MELBOURNE, Feb 17 (Reuters) - Origin Energy (ORG) said on...

MELBOURNE, Feb 17 (Reuters) - Origin Energy (ORG) said on Thursday it plans to shut the country's biggest coal-fired power plant in 2025, seven years earlier than scheduled, as an influx of wind and solar power has made the plant uneconomic to run.

Origin's announcement follows moves by its rivals to bring forward the planned closure of their coal-fired plants, all struggling with sliding power prices which have hurt plants that don't have the flexibility to switch off when there is surplus energy.

"The reality is the economics of coal-fired power stations are being put under increasing, unsustainable pressure by cleaner and lower cost generation, including solar, wind and batteries," Origin Energy Chief Executive Frank Calabria said in a statement.

The company plans to install a big battery of up to 700 megawatts (MW) at the Eraring power station site, about 120 km (75 miles) north of Sydney, which it aims to have mostly built before the 2,880 MW plant shuts.

Origin on Thursday reported an 18% rise in underlying profit to A$268 million ($193 million) for the half-year to December, boosted by record-high revenue from its stake in the Australia Pacific LNG plant, while earnings from its energy markets business fell due to lower power tariffs to customers.

Strong LNG prices also led it to raise its outlook for full year earnings before interest, tax, depreciation and amortisation by A$100 million to between A$1.95 billion and A$2.25 billion. ($1 = 1.3902 Australian dollars)