What Happens When the Grid Goes Down? Solar and Outages

Here is the truth that surprises nine out of ten Kiwi homeowners: a standard grid-tied solar system does NOT work during a power outage. When the lines go down, your panels switch off too, even if the sun is blazing on your roof. This is a safety feature called anti-islanding, and it is mandated by New Zealand electrical regulations. The only way to keep your lights on during a blackout is to add a battery with a dedicated backup circuit, or install an off-grid capable hybrid inverter. If keeping the fridge running through a Cyclone Gabrielle-style event is a key reason you are looking at solar, you need to design the system specifically for that. Most quotes you will get by default will not include this capability.

This article is for any homeowner who has watched the news during a North Island storm, looked at their roof, and thought "well at least I'd have power." We are going to gently walk through why that assumption is wrong, what islanding actually means, and how to design a system that genuinely keeps your home running when the grid fails.

It sits under our guide to NZ solar tariffs and retailers, because the question of backup is closely tied to how your system interacts with the wider grid.

What "Solar in an Outage" Actually Means for NZ Homeowners

New Zealand's grid is generally reliable, but the last few years have stress-tested that reputation. Cyclone Gabrielle in 2023 left parts of Hawke's Bay, Tairāwhiti and Northland without power for weeks. Auckland's Vector network has had multiple high-profile transmission failures. Wellington gets battered by southerlies most winters.

For a household with solar panels, the natural assumption is: "I'm generating my own power, so an outage shouldn't affect me." It is a completely reasonable thought. It is also wrong, and the reasons are technical, regulatory, and safety-driven.

Understanding this matters for two reasons. First, so you do not get a nasty surprise the next time a storm rolls through. Second, so you can make an informed decision about whether to spend extra on battery backup, and which kind.

The default behaviour: lights out

A standard grid-tied solar system (panels plus a string inverter, no battery) is designed to work in parallel with the grid. The inverter constantly measures grid voltage and frequency, and synchronises its output to match. If the grid disappears, the inverter has nothing to sync to, so it shuts down within milliseconds.

This happens whether it is night, day, sunny, or cloudy. Your panels could be producing peak generation at 1pm on a January afternoon, and the moment the lines company loses supply, your house goes dark just like every other home on the street.

What is Anti-Islanding, and Why Does It Exist?

The technical term for this safety behaviour is anti-islanding. An "island" in electrical terms is a section of the grid that becomes electrically isolated but still has power flowing through it. If your solar inverter kept pushing electricity into the grid during an outage, it would create one of these dangerous islands.

Why is that bad? Two big reasons:

• Lines worker safety. When the grid goes down, lines crews from Vector, Orion, Powerco, Wellington Electricity, Aurora or whoever your local network is, assume the wires are dead. If your solar system is back-feeding live electricity into those wires, a worker could be seriously injured or killed.
• Equipment damage. When power is restored, an out-of-sync island can cause a destructive surge as the two systems reconnect, damaging your inverter, your appliances, and neighbouring homes' gear.

Anti-islanding is required by AS/NZS 4777.2, the joint Australia/New Zealand standard that governs all grid-connected inverters in this country. Every inverter sold legally for residential install in NZ must comply. This is not a manufacturer preference; it is the law.

So how do batteries get around this?

Battery backup systems do not "get around" anti-islanding. Instead, they create a deliberate, controlled island that is electrically isolated from the grid. When the grid drops, a special switch (the automatic transfer switch, or ATS) physically disconnects your home from the lines. Your inverter then powers a defined section of your house using battery (and during the day, solar) energy, in complete isolation from the wider grid.

The lines outside your house stay safely dead. Your fridge stays cold.

The Three Ways to Have Power During an Outage

If keeping power during a blackout matters to you, there are essentially three system designs to consider. Each comes with different costs, capabilities, and trade-offs.

Option 1: Hybrid Inverter + Battery + Backup Circuit

This is the most common backup setup in modern NZ residential solar. The system includes:

• Solar panels (usually 5-10 kW)
• A hybrid inverter (Sungrow, Fronius GEN24, Goodwe, Solis hybrid models)
• A LiFePO4 battery (BYD HVS/HVM, Sungrow SBR, Pylontech Force-H2, Tesla Powerwall)
• A dedicated backup circuit wired by your electrician, typically powering the fridge, lights, internet router, and a few key outlets

When the grid drops, the ATS isolates the backup circuit and powers it from the battery. During the day, the panels can also recharge the battery. This is the realistic Kiwi setup: not whole-home backup, but enough to ride out a 24-48 hour outage in comfort.

