By Rhys Coffin: Off-Grid Solar Designer, Power Station New Zealand. Updated October 2026. About the Author

Click Any Link Below to Choose Your Generator Topic or Just Scroll Down

Looking for more? Check out this 10-minute read Beginner’s Guide to Off-Grid Solar

Unlike the tropics, New Zealand’s latitude means there is a big difference in sunshine hours between summer and winter.

Wellington, for instance, receives about 130 more hours of direct sunshine in January than it does in June.

Because of this variation, your solar system needs to be designed around the winter months when sunlight levels are at their lowest.

While most off-grid systems produce considerably more electricity than needed during summer, winter brings consecutive dark days with very little sunshine, no matter where you live in Aotearoa.

This includes areas with traditionally high average sunshine hours like Whakatāne, Nelson, New Plymouth and Napier.

Without enough stored energy or another power source (generator), your batteries will eventually run flat and the lights will go out.

That could be a minor inconvenience or it could ruin your whole week.

This image shows the relationship between your backup generator, your components, and your house

lthough we generally recommend a backup generator, there are situations where an off-grid solar system can operate reliably without one.

A bach used only during summer is one example.

Since late 2020, we’ve monitored the performance of newer Power Station systems installed throughout New Zealand, including Southland, the West Coast, Taupō and Manawatū.

What we’ve found has caused us to rethink some earlier assumptions about backup generators.

Some customers have gone through entire winters with little or no generator use, even in parts of the country where winter solar generation is particularly challenging.

There is an important distinction between having a generator that you rarely use and designing a system from the outset so that one isn’t required.

A system designed without a generator generally needs more panels and more battery storage, which adds to the cost.

Even with additional capacity, you may still need to reduce electricity consumption during extended periods of poor winter sunshine.

Your location, winter electricity use, solar array size and battery capacity all influence whether this is practical.

For households with modest and predictable electricity needs, leaving out the generator may be reasonable.

But for most households, a backup generator remains the most practical and cost-effective solution.

One of the most important parts of designing an off-grid solar system is finding the right balance between the cost of solar panels, battery storage and a backup generator.

You could install a lot more solar panels and batteries to reduce the likelihood of ever needing a generator, but the additional cost becomes difficult to justify if that extra capacity is only needed for a handful of dark winter days each year.

At the other extreme, you could save money by installing fewer panels and batteries and relying more heavily on a generator.

That approach means higher fuel costs, more noise, additional maintenance and greater dependence on fossil fuels.

The Goldilocks Zone is somewhere in between.

That means having enough solar panels and battery storage to comfortably meet your normal electricity needs through winter while accepting that a backup generator may occasionally be needed during extended periods of poor weather.

Some households might run the generator only a few times each winter, while others may need it more often or hardly at all.

The goal is not to eliminate the generator altogether, but to avoid spending thousands of dollars on additional solar panels and batteries just to save a few hours of generator running time each winter.

To learn more about battery storage and battery autonomy, check out Off-Grid Solar Batteries: A Deep Dive.

Bigger isn’t always better, but a generator that’s too small can be a false economy.

The right generator size depends mainly on two things:

1. The size of your battery bank and how much charging power it can accept.
2. Your expected peak household power demand, in other words, how many appliances and other electrical loads might be running at the same time.

For example, our Power Station systems provide approximately 25 A, 50 A or 100 A of AC power, depending on the inverter configuration.

Your generator doesn’t need to match the full inverter capacity, but we do need to consider how much electricity your home might use while it’s running.

This is particularly important on a cold winter evening, when the oven, cooktop, microwave and other high-draw appliances might all operate at once.

Undersized off-grid solar generators

A smaller generator may be cheaper, but it can take much longer to recharge your batteries, particularly if it’s also supplying electricity to the house.

We’ve had examples of an undersized generator being connected that has run out of fuel overnight before the batteries were full!

That means more running hours, more noise, additional fuel consumption and more wear and tear.

We recommend charging the battery bank at a relatively high rate for as short a period as practical, while still supplying the household’s electricity needs.

• For battery banks up to around 25 kWh of usable storage, we generally recommend a generator rated at 7 kW maximum output or higher. The final choice depends on its continuous output, battery charging limits and expected household loads.
• For smaller systems with an inverter of up to 6 kW (approximately 25 A) and less than 12 kWh of usable battery storage, a 5 kW or 6 kW generator may be suitable.

When you use electricity matters just as much as how much you use

If your home uses very little electricity during winter daylight hours, apart from essential background loads, but most of your consumption occurs after dark, a larger generator may be needed to supply the household and recharge the batteries at the same time.

That’s something we’d want to discuss with you before recommending a generator size.

The aim is to put a substantial amount of energy back into the batteries quickly, then shut the generator down rather than have it running for hours at a low charging rate.

Maximum Generator Output Versus Continuous Generator output

One thing to watch when comparing generators is that the advertised output isn’t necessarily what the generator can supply continuously.

For example, the popular Honda EU70iS is advertised as a 7 kW generator. However, Honda’s specifications show that its maximum output is 7 kW, while its rated continuous output is only 5.5 kW.

