Energy Minister Lily D'Ambrosio said the change to the government's Solar Homes scheme will save owners up to $800 on installation costs, with panels able to be fitted as electricity is wired to new homes.

"More than 210,000 Victorian homes have already got solar panels on their roofs and now we're adding an additional cash saving," she told reporters in Sunbury on Wednesday.

The Solar Homes Program was unveiled by the Andrews government before the 2018 state election as part of a plan to install panels on 650,000 homes over 10 years to drive down the cost of living and reduce carbon emissions.

It was further expanded in April to allow Victorians to access up to $2400 in rebates for both solar panels and solar hot water or high-efficiency heat pumps.

According to the government, the investment has cut Victoria's carbon emissions by 1.6 million tonnes or the equivalent output of 500,000 cars each year.

But a report by the Victorian Auditor-General's office last year found Solar Victoria was unable to measure the success of the program or determine whether it had helped lower emissions and household bills.

The coalition opposition has promised to expand the scheme to allow households to claim both a rebate of up to $1400 for solar panels and $3000 for a home battery, instead of one or the other, if it wins the November state election.

The major parties both have policies to reduce emissions by 50 per cent by 2030 and to net zero by 2050, but the opposition wants to legislate the interim target, which Labor is yet to do.

Australian Associated Press