· 7 min read
The global power sector is transforming with decarbonisation, electrification, and liberalised markets, driven by the integration of renewable sources like solar PV and wind. These intermittent sources reduce grid inertia, increasing the need for stronger interconnections and advanced stability measures to meet rising electricity demand. Together, these changes create significant challenges for grid stability in terms of voltage stability, frequency stability, and load flow management. The newsletter explores the challenges and technological solutions needed to ensure grid stability and the investments required for resilient grid infrastructure.
Introduction
The COP28 pledge to triple global renewable capacity by 2030 exemplifies the commitment to accelerate this growth, setting the stage for the continuing transformation of the power sector worldwide. In 2023, more than 3,000 GW of renewable power projects were reported to be in connection queues, and congestion management volumes and costs are rising in places such as Europe and the United States.
Grid stabilisation focuses on keeping the grid operating within safe and stable parameters in real time, especially in the face of sudden disturbances or imbalances between supply and demand. This is often measured by parameters like frequency, voltage, and phase angle, which must be kept within certain limits to prevent grid failure.
Complexity in grid stabilisation
The challenges within frequency stability, voltage stability, and load flow management are highly complex. System services are needed to support reliable grid operation.
1. Voltage stability
As power generation shifts from large, centralised plants to smaller, decentralised sources in the drive toward decarbonisation, managing voltage stability has become more complex. Electrical devices are designed to operate within a specific voltage range, and if voltage falls too low or takes too long to recover, system blackouts could occur.
To support reliable grid operation and stabilize voltages, several system services are available:
a. Dynamic Voltage Control: Reactive power output is controlled with a fast response time to ensure voltage stability at any moment.
b. Stationary Voltage Control: The full output range is provided to respond to slow grid changes initiated either by the control system or manually by operators.
c. Active filtering: Modern semiconductors improve flexibility and optimise the operating range’s remaining capacity to actively filter background grid harmonics.
2. Frequency stability
Today, more power is generated using electronic converters rather than traditional power plants with large rotating masses. This shift reduces system strength and stability, resulting in larger deviations from the nominal frequency during generation and consumption imbalances. To keep the frequency within acceptable limits, especially with high levels of converter-based generation, frequency-stabilising solutions are essential.
Several system services are available to support reliable grid operation by stabilising frequency:
a. Inertia contribution: To replace large rotating generators, alternative sources must provide system inertia.
b. Fast frequency response: Immediate additional power is required to stabilise the grid when frequency deviates from its nominal value.
c. Primary frequency response: If fast frequency response is insufficient, more active power must be deployed to correct frequency deviations.
3. Load flow management
With growing renewable energy sources and fluctuating generation, managing complex load scenarios becomes more critical. An electric power system connects transmission and distribution lines from generation to consumption, requiring careful load flow planning to prevent overload. Transmission grids follow the N-1 criterion, where components operate below maximum capacity to handle failures without disrupting power flow.
Several system services support effective load flow management:
a. Dynamic load flow control: Dynamic adjustments to power flows prevent temporary overloads caused by renewable energy fluctuations.
b. Stationary load flow control: Integrating new power generation can overload certain lines while freeing capacity on others, necessitating careful management.
c. Grid coupling: Connecting two non-synchronised grids requires an intermediate circuit to facilitate power flow.
Pathways to solutions
The below measures are primarily focused on maintaining real-time stability, ensuring frequency, voltage, and phase angle stay within safe limits during sudden fluctuations or imbalances:
1. Synchronous condensers - TRL 9-10
A synchronous condenser is a synchronous machine without a prime mover, meaning it doesn’t supply active power to the grid but supports inertia, voltage control, and short-circuit current. Converting existing generators into synchronous condensers can prevent power plants from becoming stranded assets, preserving local employment and easing socioeconomic impacts. This conversion also utilises existing infrastructure, like grid connections at critical nodes, to ensure essential grid services are maintained.
Use Cases: Inertia to the transmission system, Contribution to short-circuit power, Voltage support, Short-term overload capability, and Response Time
Providers: Siemens Energy, GE Vernova, ABB, VINCI Energies
Global Case Studies: Korea Electric Power Utility: General Electric (GE) provided KEPCO with two synchronous condensers rated at +50/-25 MVAr, enhancing the efficiency and cost-effectiveness of the Cheju-Haenam HVDC link in delivering reliable power to the island. This upgrade enabled KEPCO to retire their previous gas turbine-based synchronous condensers and increase power transmission capacity on the existing grid network.
