Two giant batteries would provide four hours of reserve power for a population roughly equal to that of Ballarat and Bendigo.

They were announced in July with much fanfare and the assistance of former US vice-president Al Gore.

The 20 megawatt batteries were to have been built and switched on in the state's west by January or earlier.

So where are they?

Time is running out to have them installed and in use by this summer, increasing pressure on the state's strained power supply.

On Tuesday the government would not say if the batteries would be switched on by the promised deadline.

The winning bidder to deliver the $25 million project was supposed to have been announced in late August, but no decision has been made.

Doubts remain about whether Victoria will get through this summer without experiencing blackouts, because there is a dearth of reserve power following the closure of the Hazelwood power plant in March.

The state's west was chosen by the Andrews government as the home for the batteries because the electricity network is relatively constrained there.

Grid-scale batteries can store renewable energy to be used at times of peak demand, improving energy security and shielding consumers from severe price spikes.

They are a key part of the government's $146 million renewable energy action plan.

Victorian Energy Minister Lily D'Ambrosio with Al Gore on one of Melbourne's soon to be solar-powered trams. Photo: AAP

It is understood the government is still assessing proposals to provide the large-scale battery storage.

"We're making sure Victoria is equipped with the next generation of energy technologies that will support a resilient energy system," a spokesman for Energy Minister Lily D'Ambrosio said.

The closure of Hazelwood has increased pressure on energy supply. Photo: Joe Armao

On Tuesday, the Australian Energy Market Operator issued another warning that Victoria faces a low supply of reserve energy this summer and in the summer of 2018-19.

This week the operator, which runs Australia's major gas and electricity markets, moved to safeguard the state's summer energy supply by bringing in diesel generators.

If required, the diesel generators will pump about 100MW of energy into the state's grid.

The operator said in September that diesel was an option to avoid possible summer blackouts in Victoria and South Australia, which also faces a summer of tight energy supply.

It will also confirm within weeks details of the Reliability and Emergency Reserve Trader, another safeguard it will apply to contract power-hungry businesses such as smelters to stop using electricity during periods of extreme heat.

David Southwick, the opposition's energy spokesman, said the government was yet to back up its renewable energy policy announcement with substance.

"This is policy on the run by Andrews government, which allowed Hazelwood to close and took 22 per cent of the state's energy supply out of the market," Mr Southwick said.

He said consumers across the state were already being hit hard because of sharp rises in the cost of energy.

Meanwhile, on Tuesday the government opened its renewable energy reverse auction, which is expected to eventually deliver up to 650MW of renewable energy into the market, though not by this summer.

The government has set a target to generate 25 per cent of the state's energy through renewables by 2020 and 40 per cent by 2025.