What size battery bank do I need for off-grid solar in Australia?

This was my biggest regret after a year living with my system — I should have gone bigger on the batteries from the start. Most people focus on solar panel output, but it's the battery capacity that gets you through overcast stretches and heavy-use days. If you're building now, oversize it. You can always add panels later, but retrofitting batteries is a real pain.

Do I really need a monitoring system for off-grid solar?

Looking back, system monitoring was the feature I wish I'd installed from day one. Without it, you're flying blind on battery state of charge, actual solar production, and where your power's going until something goes wrong. A decent monitoring setup pays for itself the first time it alerts you to a problem before it turns into an expensive failure.

Is a propane generator a good backup for off-grid solar?

After a year of living off-grid, I'm sold on having a propane generator as backup. Solar and batteries handle the bulk of your needs, but there are still times — extended bad weather, equipment faults, unexpected loads — when you want a reliable fallback. Propane stores well, runs quietly, and gives you peace of mind when the sun doesn't play ball.

Do solar batteries work properly in cold weather?

Battery performance in the cold is something I covered in the article because it's often overlooked by people planning off-grid systems. Batteries lose capacity and can be damaged in extreme cold, so if you're in a frost-prone area, you'll need to plan for battery heating or insulation. It's not just a winter thing either — repeated cold nights followed by warm days can stress batteries over time.

Off-Grid Solar: 1 Year Review, Regrets and Real Lessons

What "off-grid" actually means

An off-grid solar system runs entirely independently of the utility network. You generate, store and convert your own power, and there is no ability to draw supplemental electricity from a grid during shortages. That single fact is the root of every design choice, regret and lesson that follows.

A complete off-grid build is the largest scale of an "off-grid solar power kit," which can otherwise mean anything from a phone-charging lantern to an RV setup to a full home system with batteries, panels and an inverter. The four core components are the same regardless of scale: solar panels (collectors), a charge controller, a battery bank (reservoir), and an inverter. Scale is what changes.

The system at a glance

Specs that matter for a typical Australian household off-grid install, drawn only from verified sources:

Item	Spec / Range	Source
System voltage	48V DC battery bank typical for whole-home	Common practice
AC output	230V / 50Hz (Australia)	AU default canon
Panel dimensions, 60/120-cell	~1.07 m × 1.68 m	gogreensolar
Panel dimensions, 72/144-cell	~1.07 m × 1.98 m	gogreensolar
Panel wiring	120-cell and 144-cell use half-cut cells (slightly more efficient, more failure-tolerant)	gogreensolar
Cell type	Mono (single silicon crystal, slightly more efficient) vs poly (blended fragments, larger footprint for same output)	gogreensolar
Charge controller	MPPT required to use standard mass-produced panels effectively	gogreensolar
Inverter	Must be rated for off-grid use; most grid-tie inverters will not connect to a battery bank	gogreensolar
Battery chemistry	Deep cycle, designed for gradual discharge/recharge	gogreensolar
Battery sizing rule of thumb	Sized for one night's energy use, recharged by solar next day (one cycle per 24 h)	gogreensolar
Battery type (common)	Flooded lead-acid (FLA) is one standard option	gogreensolar
Relevant AU standards	AS/NZS 5033 (PV install), AS/NZS 3000 (wiring rules), AS/NZS 1170.2 (wind loading)	AU canon

One of my softer observations: 60/120-cell panels are easier to carry up a roof solo and offer more flexible array layouts; 72/144-cell panels are cheaper per watt to install because you need fewer mounting and combiner parts. Poly vs mono produces the same watts per panel under test, but the poly array physically takes more roof space for the same output.

Panels: what actually matters after a year

Panels convert sunlight into DC power. After a full year of running an off-grid array here in Beecher, in Central Queensland, the spec sheet stopped mattering and a few practical points took over:

Tier 1 panel brands (Jinko, Trina, LONGi, Canadian Solar) are the major BloombergNEF Tier 1 manufacturers, and that matters for warranty enforcement more than for first-year performance.
120-cell or 144-cell panels with half-cut cells are slightly more efficient and more resistant to cell-level failure than full-cell equivalents. In my experience, the half-cut architecture also performs marginally better in partial shading — which on a rural roof with tree-line shadow is not a hypothetical.
Mono vs poly is mostly a roof-space question in Australia. Given that we have plenty of roof real estate, poly is not a bad choice if the $/W is meaningfully lower.
Array sizing: oversizing PV relative to battery capacity is generally sound engineering — more harvest in shoulder seasons and cyclone build-up, less time spent in low-SoC at dusk.

The only panel regret worth naming: not buying the half-cut variant from the start.

Charge controllers and inverters

MPPT charge controllers are what let you use standard, mass-produced panels in an off-grid system. PWM controllers still work but they leave watts on the table, and they restrict panel voltage choices.

The inverter is where off-grid kits get expensive and where DIY mistakes bite. Most grid-tie inverters are not configured to connect to a battery bank, so off-grid systems require components specifically rated for off-grid use. A grid-tie inverter wired to a battery bank will not behave — and may not be safe.

Batteries: the centrepiece, and the real cost

Batteries store energy for use at any time, and they are the single component that defines the system. Solar batteries are typically sized to cover one night's energy usage and recharge from solar during the day, completing one charge/discharge cycle over a 24-hour period.

For Australia, deep-cycle lithium (LiFePO4) is in roughly the $800–$1,200/kWh installed ballpark, which is current as of writing. Flooded lead-acid (FLA) remains a common alternative and costs less up front, at the price of more maintenance, venting requirements and shorter cycle life.

