Synergy pushes its ageing coal plants to be more flexible

WA will be coal-powered for sometime and Synergy is working to ensure its Collie power stations can cope with the new world of intermittent renewable energy.

Synergy pushes its ageing coal plants to be more flexible

Despite all the talk of wind and solar, Collie coal remains the bedrock of power generation in the South West of WA and Synergy is working to keep its coal-burning fleet viable in an ever-changing energy market.

Synergy asset optimisation manager Paul Chaperon said the State-owned utility's generation fleet had loads "going up and down like a yoyo" on Good Friday 2019. The low load of a public holiday combined with wild swings in generation from rooftop solar panels with intermittent cloud cover forced the continual adjustment of the output of coal and gas-fired generators.

SW WA generation fluctuations on a low load intermittently cloudy day
Synergy large plant generation on a low-load intermittently cloudy day: 6AM-8PM 19 April 2019 Source: P. Chaperon presentation

Chaperon, speaking to an Australian Institute of Energy webinar this week, said open cycle gas turbines handled the peaks and troughs of the day well, but combined cycle gas plants and especially coal-fired power stations were not designed for rapidly varying dispatch.

"Historically generators were about sending out megawatts, the more megawatts, the better," Chaperon said.

"We need to shift that focus now to be more focussed on reliability, providing essential services and being flexible, being able to change load dramatically.

"Thermal generation must become more flexible if we want to play and be relevant in this kind of crazy market that we are in when the loads are up and down all the time."

That "crazy market" is caused by the 6.5 per cent annual growth in rooftop solar capacity that the Australian Energy Market Operator expects to exceed 2600 megawatts by 2030, dwarfing current power stations.

This so-called behind the meter generation is not controlled and floods into the South West Interconnected System in sunny weather requiring the power stations owned by Synergy and others to adjust their output.

min south west WA thermal power stations 2018 to 2019
Source: Clean Energy Regulator

The State Government's Energy Transformation Taskforce has recommended that new rooftop solar must be able to be curtailed when required.  Significant battery storage on the SWIS would also help. Until then, Chaperon is working on "low cost, low risk, no regrets improvements" to allow the coal-fired generator to keep operating.

"'It has one very simple objective, to increase market participation by expanding plant capability," Chaperon said of the work.

Aims include a reduction in the start-up time of coal-fired generators which would improve responsiveness and cut costs. Less expensive diesel would be burnt to fire up the plant before coal can be used.

Synergy is also reviewing the logic of the plants' control and instrumentation systems as well as operations and maintenance routines, some decades old.

The minimum theoretical load of a coal-fired plant is when a single coal mill, that crushes the coal before it goes to the boiler, is operating.  Chaperon said normally at least two mills are run to avoid a single trip shutting in the unit, but Synergy would investigate the feasibility of running on a single mill.

"This is the same for coal plants across the world, how to reduce that minimum load so they can avoid switching off?" Chaperon said.

The utility's generation units and organisation needed to become more responsive ahead of a planned switch in the SWIS from adjusting power despatch every 30 minutes to every 5 minutes. Also, each of Synergy's generation units will have to participate in the market separately, not as a single portfolio as is current practise.

Chaperon said Synergy needed to implement a lot of automation, train its people and develop trading systems to manage the change. A new control room at Pinjar, in Perth's north, may be needed.

South West WA power generation fuel mix - past 12 months - coal 44%, gas 43%, wind 12%
South West WA power generation fuel mix - past 12 months.Source: AEMO WA Wholesale Electricity Market Dashboard

Coal is still the most significant source of power in the South West's Wholesale Electricity Market, that does not measure the electricity from rooftop solar.

Chaperon said the coal plants were also essential to the security of the grid by providing system inertia, but Synergy received no compensation for providing this service under current market rules.

Chaperon skirted questions about the "politically-charged" issue of the closure of coal-fired power stations.

Minister for Energy Bill Johnston announced the closure WA oldest generators, Muja Power Station's two "C" units, in August 2019. The first unit will close in October 2022 and the second two years later.

The State Government issued 18 media statements in the first half of this year advertising how much it was doing for Collie, leading some to question whether more bad news for Collie power station workers and coal miners may be on the way.

The Australian Energy Market Operator's 2020 electricity statement of opportunities released in June predicted little growth in South-West power demand. Any substantial increase in renewable energy that the Energy Transformation Taskforce is preparing the market for will require the retirement of some existing thermal generation.

Main image: Muja coal-fired power station in Collie. Source: Synergy