Gas and coal-fired power stations in NSW broke down more than two dozen times last year - including one that is only 10 years old.

The ageing Liddell power plant in the Hunter region, which is due to close in 2022, suffered 11 of the 27 breakdowns, while Vales Point at Lake Macquarie shut down five times, according to The Australia Institute.

Tallawarra, a gas power station which opened in 2009, experienced three breakdowns.

The institute’s Rod Campbell said the state’s ageing coal generators are a threat to the reliability of NSW’s energy system and should be a concern for politicians.

“Every time gas or coal generators break down, hundreds of megawatts of capacity are instantaneously removed from the grid without warning,” he said in a statement on Wednesday.

“This puts undue pressure on the electricity system, risking blackouts and pushing up power prices.”

The Nature Conservation Council is calling on both Labor and the coalition to commit to adding 4000 megawatts of solar, wind and storage to the electricity grid over the next four years to help bridge the gap.

“At a time when the state is gripped by drought and people are crying out for leadership, the coalition and the ALP both still lack clear plans to slash our emissions,” chief executive Kate Smolski said in a statement.