Rules worth restating:

Deep cycle only. Car-style starter batteries are not designed for the gradual discharge/recharge pattern an off-grid bank runs every day.
Cold charging. Lithium cells must not be charged below 0 °C. Here in subtropical Central Queensland we don't design for hard frost as the baseline case — our battery enclosure priorities are heat dissipation, shade and ventilation through the hot wet summers. In colder regions of Australia (and elsewhere), if your battery enclosure can see sub-zero overnight, you need a heater, a low-temp charge lockout, or a chemistry that allows it — plan accordingly for readers in those climates.
Monitoring. A battery monitor / shunt (such as a Victron BMV-712 or SmartShunt) is standard practice. You cannot manage what you cannot measure, and "battery feels low" is a poor control input.
Sizing buffer. Size the bank at 1.5–2× your calculated nightly use if the budget stretches. The regret list fills up fast when the bank is sized to "just enough" on paper.

Generator backup: design it before you need it

Any serious off-grid install in Australia includes a generator for extended cloud cover or equipment failure. If you want auto-start on battery state-of-charge, two design points matter:

The auto-start circuit needs a manual override so a fault doesn't keep cranking the motor in the middle of the night.
The enclosure needs engineered ventilation — CO is colourless and you do not want to discover this in a fault condition.

Fuel choice matters too. Propane stores indefinitely; petrol degrades in 3–6 months and pulls moisture. For a backup unit that may sit untouched between cyclones, propane is the lower-fuss option.

Safety, standards, and when to call a licensed professional

Off-grid solar installation involves safety rules that deserve respect. Some installations are appropriate for DIY while others require professional work. Build the system to be safe and code-compliant.

AS/NZS 5033 governs the PV array installation.
AS/NZS 3000 (the Wiring Rules) governs the LV side.
AS/NZS 1170.2 governs wind loading on the array — relevant in cyclone regions.

When to call a licensed professional (electrician or CEC-accredited installer):

Any 230 V AC wiring, board work, or inverter connection on the AC side.
DC string sizing, OCPD selection and switchgear above the limits of AS/NZS 5033 DIY scope.
Battery bank installations above low-voltage / small-capacity thresholds.
Generator changeover switch wiring and auto-start interlocks.
Roof penetration, structural fixing and wind-rated mounting in cyclone regions.
Anything that requires a Certificate of Electrical Compliance in your state.

Plumbing tangent that came up in our rainwater setup: stainless or brass fittings are the right call for acidic rainwater contact. Galvanised fittings corrode fast and end up in the tank as black sediment. Worth knowing before the plumber leaves.

Regrets and real lessons, in one list

1. Size the battery bank first, then size the panels. I did it the other way around.

2. Buy half-cut cells. More efficient and more failure-tolerant.

3. Specify off-grid-rated inverters and charge controllers from day one. Grid-tie hardware will not behave.

4. Plan for temperature extremes your climate actually throws at you. For me here in Beecher that's heat and wet-season humidity, so enclosure ventilation and shading take priority; in colder regions, plan for sub-zero charging if your site can ever see it.

5. Vent the battery enclosure like it owes you money. Especially with FLA.

6. Oversize PV vs battery. Cheap insurance against bad weeks.

7. Treat the generator as part of the design, not an afterthought.

FAQ

How big should my battery bank be?

Sized to cover one night's energy usage and recharge from solar during the day, completing one cycle per 24 hours. In practice, going 1.5–2× larger pays back in resilience and cycle-life headroom.

Do I need a special inverter for off-grid?

Yes. Most grid-tie inverters are not configured to connect to a battery bank, so off-grid systems require components specifically rated for off-grid use.

Mono or poly panels?

Both produce the same watts per panel under test, but poly requires more roof area for the same output. Cell efficiency difference is small; footprint and price dominate.

60-cell or 72-cell panels?

60/120-cell panels are easier to handle and offer more flexible array layouts. 72/144-cell panels cost less to install per watt because you need fewer mounts, clamps and combiner parts.

Can I draw power from the grid when my batteries are low?

No. Off-grid means 100% responsible for your own power, with no ability to draw supplemental electricity from a utility company.

How fast is the off-grid solar market growing globally?

Per GOGLA's H2 2022 sales and impact report, global sales of off-grid solar energy kits reached 5.2 million units in the second half of 2022 — a 20% increase from H1 2022 — across lanterns, multi-light systems and solar home systems.

Do I need a licensed electrician?

For all 230 V AC wiring, inverter AC-side connection, generator changeover work, and any installation above the DIY scope of AS/NZS 5033, yes. Off-grid installation involves safety rules that deserve respect, and the boundary between DIY and licensed work is real.

Sources

https://www.gogreensolar.com/pages/off-grid-solar-system-design-installation-guide
https://luminaid.com/blogs/resources/off-grid-solar-power-kit

Worth a watch: So You Want To Go Off-Grid? (Lessons Learned) · African Homestead

The video walks through off‑grid sizing mistakes and the trap of oversizing your array, which matches the regret I noted about wasting money on panels that cook your batteries. — Dave Miller

Disclosure: some links in this article are affiliate links. If you buy through them we may earn a small commission at no extra cost to you.

When to Call a Professional

While many off-grid projects are achievable as DIY, certain situations require licensed professionals:

Always check local regulations and obtain necessary permits before commencing work.