Sixty thousand properties in South Australia were blacked out by mistake during last week's heatwave, a report into the incident has revealed, with the bungle blamed on a computer glitch.

At the height of the power supply crisis, when demand across SA hit record levels, the Australian Energy Market Operator directed SA Power Networks to shed 100 megawatts from the state’s electricity network.

But a report released by AEMO on Wednesday found that 300 mw was cut instead, pulling the plug on 90,000 consumers.

SA Power Networks has apologised to the additional 60,000 customers who were cut off and said it was the result of a fault with its automated load shedding software system.

“We have put in place steps to prevent a recurrence while continuing detailed technical investigations into why the load-shedding software did not operate correctly,” the company said in a statement.

In its report, AEMO said load shedding in SA was the only remaining viable option to avoid damage to the electricity network after demand soared higher than expected and power from wind farms fell more rapidly than forecast.

The report also revealed more details of AEMO’s negotiations over a gas-fired power unit at Pelican Point, which it determined could not be brought online in time to provide extra electricity.

“The facts in this report outline that load shedding became the only remaining available option for AEMO to restore power system security,” executive general manager Joe Adamo said in a statement on Wednesday.

“This action prevented the risk of damage to crucial infrastructure, which if impacted, could have had a prolonged, and potentially disastrous impact to energy consumers.”

South Australian Energy Minister Tom Koustantonis said the AEMO report showed that if all generators available last week had been switched on, load shedding would have been unnecessary.

“This report shows that South Australia reached its highest ever demand on Wednesday when the national operator decided to shed customers,” he said.

“But it also shows we had enough local generation to meet that record demand but it wasn’t turned on.”

In its report, AEMO also called for a united approach to managing Australia’s energy transition.

“The complexities and challenges of managing short-notice generation capacity reductions amid high temperatures and increasing electricity consumption are real. And they’re here,” Mr Adamo said.