Off-Grid Solar System Sizing: How Many Panels & Batteries Do You Need?

Off-grid solar system sizing is the process of matching your panels, batteries and inverter to your daily energy use so you never run out of power. For a typical Australian home using 20 kWh/day, you'll need roughly 8–12 kW of solar panels and 30–50 kWh of LiFePO4 battery storage, plus a 5–8 kW hybrid inverter.

Most guides on this topic either give you a vague range and leave you guessing, or hand you a US-based formula built around lead-acid batteries that's outdated for how Australian off-grid systems are actually built in 2026. This guide gives you the real maths, the right formulas for LiFePO4, and clear answers to the questions we hear most often - so you can make a confident decision before you spend a cent.

What Is Off-Grid Solar System Sizing?

Off-grid solar system sizing is how you figure out the right amount of solar generation and battery storage for a property that has no mains power connection. You're essentially building your own mini power station, and every part of it, the panels, the battery bank, the inverter, needs to be matched to each other and to how much energy your property actually uses.

The thing that trips most people up is this: off-grid systems are designed around your worst days, not your average ones. A grid-connected system can lean on the network when the sun isn't cooperating. An off-grid system can't. So instead of sizing for typical summer production, you size for a cloudy winter week, and that changes everything about how big the system needs to be.

That's why off-grid solar arrays are typically 1.5 to 2 times larger than an equivalent grid-tied setup, and why battery storage in a well-designed off-grid system covers two to three days without meaningful sunshine. As of early 2026, Australia has 28.3 GW of rooftop solar across 4.3 million homes,  but the vast majority of that is grid-connected. Off-grid is a different discipline, and the design rules reflect that.

Off-Grid vs Hybrid vs Grid-Tied: Know What You're Sizing

Before running any numbers, it helps to be clear on which system type you're actually building. The sizing approach is genuinely different for each one.

For most homes already connected to the grid, going fully off-grid doesn't make financial sense , a hybrid system gets you energy independence at a fraction of the cost. Where off-grid really pays off is on rural and remote properties where connecting to the mains can cost anywhere from $30,000 to over $100,000 depending on how far you are from the nearest line.

Already decided off-grid is right for you? Browse our pre-matched Off-Grid Solar Kits, every component sized to work together, ready to go.

How to Size an Off-Grid Solar System: 5 Steps

You don't need an engineering degree to size a system. Work through these five steps in order , each one feeds directly into the next.

Step 1: Work out how much energy you actually use

Your daily energy use in kilowatt-hours (kWh/day) is the single number everything else is built around. The easiest way to find it is to check a recent power bill , it'll show your monthly kWh, so divide by 30 to get a daily average. If you're moving off-grid from scratch and don't have a bill, list every appliance you'll run, note its wattage, multiply by daily hours of use, and add them up.

Small off-grid homes and cabins typically use 5–15 kWh/day. A family home with a fridge, washing machine, air-conditioning and regular cooking lands between 15–30 kWh/day. Farms and large properties can go well above that. Whatever number you land on, add at least 15–20% as a buffer , underestimating daily use is the most common reason off-grid systems underperform.

Step 2: Find your winter peak sun hours

Peak sun hours (PSH) measures how many hours of useful, panel-charging sunlight your location gets per day. One peak sun hour equals 1 kWh of solar energy per square metre. The key word here is winter , because that's the design condition for an off-grid system. A system sized around summer production will leave you short of power every July.

Australia's solar resource is world-class, but it varies significantly by location and season. Tropical Queensland sees 4.5–5.5 peak sun hours even in winter. Melbourne and Hobart drop to around 2.6–3.0 hours in their worst months. For your exact location, the Bureau of Meteorology's solar exposure maps give you the most reliable data to work from.

Step 3: Calculate your solar array size

Once you have your daily use and your winter PSH, the panel sizing formula is straightforward:

Solar array (kW) = Daily use (kWh) ÷ (Winter peak sun hours × 0.7)

The 0.7 efficiency factor covers real-world losses that every system experiences: wiring resistance, dust, heat de-rating, the energy used to recharge the battery, and inverter losses. It's not pessimistic , it's realistic. Ignore it and you'll end up with a system that struggles whenever conditions aren't perfect.

To convert the array size to a panel count, divide by the wattage of your chosen panel. Our kits use 475W Jinko panels, so a 8.2 kW array needs about 18 panels (8,200 ÷ 475 = 17.3, rounded up to 18).

