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Most Australian off-grid homes need a 14–24 kWh battery
If you're powering a typical family home and running one or two air conditioners for a few hours a day, the answer is almost always between 14 kWh and 24 kWh of battery, paired with 5–9 kW of solar and a 5–8 kW inverter. Add capacity if you have ducted air conditioning, induction cooking, or a workshop.
If you're powering a tiny home, caravan or cabin: 5–14 kWh of battery is plenty. If you're on acreage with multiple buildings: 30 kWh+ and you'll want to talk to our team.
Why sizing your off-grid battery matters more than the price
Off-grid systems are one of those purchases where getting the size right matters more than getting the best price. An undersized system means you sit in the dark when the cloud rolls in for three days. An oversized one means you spent thousands of dollars on capacity you'll never use. Both mistakes are common, and both are easy to avoid if you understand the four numbers that drive the calculation.
This guide walks you through every decision in the order Ernest and his team take customers through on the phone — starting with what you're powering, then working through your loads, then arriving at a specific battery, inverter and solar configuration that fits. Read it end to end and you'll be able to spec your own system with confidence.
Undersizing the system because you forgot to count an appliance — usually air conditioning, electric cooking, or a water pump. By the time you've built the system and moved in, retrofitting more capacity costs three to four times what it would have cost to oversize by a tier upfront. If you're between two sizes, go up one.
The four questions that determine your off-grid system size
Everything else is detail. If you can answer these four questions, the right system more or less reveals itself.
Section 4 of this guide takes question 2 (the air-con question) deep, because it's the one that most often gets undersized. Section 6 takes the answers from all four questions and converts them into a specific battery size and product recommendation.
Off-grid system sizing by use case
Each use case below has a typical load profile, a recommended system size, and a link to the specific products that fit. Pick yours, or keep reading for the full method.
How air conditioning affects your off-grid battery size
If you're running air conditioning, this single load will dictate your battery size more than every other appliance combined. A 3.5 kW split system running for four hours pulls 14 kWh — enough to flatten a small battery on its own. Get this number wrong and the whole system is wrong.
Why air-con dominates
A typical household has a baseline load of around 3–5 kWh per day — lights, fridge, devices, internet. Adding even a single mid-size split system for a few hours of evening cooling can double that. Adding ducted air conditioning to a whole home can quadruple it. This is why the first question we ask anyone speccing a system is whether they're running AC, what size, and how often.
The three numbers that matter
- Size of each unit (kW) — usually printed on the indoor unit. Small bedroom splits are 2 kW, living room splits are 2–3.5 kW, large splits or ducted zones are 4–6 kW, ducted whole-home is typically 8–14 kW.
- Hours of use per day — be honest. "Up to 3 hours at night" is very different from "all the time." A summer week in Queensland is not the same as a winter week in Tasmania.
- How many units — running two splits simultaneously doubles the draw.
The AC sizing table
This is the table our team uses on every call. Find your row — the right-hand column is the minimum battery capacity you need to cover the AC load plus a reasonable allowance for other household loads.
| AC system | Daily run-time | Units | Minimum battery |
|---|---|---|---|
| No air con | — | — | 5–10 kWh |
| Small (≤2 kW split) | Up to 3 hrs | 1 | 10–14 kWh |
| Small (≤2 kW split) | 3–5 hrs | 1 | 14 kWh |
| Small (≤2 kW split) | All the time | 1 | 20 kWh+ |
| Medium (2–3.5 kW split) | Up to 3 hrs | 1 | 14 kWh |
| Medium (2–3.5 kW split) | 3–5 hrs | 1 | 20 kWh |
| Medium (2–3.5 kW split) | All the time | 1 | 24 kWh+ |
| Large (4–6 kW split) | Up to 3 hrs | 1 | 20 kWh |
| Large (4–6 kW split) | 3–5 hrs | 1 | 24–30 kWh |
| Large (4–6 kW split) | All the time | 1 | 30 kWh+ |
| Ducted whole-home | Any | 1 | 30 kWh+ |
| Multiple units | Any | 2+ | Multiply & stack |
If you're running ducted air across a whole home — especially zone-controlled ducted — you're in 30 kWh+ territory regardless of run time. The startup surge alone can be 4–5 kW, and you typically run more zones at once than you'd run individual splits. Plan generously.
