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Solar Battery Bank Sizing Calculator

Free Australian solar battery bank sizing calculator. Size your bank in Ah and kWh for off-grid stations, sheds, or grid-tied storage with hybrid inverters.

Solar Battery Bank Sizing Calculator

Usable energy needed
10,000 Wh
Gross capacity needed
12,713 Wh
Bank capacity (Ah)
530 Ah
Bank capacity (kWh)
12.7 kWh

How to use this calculator

Enter your average daily load in watt-hours (Wh), choose your system DC voltage (12V, 24V, or 48V), set days of autonomy without solar input, then pick battery chemistry. The tool returns capacity in both Ah and kWh.

If you don’t know your daily load, take a quarterly electricity bill, multiply kWh by 1000, then divide by 90. The AER residential average is around 16 kWh/day in NSW and Victoria — but for backup-only sizing, only count the loads you need during a blackout (fridge, freezer, lights, internet, fans), typically 3–8 kWh/day.

The formula

Usable energy needed (Wh) = Daily load × Days of autonomy
Gross capacity (Wh)       = Usable / (DoD × Inverter eff × Battery eff)
Bank capacity (Ah)        = Gross capacity / System voltage

DoD is depth of discharge (90% LiFePO4, 50% AGM/Gel). Inverter efficiency is typically 92% for a quality pure-sine inverter (Selectronic SP PRO, Victron Quattro, Sungrow SH series). Battery round-trip efficiency is 95% for LiFePO4 and 80–85% for lead-acid.

Worked example — 8 kWh/day rural cottage

Off-grid cottage in regional Victoria with 8,000 Wh daily load, 3 days of autonomy on a 48V LiFePO4 system:

  • Usable energy: 8,000 × 3 = 24,000 Wh
  • Gross capacity: 24,000 / (0.90 × 0.92 × 0.95) = 30,504 Wh
  • Bank size: 30,504 / 48 = 635 Ah at 48V (or 30.5 kWh)

That maps to six 5kWh BYD HVM rack modules, or about three Pylontech US5000 stacks, or two Sungrow SBR HV stacks. With AGM lead-acid the same load needs roughly 1,275 Ah at 48V — twice the cells and three times the cabinet space.

Battery chemistry — the dominant cost driver

Per Clean Energy Council pricing data and SunWiz Australian Battery Market Report 2025, typical 2026 installed costs in Australia:

  • LiFePO4 lithium (rack/stack): AUD$900–1,300 per kWh installed (Pylontech, BYD, Sungrow, Tesla Powerwall 3, AlphaESS)
  • AGM lead-acid: AUD$500–700 per kWh installed nameplate, but you need 1.8–2× the kWh to match usable — uneconomic versus lithium since 2023
  • Flooded lead-acid (Trojan, Rolls): AUD$300–500 per kWh nameplate, still found on remote stations for tank-truck-accessible sites because of robustness, but new installs almost always lithium

The Cheaper Home Batteries Program rebate (from 1 July 2025) is roughly AUD$330/kWh for the first 13.5 kWh of battery, applied at point of sale by the CEC-accredited retailer.

AS/NZS 3000 and CEC compliance

The calculator handles the energy maths. AS/NZS 3000:2018 Amendment 2 (Wiring Rules), AS/NZS 5139:2019 (Battery storage), and the CEC Battery Install Guidelines add the regulatory layer:

  • Restricted location requirements for lithium > 1 kWh per AS/NZS 5139 (no habitable rooms, ceiling spaces, or under stairs)
  • DC isolation, overcurrent and arc-flash protection per AS/NZS 3000
  • Cable sizing per AS/NZS 3008.1.1 — see the Solar Panel Wire Size Calculator for sizing
  • AS/NZS 4777.2 inverter compliance for grid connection
  • DNSP pre-approval for grid-tied via your distributor (Ausgrid, Energex, AusNet, Powercor, etc.)

