Energy retailer AGL has announced it will undertake a $900 million capital raising after securing approval from the Australian Competition and Consumer Commission.

The company said in a statement the funds will be used to acquire the Great Energy Alliance Corporation.

The company currently owns a 35% stake in GEAC.

"This acquisition represents a unique opportunity to acquire a high quality generation asset and a long-term fuel resource," managing director and chief executive Michael Fraser said in a statement.

ACCC chairman Rod Sims said the proposed acquisition was unlikely to lessen competition in the energy market.

GEAC owns the Loy Yang A power plant in Victoria.