Appliance loads: how to calculate your daily kWh consumption
Once you have your AC-driven base size, add the rest of your loads on top. This table covers the appliances that meaningfully change battery sizing. The reference is daily kWh consumption for an average Australian household.
| Appliance | Typical daily load | Add to battery |
|---|---|---|
| Lights + fridge (baseline) | 2–3 kWh | Included in baseline |
| Freezer | 1–1.5 kWh | +2 kWh |
| Water / pressure pump | 0.5–1 kWh | +1 kWh |
| Washing machine (per cycle) | 1–1.5 kWh | +1–2 kWh |
| Dishwasher (per cycle) | 1–1.5 kWh | +1–2 kWh |
| Microwave / air fryer | 0.5–1 kWh | +1 kWh |
| Kettle / induction cooking | 1–2 kWh | +2 kWh |
| Pool pump | 2–3 kWh | +3 kWh |
| Power tools / workshop | Varies | +1 kWh buffer |
| TV, entertainment | 0.3–0.5 kWh | Minor — no tier change |
| WiFi / Starlink | 0.2–0.5 kWh | Minor — no tier change |
For most households the meaningful add-ons are induction cooking (it's electric and continuous), a pool pump if you have one, and a workshop or power tools if you're running anything serious in a shed. Everything else either rounds into the noise or runs in short enough bursts that it doesn't shift the system tier.
How to estimate without an energy meter
If you've been on the grid before going off-grid, your last electricity bill is the best starting point. Take your average daily kWh from the bill, multiply by 1.3 to give yourself buffer for cold nights and cloudy days, and use that as your battery target. If you don't have a previous bill, the use-case profiles in Section 6 will get you in the right ballpark.
The complete off-grid sizing matrix by use case
Here's where it all comes together. For each common use case below: typical loads, recommended system size, and the specific products that fit. Click through to view live pricing and the pre-selected variant.
🚐 Caravan, RV or boat
Typical loads: 12V DC lights, compressor fridge (~1 kWh/day), USB charging, water pump in short bursts, TV/laptop, sometimes a small inverter air conditioner used for evening cooling.
Recommended size: 5 kWh battery with a 5 kW inverter and 2–3 kW of solar input. Enough for off-grid touring with a couple of cloudy days of buffer.
🏚️ Tiny home, cabin or shed
Typical loads: Lights, fridge, freezer, water pump, TV/internet, microwave/kettle, washing machine, charging. Often a single small split system air conditioner used for a few hours.
Recommended size: 10–14 kWh battery, 5 kW inverter, 5–6 kW of solar. Comfortably handles the loads above with overnight backup and a one-day cloud buffer.
Complete kit option: The Off Grid System for Tiny Homes (Small — 14.34 kWh, 5.7 kW solar, 5 kW inverter) bundles the battery kit with a Solis hybrid inverter and Jinko solar panels in one purchase.
🏡 Off-grid family home (no AC or light AC use)
Typical loads: Full household — multiple fridges, induction cooking, washing machine, dishwasher, electric kettle, lighting, electronics, water pump. Light air-con use (1–2 hours at night with a small split) or none.
Recommended size: 14–20 kWh battery, 5–8 kW inverter, 6–9 kW of solar. Most family homes without heavy air-con sit at 14.34 kWh comfortably; if you're cooking on induction or have a workshop, step up to 20 kWh.
❄️ Off-grid family home with full air-con use
Typical loads: Everything above, plus running one or more split-systems for several hours per day or all night. Common for homes in QLD, northern NSW, WA Pilbara, NT.
Recommended size: 20–30 kWh battery, 8–10 kW inverter, 9–13 kW of solar. The battery needs the depth to hold air-con overnight; the inverter needs the headroom for compressor startup surge plus other loads simultaneously.
🌾 Rural property or acreage
Typical loads: Multiple buildings (house, shed, workshop, granny flat), bore pump, pool pump, ducted air-con or multiple splits, EV charging, heavy power tools, sometimes farm machinery. Continuous loads through the day.
