Step by Step to Decarbonization: Harnessing the Potential of Rotating Grid Stabilizers for a Sustainable Future

As the power generation system increasingly adds additional renewable energy sources such as wind and solar power, the challenge of maintaining grid stability becomes more pronounced. ?Traditional generation utilizes large rotating equipment such as turbines which provide additional contribution to rotational inertia, short circuit power, and voltage control, crucial for balancing the grid system. ?As the overall volume of these traditional sources reduces this contribution vanishes. ?Grid stability, therefore, becomes a significant concern for power plant operators and transmission and distribution network operators.

Rotating Grid Stabilizers (RGS) present an exciting opportunity to repurpose existing power plant assets to achieve grid stability. ?By utilizing existing power plants, RGS conversions provide necessary system inertia, short circuit power, and reactive power to the grid for this balance. This not only contributes to ecological sustainability but also makes economic sense as it prevents assets from becoming obsolete by exploring alternative business cases for fossil-fired plants.

The risks associated with losing inertia in the grid became evident in August 2019, when a blackout caused widespread disruption in England and Wales. Investigations by National Grid suggested that the world's largest offshore wind farm, Hornsea, unexpectedly went offline. At the same time, a gas turbine power plant went offline as well, resulting in a large imbalance in power and as a result triggering the blackout. With reduced grid inertia, these events caused a more dramatic change of frequency, leaving grid operators with the dilemma for how to react and stabilize the system.

?

The Promise of Rotating Grid Stabilizers

In our pursuit to reduce our carbon footprint, non-synchronous renewable energy sources like wind and solar power, which provide no system inertia, are increasingly adopted. Therefore, innovative solutions are needed to address the reducing system inertia without compromising on our commitment to environmental sustainability. This is where the concept of Rotating Grid Stabilizers (RGS) comes into play.

?

The Path Forward: Hybrid Conversion and a Decarbonized Future

The conversion of generators to a synchronous condenser through RGS can be achieved in three ways: Basic RGS conversion, Flywheel conversion, and Hybrid conversion.

?

1.?????? The Basic RGS Conversion: A Cost-Efficient Solution

?

The first solution, the Basic RGS conversion, serves as an economically efficient method. It swiftly transforms existing turbogenerators into synchronous condensers, providing the necessary inertia, short circuit power and reactive power to the grid. This contributes significantly to grid stability, making it a viable option for power systems aiming for a cost-optimized solution.

?

2.?????? Flywheel Conversion: Maximizing Inertia for Rapid Response

?

The second solution, the Flywheel conversion, adds an additional rotating mass from a flywheel to the existing generator. This increases the system's inertia compared to the basic RGS conversion, as it compensates the loss of inertia from removal of the turbine, resulting in a more robust response to grid frequency fluctuations. Particularly effective in situations where a rapid response to sudden changes is crucial, the Flywheel conversion offers enhanced stability while accommodating the unpredictable nature of renewable energy sources.

?

?3.?????? Hybrid Conversion: The Best of Both Worlds

?

Lastly, the Hybrid conversion solution offers maximum flexibility by integrating a gas or steam turbine with an additional Synchro-Self-Shifting (SSS) clutch between the generator and the turbine. This setup not only enables the generator to operate independently of the turbine but also allows the addition of extra inertia from a flywheel coupled to the existing shaft line. The ability to operate in a dual-mode, enabling the plant to generate power while simultaneously stabilizing the grid, makes the Hybrid conversion an attractive option. This efficient use of infrastructure caters to power plants aiming for both grid stability and power generation, truly offering the best of both worlds.

The Hybrid conversion is particularly noteworthy as it allows the existing plant to continue generating power while simultaneously being used for stabilizing the grid through a single grid connection.

?

Factoring in Site-Specific Elements

Selecting a suitable solution requires an in-depth evaluation of regional and site-specific factors, as Andrew Crosby explains in “Three Considerations for Power Plant Operators Interested in Pursuing a Synchronous Condenser Conversion”.

The need for grid stabilizing solutions can significantly vary from one region to another, influenced by numerous variables. A significant consideration is the composition of the energy mix, particularly the proportion contributed by renewable sources such as solar and wind power plants, which do not provide rotational inertia. Ultimately, it falls to the local grid operator, with their in-depth knowledge and expertise, to accurately determine the specific grid requirements.

Subsequently, the equipment and configuration of the existing power plant, in addition to the surrounding infrastructure, must be taken into account. These elements not only determine the feasibility of a RGS implementation but also shape the project's overall direction.

Following these assessments, a feasibility study for the selected solution should be undertaken to uncover any potential roadblocks posed by the previously mentioned boundary conditions.

Admittedly, a greenfield approach, which begins with a clean slate, might have fewer limitations when it comes to defining the optimum solution. However, a brownfield project, which leverages the existing equipment and infrastructure can lead to significant advantages, resulting in both cost and time efficiencies. Moreover, this solution offers a second life to existing power plants, preventing them from becoming stranded assets on the way to a more decarbonized energy mix. It safeguards resources by repurposing existing power plants to use the generators as RGS, as well as maintaining use of the existing grid connection, thus promoting a circular economy approach.

?

A Success Story: Uniper’s Killingholme Power Station Site

One successful example of RGS implementation is at Uniper’s Killingholme power station site in Lincolnshire, UK, where a custom-designed, rotating grid stability technology is now in operation. Developed in collaboration with Siemens Energy, this solution contributes significantly to maintaining a stable power system as more renewable generation comes online. Uniper appointed Siemens Energy in 2020 to install and commission two synchronous condenser units at Killingholme, which included repurposing two steam turbine generators and installing flywheels at the site. These units are connected to the existing grid connections on-site and allow Uniper to deliver essential grid stabilizing services.

Killingholme is just one example out of many – all around the world, RGS solutions are being implemented, contributing to the stability of the grid and helping us to get one step closer to decarbonization.

In conclusion, as we progress towards a sustainable future, solutions like RGS become increasingly crucial as they help prevent blackouts due to rapid frequency changes and maintain a stable grid. When implemented in a brownfield approach, they also promote resource efficiency, economic viability, and environmental sustainability. By leveraging the potential of Rotating Grid Stabilizers, we can facilitate a smooth transition towards a decarbonized future without compromising on the reliability and stability of our power systems.