Option 2: Whole-Home Backup

Some premium systems (notably Tesla Powerwall 3 and certain Sungrow configurations) can island the entire house, not just a sub-circuit. This requires:

• A larger battery (or stacked batteries)
• A higher-capacity inverter
• Sometimes a Gateway/Backup Box (Tesla calls theirs the Powerwall Gateway)
• Careful load management, you cannot run the oven, heat pump, kettle, and dryer simultaneously off battery

Whole-home backup costs more, usually $5-15k above the basic backup-circuit option, but it is genuinely the closest you get to "the grid never went down" experience.

Option 3: True Off-Grid

For most Kiwi homes this is overkill, but for genuinely remote rural properties (Coromandel baches, Northland lifestyle blocks, parts of the West Coast) it can be the right call. True off-grid means no grid connection at all, a much larger battery bank, often a generator backup, and a system designed for autonomy through multiple cloudy days.

If you are considering this, our quote service can connect you with installers who specialise in standalone power systems.

What This Means for You

How you should think about outage protection depends a lot on what kind of homeowner you are.

The ROI Pragmatist

If you are buying solar for payback and cost savings, backup capability is a premium feature that does not pay back financially. A battery with backup typically adds $10-18k to a system cost, and the battery itself can be justified on dynamic tariff arbitrage and self-consumption (see our deep dives on Octopus Energy tariffs and Ecotricity's Resi-Flex plan), but the backup function itself is insurance, not investment.

Be honest with yourself: how often do you actually lose power for more than two hours? If the answer is "once a year, maybe," a quiet petrol generator at $1,500 is a far cheaper insurance policy than a $15k battery backup.

The Tech-Savvy Optimiser

If you are already going to install a battery for dynamic tariff arbitrage, EV charging optimisation, and self-consumption, then adding backup capability is incremental. The battery is doing the expensive heavy lifting; the backup circuit and ATS add only $1-3k. At that point, why wouldn't you?

Make sure to ask your installer about black start capability (can the system restart on its own from a completely flat state), and whether the inverter can recharge the battery from solar while in island mode. Not all of them can. Sungrow's hybrid range and Tesla Powerwall 3 do this well.

The Eco-Conscious Family

If energy independence and resilience are core values, backup is probably worth the spend. There is a real peace-of-mind benefit to knowing your kids have a warm meal and a working fridge through a storm, regardless of what the lines company is up to.

Just go in with realistic expectations: a typical backup circuit will power lights, fridge, freezer, internet, and a couple of outlets. It will not power your heat pump, electric oven, instant gas hot water (which needs electricity to ignite), or EV charger at the same time.

Common Pitfalls: What Installers Won't Always Tell You

This is the part of the conversation where the trust proxy bit really matters. Solar quotes vary wildly in how they handle backup, and some of these gotchas only show up after you have signed.

• "Battery-ready" does not mean backup-ready. Many quotes describe a system as "battery-ready" or "future-proof." This usually just means the inverter is a hybrid. It does NOT mean the wiring or the consumer board has been set up to support backup circuits. Adding that capability later can cost thousands.
• Default battery installs often skip the backup circuit. A surprising number of installs include a battery but no backup function at all. The battery just does self-consumption and grid arbitrage. When the grid drops, the whole system shuts down anyway. Always ask explicitly: "does this quote include a backup circuit and ATS?"
• Backup circuit sizing. Some installers wire a minimal backup circuit (lights and one outlet). Others wire a generous one (whole kitchen, lounge, office). Get specific: which appliances and which rooms will be on the backup side?
• Heat pumps and ovens. High-draw appliances often cannot be on the backup circuit because they exceed the inverter's island-mode power output. If you want your heat pump to run during an outage, you need a high-output hybrid inverter (10kW+) or whole-home backup, not a basic 5kW setup.
• Gas hot water still needs electricity. Instant gas hot water systems (Rinnai, Bosch) need mains power to ignite. If your backup circuit does not include the hot water unit, no showers during a blackout.
• Internet and phones. Modern fibre internet runs through an ONT (Optical Network Terminal) that needs mains power. Put it on the backup circuit, and put a UPS on the router itself for instant cutover.
• Inverter island-mode capacity. A 5kW hybrid inverter might output the full 5kW when grid-tied but only 3-3.5kW in island mode. Read the datasheet, do not just trust the headline rating.

How the Network Operators Affect This

Your lines company (Vector, Orion, Wellington Electricity, Powerco, Aurora, Unison, Top Energy, Northpower, WEL Networks, etc.) sets the rules for how grid-connected inverters behave in their territory. Every install needs network approval before commissioning.

