Construction on the expansion of the Woden site will begin next year, to include an emergency, surgical and critical care facility and is expected to be completed by 2024.

The ACT government had initially pledged the project, expected to cost about $500 million, would be open by 2022 but it has been hit with several delays.

On Wednesday, Climate Change and Sustainability Minister Shane Rattenbury said the building would be powered by electric heat pumps through renewable sources, in a step toward an emissions-free health sector.

Mr Rattenbury said it was the first fully-electric public hospital in Australia, with the emissions saved equivalent to taking 760 cars off the roads each year, or 1886 tonnes of carbon dioxide being released into the atmosphere.

"At a time of climate emergency, every decision made by governments must consider climate impacts. Across all sectors and across government, we must act now to put our climate first," he said.

"Buildings like these will last for decades to come, and would otherwise be gas-powered - at significant health and financial cost to our community.

"Gas is a polluting fossil fuel, and the ACT government has committed to transitioning away from climate-warming energy sources and instead, is fully embracing the renewable energy revolution."

The government announced contractor Multiplex had been chosen to build the expansion, in a rebranding of the long-promised development.