Recommended size: 30 kWh+ battery, 10 kW+ inverter (often three-phase), 16+ solar panels (8 kW+ of solar). For properties this size we strongly recommend speaking with our team before purchasing — there are configuration decisions (three-phase vs single, multiple inverters, EV integration) that depend on the property layout.
For rural properties and acreage, the right configuration depends on the property layout, distance between buildings, what's on three-phase, and how you intend to expand later. Call 1300 375 257 and we'll spec the system with you before you buy.
Not sure which row is yours?
Use the System Builder on any product page — it asks the same questions and recommends the exact battery, inverter and solar package for your situation.
How many solar panels do you need for off-grid?
Your battery holds the energy. Your solar panels put energy in. Get the ratio wrong and you have a battery that never fully recharges (too little solar) or panels that hit full battery by 10 a.m. and waste the afternoon (too much solar). Here's how to size it.
The formula
For Australia, assume 4–5 peak sun hours per day on average (conservative — most of the country gets more). Multiply your battery kWh by 1.25 (for buffer) and divide by 4.5 (the average peak sun hours). That gives you the solar wattage needed in kW. Divide by 0.475 (because Jinko 475W panels are the standard) and you get your panel count.
Panels needed = (Battery kWh × 1.25 / 4.5) / 0.475
Example: a 14 kWh battery needs about (14 × 1.25 / 4.5) ÷ 0.475 = 8 panels.
By battery size
| Battery size | Solar needed | Jinko 475W panels |
|---|---|---|
| 5 kWh | ~1.5 kW | 3–4 panels |
| 10 kWh | ~2.5–3 kW | 5–6 panels |
| 14 kWh | ~3.5–4 kW | 7–9 panels |
| 20 kWh | ~5 kW | 10–11 panels |
| 24 kWh | ~6 kW | 12–13 panels |
| 30 kWh+ | ~7.5–8 kW | 16–17 panels |
When to oversize the solar
- Heavy cloud cover regions — Tasmania, southern VIC, far north QLD wet season. Add 20% more panels.
- Fully off-grid with no generator — you need the buffer for three- or four-day cloudy stretches.
- Tree shading or non-optimal roof orientation — east/west facing roofs produce ~80% of north-facing output.
- Future EV charging planned — add 3 kW of solar per EV you plan to charge from the off-grid system.
How to size your off-grid inverter
The inverter converts battery DC to household AC. Its size (in kW) determines the maximum instantaneous load your house can pull — not how much energy you can use per day. That number is set by the battery. The inverter just sets the ceiling on how much you can run at once.
How to size it
Add up everything that could realistically run at the same time, plus 30% for compressor startup surge on motors and air-con.
- Tiny home, RV, simple cabin: 3–5 kW inverter is plenty
- Family home, single small AC: 5–8 kW inverter
- Family home with multiple AC units, induction cooking, pool: 8–10 kW inverter
- Rural property, ducted AC, workshop: 10–15 kW inverter, often three-phase
Air conditioners, fridges, water pumps and washing machines all draw 2–3× their rated power for the first second when their compressor kicks in. A 3.5 kW AC can pull 10 kW for a moment at startup. If your inverter can't handle the surge, the AC won't start — even though your average load is well within capacity.
DIY battery kit vs pre-assembled battery: which should you buy?
This is the question most off-grid buyers wrestle with. Both approaches deliver the same usable kWh and the same chemistry (LiFePO4). The difference is in how they're built, how they're serviced, and how they fail. Here's the honest version.
- You assemble the battery from cells and a smart BMS
- Lower upfront cost per kWh
- Component-level repair — if one cell fails, you replace it for around $200
- Full visibility into every component
- Requires basic mechanical and electrical confidence (no soldering — just bolts and torque)
- Electrician sign-off still required for the install
- Sealed, plug-and-play module — installer connects and goes
- Higher upfront cost than the kit equivalent
- If the unit fails out of warranty, the whole module is replaced (~$2,500+)
- Faster install — fewer connections, less commissioning
- Stackable — easy to add capacity later
- Sparky's preferred option for residential installs
Should you add a backup generator to your off-grid system?
A generator is the difference between sleeping easy and watching the weather radar. For about $2,000, you add a fallback that lets you size the battery one tier smaller — saving thousands on the system overall.
When a generator makes sense
- You're fully off-grid in a high-cloud region (Tasmania, south-west WA, far north wet season).
