EV Chargers and Solar: Smart Charging Basics

A smart EV charger like the Zappi watches the live flow of electricity at your meter and quietly pushes only your surplus solar into the car, so you charge on sunshine instead of selling it back to the grid for a pittance. That matters because most New Zealand retailers pay around 7 to 17 cents per kWh for the power you export, while you pay 25 to 40 cents per kWh to buy it back at night (per published retailer plans in 2025). Diverting that same energy into your EV instead is worth the full retail rate you avoid paying, so a typical solar household can charge a car for the equivalent of $2 to $4 of "lost" buy-back per day and turn it into $8 to $12 of avoided petrol or grid power. Done right, your car becomes the single best thing you can do with spare solar.

Why this question matters more than people think

Here's the thing nobody tells you when you buy solar: the panels are the easy part. The hard part is using the power yourself instead of dumping it to the grid for a low buy-back rate.

A typical 5kW system in a sunny spot will push out a fair chunk of energy in the middle of the day, exactly when most people are at work and the house is using almost nothing. That surplus gets exported, and you're paid the wholesale-ish rate your retailer offers. We dig into how poor that trade can be over here, where we break down the buy-back maths properly.

An EV changes the entire equation. A car battery is enormous compared to a house: a Nissan Leaf holds around 40kWh, a Tesla Model Y around 60kWh, a BYD Atto 3 around 60kWh. That's the equivalent of four to seven home batteries sitting in your driveway. If you can fill even part of it with midday sun, you've solved the self-consumption problem and cut your fuel bill at the same time.

What a smart solar charger actually does

A standard EV charger has one setting: on. Plug in, and it pulls power at whatever rate it's rated for, usually 7kW on a single-phase home, drawing from solar and grid indiscriminately. If your panels are only making 2kW at that moment, the other 5kW comes off the grid at full retail price. Not clever.

A solar-aware charger is different. It has a sensor clamp (a CT clamp) fitted at your switchboard that reads the live import and export at your connection point, hundreds of times a second. It knows, in real time, exactly how much surplus you're exporting. Then it modulates the charge rate to match.

The Zappi, made by myenergi, is the one most New Zealand installers reach for, and it has three core modes worth understanding:

• Eco+: charges using only genuine surplus solar. If a cloud rolls over and your export drops, the charge rate winds down or pauses until the sun returns. Pure sunshine charging, zero grid import.
• Eco: charges from surplus solar but tops up from the grid so the car keeps charging at a minimum rate. Useful when you need the car ready by a deadline but still want to soak up free sun.
• Fast: ignores solar entirely and charges at full speed from whatever's available. This is your "I need 80% by 6am" mode.

Other smart chargers do similar things. The Fronius Wattpilot pairs neatly with Fronius inverters, the EVNEX chargers (designed and built in Christchurch) offer scheduling and load management, and the Tesla Wall Connector can do basic solar-aware charging when paired with a Tesla Powerwall. But for divert-the-surplus charging on a mixed-brand system, the Zappi is the default for a reason: it doesn't care what panels or inverter you have.

The single-phase minimum nobody mentions

Here's a genuinely useful quirk that catches people out. On a single-phase home (which is most NZ houses), an EV charger can't ramp infinitely low. The practical floor for charging a car is around 1.4kW (roughly 6 amps). Below that, the car's onboard charger won't reliably accept the power.

That means in pure solar-only mode, your charger won't even start until you're exporting at least 1.4kW of surplus. On a grey Auckland winter afternoon when your 5kW system is making 1.5kW total and the house is using a kilowatt of it, you'll have nothing left to charge with. This is exactly why people who expect to run their car entirely on sunshine through winter end up disappointed. The maths works beautifully in summer and patchily in winter, and that seasonal reality is worth planning around before you spend the money.

Treating your EV as a battery on wheels

This is where it gets interesting, and where most household battery business cases quietly fall over.

A dedicated home battery (a Tesla Powerwall, a BYD, a sonnen) costs a serious amount once installed, often $12,000 to $18,000 for a usable 10 to 13kWh, based on installed pricing we see across the market in 2025. Its job is to store your midday surplus and feed it back to the house at night.

Your EV already has a battery four to seven times that size, and you paid for it as a car. If your daily routine lets you park it at home through the sunny hours, even a few days a week, you get a huge chunk of the "store my surplus" benefit without buying a second battery at all.

