$300m Tallawarra B power plant in final testing phase before being switched on

The new plant on the shore of Lake Illawarra is going through its final testing phase before being officially switched on.

However, Tallawarra B won't operate all the time; a "quick-start" plant it is designed to reach full capacity in 30 minutes of turning it on (compared to two to eight hours for the existing plant) to provide extra power to the network during peak periods.

"The role of Tallawarra B is to generate at times of high demand," said EnergyAustralia's managing director Mark Collette.

"NSW during a very hot day needs just about every single piece of equipment turned on and generating in order to be able to meet that peak demand. The role of Tallawarra B on those very high demand days is to be on and running."

It will also be switched on at times when renewable options like wind and solar are low.

It was also hoped that Tallawarra B itself would be powered by green energy, using hydrogen as part of the fuel mix by 2025 and gradually increasing that percentage.

This year, EnergyAustralia will also spend $90 million on the Tallawarra A plant to allow it to burn 37 per cent hydrogen as part of its fuel mix.

Mr Collette said the hydrogen-focused investment showed the company was "all-in" on a renewables future.

"We see Australia as on a path where there's no other choice, there's a move from coals to renewables," Mr Collette said.

"Even if there weren't obvious climate change drivers the coal is getting to the point where it is old and needs a replacement. From where we stand the best form of replacement for Australia is a combination of wind, solar batteries and gas-fired generation turning into hydrogen over time."

While there wasn't a large-scale hydrogen gas supplier in the Illawarra, Mr Collette said it was better to start the change to the power plants now, rather than having to react when more coal-fired plants closed.

"Our ambition is to create enough demand to kickstart a hydrogen industry in this region," he said.

"We are reliant on the green hydrogen supply chain developing within the region to enable that fuel to be available.

"Green hydrogen offers the prospect for gas-fired power stations to become zero emissions over time. That's the ambition we have for both of these power stations."

One unusual addition to Tallawarra B is the large disc-shape at the top of the plant.

Weighing 54 tonnes and costing $13.5 million, it was a specifically engineered solution to deal with the gas plume velocity due to the proximity of Shellharbour Airport.

"We're quite close to the Shellharbour Airport and some aircraft circle right above our heads," Tallawarra B project director Ian Black said.

"That disc is an engineered solution to ensure an adequate level of aviation safety. What that means is the lid on the top stops that plume going up, the jets point it out sideways where it mixes with the colder air and that results in a much lower velocity. So the plume goes up in accordance with the Civil Aviation Safety Authority's requirements."

Also, due to the intermittent nature of the plant's operations, lights on the tower will flash to warn pilots whenever it is turned and generating power.