“Preparing for high instantaneous penetrations of renewables – and the first period of 100% instantaneous operation – is a critical part of enabling future power system operability at net-zero emissions,” Westerman says in his introduction to the 100-page Engineering Roadmap to 100% Renewables report.
“At these times, coal generators will be offline; either intentionally decommitted, unexpectedly offline for maintenance or failures, mothballed, or retired.
“Coal plants take many hours, or even days, to restart operation, so once taken offline, they can’t be relied on to meet immediate intraday energy demands, or provide system restart services.
“Operating regularly with 100% renewable power also means reducing the need for regular reliance on gas-fired generators to firm the electricity supply.”
Two big challenges
Westerman says there are two main challenges with running a grid on wind and solar alone. The first is dealing with the variability of output, which will require significant levels of storage and demand management, including controls on rooftop solar – as was recently witnessed in South Australia.
The second challenge is managing a changed system. Wind, solar and batteries use inverter based technologies, which is as different to traditional synchronous generation as analogue is to digital.
AEMO has to be to manage the transition and switch between the two different systems, and keep the lights on at the same time.
AEMO is cheered by the success of the four synchronous condensers which have been installed in South Australia, and which allows that state to operate the grid at high levels of wind and solar (up to 146% of demand) with a bare minimum – just 80MW and soon to reduce to 40MW and then zero – of gas generation.
It estimates the main grid will need the equivalent of 40 syncons across the main grid, known as the National Electricity Market to accommodate the 100% renewables scenario.
Batteries and advanced inverters
It points out, however, that they don’t need to be syncons themselves (big spinning machines that do not burn fuel), but it could battery storage with advanced inverters that can provide the same services. Some batteries, such as Hornsdale, are already trialling those services. More are expected to follow.
The ‘roadmap’ is divided into three broad technical themes – power system security, system operability and resource adequacy – with associated preconditions and actions to operate NEM for periods of up to 100% renewable generation.
“The roadmap provides a clear view of the urgent engineering and operational steps required to be ready to leverage the benefits of high renewable generation levels,” Westerman says.