Step 4: Size your LiFePO4 battery bank

The battery bank is what keeps your lights on at night and through cloudy spells. The formula for solar battery sizing is:

Battery storage (kWh) = Daily use (kWh) × Days of autonomy ÷ Depth of Discharge

Days of autonomy is how long your battery bank can power the house without any solar input. Two days is the standard starting point for most of Australia; three days is worth considering if you're in a consistently cloudy region like coastal Victoria or Tasmania, or if you want to run without a backup generator.

Depth of Discharge (DoD) is the proportion of the battery's capacity you can actually use before needing to recharge. This is where LiFePO4 genuinely changes the numbers. Old lead-acid batteries were limited to around 50% DoD to preserve their lifespan. LiFePO4 chemistry handles 80–90% DoD comfortably across thousands of cycles , which means you need significantly less nameplate capacity to store the same usable energy. Our DEYE AI-W5.1B battery modules are rated at 5.12 kWh each, run at 51.2V nominal, and carry a 10-year warranty with over 6,000 rated cycles. To find how many modules your system needs, divide your required nominal storage by 5.12 and round up.

Step 5: Size the inverter and charge controller

The inverter converts DC power from your batteries into the 240V AC power your appliances actually use. For off-grid systems, you need a hybrid inverter/charger that also handles solar input and can accept a generator for backup charging. The key rating to look at is continuous output , and it needs to exceed the peak load you'll ever draw at one time.

Work out what appliances could realistically run at the same moment , the fridge cycling on while the pump runs and you've got the air-con going is a common scenario. Add those peak loads together, then add about 25% for safety and motor surge currents. Our DEYE single-phase hybrid inverters come in 5 kW, 8 kW, 10 kW and 16 kW ratings, covering everything from a small cabin to a large homestead. For the charge controller, make sure its input rating handles your array's voltage and current at your chosen battery voltage , 48V is the standard for whole-home off-grid systems.

Match your brains to your bank: explore DEYE Off-Grid & Hybrid Inverters and MPPT Solar Charge Controllers.

Sizing at a Glance: Worked Example

Here's what the formulas look like for a typical Australian family home using 20 kWh/day in a region with 3.5 winter peak sun hours, wanting 2 days of autonomy using LiFePO4 at 90% DoD:

Plug your own daily kWh and winter PSH into the same three lines and you'll get your numbers. The one figure you genuinely can't shortcut is the inverter , you have to add up what runs at the same time, because that's what sets the continuous output requirement, not how much energy you use in a day.

How Many Batteries Do You Actually Need?

This is the question we get asked more than any other. The table below shows how the solar battery sizing formula works out across different Australian household types, at both 2 and 3 days of autonomy. The final column shows how many 5.12 kWh DEYE modules that translates to.

Most off-grid Australian homes land somewhere between the 20–30 kWh/day rows. Battery storage has become significantly more accessible in the past couple of years , Australians bought roughly 85,000 battery units in the first half of 2025 alone, a 191% increase over the same period in 2024, driven by falling LiFePO4 costs and growing interest in genuine energy independence.

One thing worth knowing about LiFePO4 versus older battery chemistry: at 90% usable DoD compared to lead-acid's 50%, you need nearly half the nameplate capacity to store the same usable energy. The upfront cost is higher per kWh of the nameplate, but the cost per usable kWh over the battery's life is dramatically lower when you factor in cycle life and avoid replacements. (See our guide: LiFePO4 vs AGM for Off-Grid.)

Size your storage with confidence  browse our Pre-Assembled LiFePO4 Batteries or start from cells with our LiFePO4 Cell range.

Off-Grid System Cost: What to Budget For

Off-grid system costs scale directly with how much storage and generation you need, which is why accurate sizing matters so much , oversize it and you're wasting money; undersize it and you're back to problem-solving in winter. Here are indicative installed ranges for 2026 in Australia:

Installed cost includes panels, batteries, inverter, charge controller, wiring and labour. Remote properties will pay more for freight and travel. DIY builds with quality components cost significantly less.

Two things reliably reduce cost without sacrificing reliability. First, reduce your daily load before sizing , switching to an energy-efficient fridge, LED lighting and a heat-pump hot water system can cut daily use by 20–30%, which shrinks every component in the system. Second, include a backup generator: sizing for 2 days of autonomy instead of 3 and running the genny for one or two days a year in genuinely bad weather can save thousands on battery spend upfront.

Six Mistakes That Ruin Off-Grid Systems

These come up constantly in conversations with customers who've either bought poorly-designed systems or are trying to fix an existing one.

