A battery sizing guide for Mid North Coast NSW homes
What Size Solar Battery Do I Need?
The right battery isn’t the biggest one you can afford. It’s the one that covers what you use after the sun goes down, that your panels can still fill on a grey June day, and that makes the most of how the rebates are tiered. Here’s how to work that out for a home anywhere from Coffs Harbour to Forster.
The short answer
Most Mid North Coast homes suit a battery with 10–16kWh of usable capacity. Larger homes with evening air conditioning, a pool pump or regular long blackouts can justify 20–28kWh.
The quick rule: match the battery to what you use between sunset and sunrise, then make sure your solar system can refill it on a winter day. Because the federal rebate pays its full rate on the first 14kWh and the NSW VPP incentive stops counting at 28kWh, capacity beyond those points costs you noticeably more per kWh.
How to Size a Home Battery in Four Steps
You'll need a recent power bill, and your solar system size if you already have one.
1
Find your overnight usage
A battery’s main job is covering the hours your panels aren’t producing, roughly 4pm to 7am. The best source is the half-hourly data from your retailer’s app or portal, which shows exactly how much you use in that window.
No interval data? For a household that’s out during the day, 60–70% of total daily use typically happens after dark. So a home using 16kWh a day is likely using 10–11kWh overnight.
2
Decide what the battery is for
Bill savings, blackout backup, or both. For bill savings, you want enough capacity to cover the evening peak and overnight use. For backup, you also want a reserve left in the battery at all times, often 20–30%, so there’s something there when the power drops.
If storms knock out your supply a few times a year, that reserve is worth planning for rather than hoping the battery happens to be full.
3
Check your solar can fill it in winter
On the Mid North Coast, each kW of panels makes about 3kWh on a June day. Multiply your system size by 3, take away what you use during the day, and what’s left is the largest battery you can reliably fill in winter.
A 6.6kW system makes about 20kWh in June. With 6kWh of daytime use, that leaves around 14kWh for the battery. Anything bigger will sit partly empty for a few months of the year unless you add more panels.
4
Check the power, not just the capacity
Capacity (kWh) is how long a battery lasts. Power (kW) is how much it can run at once. A battery that can deliver 5kW won’t run a ducted air conditioner, an oven and a kettle at the same time, no matter how full it is.
For whole-home backup, check the backup power rating and whether the whole switchboard or only selected circuits are backed up.
Battery Size by Overnight Usage
Use this as a starting point. Your interval data will tell the real story.
| Overnight use (4pm–7am) | Typical household | Suggested usable capacity | Solar needed to fill it in winter* |
|---|---|---|---|
| 5–8kWh | Couple, gas cooking, modest evenings | 8–10kWh | 6.6kW |
| 8–12kWh | Family of 3–4, split systems | 10–14kWh | 6.6–8kW |
| 12–16kWh | Family of 4–5, electric cooking, dryer | 14–18kWh | 8–10kW |
| 16–25kWh | Large home, evening air con, pool or pump | 20–28kWh | 10kW inverter with ~13kW panels |
*Assumes a north-facing Mid North Coast roof making about 3kWh per kW on a June day, with typical daytime use. East–west roofs and shaded sites need more panels to do the same job.
Three Battery Sizing Examples From Around the Region
The same four steps, applied to three very different homes.
Retired couple, Laurieton
14kWh a day · home most of the day · existing 6.6kW solar
Because they’re home, about half their power is already used straight from the panels. Overnight use is around 7kWh.
What we’d suggest: a battery of about 8–10kWh. Their solar has plenty left over to fill it even in winter, and going bigger wouldn’t save them more because they simply don’t use more than that at night. A smaller battery also sits entirely in the full-rate rebate tier.
Family of four, Port Macquarie
16kWh a day · out until mid-afternoon · existing 6.6kW solar
The same family from our solar sizing guide. Overnight use is around 10–11kWh, and they lose power a couple of times a year in storms.
What we’d suggest: about 13–14kWh usable, which covers the night with a 20% backup reserve and is about the most their 6.6kW system can refill on a June day. If they want 16kWh or more, we’d add panels at the same time.
Acreage near Taree
28kWh a day · evening ducted air · tank pump · rural line
Overnight use is 16–18kWh, and outages after storms can last more than a day. Their old 5kW solar system makes barely 15kWh in June, which can’t fill a meaningful battery once the house is running.
What we’d suggest: upgrade to a 10kW inverter with about 13kW of panels, and install a 20–25kWh battery. For long outages, solar refilling the battery each day does more than a bigger battery would. Rural supply lines can have tighter connection limits, so we confirm approvals first.
Sizing for Blackouts on the Mid North Coast
When an east coast low brings down lines between Kempsey and Taree, the question isn’t “how big is my battery” but “what do I need to keep running, and for how long?”
Essentials are smaller than you’d think. A fridge, freezer, lights, internet and a water pump use roughly 5–8kWh a day. Keeping a 30% reserve in a 14kWh battery holds back about 4kWh at all times, which gets those essentials through the night.
Solar is what gets you through day two. If your battery can keep your panels running during an outage, even a cloudy day will top it back up. That’s worth checking before you buy, because not every system does it the same way.
Big loads drain it fast. Ducted air conditioning, an electric oven or a pool pump can use more in an hour than the essentials use all day. During an outage, turning those off does more than a bigger battery.
