Battery sizing for a Townsville home — kWh vs load profile.
A 13 kWh Powerwall isn’t the right battery for most Townsville households. The right size is driven by your evening-peak interval data, your daytime export excess, and whether you’re charging an EV. Here’s how the maths actually works.
Why 13 kWh isn’t the right battery for most Townsville homes.
The southern-state household the 13 kWh is sized for.
The 13 kWh battery size that anchors most of the major manufacturer brochures — Powerwall 3, the larger BYD Premium stacks, the bigger Sungrow SBR configurations — was sized around a Sydney-Melbourne-Adelaide household running 25 to 30 kWh per day, with ducted gas heating in winter, a heat-pump or electric hot water tank, and an evening peak from 5pm to 9pm driven by cooking, TV and pre-bed heating.
The Townsville household it doesn’t fit.
Townsville households run noticeably differently. Average daily usage sits in the 18 to 24 kWh band for a 3 to 4 bedroom home, gas is rare so almost everything is electric, hot water is usually instantaneous gas or heat pump, and the load profile is dominated by an air-conditioning evening peak from about 4pm to 10pm. The night-time floor is usually low (one or two split systems on overnight in the bedrooms). Add it all up and the evening peak you actually need to cover with a battery sits at around 8 to 11 kWh on a typical day, with maybe a 13 kWh draw on the hottest 10 days of the year.
The number to watch — cycles per year.
A battery pays back by cycling. A 10 kWh Townsville battery on a typical household cycles 95 to 110 percent of its usable capacity, 320+ days a year. A 13 kWh battery on the same household cycles maybe 85 to 95 percent — the last 2 to 3 kWh sit unused on most days because the morning solar fills the battery faster than the household can empty it. Those unused kWh are dollars of hardware that never pay back.
How to size a Townsville battery in three numbers.
Number 1 — evening peak from 4pm to 10pm.
Pull your interval data from your Ergon Energy retailer’s portal (Ergon Retail, Origin, AGL and Alinta all expose 30-minute interval data for free under the rules). Add up the consumption from 4pm to 10pm for an average summer day, an average winter day, and the hottest 5 days of the year. That’s your evening-peak demand — the kWh the battery needs to deliver after the sun is off the panels.
Number 2 — daytime export excess.
Look at the same interval data through the middle of the day. How many kWh per day are exporting to the grid by 2pm in summer? That’s your daytime excess — the kWh available to fill the battery before the evening peak. For most Townsville homes with a 6.6 kW or 10 kW array this number sits at 12 to 25 kWh per day in summer, so it’s not usually the constraint — but on smaller systems (5 kW or below) it can be.
Number 3 — the EV charge load (if any).
If you’re running an EV at home, when do you charge it? Daytime charging on solar lifts the daytime self-consumption and doesn’t change the battery size you need. Overnight charging on a battery (rare in Townsville because most homes are on a flat tariff, not a time-of-use peak) bumps the right battery size up by 6 to 10 kWh.
Putting the three numbers together.
The right battery is roughly equal to the evening peak demand (number 1), capped by the daytime excess available to charge it (number 2), uplifted for EV overnight charging if relevant (number 3). For 90 percent of Townsville homes the answer lands in the 8 to 12 kWh band — not the 13 kWh brochure default. The other 10 percent are big homes (5 bedrooms+, pool, dual aircon, EV overnight) where 13 to 15 kWh genuinely cycles.
10 kWh vs 15 kWh in Townsville — what actually pays back faster.
On current Ergon Energy retail rates (around 32 c/kWh peak, 8 c/kWh feed-in) and 2026 Cheaper Home Batteries rebate values, the breakeven on a 10 kWh Townsville battery on a household with $400-plus quarterly bills is 7 to 9 years. A 15 kWh battery on the same household stretches to 10 to 13 years because the marginal 5 kWh cycles less. The breakeven flips toward the bigger battery only on time-of-use tariffs with a wide evening peak, overnight EV charging on the battery, or a household running 30+ kWh per day. The right answer is the interval data, not the brochure.
Townsville battery sizing — FAQ.
Is a 13 kWh battery right for a Townsville home?
Not for most. Typical Townsville household evening peak is 8 to 11 kWh, so a 13 kWh sits with unused capacity most days. Bigger homes with EV charging or 30+ kWh daily use are the exception.
How do I work out the right size?
Three numbers off your Ergon interval data — evening peak (4pm-10pm), daytime export excess, and EV charge load if any. We’ll pull and model the data for you.
Breakeven on 10 kWh vs 15 kWh in Townsville?
10 kWh pays back in 7 to 9 years on most households. 15 kWh stretches to 10 to 13 years unless you’re cycling it overnight on an EV or a wide time-of-use peak.
Who designs the battery in Townsville?
Townsville Solar Cleaning — interval-data sizing, AS/NZS 5139 battery compliance, AS/NZS 4777 hybrid commission, Ergon network paperwork. CEC-accredited.
Size it on your data, not the brochure.
Free Townsville battery design from your Ergon interval data. The right kWh, not the upsold one.