Negative electricity prices in Tasmania: what they are and what they're worth

Negative electricity prices sound like a glitch. They aren’t — they’re an ordinary and increasingly common feature of the Australian wholesale market, and in Tasmania they now occur often enough to matter.

They are also the single most misunderstood thing in spot pricing. Almost everyone’s first reaction is “prices are negative, so I should use as much power as possible.” That reasoning is usually wrong, and this article explains why.

Why prices go below zero

A negative price means generators are paying to keep producing rather than paying to stop.

That seems irrational until you look at what shutting down costs. Some generators are slow and expensive to stop and restart. Others earn certificates or incentives tied to output, so a small negative price is still better than producing nothing. Meanwhile, rooftop solar across the state keeps generating regardless of price — nobody’s inverter checks the market before it exports.

So on a mild, sunny, windy, low-demand day, supply exceeds what anyone wants to buy, and the price falls through zero until enough generation withdraws.

How often does this happen in Tasmania?

More than most people would guess. Taken from AEMO’s public price data for the Tasmanian region:

Period	Intervals below zero	Hours below zero	Share of all intervals	Average price
August 2026	688	57.3	7.7%	$57.96/MWh
September 2026 (to the 23rd)	1,427	118.9	21.5%	$38.89/MWh

In September 2026, more than one five-minute interval in five was priced below zero in Tasmania. That is not a rare event. It is a routine feature of spring, when demand is mild and renewable output is strong.

Notice too that the monthly average price fell from $58/MWh to $39/MWh between those two months. Spring is cheap. Winter is not. Any assessment of spot pricing based on a few weeks of data is measuring a season, not a plan.

The part almost everyone gets wrong

Here is the thing to internalise:

A negative wholesale price is not a negative electricity bill.

Your import price is not the wholesale price. It’s the wholesale price plus environmental certificate costs, plus the network charge, all plus GST. Certificates and network charges are positive numbers, and they do not move with the market. Wholesale has to fall a long way below zero before the total reaches zero.

How far depends on your network tariff:

Your tariff	Wholesale price at which importing becomes free
Tariff 97 (off-peak)	about −$36.70/MWh
Tariff 93 (off-peak)	about −$48.40/MWh
Tariff 31 (legacy flat rate)	about −$101.70/MWh

Now compare that against reality. Most Tasmanian negative events land between −$1 and −$18/MWh. At those prices the wholesale line is negative and the total bill is still comfortably positive, on every tariff in the table.

In other words: the overwhelming majority of “negative price” events in Tasmania do not mean free power for anyone. They mean slightly cheaper power.

We measured a genuinely deep one on 20 September 2026 — wholesale hit −$58.91/MWh. At that price, a home on Tariff 97 was being paid about 2.6 c/kWh to import, a home on Tariff 93 about 1.2 c/kWh, and a home on the legacy flat Tariff 31 was still paying about 5 c/kWh. Thirty minutes later the price had already recovered to −$24.90. The genuinely-paid-to-import window lasted roughly an hour.

So the import credit is real, but it is small and brief. Which raises the obvious question.

Where the actual money is

If the import credit is only a couple of cents for an hour, why care about negative prices at all?

Two reasons, both much larger than the credit.

1. Not exporting into them. This is the big one, and it’s the mirror image of the thing everyone focuses on. If the wholesale price is −$58.91/MWh, then every kilowatt-hour you export is costing you about 6.2 c/kWh. A house with a full battery and a sunny roof can quietly push several kilowatts into the grid at a price that charges it for the privilege. Across an afternoon that adds up far faster than the import credit does.

The first job during a negative price event is therefore not to buy more. It is to stop selling.

2. Free fuel for the evening peak. This is where the real value sits. During a negative or near-zero price window, surplus solar and cheap grid energy can be stored — in a home battery, in an EV, in hot water. That stored energy then displaces power you would otherwise buy during the evening peak at 25–36 c/kWh.

Compare the numbers. The import credit at a deep negative price is around 2.6 c/kWh. The energy you store and use at peak is worth 25–36 c/kWh. The stored energy is worth roughly ten times the credit.

That ordering has a practical consequence we apply across every site we manage. When prices go deeply negative, the correct sequence is:

Fill every available sink first — batteries, EVs, hot water. This is the valuable step.
Then import to fill whatever room is left, while the credit lasts.
Only curtail solar as a last resort, when everything is full and the alternative is exporting at a negative price.

Curtailing your solar while a battery still has room gets this exactly backwards: it throws away the expensive thing to capture the cheap one.

One important exception

If you’re on a fixed feed-in tariff rather than a spot plan, none of the above applies to your exports, and one piece of it is actively harmful.

On a fixed feed-in tariff you’re paid the same rate per exported kilowatt-hour regardless of what the wholesale market is doing. A negative wholesale price costs you nothing. Curtailing your solar or holding back exports during a negative event doesn’t protect you from anything — it just destroys real credit you would have earned.

This is a genuine fork in the logic, and it’s worth knowing which side of it your own house sits on before acting on anything you read about negative prices.

What this means for a household

A few honest conclusions:

Negative prices are common in Tasmania, especially in spring — roughly one interval in five through September 2026.
They rarely mean free power. The network charge and certificates sit on top and don’t move.
The credit for importing is small and short-lived — a couple of cents for about an hour, in the deep events.
The real value is storage: capturing cheap energy for the evening peak, where it displaces power worth ten times as much.
The real risk is exporting into them with a full battery and nowhere to put the surplus.
None of this applies to exports on a fixed feed-in tariff, where a negative market is simply not your problem.

Which means the useful question isn’t “how do I get paid to use power?” It’s “when prices are cheap, does my house have anywhere to put the energy?” If the answer is no, negative prices are an interesting statistic and not much else.

This guide was written by the Tasmanian solar team at Solar Generation Tasmania. Price figures are from AEMO’s published Tasmanian region data.

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Published by Solar Generation Tasmania. General information current as at publication — rebates, tariffs and prices change, so confirm current figures before deciding.