For grid-tied storage, your installer must hold both PV and battery endorsements from the Clean Energy Council to claim STCs and the Cheaper Home Batteries rebate. The CEC-accredited installer checklist is mandatory before commissioning.

How to estimate daily load

A typical Australian load table for off-grid or backup sizing:

  • Fridge-freezer (5-star rated): 1.0–1.5 kWh/day
  • Chest freezer (separate): 0.8 kWh/day
  • LED lighting (8 fixtures × 5 hours × 10W): 0.4 kWh/day
  • Laptop + NBN router: 0.4 kWh/day
  • Bore/water pump (1 hp, 1 hour): 0.7 kWh/day
  • Reverse-cycle split (2.5kW, 4 hours): 4–6 kWh/day in summer
  • Microwave/induction/kettle (intermittent): 0.8–1.5 kWh/day

Add 15% for inverter standby, ghost loads, and BMS draw. Real-world Australian cabin baselines run 4–8 kWh/day; full-house off-grid stations typically run 15–25 kWh/day in summer with cooling.

Sources cited

  • Clean Energy Council Battery Install Guidelines (2024 edition)
  • AS/NZS 5139:2019 Electrical Installations — Safety of Battery Systems for Use with Power Conversion Equipment
  • AS/NZS 3000:2018 Amendment 2 (Wiring Rules)
  • AS/NZS 4777.2:2020 Inverter Requirements
  • SunWiz Australian Battery Market Report (2025)
  • AER Default Market Offer 2025-26 retail tariff figures
  • DCCEEW Cheaper Home Batteries Program guidelines (effective 1 July 2025)

Cross-check your final design with a CEC-accredited installer holding the battery endorsement before purchasing — the rebate, STCs, and DNSP approval all require accredited sign-off. DIY installs forfeit all three.

Frequently asked questions

What size battery do I need for an off-grid Australian shed or station?
For a typical off-grid shed running 5–8 kWh/day with two days of autonomy, you usually want 300–500 Ah at 24V (or 150–250 Ah at 48V) of usable lithium. Remote pastoral stations running fridges, water pumps, and air-con often run 15–25 kWh/day, requiring 25–40 kWh of LiFePO4 — typically four to eight rack modules at 48V.
Is a battery worth it on top of rooftop solar in Australia?
With a flat retail tariff around AUD$0.33/kWh in 2026 and feed-in tariffs at $0.05–0.08/kWh in most states, every kWh you self-consume saves about $0.25. A 10 kWh battery cycling daily can save $700–900/year — payback of 8–10 years on a $9,000–11,000 install. The federal Cheaper Home Batteries Program from July 2025 cuts upfront cost roughly 30%, dropping payback to 5–7 years.
Should I pick 24V or 48V for an Australian system?
Use 24V for systems below ~5 kWh/day (small shacks, weekenders). Use 48V for anything larger — it's the standard for hybrid inverters from Sungrow, Selectronic, Victron, GoodWe, and SolarEdge, and required for stack-style residential batteries (Tesla Powerwall, BYD HVM, Sungrow SBR). 48V cuts cable current by 4× compared to 12V, which matters for AS/NZS 3000 compliance.
How many days of autonomy should I plan for in Australia?
Two days is standard for grid-tied backup. Off-grid in inland WA, NT, or northern QLD plans for 2–3 days. Tasmania and the Victorian high country often size for 4–5 days due to winter cloud cover. Above 5 days a diesel or LPG genset (Honda EU22i, Pramac) becomes more economical than additional cells.
Does the Cheaper Home Batteries Program apply to off-grid?
Yes — from 1 July 2025 the Cheaper Home Batteries Program offers a federal rebate via the SRES expansion for batteries 5–50 kWh installed by a CEC-accredited installer. Both grid-tied and standalone (off-grid) systems are eligible if the battery is on the CEC approved product list and the installer holds the relevant battery endorsement.

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