Key points:
- Electricity systems are complex networks where a failure in one component can lead to a cascade of failures elsewhere, resulting in widespread blackouts. These blackouts can have severe impacts on all aspects of society and the economy.
- Blackouts are typically caused by a combination of interrelated factors, rather than a single event. Common causes include equipment failure – often due to ageing infrastructure and underinvestment – grid overload, human error, cyberattacks, fuel supply issues, and natural disasters or extreme weather.
- While power generators have sometimes been blamed for blackouts, the 20 major blackouts described in this briefing are overwhelmingly driven by failures in network infrastructure, human error or severe weather.
- As electricity systems evolve to accommodate renewable technologies, increased use of energy storage technologies and interconnections between different countries’ systems can enhance system security.
- Grids need to expand and develop as energy systems decarbonise, but investment is currently inadequate. The IEA said there is a risk of grids being “the weak link” in the energy transition.
Introduction
Electricity systems are complex networks of interrelated components, including power plants, transmission and distribution lines, the technologies that control them, and large and small consumers. A failure in one component can disrupt other components or cause them to fail, creating a cascade effect that can result in a blackout covering a wide area.
The April 2025 Iberian Peninsula blackout affecting Spain and Portugal was characteristic of this complex cascade effect. Blackouts can have severe impacts on all aspects of society and the economy.
The briefing outlines the main causes of a selection of significant blackouts over the last 20 years.
What causes blackouts?
Blackouts tend to be the result of a number of interrelated factors, rather than being caused by one single event. The different factors might include:
- Equipment failure: Ageing infrastructure in transmission or distribution networks, faulty components like transformers, generators, and circuit breakers, and material fatigue – when materials crack and eventually fail from repeated stress – can all lead to system failures. This is often exacerbated by underinvestment in maintenance and upgrades.
- Grid overload/instability: When electricity demand suddenly exceeds the available supply or the grid’s capacity, it can lead to cascading failures as parts of the system automatically disconnect themselves from the grid – known as tripping – to prevent equipment damage. This can be caused by high demand, like during heat waves, or unexpected loss of generation.
- Human error: Mistakes during operation, maintenance or dispatching can trigger outages that can cascade across the system.
- Cyberattacks: As grids become more digitised, they are increasingly vulnerable to malicious cyberattacks targeting control systems.
- Fuel supply issues: Disruptions to the supply of fuel for power plants, like coal or gas, can lead to a sudden drop in generation capacity and cause grid disruption and blackouts.
- Natural disasters and extreme weather: Severe storms, floods and earthquakes can directly damage infrastructure, while events such as heatwaves raise electricity demand and cause equipment strain. Climate change is increasing the threat that extreme weather poses to electricity systems, and large-scale power disruptions were experienced around the world in 2024.
Infrastructure failure was the leading cause of blackouts over the last two decades
Table 1 shows a selection of blackout events that occurred over the last twenty years and indicates the initial event likely to have led to a blackout. Appendix 1 provides more details on the events.1These events were selected because of the number of people affected and also to give a broad geographical spread. The list is far from exhaustive. There is a longer list on Wikipedia (which also may not be exhaustive). World Population Review provides an overview of some of the countries most affected by blackouts, and detail on the number of firms that experience electrical outages in different countries is included in the results of the World Bank’s Formal Sector Enterprise Surveys.
Of this selection, the most common initial causes are:
- Infrastructure failure, often faults in transmission lines.
- Human error, including failure to implement protection standards or to inform other system actors of changes in operating conditions.
- Extreme weather, often damaging infrastructure or preventing it from working properly.
Table 1
Upgrading the grid can prevent blackouts and support renewables
Variable renewables have often been erroneously blamed for blackouts, including in relation to the recent Iberian Peninsula event. However, as can be seen in Table 1, blackouts are overwhelmingly driven by failures in network infrastructure, with the resulting grid disruption driving all types of power plants offline.
The increasing deployment of renewable energy technologies means that electricity grids will need to change and adapt to accommodate these new technologies and practices while also maintaining system security.
While the technologies and practices exist to enable renewables and storage to make a greater contribution to grid security, they are not yet receiving adequate political attention or investment. The security and resilience benefits of decarbonised electricity systems are being missed because electricity grids have not yet been upgraded to cope with the new technologies.
With grid upgrades, renewables can provide a secure electricity supply
The security of electricity systems can be defined by three qualities:
- Adequacy: the system’s ability to meet demand at all times under normal operating conditions.
- Operational security: The system’s ability to retain a normal state during any type of event, or to return to a normal state as soon as possible afterwards.
- Resilience: the system’s ability to absorb, accommodate and recover from short- and long-term shocks.
Traditional electricity systems were designed around very large-scale fossil fuel, nuclear or hydroelectric power plants, relying on the transmission network to deliver their output over long distances. The qualities of system security tended to be provided by fossil fuel or hydroelectric plants.
The increased deployment of renewables means that there is a more diverse set of smaller power plants that often provide variable output in response to the availability of wind or sun.
Renewable energy integration involves modernising electricity grids with innovative technologies and enhanced operational flexibility, creating a more dynamic and resilient power system. The technologies to ensure stability and security in decarbonised electricity networks already exist, but are often underutilised.
A renewables-based system can meet the three qualities of a secure grid in the following ways:
Adequacy
- Building variable renewable projects coupled to electricity storage means that excess output can be stored and released when output falls or the demand for electricity grows. The costs of wind, solar and electricity storage technologies have plummeted in recent years, making them an increasingly viable alternative to fossil fuels.
