Firefighters have called in expert technicians to help deal with a dangerous heat build-up at a cutting-edge renewable energy storage plant but the incident has been stabilised.
MGA Thermal is behind a new form of thermal energy storage that allows retrofitted coal-fired power stations to distribute renewable energy long after it was produced.
But the company had to call in firefighters on Friday morning at its demonstrator plant in the Tomago industrial area, north of Newcastle.
Initial assessments of over-heating machinery led to the evacuation of 15 businesses.
Hazardous materials crews in breathing apparatus later detected smoke emanating from power cables on the 14m-long structure.
A bulk carbon dioxide tanker from Sydney cooled the machinery while dry chemical powder was used to douse the burning cables.
A Fire and Rescue NSW spokesman said the incident and factory was not something the crews had encountered previously and they expected it to be protracted.
"That's why we have called in our scientific team too and we're working with their engineers who are the experts in their field," he told AAP.
The scene was deemed to be in a steady state about mid-afternoon and the emergency was scaled down.
The exclusion zone had earlier been reduced, allowing most businesses and an arterial road for the Port Stephens area to reopen.
A Fire and Rescue hazardous materials crew will remain at the scene for the next day or two to monitor the situation.
Developed by University of Newcastle scientists and backed by several government agencies, MGA Thermal's blocks are about the size of two bread loaves and allow renewable energy to be transported and used on demand.
The alloy inside the blocks traps heat almost indefinitely, the company's chief executive Erich Kisi told reporters last year.
"They sit at around 600C storing heat almost indefinitely, (losing) very little heat over time," Professor Kisi said.
"The energy is then dispatched by making high-temperature, high-pressure steam for power generation, or we can de-rate it to address the hard-to-abate markets."
Those hard-to-abate sectors, such as aluminium smelters, could benefit from the technology.
The energy storage plant is located close to Tomago Aluminium, Australia's largest aluminium smelter.
