How to Arbitrage Battery Storage with Smart Tariffs

Battery arbitrage means charging your home battery when power is low-cost (usually overnight, sometimes under 10c/kWh on a free-hour or off-peak window) and using or exporting it when power is dear (peak rates can sit at 35c to 45c/kWh, and a handful of peak-export plans pay you 40c+/kWh to send it back). On the right tariff, that price gap is real money: a typical 10kWh battery cycled once a day on a wide spread can return roughly $2.50 to $4 a day in avoided cost and export credit, depending on your retailer and network. The catch, and there's always a catch, is that the maths only works on the right plan, with the right hardware, and the right daily habits. Get one of those wrong and you're just cycling an expensive battery for fun.

Let's walk through exactly how it works in Aotearoa, what the numbers really look like in 2025, and where it quietly falls apart so you don't find out the hard way.

What "arbitrage" actually means for a home battery

Arbitrage is just buying low and selling high. In the power world, your battery is the bucket you fill when electricity is low-cost and empty when it's expensive. There are two ways the savings show up:

• Avoided import: you charge the battery on low-cost night power, then run the house off the battery during the expensive evening peak instead of buying from the grid.
• Paid export: on certain plans you can discharge the battery back to the grid during a high-value window and get paid a premium buy-back rate for every kWh you send out.

The first one almost everyone can do. The second one is newer, smaller, and tightly capped, and it's where most people get over-excited. We'll keep them separate, because the maths is very different.

Why the New Zealand market makes this possible now

For years, NZ retailers offered one flat rate per kWh, so there was nothing to arbitrage. That has changed. The Electricity Authority's push toward time-of-use pricing, combined with smart meters being in the vast majority of NZ homes, means a growing number of retailers now publish tariffs that vary by time of day.

Octopus Energy NZ, Electric Kiwi, Ecotricity, Contact, Meridian and others now offer plans with genuinely different day and night prices, free hours, or premium peak export. That price spread is the raw material for arbitrage. No spread, no arbitrage. It really is that simple.

We keep a plain-English rundown of who offers what over at our guide to NZ solar tariffs and retailers, because the plans change often and the fine print matters more than the headline rate.

Step by step: how the arbitrage cycle works

Step 1: Find your price spread

Open your power plan and write down three numbers: your lowest import rate (off-peak or night), your most expensive import rate (peak), and your export buy-back rate. The gap between lowest import and peak import is your self-consumption spread. The gap between lowest import and export rate is your export spread.

As a rough 2025 picture across NZ time-of-use plans, night rates land somewhere around 12c to 17c/kWh, peak rates around 30c to 45c/kWh, and standard buy-back around 7c to 12c/kWh, with a few premium peak-export windows reaching far higher. Your own plan is the only one that counts, so use your real figures.

Step 2: Charge low-cost

You program the battery to charge from the grid during your lowest-cost window. On Electric Kiwi that might be your free hour of power; on an Octopus or Contact night rate it's the small-hours block. A modern battery system (Tesla Powerwall, Sungrow, Fronius with BYD, SolarEdge and the like) lets you set a time-of-use charge schedule in the app. You tell it: fill up between, say, 11pm and 7am.

Step 3: Use or sell at peak

When the expensive evening peak hits (typically 7am to 9am and 5pm to 9pm on most NZ networks), the battery discharges. If you're doing avoided-import arbitrage, the house simply runs off the battery and you buy nothing from the grid at peak prices. If you're on a paid-export plan, the battery pushes energy out to the grid during the paid window and you bank the credit.

Step 4: Let solar top it up by day (if you have panels)

If you have solar panels too, the sun refills the battery for free during the day, which is the lowest-cost energy of all. That's the holy trinity: free solar charge, low-cost grid charge as backup, expensive peak avoided or sold. A battery with no solar can still arbitrage purely on the day-night price gap, it just leans entirely on that grid price spread.

The worked example most installers won't do for you

Let's take a real-feeling scenario. A 1990s brick-and-tile home in Rolleston, Canterbury, on the Orion network, with a 10kWh usable battery and a time-of-use plan. Say night import is 14c/kWh, peak import is 38c/kWh, and the household reliably uses most of its evening peak load off the battery.