Run the numbers on a real household. Say you're in Hamilton with a 6kW system, you work from home two or three days a week, and you drive a BYD Atto 3 about 50km a day:

• 50km of driving uses roughly 8 to 9kWh (the Atto 3 sips around 16-18kWh/100km in real NZ conditions).
• On a clear day your 6kW system can dump 15 to 25kWh of surplus into a midday window once the house has taken its share.
• Charge the car on that surplus and you've covered your driving with energy that would otherwise have earned you maybe 10c/kWh exported, while avoiding around $5 to $7 of equivalent petrol for that distance.

Over a year, a home-charging EV owner on solar can knock a meaningful amount off both their fuel and their power costs, far more than the same surplus would earn sitting on a buy-back tariff. If you want to model what a system would actually return on your roof, our calculator lets you play with the numbers: https://nzsolaris.co.nz/solar-roi-calculator/.

The honest catch: most EVs can't yet power your house

"Battery on wheels" is a great way to think about charging, but be clear on the limit. True vehicle-to-home (V2H) and vehicle-to-grid (V2G), where the car powers your house back through the wall at night, is still in its infancy in New Zealand.

Only a handful of models support it (some Nissan Leaf and Ariya variants via the CHAdeMO standard, and a growing list of bidirectional-capable cars), the bidirectional chargers are expensive and thin on the ground here, and the network rules around exporting from a car are still being worked through. So for now, your EV is brilliant at soaking up surplus solar, but it generally can't yet pour it back into your kettle at 7pm. Plan around what's real today, not the brochure future.

The off-peak overnight angle people forget

Smart charging isn't only about solar. Some of the best value in NZ right now comes from pairing an EV with a time-of-use power plan.

Several retailers offer genuinely low overnight or off-peak windows. Electric Kiwi's "Hour of Power" gives a free hour daily, and various plans from the likes of Octopus Energy NZ, Contact and Mercury price overnight electricity well below daytime rates. A schedulable charger (the Zappi, Wattpilot and EVNEX all do this) lets you charge the car at low cost at 2am when you genuinely need a fast top-up, and on free sun when you don't.

The smartest setup uses both: sunshine through the day, low-cost off-peak overnight as backup. That combination is what actually flattens an EV household's bill across a NZ winter, when solar alone won't carry you. Always check your retailer's current plan and rates directly, because these change often and the right plan can be worth more than a chunk of extra panels.

Sizing your solar with an EV in mind

If you already own or plan to buy an EV, it changes how big a system makes sense. The old rule of thumb that "5kW suits the average home" assumes a household that isn't also fuelling a car off the roof.

Adding a car to the mix is one of the few genuinely good reasons to go bigger. An EV gives you a large, flexible daytime load that can absorb surplus you'd otherwise export at a low rate, which means a 7kW to 10kW system can pencil out where it wouldn't for a household with no daytime use.

A few practical pointers:

• Match panels to your driving pattern. Big daily kilometres and home-based work favour more panels. A car that's at the office all day won't see much midday sun, so don't oversize on the EV's account alone.
• Get the inverter sized right. Your charger can only divert the surplus your inverter is producing. A pinched inverter caps the whole thing.
• Mind your phases. Three-phase homes can charge faster and divert more flexibly. If you're on single-phase, the 1.4kW floor and the 7kW ceiling shape what's possible.
• Think about panel quality and degradation. An EV-sized system is a bigger investment, so the panels' long-term output matters more. We explain why the newer N-type cells hold up better in NZ conditions over here: https://nzsolaris.co.nz/n-type-vs-p-type-solar-panels-nz/, and what "Tier 1" really means for your warranty here: https://nzsolaris.co.nz/tier-1-solar-panels-meaning/.

If you want the full rundown on inverters, batteries and the rest of the kit that sits behind a good EV-and-solar setup, we've put it all in one place: https://nzsolaris.co.nz/your-guide-to-nz-solar-hardware-and-tech/.

Where this genuinely doesn't stack up

Honesty time. A solar-aware charger is brilliant for the right household and a waste for the wrong one.

It won't help much if your car is never home in daylight. If you and the car both leave at 7am and return at 6pm, there's no surplus to divert into it during the sunny hours. You'll be charging from off-peak grid power instead, which is fine, but you don't need a fancy diverting charger to do that, a basic schedulable one will do.

The winter gap is real. In Dunedin, Invercargill or anywhere with short, low-sun winter days, solar-only charging slows to a trickle for a few months. NIWA's solar radiation records show how dramatically daily sunshine energy drops in southern winter. Don't buy a setup expecting to fuel your car on sunshine in July.