That’s a difference of around 21%.

You may also see generators rated in kVA rather than kW. These aren’t necessarily the same, so it’s important to check the manufacturer’s specifications.

When sizing a generator for an off-grid solar system, we look at its rated continuous AC output, not just the maximum output advertised.

We generally recommend a quality, pure sine-wave inverter generator that’s been approved for use with your off-grid solar system.

A generator has a serious job to perform, and not one we’d leave to a cheap machine picked up from Bunnings.

Why We Recommend Pure Sine-Wave Inverter Generators

The electricity supplied to your home needs stable voltage and frequency, along with a clean, consistent waveform known as a pure sine wave.

When you’re connected to the national grid, you don’t have to think about the quality of your electricity supply. But when you’re off-grid, the generator becomes another source of power, and its output quality matters.

An inverter generator uses electronics to regulate its AC output, producing electricity with a stable frequency and smooth sine wave. This is particularly important for sensitive equipment such as computers, televisions and other modern electronics.

Poor-quality generator output can also cause problems for the solar system’s inverter/charger, which may reject the generator’s electricity if the voltage, frequency or waveform falls outside acceptable limits.

Petrol or Diesel?

Both can be suitable, and the choice is largely yours.

One important consideration is noise. Some diesel generators produce over 80 dBA, compared with just 52 dBA for the Honda EU70iS. That’s a substantial difference, particularly if the generator is running at night or close to your home.

There are also differences in purchase price, fuel consumption, servicing and expected operating life.

Will Any Generator Work With an Off-Grid Solar System?

No. Even a generator with sufficient power output may not be compatible with your solar system’s inverter/charger.

Voltage, frequency, waveform quality and the generator’s ability to handle changing loads all matter. That’s why we recommend using a generator that’s been tested and approved for your particular system.

Which off-grid solar generator do we recommend?

We have tested a number of generators and can recommend brands and sizes depending on your Power Station system, battery capacity, electricity use, preferences and budget.

Our advice is to talk to us before purchasing a generator, even if you’ve already found one that appears to have the right specifications.

There are several practical considerations when deciding where to locate your backup generator, particularly noise, weather protection, ventilation and its distance from your Power Station system.

Keeping the Generator’s Starting Battery Charged

During summer, your backup generator may go for months without being needed. If its starting battery goes flat, it may not start when you finally need it.

Some generators have a built-in battery maintenance or trickle-charging facility to keep the starting battery topped up.

Others require the electrician to arrange a suitable trickle charger supplied from the Power Station system.

It’s a small detail, but an important part of making sure your backup generator is ready when you need it.

Running Your Generator During Summer

We also recommend starting and running your generator for at least one hour each month during summer, preferably with some electrical load.

This helps keep the engine in good working order and confirms that the generator starts and runs properly.

The last thing you want is to discover that your backup generator won’t start when you need it most.

A correctly sized generator may cost more to purchase, but it can be better value over time because it can recharge your batteries more quickly than an undersized generator, reducing the number of hours it needs to run.

Depending on your household electricity use, the size of your solar system and where you live, your generator might only be needed a few times each winter, running for a few hours each time.

How much fuel will an off-grid solar generator use?

A larger inverter generator of 6 kW or more might consume around 3 litres of fuel per hour, depending on the electrical load. Smaller generators will generally use less.

Let’s assume your petrol generator runs for three hours at a time, six times each year.

• 6 starts × 3 hours = 18 hours annually
• 18 hours × 3 litres = 54 litres of fuel
• 54 litres × $3.60* = $194.80 per year [*pricing as at October 2026]

That’s not a particularly large annual fuel bill for the reassurance of having backup electricity available when you need it.

Of course, your actual fuel consumption and running hours will depend on your system, household loads and winter weather conditions.

*Petrol pricing as at October 2026

What About Generator Servicing?

We recommend having your generator serviced **once a year**, even if it hasn’t been used much.

Choose a convenient time, perhaps at the end of summer or after winter, and stick to it.

A typical generator service, including oil and parts, might cost between $100 and $300, depending on the model and what’s required. If you’re comfortable carrying out basic maintenance yourself, the cost can be considerably less.

Why Regular Maintenance Matters

Think about your lawnmower. You leave it sitting in the shed all winter, pull it out in spring, and discover it won’t start because it hasn’t been maintained.

That’s inconvenient, but the worst that happens is your lawns get a bit longer.

A backup generator that won’t start when your batteries are running low is a much bigger problem.

One of the realities of off-grid living is that you’re responsible for your own electricity supply. Keeping your generator serviced and ready to operate is part of that responsibility.

I f you have an off-grid solar project and you would like some help, consider our Free Design Service or get in touch.

If you’re still researching, try the following l.nks:

• See Systems and Pricing
• Browse our Off-Grid Solar Library
• Download our comprehensive Free Off-Grid Solar eBook

Rhys has been part of the Power Station founding team since 2018. He is passionate about sharing knowledge, especially with people new to off-grid solar. He has personally been involved in designing and planning hundreds of off-grid solar systems throughout New Zealand including the Pacific region.

Contact: rhys@powerstation.nz