Avoided-import maths, one cycle a day:

• Charge 10kWh overnight at 14c = $1.40 cost
• Displace 10kWh of peak power at 38c = $3.80 value
• Daily gross benefit = $2.40

Round-trip efficiency steals a slice of that. A lithium battery loses roughly 10% to 15% in the charge-discharge round trip, so you don't get all 10kWh back out. Knock the daily figure down to around $2.00 to $2.15 after losses. Over a year that's roughly $730 to $785 from arbitrage alone, on top of whatever your solar saves you.

Now the bit nobody volunteers: that figure assumes you actually use 10kWh at peak every single day. Plenty of homes don't. A retired couple in a well-insulated place might only pull 4kWh to 5kWh across the evening peak. Their arbitrage benefit is half the number above, because you only capture the spread on the energy you genuinely shift. The identical battery, the identical tariff, half the result, purely because of the household's usage shape. This is the single biggest reason two neighbours get wildly different payback from the same kit.

The unique trap: cycling cost eats into your spread

Here's something installers almost never put in writing. Every charge-discharge cycle uses up a slice of your battery's finite life. Most lithium home batteries are warranted for somewhere around 3,650 to 6,000 cycles or a 10-year throughput figure, per the manufacturer warranties you'll see on a quote.

If you force a full extra cycle a day purely to chase a grid price spread, you're spending battery life to earn that spread. Suppose your battery costs $11,000 and is warranted for 4,000 cycles. That's roughly $2.75 of capital per full cycle before you count any energy at all. If your arbitrage spread only earns $2.40 a day gross, you can actually be running at a loss once you account for the wear you're putting on the asset.

This is why blind, aggressive cycling is a mistake. The smart move is to arbitrage only when the spread comfortably beats your per-cycle wear cost, and to let solar do the free charging whenever the sun's out. A battery filled by your own panels costs you nothing in energy, so those cycles are far more worth having than grid-charged ones. Run the per-cycle number on your own quote before you decide how hard to cycle. You will not see this calculation on a sales sheet.

Paid peak export: the high-value, low-volume play

A few NZ retailers now pay a premium to export during peak. Ecotricity's peak export approach and Octopus's peak-focused plans are the standout examples, and they can pay materially more per exported kWh than a flat buy-back. We break down how Ecotricity's plan actually works over at our explainer on Ecotricity's Resi-Flex peak export plan, and we do the same for the Octopus options in our breakdown of OctopusPeaker vs OctopusFlexi.

The appeal is obvious: if you can buy at 14c and sell at, say, 40c+ during a paid peak window, that's a much bigger spread than avoided import. But read the fine print carefully, because these plans usually come with conditions:

• Export caps: the premium rate often only applies up to a set number of kWh per day or only within a narrow time window.
• Network export limits: your lines company (Vector, Orion, Wellington Electricity, Powerco and others) sets a maximum export limit at your connection. You can't push out more than the network allows, regardless of what your battery could deliver.
• Inverter and consenting requirements: exporting from a battery sometimes needs specific inverter certification and network approval. Not every grid-tied setup is approved to discharge to the grid on demand.

Because both Meridian and others structure their buy-back differently, it pays to compare. We lay out Meridian's approach in our Meridian solar buy-back explainer. And before you commit to any of them, run your own numbers through our tariff and buy-back engine, which lets you model the spread against your actual usage instead of guessing.

Who this genuinely works for, and who should not bother

Arbitrage rewards a very specific shape of household. It works well when:

• You have a wide day-night price spread on your plan.
• You have real peak-time load to shift: a heat pump running in the evening, EV charging, cooking, hot water.
• You're home in the evenings to actually consume the stored energy, or you're on a paid-export plan.
• You're comfortable using the battery app and willing to tweak schedules seasonally.

It works poorly, and sometimes not at all, when:

• You're on a flat-rate plan with no meaningful price difference by time. No spread, no arbitrage, full stop.
• Your evening peak load is tiny. Low usage means you simply can't capture much spread.
• You're renting, or planning to move within a few years, so you'll never see the payback.
• Your network export limit is very restrictive, which guts the paid-export angle.

Be honest with yourself about your evening usage before you spend $10,000-plus chasing a spread you may not be able to fill.

The seasonal reality nobody puts on the brochure

NZ winters change the picture. In June and July, your solar contributes very little to the battery, especially in places with genuinely low winter sun like Wellington or the West Coast. That means most of your battery charge has to come from the grid at night, so you lean entirely on the day-night price spread, not free solar.

