Two-shifting coal generators: A new phase in Australia’s energy transition

As Australia progresses toward a renewable energy future, the challenge of integrating intermittent sources like solar and wind into the grid has sparked innovative approaches to managing traditional coal power. One such approach is "two-shifting," a technique that allows coal-fired power stations to shut down and restart within the same day. This capability is crucial for adapting coal to a grid increasingly dominated by renewables. Recently, the first successful trial of two-shifting in Australia was completed at AGL’s Bayswater power station in the Hunter Valley, marking a significant step in the energy transition journey.

The Mechanics of Two-Shifting

Traditionally, coal plants have operated on a "baseload" model, running continuously to provide a stable supply of electricity. However, with the rise of solar and wind generation—particularly rooftop solar—daytime electricity demand is increasingly met by renewable sources. This has caused significant fluctuations in the demand for coal-based electricity, leading to situations where coal plants either remain online at a loss or shut down for extended periods. In this context, two-shifting allows coal generators to be turned off during low-demand periods (such as the middle of the day when solar generation peaks) and quickly restarted when demand rises again in the evening.

AGL’s successful implementation of two-shifting at Bayswater involved taking a coal unit offline and bringing it back online within a 12-hour window. According to Len McLachlan, AGL’s head of operations at Bayswater, the trial exceeded expectations: “Our team desynchronised 20 seconds ahead of the 10am target and resynchronised within 50 seconds of the 3pm target. This level of precision on our first attempt is extraordinary and sets a new benchmark for our operations”. The trial was part of a broader effort to integrate coal’s flexibility into a future dominated by renewables.

Implications for the Energy Ecosystem

The ability to two-shift has far-reaching implications for the energy generation ecosystem. With coal generators now able to temporarily shut down during peak solar hours, more room is made for renewable energy sources. This could reduce the need for curtailing solar and wind energy, which often occurs when coal plants are forced to stay online, bidding at negative prices to remain competitive.

Furthermore, two-shifting enhances grid flexibility—a critical component of Australia’s goal to reach 82% renewable energy by 2030. Dylan McConnell, an energy systems analyst at the University of New South Wales, highlighted the potential of this development: “It’s one thing to be technically capable of doing this—it’s another for it to be economically viable. It’s also more of a stay of execution rather than something that will significantly extend coal generation”. In other words, while two-shifting is a valuable tool in the short term, it is not a long-term solution for coal, as its eventual phase-out remains inevitable.

However, this shift in coal operations also introduces challenges. Large-scale batteries, which rely on price volatility to remain profitable, may face reduced market opportunities as coal plants can now shut down more efficiently. Additionally, two-shifting may not be compatible with all types of power plants, as aging infrastructure and the physical wear of cycling coal units on and off could lead to higher maintenance costs.

Coal’s Future in Australia’s Energy Market

While two-shifting provides a temporary reprieve for coal plants in Australia, the long-term outlook remains firmly aligned with the country's transition to renewable energy. Major coal plants like Bayswater are slated for closure within the next decade, with AGL planning to keep it operational until 2033 and Loy Yang A in Victoria until 2035. The increasing feasibility of two-shifting supports a smoother transition by allowing coal to operate in a more flexible, complementary role alongside renewables.

This experiment underscores a key aspect of Australia’s broader energy transition: balancing the decline of coal with the growth of renewable capacity. The Australian Energy Market Operator (AEMO) has highlighted the need for 45 gigawatts (GW) of storage capacity, including batteries and pumped hydro, by 2050 to replace coal’s role in maintaining grid stability. As coal’s dominance fades, the success of trials like Bayswater’s two-shifting demonstrates the potential for a more flexible and renewable-centric energy grid.

Nevertheless, as coal plants inch toward their scheduled retirements, the energy sector will increasingly turn to alternative forms of grid stabilisation, such as large-scale storage and demand response technologies.

The two-shifting experiment at Bayswater offers immediate benefits in terms of grid flexibility and integration of renewables, but also serves as a reminder of coal’s diminishing role in the future of energy. As Australia moves towards its 2030 renewable energy goals, innovations like two-shifting will play an important role in bridging the gap between coal’s decline and the rise of a cleaner, more sustainable energy system.