The price premium has to earn its keep. A solar-diverting charger costs more than a plain one, often several hundred dollars more once installed. If you'll only ever charge overnight on a low off-peak rate, that premium may never pay back. Be clear on how you'll actually use the car before you spend up.

What to ask before you buy

When you're talking to an installer about adding an EV charger to a solar system, a few specific questions separate the good outfits from the order-takers:

• "Where does the CT clamp go, and will it read true surplus?" A solar-divert charger only works if its sensor is fitted at the right point in your switchboard. Get this confirmed.
• "Single or three phase, and what's my realistic charge rate?" This shapes everything about how the divert behaves.
• "Does the charger work with my existing inverter brand?" The Zappi is brand-agnostic; some others want a matched ecosystem.
• "Can it schedule off-peak charging as well as solar charging?" You want both, not one or the other.
• "Is the install certified and does it meet the wiring rules?" An EV charger is a fixed appliance on a dedicated circuit and must be installed by a registered electrician to the relevant standards.
• "What does the app actually show me?" Good visibility of solar generated, diverted to the car and pulled from grid is half the value. You learn your own house's rhythm fast.

A fair installed price for a quality solar-aware charger and the wiring sits in the low thousands depending on cable runs and your switchboard. Get it quoted alongside the panels rather than as an afterthought, because doing both at once often saves on the electrical work.

Frequently Asked Questions

Do I need a special charger to use solar for my EV?

Not strictly, but to charge from genuine surplus only you need a solar-aware charger like a Zappi, Fronius Wattpilot or a compatible EVNEX. A standard charger will draw whatever it needs from solar and grid together, so on a partly cloudy day you'll be buying a chunk from the grid without realising. The smart charger is what guarantees you're charging on sunshine rather than full-price power.

How much of my driving can solar realistically cover?

In a sunny region with a 6kW or larger system and a car that's home during the day, many households cover the bulk of their daily driving from surplus solar for much of the year. Through a southern NZ winter that figure drops sharply because there simply isn't enough midday surplus. Think of solar as covering most of your fuel in the lighter months and a useful slice in the darker ones.

Can my EV power my house during an outage?

For most cars sold in New Zealand today, no. True vehicle-to-home capability needs a bidirectional-capable car (only a handful, mostly via the CHAdeMO standard) plus a bidirectional charger, and these are still scarce and costly here. For now an EV is excellent at absorbing surplus solar but generally can't feed your house back at night.

Is it cheaper to charge from solar or from an off-peak power plan?

Surplus solar is usually the lowest-cost option of all, because the alternative use of that energy is a low export buy-back rate. Off-peak grid charging is the next best thing and is genuinely good value on plans with low overnight windows from retailers like Electric Kiwi, Octopus Energy NZ or Contact. The ideal setup uses solar by day and low-cost off-peak power overnight as backup.

Will charging my EV void my solar warranty?

No, charging an EV is just another load on your system and won't affect panel or inverter warranties. What matters is that the charger is installed correctly by a registered electrician on its own circuit. A botched install is the real risk, not the car itself.

How big should my solar system be if I have an EV?

Adding an EV is one of the better reasons to size up, often into the 7kW to 10kW range, because the car gives you a large daytime load to absorb surplus you'd otherwise export at a low rate. The right size depends on your driving distance and whether the car is home during sunny hours. A car that's at the office all day won't justify extra panels on its own.

Does the Zappi work with any solar system?

Yes, that's a big part of its appeal. The Zappi uses its own CT clamp at your switchboard to measure surplus, so it doesn't care which panel or inverter brand you have. That makes it the common choice for mixed-brand or existing systems where a matched-ecosystem charger wouldn't fit.

What's the minimum surplus needed before solar charging starts?

On a single-phase home the practical floor is around 1.4kW of surplus (about 6 amps) before the car will reliably accept a charge. Below that the charger waits. This is why solar-only charging pauses on dull days and through winter when your export rarely climbs above that threshold.

The Bottom Line

Pairing an EV with solar is one of the genuinely smart moves available to a New Zealand homeowner. Instead of selling your midday surplus for a handful of cents, you pour it into a battery you already own and drive on sunshine. A smart charger like the Zappi makes that automatic, and it sidesteps the cost of a dedicated home battery for a lot of households.

Just go in with clear eyes: the magic happens in the lighter months and when the car is home during the day, and you'll lean on off-peak grid power through a NZ winter. Size the system for how you actually live, get the charger quoted alongside the panels, and insist on a proper certified install.

If you're weighing up the whole system, from the panels themselves to whether a battery still makes sense alongside the car, it's worth getting your head around the kit first, then running real numbers on your own roof.