1. Designing for summer sun. A system that sails through December will often struggle in June. Design for winter PSH, every time.

2. Guessing at daily energy use. Phantom loads, a second fridge in the garage, electric hot water and even standby power add up. Measure or estimate carefully, then add a buffer.

3. Using lead-acid DoD maths on LiFePO4 batteries. Sizing a lithium bank at 50% DoD means you're buying about 40% more battery than you actually need. Use 80–90% DoD for LiFePO4.

4. Under-sizing the inverter for surge loads. Pumps, compressors and motors draw 3–7 times their running wattage on startup. Your inverter needs to handle those spikes without tripping.

5. Forgetting to plan for expansion. Energy needs tend to grow. Leave physical and electrical room to add panels or batteries later without redesigning the whole system.

6. Poor battery ventilation. LiFePO4 is the safest lithium chemistry available, but all batteries perform better , and last longer , when operating temperatures are managed. Don't install them in a sealed box in direct sun.

Frequently Asked Questions

How many solar panels do I need for an off-grid house in Australia?

For a typical Australian home using 20 kWh per day, you'll need roughly 8–12 kW of solar, which works out to around 18–25 panels at 475W each. The exact number depends entirely on your daily energy use and your winter peak sun hours , a property in tropical Queensland needs fewer panels than the same home in Melbourne or Hobart because winter sun hours are much higher in the north.

How much battery storage does an off-grid home need?

Most Australian off-grid homes need between 30 and 50 kWh of LiFePO4 battery storage to cover two to three days of cloudy weather. At 5.12 kWh per module, that's roughly 6 to 10 DEYE battery modules. The formula is: daily use (kWh) × days of autonomy ÷ 0.9. Homes in low-winter-sun regions or without a backup generator should lean toward the higher end.

What size inverter does an off-grid system need?

Your inverter needs to handle the maximum load you'll ever draw at one moment , not your daily average. Add up the wattage of everything that could run at the same time (fridge, pump, air-con, any heating element) and choose an inverter rated comfortably above that. For most family homes, a DEYE 5 kW or 8 kW single-phase hybrid inverter covers the base, with the 10 kW and 16 kW models suited to larger properties or heavier electrical loads.

Why do off-grid systems need more panels than grid-connected solar?

Because they can't borrow from the grid when generation falls short. A grid-tied system only needs to cover your average use, since the network fills the gaps. An off-grid system has to generate enough power to run your home and fully recharge the battery bank each day, even in winter , that's why arrays are typically 1.5 to 2 times larger than their grid-connected equivalents.

How many days of battery autonomy should I aim for?

Two days is the standard for most of Australia, combined with a backup generator for extended bad weather. If you're in a region with long overcast periods , coastal Victoria, Tasmania, or the ranges in NSW , or if you'd rather not rely on a generator at all, design for three days of autonomy. Every extra day of storage adds a meaningful cost, so it's worth thinking about your local climate and your appetite for running a genny before you commit to a battery size.

Can I size an off-grid solar system myself?

Yes, and the formulas above are exactly what professional system designers use for first-pass sizing. Where things get more detailed is in the electrical design , cable sizing, protection devices, earthing and compliance with AS/NZS 5139. The sizing calculations you can absolutely do yourself; the installation and sign-off generally requires a licensed electrician with solar accreditation.

Ready to Build Your Off-Grid System?

Getting your off-grid solar system sizing right from the start means you get reliable power, a fair price, and a system that grows with your needs. Three numbers drive every decision: your daily kWh, your winter peak sun hours, and how many days of autonomy you want. Once you have those, the rest follows.

• Off-Grid Solar Kits , DEYE inverter, Jinko 475W panels and LiFePO4 batteries, pre-matched and ready to go

• Solar Panels , 475W Jinko modules

• Pre-Assembled LiFePO4 Batteries and LiFePO4 Cells

• DEYE Hybrid Inverters , 5 kW, 8 kW, 10 kW and 16 kW single phase

• MPPT Solar Charge Controllers

• All-In-One Energy Storage Systems

Not sure where to start? Call our team, we'll sanity-check your numbers and point you to the right kit.

Sources: Bureau of Meteorology (Average daily solar exposure maps); Clean Energy Council and Clean Energy Regulator (battery and rooftop solar installation data, 2025–2026); PV Magazine Australia. This article is general educational information, not electrical or installation advice. Off-grid solar installations in Australia must comply with AS/NZS 5139 and be completed or signed off by a licensed electrician.