If you’re installing a complete off-grid solar system with roof panels, batteries in the shed, and no electricity bill, why might you still want a petrol or diesel generator?
That’s a good question. While adding a generator is optional, it’s important to know what you might be missing if you decide not to include one.
While we don’t currently install off-grid systems at PSC Energy, we have in the past and we are expert installers. Today, we’re acting as educators only. We mostly install Sigenergy systems and want to be clear about that, but what we explain here applies no matter which brand you pick.
By the end of this article, you’ll learn:
- What a generator does in an off-grid solar system.
- What happens if you don’t use one.
- How modern systems manage backup power automatically.
- How to decide if you need a generator in your setup.
Off-Grid Solar Systems Don’t Require a Generator
There’s no rule that says you must have a generator. If you choose to skip it, you can add more panels and batteries to prepare for bad weather. That’s a valid option.
But the reality is this: without a generator, your batteries are your only backup. When they run out, so does your power. There’s no grid to rely on. The lights go off and stay off until the sun shines again.
If you decide to go without a generator, you can lower your risk by:
- Monitoring your battery levels closely during cloudy or rainy stretches.
- Running heavy appliances like washing machines and air conditioners only when batteries are healthy.
- Postponing big energy tasks during extended bad weather.
- Using your system’s app or display to stay on top of your usage daily.
Here are the risks of not having a generator:
- No backup during long stretches of cloudy or rainy weather.
- No way to recharge batteries without solar input.
- A complete loss of power until conditions improve.
- No fail-safe if your solar production falls short of expectations.
For some households, that risk is okay. But for most, it’s not.
If you’re interested in solar batteries, you might want to check out the following article titled, Are Solar Batteries Worth It in NSW? PSC’s Ultimate Guide for 2026.
What a Generator Does in an Off-Grid Solar System
When you’re on the grid, it’s your fail-safe. If your solar falls short and your batteries run low, the grid steps in without you noticing.
But when you go off-grid, you lose that safety net. A generator takes its place and acts like your grid.
In a well-designed off-grid solar power system, the generator:
- Sits quietly in the background, doing nothing most of the time.
- Activates automatically when batteries drop to a pre-set level, typically between 20 and 30 per cent capacity.
- Recharges the batteries without you needing to intervene.
- Shuts off automatically once the batteries are back to a healthy level.
The keyword is automatically. You don’t go outside and pull a cord. The controller manages it all when installed correctly.
How Your Off-Grid Solar Batteries Are Sized: Three Days of Power
When an installer designs your off-grid solar system, they calculate something called autonomy. It’s the number of days your batteries can run your home with zero solar input.
In Australia, the standard for off-grid solar batteries is three days of backup. Here’s how that’s calculated:
- Your installer calculates your average daily energy usage in kilowatt-hours.
- They multiply that by three to get your three-day baseline.
- They add a buffer for unexpected loads or higher-than-usual usage.
- The result sets the minimum battery capacity your system needs
Three days is the standard because that’s about how long a bad weather stretch usually lasts in most parts of NSW. A generator helps if it lasts longer.
Without a generator, you’d have to add a lot more battery storage to cover four, five, or six days of cloudy weather with confidence.
If you’re interested in learning a bit more about the price of solar batteries, you might want to check out the following article titled, How Much Are Solar Batteries? A Full Breakdown of Prices, Rebates, and Value in 2026.
Can You Just Add More Solar Panels and Off-Grid Solar Batteries?
Adding panels and batteries instead of a generator can work if:
- Your location gets consistent sun for most of the year.
- Your energy usage is modest and predictable.
- You’re comfortable with the small risk of losing power during an unusual weather stretch.
- Your budget allows for a significantly larger battery bank.
A good quality generator for an off-grid solar system usually costs between $3,000 and $8,000 installed. The extra battery storage needed to replace that backup could cost a lot more depending on your usage. Prices vary, so ask your installer to provide quotes for both options before deciding.
What Size Generator Do You Need for an Off-Grid Power System?
Generator sizing comes down to two things: your household loads and your controller’s maximum input.
Here’s what shapes the decision:
- The controller in your off-grid system has a maximum input it can accept from a generator.
- Your generator needs to match or sit within that limit.
- A generator that’s too large can overload the controller.
- A generator that’s too small won’t charge the batteries efficiently.
Most residential off-grid solar systems in NSW work well with generators in the 5-15 kVA range.
A kVA (kilovolt-ampere) is a unit that measures the total electrical power a generator or other device can handle, and for practical purposes it’s close enough to kilowatts (kW) that most people treat them as the same thing.
If you have a large home or a two-stack battery system, your installer may recommend upsizing the controller at the same time.
Have your installer size the generator based on your real usage before you buy. Getting it wrong can be an expensive mistake.
If you’re interested in looking at some solar battery choices, you might want to check out the following article titled, Which Solar Battery Should I Buy?
Wrapping Up: Adding a Generator is Fuel for Thought
Now you know what a generator does in an off-grid solar system, why most installers suggest having one, and how to weigh the trade-offs between extra batteries and a backup generator.
PSC Energy serves all of NSW, from Western Sydney to regional and rural areas. Whether you’re planning your first off-grid solar system or checking a quote that seems high, we’ll guide you through your options honestly. It’s what we do.
If you’re interested in learning more about the Cheaper Home Batteries Program and it’s recent changes, you might want to check out the following article titled, Changes to the Australian Government’s Cheaper Home Batteries Program Explained.
FAQ: Generators and Off-Grid Solar Systems
How much does a generator cost for an off-grid power system?
A quality generator suitable for an off-grid solar system typically costs between $3,000 and $8,000 installed, though prices vary considerably depending on size and brand. Get your installer to model both scenarios, generator versus extra batteries, so you can compare the actual numbers for your situation.
Can I skip installing a generator and just add more off-grid solar batteries instead?
Yes, but it comes with trade-offs. More batteries give you more storage, but they can only hold what your panels produce. A generator creates power independently of the weather. For most NSW households, a generator is the more cost-effective fail-safe compared to the battery storage you’d need to replace it.
Do I need a generator for an off-grid solar system?
You’re not legally required to have one. But without a generator, your off-grid solar batteries are your only backup. If they run out during a stretch of bad weather, your power goes out and stays out until the sun returns.
How long should my off-grid solar batteries last without any solar input?
The industry standard for off-grid solar battery sizing is three days of autonomy. That means your batteries should run your home for three full days with zero solar production. A generator covers you if bad weather lasts longer than that.
What happens if my off-grid solar batteries run out completely?
In older off-grid systems, the power cut out until the generator turned on and restabilised the system. In modern off-grid solar electric systems, the controller prevents this by turning on the generator before the batteries reach zero, so you never actually lose power.
What size generator do I need for an off-grid solar system?
It depends on your household loads and your system’s controller. Most residential off-grid solar power systems in NSW work well with generators in the 5-15 kVA range. Your installer will size the generator to match your controller’s maximum input and your daily energy usage.