Most networks happily approve battery systems with backup capability, as long as the install complies with AS/NZS 4777.2 and the ATS is wired correctly. But the application process and timelines vary. Vector approvals can take 2-4 weeks in Auckland; some smaller networks are faster. Your installer should be handling all of this for you.

If you are in a region prone to long outages (Tairāwhiti, Northland, parts of Hawke's Bay), it is also worth asking your retailer about their medical dependency and vulnerable customer policies. These do not replace battery backup, but they affect prioritisation when supply is being restored.

Will Buy-Back Earnings Be Affected During an Outage?

Short answer: yes, but only for the duration of the outage. While your system is islanded, you are not exporting to the grid, so you earn no buy-back during that window. Once the grid comes back and your inverter reconnects, normal export resumes.

This is one reason long outages are still painful even with backup: you lose the export revenue. For most households this is trivial (a few dollars), but it is worth being aware of.

If buy-back economics are central to your solar decision, our Dynamic Tariff and Buy-Back Engine is the best place to compare current rates across retailers including Meridian, Genesis, Contact, Mercury, Octopus, and Ecotricity.

Frequently Asked Questions

Does my existing solar system work in a power cut?

Almost certainly not. If you have a standard grid-tied system with no battery, your inverter will shut off the moment the grid drops, even if the sun is shining. This is a legal safety requirement (anti-islanding) under AS/NZS 4777.2.

Can I add a battery to my existing solar to enable backup?

Often yes, but it depends on your current inverter. If you have a standard string inverter (not a hybrid), you will need to either replace it with a hybrid model or add an AC-coupled battery system (like a Tesla Powerwall) that has its own integrated inverter. Get an installer to assess your existing setup.

How long will a battery power my house during an outage?

It depends on battery size and your load. A typical 10kWh battery powering a backup circuit (fridge, lights, internet, a few outlets) will usually last 12-24 hours overnight. During the day, your solar panels can recharge it, so in a multi-day outage with good weather you can effectively run indefinitely on the backup circuit.

Will my solar panels charge the battery during an outage?

Only if your inverter supports it. Many hybrid inverters can run in "island mode" with solar input, recharging the battery and powering the backup circuit during daylight. But some cheaper hybrids only support battery discharge during outages, not solar recharge. Always confirm this with your installer.

What's the difference between backup and off-grid?

Backup means you are still connected to the grid for normal operation, but you can island your home during outages. Off-grid means you have no grid connection at all. Off-grid systems are typically 2-3x more expensive because they need much larger battery banks, often a backup generator, and are designed for full autonomy.

Can I just use a generator instead?

For occasional short outages, yes, a quiet inverter generator ($1,500-3,500) can be a cost-effective backup option compared to a $15k battery system. The trade-offs: you need to store petrol, manually start and connect it, and it does not double as a solar self-consumption tool the rest of the year. Many rural Kiwis run both: solar with a modest battery for day-to-day, generator for multi-day events.

Will my EV charger work on backup?

Generally no. Most home EV chargers draw 7kW+, which exceeds the island-mode output of typical residential hybrid inverters. Whole-home backup setups with larger inverters (10kW+) can sometimes support slow EV charging, but it will deplete your battery quickly. Plan for EV charging to be paused during outages.

Does my retailer or lines company need to know I have backup capability?

Yes. Any battery and backup install needs network approval before commissioning, just like the original solar install. Your installer handles this paperwork. Your retailer also needs to know if you have a battery so your tariff and metering are set up correctly.

Is whole-home backup worth the extra cost?

For most NZ households, no. A well-designed backup circuit covers the appliances that actually matter (fridge, freezer, lights, internet, hot water if gas/electric storage) at a much lower cost. Whole-home backup makes sense if you have a home office that cannot tolerate any inconvenience, medical equipment, or genuinely live in an outage-prone area.

Where to Go From Here

If outage resilience is one of your reasons for going solar, the key takeaway is to be specific with installers from the very first quote. Ask explicitly for a battery with a backup circuit, and list the appliances you want covered. Do not assume a "battery-ready" or "hybrid" system includes backup; it usually does not.

From here, you might want to dig into the tariffs and retailers pillar to understand how a battery pays back through dynamic pricing, or jump into specific tariff explainers like Octopus Energy and Ecotricity Resi-Flex. If you are leaning toward Meridian for simplicity, our Meridian solar plans guide walks through their offering.

The single best thing you can do now is get a few quotes from installers who actually understand backup design. Some do this well; others treat batteries as a bolt-on afterthought. The difference shows up the first time the lines go down.