Battery sizing for a Bendigo home - kWh on the spec sheet isn’t the answer.
Half the battery quotes we replace in Bendigo are oversized. Owners are sold a 13.5kWh unit when their interval data says 8.5kWh would cycle full every day and pay back twice as fast. The right size is the one your house actually fills overnight - here’s how to work it out.
Your retailer already has the answer. You just have to ask.
The single most useful piece of paper for sizing a Bendigo home battery is your half-hourly interval data from your electricity retailer. Under the National Energy Retail Rules every customer on a smart meter (which Victoria has had since the 2009 rollout) can request this free of charge. AGL, Energy Australia, Origin, Red, Powershop and Lumo all provide a CSV download through their customer portal - usually under “usage” or “energy insights”. If they don’t, a written request gets you the file within 5 business days.
What the file tells us is when your house actually draws power. Two households with identical 30kWh-per-day averages can have completely different battery requirements: one drains heavily 5pm-10pm (ducted reverse-cycle, electric oven, EV charge) and needs ~12kWh of discharge; the other spreads load through the day (work-from-home, server room, pool pump) and barely needs 6kWh of evening storage because the panels cover daytime directly. The nameplate kWh on the battery is irrelevant without that profile.
What we actually look at in the data.
- Evening peak (5pm-10pm) - the chunk a battery has to cover when solar is gone.
- Overnight baseline (10pm-6am) - fridge, standby loads, pool, server - usually 0.3-0.6kWh per hour in Bendigo homes.
- Morning shoulder (6am-9am) - hot water, kettle, before-school showers - matters because the panels haven’t come up to full yield yet.
- Seasonal swing - Bendigo summer peak vs winter peak are different beasts. Winter is heating-driven (longer, higher); summer is cooling-driven (shorter, hotter days but also higher solar yield).
What 10kWh, 13kWh and 15kWh actually mean in practice.
The three common sizes in Bendigo right now.
- ~10kWh (Tesla Powerwall 3 single, Sungrow SBR096, BYD HVS 10): good fit for a 2-3 person Bendigo household drawing 15-22kWh/day, no EV, gas cooktop, ducted reverse-cycle but moderate evening use. Cycles full most nights. Honest payback in 7-9 years against current Bendigo tariffs.
- ~13kWh (Powerwall + half, Sungrow SBR128, BYD HVS 12.8): sweet spot for a 3-4 person home drawing 25-35kWh/day, electric or induction cooking, ducted heating, occasional EV top-up. Usually the right answer for a typical Strathdale or Kangaroo Flat family home.
- 15kWh+ (stacked Powerwall 3, multiple Sungrow modules, BYD HVS 16): justified only for homes drawing 40kWh+/day - daily EV charge, pool, big house, work-from-home heavy electrical. Without that load it sits half-empty and the extra $4-6k of capex never pays back.
Why “just get the biggest one” is the wrong instinct.
Battery economics live and die on cycling depth. A battery that goes from 100% to 20% every single night returns its capex in 8-10 years. A battery that goes from 100% to 60% (because you bought 50% more capacity than your house actually uses) returns its capex in 14-16 years - close to the warranted cycle life. The bigger unit literally pays itself back slower.
Q: Is 13kWh the right size for a typical Bendigo home?
Sometimes. Suits 25-35kWh/day households with heavy 5pm-10pm peak. For a smaller two-person Bendigo home on 12-18kWh/day a 10kWh unit is closer to right.
Q: How do I get my interval data?
Free request through your retailer’s portal under the National Energy Retail Rules. CSV download with half-hourly intervals. We feed it into the sizing tool.
Q: Breakeven on 10kWh vs 15kWh in Bendigo?
10kWh in a well-matched household: 7-9 years against 28c/kWh imports and 4-6c feed-in. 15kWh in the same household: 11-13 years because the extra capacity rarely fully cycles.
Three Bendigo-specific design decisions most quotes skip.
1. Cold winter peak shifting.
Bendigo overnight winter lows of -2°C to -4°C drive a real reverse-cycle heating load - not the gentle 1kW most coastal installs see, but a sustained 3-5kW for several hours. You want enough continuous discharge rating on the hybrid inverter (5kW+ continuous, 7kW+ peak) so the battery can actually deliver evening heating without falling back to grid. That’s an inverter-spec decision, not a battery-capacity one.
2. Backup circuits during grid outages.
Powercor’s rural-fringe Bendigo lines (Junortoun, Marong, out toward Maiden Gully) take longer to restore in a summer thunderstorm than CBD circuits. If backup matters, wire a backup-circuit subpanel at install: the fridge, a couple of lighting circuits, one heating/cooling circuit, the NBN. Don’t try to keep the whole house running; you’ll drain the battery in two hours. Backup wiring done at install is a few hundred dollars; retrofit is several thousand.
3. Expansion path.
Households change. Kids move out, EVs arrive, work-from-home patterns shift. Choose a battery family with a documented expansion path - Tesla Powerwall 3 stacks to 3 units, Sungrow SBR modules add in 3.2kWh increments, BYD HV chains modularly. Avoid closed-architecture units where adding 5kWh means buying a second standalone system and re-wiring the switchboard.
Q: Do I need to oversize for cold Bendigo winters?
Oversize the inverter continuous-discharge rating, not the battery. Battery handles winter load fine if sized to profile. Hybrid inverter 5kW+ continuous, backup-circuit wiring, keeps heating during outages.
Q: Can I add a second battery later?
Yes - modern modular systems (Powerwall 3, Sungrow SBR, BYD HV) support documented expansion. Cheaper per kWh than oversizing upfront. Avoid closed-architecture units.
Want an honest Bendigo battery size, based on your actual data?
Send us your retailer interval CSV (or we’ll pull it with you). We’ll show you 10kWh vs 13kWh vs 15kWh payback on YOUR profile, not a generic spreadsheet.