Source: By Mriya - Self-photographed, CC BY-SA 3.0
2. Flexible AC transmission systems (FACTS) - TRL 9-10
-> Static Synchronous Compensator (STATCOMs)
Allows grid operators to gain accurate control of reactive network power, increase power transfer capability, and improve the steady-state and dynamic stability of the grid.
Use Cases: Fast voltage control under various load conditions during steady-state and dynamic events, Reactive power control, Unbalance control, Power factor regulation, Power oscillation damping, and Improved flicker reduction in industrial applications
Providers: Siemens Energy SVC Plus, General Electric’s Static Var Compensator, Hitachi Energy, ABB Limited
-> Other FACTS solutions include Static VAR Compensator (SVC) and Thyristor Controlled Series Capacitors (TCSC)
Global Case Studies: Sophisticated solutions for US Steel Mill (ABB): High Power Rectifiers in Turgi, Switzerland, delivered two static VAR compensation (SVC) systems to a steel mill in the USA. The installation, as well as the pre-commissioning, has been completed successfully.
Source: By Tombo12354 - Own work, CC BY-SA 4.0
3. Unified power flow controller
The unified power flow controller (UPFC) can balance load flow in the AC grid, rapidly bypass overloaded line sections, provide reactive power and dynamic voltage control, and utilise assets to physical limits without needing safety margins. It controls power flow in milliseconds, stabilising the AC grid even when critical situations suddenly develop (grid code N-1).
Features: Within response time of milliseconds, Load flow control and reactive power compensation in one solution, all system voltages can be addressed up to 500 kV (flexible), and better utilisation of existing infrastructure (powerful)
4. Other solutions include Automatic Generation Control (AGC), Phasor Measurement Units (PMUs) and Advanced Monitoring Systems, Grid-Forming Inverters
Source: By Tombo12354 - Own work, CC BY-SA 4.0
Investment needs
IEA analysis shows that global annual grid investment needs to double by 2030 to stay on track to meet country pledges on energy and climate goals. As a result of insufficient grid investment, at least 1,500 GW of solar and wind projects at an advanced stage were waiting for grid connection as of mid-2023. In the United States, for example, congestion management costs rose from USD 6 billion in 2019 to almost USD 21 billion in 2022, the latter equalling more than USD 4 per MWh consumed. Furthermore, delayed grid development also increases the risk of power outages, which already cost the world at least USD 100 billion annually (0.1% of global GDP).
End Remarks: Existing technologies are successfully helping to tackle the challenges associated with integrating high shares of VRE. Systems such as those in Denmark, Ireland, South Australia, and Spain have integrated from 35 to 75% of VRE in their annual generation, depending on the system. As renewable penetration targets continue to rise, expanding dynamic system services like synchronous condensers, flexible AC transmission systems (FACTS), and unified power flow controllers will be essential. To avoid potential energy curtailments of up to 15% of VRE generation in 2030, countries must commit to implementing stabilisation measures that align with ambitious climate and energy pledges.
This article is also published on the author's blog. illuminem Voices is a democratic space presenting the thoughts and opinions of leading Sustainability & Energy writers, their opinions do not necessarily represent those of illuminem.
References
Siemens Energy (2023). Supporting Grid Stability. Available at: https://p3.aprimocdn.net/siemensenergy/ae3c4b5b-0daa-4762-a0fd-b1570070098d/Whitepaper_Supporting-Grid-Stability_final_DIGITAL-pdf_Original%20file.pdf
International Energy Agency (IEA) (2023). Integrating Solar and Wind. Available at: https://iea.blob.core.windows.net/assets/4e495603-7d8b-4f8b-8b60-896a5936a31d/IntegratingSolarandWind.pdf
Additional links
Podcasts
The Role of Inertia in Managing Grid Frequency. Available at: https://www.oxfordenergy.org/wpcms/wp-content/uploads/2024/05/300-Electricity-Inertia.mp3