- Using domestic renewable resources avoids the need to import fuel from elsewhere. In 2023, the renewable power deployed globally since 2000 saved an estimated USD 409 billion in fuel costs in the electricity sector.Interconnecting multiple electricity systems can enhance the ability to meet demand by using output from different sources if needed. Interconnections can also help reduce costs by enabling power trade between countries, especially when renewable electricity prices are low.
Operational security
- Storage, coupled with renewables projects, can also enhance operational security by providing services to ensure the grid remains balanced under changing operating conditions.
- Interconnections can also provide these grid services.
- Renewable projects are often smaller in scale than traditional fossil fuel or nuclear power plants and are spread out over a larger number of sites, known as decentralisation. This reduces the impact of a single point of failure.
- Demand response encourages consumers to shift their electricity demand to periods when there is either more supply or less demand. Encouraging demand response measures can help accommodate the variable characteristics of some renewable technologies as well as reduce the need to invest in new network infrastructure by avoiding dramatic peaks and troughs in demand. This will be particularly important as demand for electricity grows to provide power for heat and transport.
Resilience
- Energy storage technologies such as batteries or pumped storage can help electricity grids restart after a blackout, a process known as a ‘black start’. These technologies have rapid response times, stable voltage and frequency, and can operate independently of the grid, known as ‘island mode’, meaning they can kickstart blacked-out areas of the grid.
- To date, grid operators have not usually required renewable power projects to have black start capabilities. However, the increasing deployment of renewables has focused attention on whether they can deliver these services. ScottishPower has successfully shown that wind power can restore a blacked-out section of the transmission network, using grid-forming technology to regulate the voltage and frequency of the wind farm’s output and allow it to contribute to stabilising or even restarting the grid.
Renewables, ageing assets and increasing demand mean grids need more investment
Electricity grids urgently need investment to deal with future challenges of electricity production and use. While the growth in renewables is often highlighted as responsible for this need, in reality, there are several factors driving the need for investment to expand and upgrade electricity grids:
- Integration of new generation: The rapid expansion of renewable electricity generation means that grid infrastructure has to be updated and expanded to allow these sources to connect. Often, renewable projects are based in new areas, rather than in places where generation has traditionally taken place, requiring new lines to be built. In addition, the operating characteristics of variable renewable projects may mean upgrading or replacing grid management technologies to maintain grid stability. Other power plants might also require grid construction or expansion.
- Ageing assets: Much of the existing network infrastructure in mature electricity systems was built decades ago, often in the mid-20th century. This equipment is reaching or has exceeded its design lifetime. Investment is needed for the maintenance, refurbishment or replacement of ageing components.
- Increased electricity demand: Global electricity demand is rising, driven by climate change, population growth, economic development, and increasingly, the electrification of other sectors such as transport and heating. Data centres are also emerging as a major driver of increasing electricity demand. Existing grids may not have the capacity to handle this growing demand, necessitating upgrades and expansion to prevent overloads and ensure a reliable supply. Electrolysers for hydrogen production are also expected to need grid investment.
- Modernisation and digitalisation (smart grids and decentralised generation): This requires improved network monitoring and control, demand-side management techniques, and enabling two-way power flows on networks. The development of smart grids is often coupled with the decentralisation of electricity systems and the use of more locally generated power, sited on lower-voltage distribution lines as well as transmission lines.
Data from Bloomberg New Energy Finance (BNEF) gives an indication of how investment will be split between these categories until 2050 (Figure 1). In BNEF’s Net Zero scenario2BNEF’s Net Zero Scenario describes a pathway to net zero greenhouse gas emissions by 2050 consistent with 1.75°C of warming. the deployment of renewable generation is the largest single driver (35%), but it is closely followed by the need to replace ageing assets (30%). Overall, drivers that are not directly related to decarbonisation (ageing assets, increasing demand and non-renewable generation) make up more than 50% of the projected investment in grids up to 2050.
Figure 1
Although not explicitly addressed in the BNEF figures, the need to ensure grid resilience and security in the face of more frequent and severe weather-related damage due to climate change is also a key driver. Cybersecurity threats to grid control systems are also a growing concern, requiring significant investment in advanced security measures and monitoring capabilities.
Grids risk being the “weak link” in the energy transition, says IEA
Grid investment has not kept pace with the rate of increase in electricity demand and the growing deployment of renewables, and falls far short of what is needed. The International Energy Agency (IEA) estimates that USD 390 billion was invested in electricity grids in 2024, an increase of nearly 20% since 2015, but still much less than the USD 600 billion a year needed globally by 2030 to ensure that grids can deliver a secure energy transition.
Figure 2 shows that investment in renewables has more than doubled since 2015, while investment in grids has only grown by 24% in the same period. Although the level of investment compared to growing electricity demand has improved since about 2021, it still lags behind demand growth. The IEA believes that this disparity means that grids risk being the “weak link” in the energy transition.
Figure 2
The IEA has also expressed concern that grid infrastructure is “one of the biggest energy security risks” at present due to the lack of investment. The recent blackout on the Iberian Peninsula focused attention on the state of the region’s grid, as well as on electricity generation. Figure 3 shows that, although investment in the Iberian grid has grown in the last couple of years, it still lags behind other similar economies.
The challenges faced by the Spanish grid were reassessed as a result of the blackouts, with the Spanish government announcing an additional EUR 750 investment in increasing its resilience.
Figure 3
Appendix