- You're building on a budget — a generator + 14 kWh battery is cheaper than a 24 kWh battery, and covers the same use cases.
- You're a worst-case planner — extended cloud stretches happen once or twice a year. A generator means they don't become a problem.
- You have heavy intermittent loads like welders, large pumps, or workshop machinery that spike beyond what the inverter can handle.
When you don't need one
- You're grid-connected or hybrid — the grid is your fallback.
- You're in a high-sun region (most of QLD, NSW inland, NT, WA goldfields) and have generous solar.
- You've sized the battery for the worst case already.
A 5 kW diesel generator is the sweet spot for most off-grid homes. It's enough to run essential loads while charging the battery, runs efficiently, and fits the inverter charging spec of every system we sell.
Solar mounting rails — what they are and when you need them
Solar panels don't bolt directly to your roof. They mount onto rails, which mount onto the roof structure (or ground-mount frames). The rails carry the weight, allow for thermal expansion, and let installers route the wiring safely.
You need rails if:
- You're putting panels on a tin/Colorbond roof, tile roof, or shed roof
- You're ground-mounting on poles or a frame
- You don't already have mounting infrastructure from a previous system
You don't need rails if:
- You're replacing panels on existing rails (check condition first)
- You're installing tilt-frame ground mounts that come with their own structure
- You've sourced rails separately through your installer
If you're not sure, include them. They're a small cost relative to the panels themselves, and they're the most common item customers forget on the first order.
Installation — three paths from purchase to switched-on
All off-grid systems require an electrician to commission the high-voltage side and sign off on the install. The variable is how much of the work you do yourself.
- You build the battery pack from the kit
- You mount panels and route DC cable
- You position the inverter and run AC out to your switchboard
- Electrician connects to switchboard, commissions, signs off
- You handle the prep work — pad, framing, panel mounting
- Electrician does all the electrical work alongside you
- Best of both worlds: speed and learning
- Electrician (often with assistant) does the entire install
- You provide site access and pay the labour bill
- Typically pairs with the pre-assembled battery for fastest install
Regardless of which path you take, the electrical work must be commissioned and certified by a licensed electrician. This is for insurance, for safety, and for grid-compliance if you ever connect to the grid in future. Don't skip it.
The 7 most common off-grid sizing mistakes (and how to avoid them)
From years of supporting customers through their first off-grid system, these are the mistakes that come up over and over. Avoid them and you'll be ahead of 90% of new off-grid owners.
- Forgetting about air conditioning startup surge. Average load is fine, but the inverter has to handle the instantaneous spike when the compressor kicks in. Size the inverter for surge, not steady-state.
- Undersizing the solar relative to the battery. A big battery that recharges slowly is a small battery in practice. Match the solar to the battery using the formula in Section 7.
- Assuming a grid-tied solar system will work off-grid. It won't. Grid-tied inverters need the grid to operate — they shut down when it disappears. Off-grid systems need a different class of inverter entirely.
- Buying the battery before checking inverter compatibility. Not every inverter speaks to every battery's BMS. Confirm 48V LiFePO4 compatibility with your inverter brand before purchase.
- Sizing for current household load instead of future. An EV, a workshop expansion, or moving to induction cooking can change the calculation by 30%. Plan for two years out, not today.
- Skipping the generator on a tight budget. A $2,000 generator covers worst-case days far cheaper than the extra battery capacity you'd otherwise need.
- Going off-grid without a previous electricity bill to anchor the calculation. If you don't know your current daily kWh, you're guessing. The bill tells you in black and white.
Off-grid solar system FAQ — your questions answered
Quick answers to the questions our team gets every week, plus the questions Australians most commonly type into Google. Looking for the full breakdown on a specific topic? Each answer links to a deeper guide where available.
Sizing & capacity
Costs & pricing
Off-grid vs hybrid vs grid
How off-grid systems work
Australian legal & DIY
Pros, cons & reliability
Air conditioning & other loads
System lifetime & expansion
Ready to spec your system?
The fastest path: use the AI System Builder on any product page. It asks the same questions as this guide and recommends the exact products you need. Or speak with Ernest's team directly — we've helped thousands of Australians go off-grid.
