The closure of the Liddell coal-fired power station in the NSW Hunter Valley in April has helped drive up energy costs, a new report shows.

A report by the Australian Energy Regulator (AER) said wholesale electricity prices rose over the second quarter of the year because of higher demand in southern states, lower solar generation, and reduced cheap coal capacity in NSW and Queensland.

"In NSW, the reduction in black coal capacity largely reflected Liddell power station's exit," the report said.

"Had Liddell's capacity still been available, prices would have been lower."

AER board member Justin Oliver said wholesale prices remained well below the unprecedented highs of 2022.

"We have seen far fewer coal generator outages and more coal capacity offered into the market than the same period last year," Mr Oliver said.

NSW Energy Minister Penny Sharpe, who previously insisted the closure of Liddell would not drive-up power prices, said the report showed the energy transition was a "lumpy process".

"[The report] shows that the baseload coal power [capacity reduction], which was actually planned for did have an impact on prices," Ms Sharpe said.

"We need to be up-front about that and accept that, look, here's the learnings in this."

Coal plant's closure partly offset by renewables

The AER report said new solar, wind, and battery capacity partly offset Liddell's exit.

"June saw record monthly wind output," the report said.

"What that AER report shows today is that the increased wind generation helped actually with replacing energy into the grid and help prices down," Ms Sharpe said.

"It's still a very lumpy process. We know that Liddell and then the impact of a possible Eraring [Power Station] closure is problematic."