Why switch to a spot price plan — and how much could you actually save?

The objection everyone has

Ask anyone why they haven't switched to a spot price electricity plan and you'll hear the same thing: "Prices can go crazy. I don't want to be caught paying $3 a kilowatt-hour."

It's a fair instinct. And without a way to monitor prices, the concern is rational — you'd be flying blind. But here's the thing: the households that have switched to spot plans and pay even modest attention to when they use power are, on average, saving money. Not a little money — meaningful money, especially if they have solar or a battery. The risk is real but manageable. The upside is structural.

What a flat-rate plan is really costing you

On a standard flat-rate plan, your retailer buys electricity on the wholesale market, hedges their position with financial contracts, and charges you a flat rate — typically 28–35 cents per kWh in NZ, or 25–40 cents in Australia depending on state and network. That flat rate includes:

• The actual average cost of wholesale electricity
• The cost of financial hedges (insurance against price spikes)
• The retailer's margin
• A risk premium — you're paying for price certainty you may not need

Retailers aren't running a charity — they price flat plans to be profitable even in bad years. In most years, the wholesale market is considerably cheaper on average than what they're charging you. The difference between what you pay and what the electricity actually costs is the peace-of-mind tax.

The savings numbers — realistic scenarios

The saving isn't simply "retail rate minus wholesale average times your kWh" — you don't use power uniformly across the day, and each period has its own spot price. The outcome depends on when your consumption falls relative to cheap and expensive periods, and what the market does that month. Last month happened to be favourable. Some months the gap is smaller. Some are larger.

Warden ran 12 months of Auckland wholesale prices (June 2025 – June 2026) through the same three models the calculator uses, at 800 kWh/month. Here's what came out:

These figures cover the electricity rate component only — lines charges, metering and levies are identical on any plan. Results are seasonal and variable; this 12-month window happened to include good conditions for spot. Use the Warden savings calculator to run your own region and date range.

That last stat is the most important one. Price spikes are real, they're alarming when you see them, but they represent a tiny fraction of total consumption. The upside — cheap periods, overnight prices, midday solar suppression — is far more frequent and persistent.

If you have a battery: the arbitrage case

Everything above applies to any household. If you have a battery, you're playing a different game — one where the savings potential is much larger because you're not just shifting consumption, you're storing cheap energy and using it when it's expensive.

A 10 kWh battery cycling once per day at a modest average spread of $120/MWh generates around $1.20 per cycle. At 300 cycles per year, that's $360 purely from arbitrage — in addition to the time-shifting savings above, and in addition to any solar self-consumption benefit. In years with significant price events, the spreads widen and the arbitrage value increases substantially.

The genuine risk — and how it actually plays out

This guide wouldn't be honest if it didn't engage seriously with the downside.

Scenario: cold snap, July, hydro low

Overnight temperatures drop to 2°C in Wellington. People are heating all day. The hydro lakes are at 60% of average. A gas peaker trips offline at 5pm. Spot prices hit $2,000/MWh for three consecutive half-hour periods. A household drawing 3 kW during that 90-minute window consumes 4.5 kWh. At $2,000/MWh ($2/kWh), that's $9 in wholesale electricity costs — roughly $7–8 above what a flat plan would have charged. Spread across the rest of the month of cheap prices, the net position is still ahead.

Scenario: forgetting to charge the EV before a spike

You plugged the car in at 6pm and forgot to set a scheduled charge. Prices are at $500/MWh for two hours. The car draws 7 kW, adding 14 kWh. Wholesale cost: $7. On a flat plan, the same charge would have cost $4.50–5. The difference is $2–2.50. This is the risk in context — uncomfortable, but not the bill shock horror story that keeps people on flat plans.

The real risk: a sustained high-price year

The scenario worth taking seriously is a prolonged dry year — 2001 and 2008 both produced extended periods of high prices in NZ. In those years, a spot plan with no behaviour change could cost materially more than a flat plan. This is the genuine risk, and it's the reason a service that monitors conditions and helps you respond matters.

Why Warden is the missing piece

Here's the honest version of the spot pricing pitch before Warden existed: the upside is real, but you have to watch the market. Constantly. Miss a spike because you're at work and left the hot water cylinder on, and you're paying the tax. Nobody has time for that.

That's the problem Warden solves. Not by replacing your judgment, but by doing the watching so you don't have to.

