Federal government-owned Snowy Hydro is forging ahead with plans for a huge gas power plant in the Hunter Valley despite a wave of new mega battery projects in NSW, setting up the state as a battlefront between storage and gas generation to provide back-up energy for surging renewables.

Origin Energy confirmed its plan to add a four-hour, 700 megawatt battery at its Eraring power station on NSW's Central Coast, where it is increasingly having to modify generation through the day to adapt to the flood of renewable energy.