The state's newest coal-fired power station has endured "significant disruptions" to its fuel supplies from a nearby mine, curtailing its output by almost half, and prompting it to seek increased amounts to be trucked in.

EnergyAustralia's Mt Piper plant near Lithgow, which supplies as much as 15 per cent of NSW's electricity, is mostly supplied by Centennial Coal's nearby Springvale mine. That mine, though, has hit "geological issues", with the operator extracting coal of lower quality and quantity than expected.

Steam plume from the Mt Piper coal-fired power station near Lithgow. Credit:Nick Moir

"We have faced significant disruptions to our operations due to coal supply issues over recent months which have directly impacted our ability to generate into the electricity market," an EnergyAustralia spokesman said, noting Mt Piper's output so far this year is down 42 per cent from the same period in 2018.

Centennial has asked the Berejiklian government for approval to increase the amount of coal it can truck to the 1400-megawatt power plant from its Clarence Colliery, also near Lithgow.