The right home battery size comes from your bills, not a price list. How to size one to your evening usage and solar surplus in 2026, and the Victorian mistakes that waste money.
The first question almost everyone asks when they start looking at a home battery is “how many kilowatt-hours should I get?” It feels like the right question. It usually gets answered with a number pulled off a price list, one that has more to do with what the installer wants to sell than with how your household actually uses power. The honest version is that the right size is the one that matches your bills, and working that out takes about ten minutes with your own usage data. Here is how to do it.
A home battery does one core job: it stores your cheap or self-generated daytime energy and gives it back in the evening and overnight, so you buy less power at the expensive times. That means the useful size of a battery is not set by your total usage, or by the size of your roof. It is set by two things: how much energy you use when the sun is down, and how much surplus solar you have during the day to fill it back up. Buy more capacity than those two numbers can cycle, and you are paying for storage that sits empty.
Before anyone quotes you a battery, you want three figures. All of them come from data you already have.
You do not need special software for this. Your electricity retailer can give you your interval data, and most now show a daily usage breakdown in their app or on the bill itself. Two things are worth pulling out:
This is what we mean when we say we size a system to your bills rather than to a package. The number falls out of your data, not out of a brochure.
| Mistake | What it looks like | What it costs you |
|---|---|---|
| Oversizing | A big battery bought on “future-proofing”, far larger than your evening use or solar surplus | You pay upfront for capacity that never cycles, so it never earns its keep |
| Undersizing | A small battery that empties by 9pm | You are back on peak-rate grid power for the rest of the night |
| Ignoring future load | Sizing only for today, with an EV or heat pump coming | A system that fits now but is too small in two years |
| Sizing to the roof | Matching the battery to solar capacity instead of usage | Storage you cannot fill, or cannot use in the evening |
As a rough orientation only, the federal Cheaper Home Batteries Program supports systems from 5 kWh up to 100 kWh, with the incentive counting the first 50 kWh of usable capacity. Most single Victorian homes land well inside the lower end of that band, because a typical household does not have the overnight load or the daytime surplus to justify the top of the range. Where exactly you sit depends on your evening usage, your solar, and whether you are adding an EV. There is no single “right” number that applies to every home, and anyone who gives you one without looking at your data is guessing.
Sizing advice is only honest if the person giving it is not tied to a single product. E3 Energy installs both Fox ESS and Sigenergy, which means the sizing conversation comes first and the product follows, rather than the other way around. We are a Solar Victoria Authorised Retailer and a New Energy Tech Consumer Code (NETCC) Approved Seller, so the quote you get has to meet those consumer protections. We will look at your actual usage data, check what your solar can realistically fill, and recommend a size that fits your household in Melbourne or across Victoria, not a box off a menu.
There is no single answer, because it depends on how much power you use in the evening and overnight and how much daytime solar surplus you have to recharge it. Most single Victorian homes sit at the lower end of the eligible range rather than the top. The reliable way to find your size is to look at your own interval data and evening usage rather than a package figure.
No. A battery only earns its keep on the energy it cycles each day. If it is larger than your evening usage or your daytime solar surplus, part of it sits empty and you have paid for storage you never use. The goal is the right size, not the biggest.
In most cases, yes. Many homes add storage to a solar system they already have. The right size still comes from the same two questions: your evening and overnight usage, and how much surplus your existing panels export during the day. We assess compatibility before recommending anything.
It is worth factoring in. An EV, or a heat pump, materially changes your usage and can justify a larger battery than your current bills alone would suggest. If a big new load is likely within a couple of years, we size with that in mind rather than leaving you to replace the system.
We start from your electricity data: your daily usage split into peak and off-peak, your seasonal swing, and how much solar you currently export. From there we match a battery, from either Fox ESS or Sigenergy, to what your household actually uses, and confirm the recommendation with you before you commit.