Instead of remembering to check, you get a notification at 1am that prices are cheap — start the dishwasher, charge the car. Instead of being caught off-guard by an evening spike, you get a heads-up at 4:30pm. Your Home Assistant automation reads Warden's alert level sensor and switches the battery to discharge mode automatically.

What Warden does for Home Assistant users

Warden exposes nine entities per node including a live price sensor, alert level (normal / high / spike), binary spike sensor, 30-minute rolling average, and a percentile sensor that shows where the current price sits in the 30-day distribution for this time window. These feed directly into automations:

• "If Warden price drops below $50/MWh, start the hot water heat pump"
• "If Warden alert level is spike, pause EV charging and switch battery to discharge"
• "If Warden percentile is below 20, run the washing machine"

Price-responsive automations rather than time-based ones — they work with what the market is actually doing rather than assuming 2am is always cheap.

How to get started

Check if you're eligible

You need a smart meter with half-hourly read capability (AMI or HHR type in NZ). Most urban homes have one. If you're not sure, your retailer or network company can confirm.

Switch plans

In NZ, the main spot-price retailers are Flick Electric, Electric Kiwi, and Ecotricity (ecoWholesale plan). All three are legitimate with good track records. Shop around — their standing charges and per-kWh margins differ. In Australia, market contract options vary by state; contact your retailer to ask about time-of-use or market contracts that reflect wholesale prices.

Create a Warden account

Warden monitors your node every 5 minutes. Enter your ICP number at signup and it finds your grid connection point automatically. Set your alert thresholds — start with the defaults and adjust once you have a feel for how your node behaves. Trial accounts get full access for 90 days, no credit card required.

Set a few simple rules

You don't need to overhaul your household. Start with two or three changes that don't inconvenience you: schedule the dishwasher to run at 1am, set EV charging to start at 2am, pre-heat the house in the morning before peak pricing. These alone, combined with Warden alerts for the spikes you want to avoid, will put you ahead of a flat plan in most years.

Spot pricing isn't for everyone. If you have no load flexibility — every appliance runs when it needs to run, no batteries, no EV — the upside is limited, though you'll likely still save something. If you have an EV, solar, or a battery, the maths gets considerably more interesting.

The objection — prices can spike — is real but overstated when you look at what those spikes actually cost versus the savings from cheap periods. The genuine risk is sustained high-price conditions that run for weeks, not days. That risk is real and worth taking seriously. It's also exactly the risk that active monitoring mitigates.

The households getting the most value from spot pricing aren't glued to their retailer's app. They set up good defaults — scheduled overnight charging, Warden alerts, a few HA automations — and then largely forget about it. The market does the work. Warden does the watching. You save the money.

Common questions

Is spot pricing actually worth it in NZ?

For most households, yes. Warden's modelling of 12 months of Auckland wholesale prices (June 2025 – June 2026) shows a household using 800 kWh/month would have paid $878.60 on an unmanaged spot plan versus $2,880 on a standard 30¢/kWh retail rate — a 69.5% saving on the electricity rate component. Smart scheduling brings this to 80.4%, and battery arbitrage to 82.6%. Lines charges, metering and levies are the same on any plan and aren't included in these figures.

Which NZ retailers offer spot price plans?

The main options are Flick Electric, Electric Kiwi, and Ecotricity (ecoWholesale plan). All three pass through wholesale electricity prices rather than charging a flat retail rate. Their standing charges and per-kWh margins differ — worth comparing based on your usage profile.

What's the actual risk of a spot plan?

Price spikes are real but short-lived and represent a small fraction of total annual consumption. A spike to $2,000/MWh lasting 30 minutes costs a typical household around 50¢ extra. The more serious risk is a prolonged dry year when hydro lakes are low — 2001 and 2008 are the NZ examples. Active monitoring with Warden mitigates this by alerting you when prices are elevated so you can shed load.

Do I need a smart meter?

Yes — a smart meter with half-hourly read capability (AMI or HHR type). Your retailer bills you at the actual wholesale price for each 30-minute period, so they need interval data. Most urban NZ homes built or renovated in the last decade already have one. If you're not sure, ask your retailer.

How much does a battery add on a spot plan?

Warden's modelling shows a 15 kWh battery achieves 82.6% savings on the electricity rate component versus retail — compared to 69.5% unmanaged. The battery charges during cheap overnight or midday windows and discharges during expensive evening peaks, capturing the price spread automatically every day.