At the same time, your peak demand is at its highest in winter, with the heat pump working hard. So the avoided-import value can actually be strongest in the cold months, even though the solar side is at its weakest. In Central Otago, where clear, frosty winter days deliver surprisingly decent midday solar, the mix shifts again. The point is that your best arbitrage strategy in January is not your best strategy in July, and a set-and-forget schedule leaves money on the table.

How to set it up properly

If you want to actually do this rather than just read about it, here's the practical order of operations.

• Confirm your hardware can grid-charge. Not every battery is configured to charge from the grid by default. Ask the installer to enable and demonstrate time-of-use grid charging before you sign off.
• Confirm it can export from the battery if you want the paid-export play, and confirm your network has approved that export.
• Choose the tariff before you finalise the system. The plan dictates the strategy, not the other way around.
• Set conservative schedules first. Start with one low-cost-charge window and one peak-discharge window, watch a month of data, then refine.
• Track your real spread monthly. Retailers change rates. A spread that paid in summer can shrink in winter or after a price review.

When you're getting quotes, ask the installer to state the battery's usable capacity (not nameplate), its round-trip efficiency, its warranted cycle count or throughput, and whether grid charging and battery export are supported and network-approved. If they can't answer those four things clearly, keep shopping.

Frequently Asked Questions

Do I need solar panels to arbitrage a battery?

No. A battery can arbitrage purely on the grid day-night price spread, charging low-cost at night and discharging at peak. But solar makes it far stronger, because free daytime charging means those cycles cost you nothing in energy. Without solar you're entirely dependent on having a wide enough import spread to beat your per-cycle wear cost.

How much can I realistically save with battery arbitrage?

On a 10kWh battery with a wide spread and genuine evening load, roughly $2 to $4 a day in combined avoided cost and export credit is realistic after efficiency losses. Lower usage or a narrow spread can cut that in half or worse. Your own usage shape and tariff are the deciding factors, so model them rather than trusting a headline figure.

Won't all this cycling wear my battery out faster?

Yes, and that's the cost most people ignore. Every full cycle uses a slice of the battery's warranted life. Work out your capital cost per cycle (battery price divided by warranted cycles) and only chase a grid-charged arbitrage cycle when the spread comfortably beats that wear cost. Solar-charged cycles are far better value because the energy is free.

Which NZ retailers have plans good for arbitrage?

Octopus Energy NZ, Electric Kiwi, Ecotricity, Contact and Meridian all offer time-varying pricing or premium export windows that can support arbitrage, though the structures differ a lot. The right one depends on your usage and network. Compare the actual rates rather than the marketing, because the spread is what matters.

Can my lines company stop me exporting from my battery?

They can limit how much you export. Networks such as Vector, Orion and Wellington Electricity set a maximum export limit at your connection, and battery export sometimes needs specific approval and certified inverter settings. Always confirm your network's export allowance before banking on a paid-export strategy.

Is paid peak export better than just avoiding peak import?

The per-kWh spread on paid peak export can be larger, but the volume is usually capped by the plan and your network limit. Avoided import tends to be steadier and available to more households. Many homes do best with a blend: cover their own peak load first, then export any surplus into a paid window if their plan offers one.

Does arbitrage still work through a NZ winter?

It can work better in some ways and worse in others. Solar charging drops off in winter, so you lean on grid charging, but peak demand and peak prices are highest in the cold months, which lifts the avoided-import value. The best approach changes by season, so adjust your charge and discharge schedules rather than setting and forgetting.

How do I actually program the charge and discharge times?

Modern battery systems like Tesla Powerwall, Sungrow and SolarEdge let you set time-of-use schedules in their app: a window to charge from the grid and a window to discharge or export. Ask your installer to set the first schedule with you and confirm grid charging is enabled, then refine it once you've watched a month of real data.

The Bottom Line

Battery arbitrage is genuinely one of the smartest things a NZ homeowner can do with a battery, but only when three things line up: a wide enough price spread on your tariff, enough real peak load to fill the spread, and a clear-eyed view of what each cycle is costing you in battery wear. Get those right and you can stack solar savings, avoided peak cost and paid export into a return that meaningfully changes your power bill, especially through winter.

Get them wrong and you're cycling an expensive asset for thin or negative returns. So start with the tariff, not the hardware. Have a proper read of the tariff and retailer rundown to find the spread that suits your home, then model it against your real usage in the buy-back engine before you spend a cent on kit. That's the order that keeps you on the right side of the maths.