Changing energy mix and its impact on grid stability

Clean energy underpins the global effort to shift towards a sustainable future. A report by the International Renewable Energy Agency (IREA) shows that to date, among the 190 parties who have ratified the Paris Agreement, 134 included quantified renewable energy targets1.

While scaling up renewables in the energy mix can sharply reduce one major source of CO2 emission, integration of a large share of renewable energy poses an increasing challenge to power system stability.

Grid stability incidents have already emerged. For instance, the blackout in South Australia on 28 September 2016 is the first known blackout linked to high penetration of renewable energy2. The incident resulted in 850,000 South Australia customers losing electricity supply, affecting households, businesses, transport, and major industries3. Although several factors contributed to the 2016 blackout, the event highlighted the challenges to overcome as we transition towards a decarbonised electricity supply.

The top challenges

Renewable energy sources (RES) are expected to account for more than half of 2021’s new energy generation. With RES penetration on an upward trajectory, managing grid stability becomes a top priority with three significant challenges:

  1. Ensuring sufficient flexibility for power system operations and supply
  2. Tackling increased operational complexity of the power system
  3. Integrating inverter-connected devices

The integration of a large share of RES in the energy mix means potentially significant power injection during peak load hours, which requires more system flexibility to balance energy supply and demand. The swift change in energy supply will also compound operational complexity by demanding rapid and significant adjustments of conventional energy providers.

Another challenge from the energy transition comes from the essential integration of inverter-connected devices. The inclusion of such devices can decrease system inertia and reduce short-circuit power, reducing overall system stability.

How do the top challenges differ by country?

The challenge to maintain grid stability differs significantly by country and region. For instance , having flexible and dispatchable energy sources - such as hydropower and gas-fired generation plants, can offset the variability introduced by RES. Therefore, the European energy network may face less challenges in maintaining grid stability as it can benefit from the Swiss hydroelectricity production.  In contrast, Australia struggled with grid stability despite having a high share of natural gas in their domestic electricity production portfolios. 

The reason for such a contrasting situation is that the scope of the challenge facing each country depends strongly on context. The existing generation mix, geography, regional cooperation and power grid interconnection are all contributing factors.

What are the possible methods to mitigate risks from reduced inertia?

Reduced inertia is becoming a critical issue with increasing solar PV and wind integration, and threatens power system stability worldwide. One of the possible mitigation methods is to deploy different forms of non-synchronous renewable generation and energy storage such as hydropower or pump storage capacity4. For countries with lower transmission capacities, such as Australia, improving the interconnection can further mitigate the effects of reduced inertia. And finally, improving the fault ride-through of wind generation could be an additional puzzle piece to the inertia reduction challenge.

In this paper, Swiss Re and the Reliability and Risk Engineering Laboratory at ETH Zurich discussed a series of crucial questions on the grid stability topic. The discussion spotlights the key challenges from the increasing share of RES within the energy mix, how they can be managed, and what system-level solutions are available. 

Further key topics in this report include:

  • What is the impact of inverters on overall system strengths?
  • Who is responsible for managing reactive power, short-circuit current, and frequency stability on the grid and how are they addressing these growing issues?
  • Can the uptake of nuclear energy smoothen out the negative effects on grid quality from the decommissioning of coal plants?
  • Will the risk of power blackouts increase?
  • Future outlook
 
1. https://irena.org/publications/2020/Dec/Renewable-energy-and-climate-pledges
2. R. Yan et al., IEEE Trans. Power Syst., vol. 33, no. 5, 2018, doi: 10.1109/TPWRS.2018.2820150
3. https://www.aemo.com.au/-/media/Files/Electricity/NEM/Market_Notices_and_Events/ Power_System_Incident_Reports/2017/Integrated-Final-Report-SA-Black-System-28-September-2016.pdf
4. S. C. Johnson, J. D. Rhodes, and M. E. Webber, “Understanding the impact of non-synchronous wind and solar generation on grid stability and identifying mitigation pathways,” Appl. Energy, vol. 262, p. 114492, Mar. 2020, doi: 10.1016/j.apenergy.2020.114492.

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