VPPs and backup can work together. If you join a Virtual Power Plant for the NSW incentive, set your backup reserve so the VPP can’t draw the battery below it. Ask how this works before you sign up.
| Essential load | Approx. energy per day |
|---|---|
| Fridge | 1–1.5kWh |
| Chest or upright freezer | 0.7–1kWh |
| Lights, TV, internet, phone charging | 1.5–2kWh |
| Water pressure or tank pump | 0.5–3kWh |
| CPAP or other medical equipment | 0.5–1kWh |
| Typical essentials total | 5–8kWh |
Indicative figures. Older fridges and deep freezers can use considerably more.
How the Rebates Shape the Right Size
Both battery incentives available in NSW are calculated on usable capacity, and both give less back as batteries get bigger.
The federal Cheaper Home Batteries Program pays its full rate on the first 14kWh, a reduced rate up to 28kWh, and a much smaller rate beyond that. The NSW VPP incentive applies to batteries up to 50kWh but is only calculated on the first 28kWh.
What that means in practice: every kWh you add past 14kWh costs you more out of pocket than the one before it, and past 28kWh you’re paying for nearly all of it yourself. That’s fine if you’ll use it every night. It’s poor value if it only gets used during the odd blackout.
The federal rate also steps down roughly every six months, so a battery you’re confident you’ll grow into is often better installed now than added later.
| Usable capacity band | Federal rebate | NSW VPP incentive |
|---|---|---|
| First 14kWh | Full rate | Counted |
| 14–28kWh | Reduced rate | Counted |
| 28–50kWh | Much smaller rate | Not counted |
Rebate rates change regularly. Your written quote should show the usable capacity, certificate count and rebate rate assumed.
Battery Sizing Mistakes We See on Other Quotes
Most come from sizing to a daily total instead of an overnight one.
Sizing to total daily usage
If you use 16kWh a day but 6kWh of it comes straight from your panels, you don’t need a 16kWh battery. You need one that covers the other 10kWh.
Forgetting winter
A 20kWh battery on a 6.6kW system looks great in January and sits half empty in July. The panels have to be able to fill it.
Comparing total instead of usable capacity
Two batteries with the same number on the brochure can deliver quite different amounts of usable energy. Always compare usable kWh.
Ignoring the power rating
A big battery with a small power output can still trip out when the air conditioner and oven run together. Check the kW figure, especially for backup.
Planning to charge the EV from the battery
An EV can empty a home battery in a couple of hours. Charging the car from solar during the day and keeping the battery for the house is almost always the better arrangement.
Buying for a blackout that happens twice a year
Doubling a battery’s size to cover rare, long outages is expensive. Solar recharging, a sensible reserve and turning off big loads usually does the job for far less.
Battery Sizing FAQs
Most Mid North Coast homes suit a battery between 10kWh and 16kWh of usable capacity. Size it to the power you use between sunset and sunrise, then check your solar panels can refill it on a winter day. A couple using 7kWh overnight suits about 10kWh; a family using 11kWh overnight suits 13–16kWh.
For a family out during the day with gas cooking or modest evening use, often yes. For a family of four running split systems, an electric oven and a dishwasher at night, overnight use is usually 10–14kWh, so a 13–16kWh battery is a better fit and leaves room for a blackout reserve.
It depends on what’s running. Essentials like the fridge, freezer, lights, internet, TV and a water pump use roughly 5–8kWh a day, so a 13kWh battery with a sensible reserve can carry them through a night and into the next day. With solar recharging it during the day, many homes can ride out multi-day outages on essentials. Running ducted air or an electric oven drains it much faster.
Total or nominal capacity is what the cells hold; usable capacity is what the battery will actually let you draw. Always compare batteries on usable kWh. The federal rebate and the NSW VPP incentive are both calculated on usable capacity too.
The Cheaper Home Batteries Program pays its full rate on the first 14kWh of usable capacity, a reduced rate from 14kWh to 28kWh, and a much smaller rate from 28kWh to 50kWh. That means each extra kWh costs you more out of pocket as the battery gets bigger, so capacity you won’t use overnight is poor value.
The NSW VPP incentive is available for batteries between 2kWh and 50kWh, but it’s calculated on usable capacity up to 28kWh. Combined with the federal rebate tiers, that makes 28kWh a natural ceiling for most homes unless you have a genuine need for more.
Usually, but check the winter numbers. A 6.6kW system makes around 20kWh on a June day on the Mid North Coast. Take away what you use during the day and what’s left is the most battery you can reliably fill. Older 3–5kW systems often can’t fill more than 8–10kWh in winter, so adding panels is worth considering. Our solar system sizing guide walks through the maths.
Generally no. Charging a car overnight from the battery empties it fast and loses some energy in the round trip. It’s better to charge the EV directly from solar during the day and let the battery cover the house at night. If you can only charge at night, size the battery for the house and let the car charge on an off-peak tariff.
With a modular battery, yes, as long as the extra modules are still available and compatible. It’s cheapest and simplest to add them within the first few years. Keep in mind the rebate rate steps down every six months, so capacity added later attracts a smaller discount.
Across the Mid North Coast of NSW, including Coffs Harbour, Sawtell, Woolgoolga, Bellingen, Urunga, Nambucca Heads, Macksville, Kempsey, South West Rocks, Port Macquarie, Wauchope, Laurieton, Taree, Wingham and Forster-Tuncurry. If you’re nearby but not listed, give us a call and we’ll tell you honestly whether we’re the right fit.
Send Us Your Bill. We'll Size the Battery.
Free, no obligation, and based on your overnight usage rather than a guess.
We’ll look at when you actually use power, check whether your current solar can fill a battery through winter, and recommend a usable capacity with the rebate and VPP incentive shown separately. If a smaller battery, or no battery yet, makes more sense for you, we’ll say so.
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