Victoria's energy security has been thrown into question, with the state facing an unprecedented 72 days of possible power supply shortfalls over the next two years following the shutdown of the Hazelwood plant next week.

Australia's electricity grid operator has warned that the looming shutdown of the ageing plant, which supplies up to a quarter of the state's power, could lead to breaches of the minimum energy reliability benchmark next summer.

Its data shows 72 days of potential power "reserve shortfall".

While the prediction does not mean Victoria is facing imminent blackouts, it does highlight the risks to the state's power supply as the Andrews government prepares for next year's election, with toxic state-federal relations and energy policy uncertainty blamed for inhibiting new investment.

The figures, from the Australian Energy Market Operator, also highlight the extent to which Victoria and South Australia will be critically reliant on imported power from NSW and to some extent Tasmania, with no guarantees it will be available.

In a recent assessment, the market operator said there was limited scope for Victoria to import more power from NSW because Snowy Hydro's two power plants near the town of Khancoban were nearing maximum capacity.

The assessment has heightened the risks of load shedding if next summer turns out to be hot as predicted. This is where major power users – typically big manufacturers – are forced to temporarily cease production to take strain off the grid.

Matthew Warren, chief executive of the Australian Energy Council, which represents power businesses, said Victoria's energy security was looking increasingly fragile. He said the prediction of 72 days of possible reserve shortfall was unprecedented in recent history.

"Under high demand conditions, being able to maintain reliable supply without blackouts or load shedding for industrial customers requires a lot of things to go right," Mr Warren said.

"There has to be a lot of available power from Tasmania and Snowy Hydro, and most [generation] units will have to function and operate at maximum capacity."

As revealed by Fairfax Media last September, Hazelwood will be switched off by the end of the month. The first of the plant's eight turbines will be turned off this Friday, with a complete shut down by next Wednesday.

Last week the Andrews government announced it would hand over $25 million to support energy storage companies that specialise in technologies such as batteries, pumped hydro or solar thermal.

It said this would boost energy storage capacity by up to 100 megawatts by the end of 2018 – enough to power a town the size of Bendigo for up to four hours during a peak demand period.

But there are now serious questions about whether such an investment will be enough, with one well-placed industry source warning the state could be forced to follow South Australia and tender for back-up diesel generators, which are polluting and expensive, to increase the buffer.

Energy Minister Lily D'Ambrosio said the market operator had confirmed there would not be energy shortfalls in Victoria.

"To claim otherwise is simply wrong," she said. "We're not considering any diesel back-up because we are building the generation and storage necessary to protect Victorian consumers."

Dylan McConnell, from the University of Melbourne's Climate and Energy College, said the market operator projections were based on an "extreme demand scenario" – effectively assuming a once-in-a-decade level of electricity use across the state for any given day.

"If there's a 45-degree day, or three 45-degree days in a row, or a generator fails you could have demand at that level and get a shortfall in Victoria, but it's not going to happen 72 times in two years," he said.

Grattan Institute energy program director Tony Wood said the electricity supply was likely to be uninterrupted over the next couple of summers, but Hazelwood's closure would reduce the buffer of excess generation.

"The most likely outcome at the moment is that we will get through this," Mr Wood said.

He said the market operator needed to ensure that generators were brought online when required, unlike in South Australia last month, when part of the Pelican Point gas plant lay dormant and tens of thousands of houses briefly lost power.

Last month Ms D'Ambrosio said she had been asked by the market operator whether Ballarat or Bendigo could face power outages to help NSW deal with extreme electricity demand from a heatwave.

Meanwhile, Deputy Prime Minister Barnaby Joyce claimed Victoria faced an "absolute shit sandwich" when Hazelwood shut, including potential power shortages.

Job losses in manufacturing could also follow because of rising power prices and unreliable supply.

Mr Joyce said the federal government should be focused on helping to fix the nation's power problems, not issues like changes to Australia's racial discrimination laws.

"Hazelwood is going to close in the next few days and you [Victoria] have got an absolute shit sandwich you are going to eat," he said.

- The Age, with Adam Morton and James Massola