flat rate in Victoria is worth a look too, because the tariff you are on changes what a battery is worth.

Common questions