On 28 April 2025 the world was jolted back to reality when Spain and Portugal witnessed the most severe blackout in Europe in decades and only a few days later on 2nd May the island of Bali also went dark.
If you rely on electricity…and who doesn’t, this isn’t just another energy think piece. It’s a reality check. I write about what causes blackouts, why they’re increasing, and what simple steps individuals, engineers, and policymakers can take now to avoid a dark and fragile energy future.
Blackouts are an uncomfortable subject. We understand the crucial aspect of a functioning power system … without which elevators, traffic lights, schools, trains, hospitals, sanitary systems, electric vehicles and gas stations, even heat pumps and of course the internet and our phone network have no way of functioning.
My blog unpacks the escalating risk of blackouts through real-world examples, from the 2025 collapses in Spain, Portugal, and Bali to the historic 2003 New York event. It breaks down the root causes, from human error and weather extremes to grid design flaws, and explains the rising threat of brownouts as a more common, managed alternative to a full collapse.
We will explore how inverters, essential for solar and wind, can destabilize the grid, and why traditional rotating mass still matters for inertia and stability. Spain’s blackout becomes a key case study, revealing how too much non-synchronous generation leads to chaos. I also question whether new tech like grid-forming inverters and flywheels can realistically save us, and shows what it takes to restart a grid once it fails.
In the final section I address energy security, weighing the hard trade-offs between “renewables”, conventional fuels, and nuclear. This is just a clear look at the fragile future of our power systems, and what must be done to keep the lights on.
As is often the case, some of what I write may be unpopular, but it is not motivated by politics nor financial gain, it is motivated by truly making a positive difference to our societies… by securing reliable, usable energy that is affordable and comes with the least possible environmental impact.
- What happened in New York in 2003 and in Spain in 2025?
When communication, transport and all electricity dependent systems fail, our brains plays tricks on us… all kinds of horror-thoughts go through our minds when either stuck in a dark, hot elevator or when one cannot reach loved ones. Exactly this kind of Blackout hit Spain and Portugal on 28th April 2025! Only days later, on 2nd May 2025, the entire island of Bali also experienced a Blackout.
Don’t forget about the large New York or Northeast Blackout in 2003, where large parts of the Northeast US was without power, impacting 50 million North Americans. Subsequently “Reliability First”, a government organization, was founded to ensure that such events never happen again… Reliability First authored this video commemorating the 20th anniversary of the New York Blackout (YouTube here [1]) that is worth watching.
The New York blackout in 2003 can largely be attributed to software failures, human error, and inadequate tree trimming near power lines. [2]
The Iberian blackout in 2025 – also affecting 50 million people – can be largely attributed to power oscillations (see box – What are oscillations and what happened in Spain?) or variations that may not be that uncommon. It seems that the grid system was not able to “smoothen” out these oscillations leading to a cascading effect of grid portions shutting down within seconds.
It appears that the first potential mistake made by the Spanish grid operator “Red Electrica” was to have an electricity mix with a low percentage of dispatchable power and the second is to, simultaneously have a very low percentage of generation providing synchronous rotating inertia… more on this later.
Only 15% of generation, seconds before the blackout, came from nuclear and gas-fired power stations which operate large rotating masses. Consequently, in just five seconds, Spain lost practically all of its power.
- Note: officially only 60% of national electricity demand [6] was lost, but in reality it appears that most of Spain went dark.
- Officially, solar was still providing 3% of power at 10.45pm, see Figure 1, which is highly questionable at that time of night.
Figure 1: 28 April 2025 – Spanish generation at 10.45pm 13% from solar? [8]
The Bali blackout on 2 May 2025 appears to have been caused by disruption in the subsea cables which connect the electricity system in Bali with Java island, triggering blackouts in a number of areas in Bali. [3]
These three blackouts are just a fraction of the story, but countless others are out there if you care to search. The causes being either (1) human error or sabotage, (2) weather, or (3) system related. The risks of human error and sabotage we have to mitigate as best we can. System related risks we can avoid by thinking critically and ensuring the financial and human resources to execute a risk mitigation or – in some instances – risk elimination plan. Weather we cannot control but we can also adequately prepared with backup and reserve margins.
Below, some additional blackout examples of the past 10 years, not in order of importance and not exhaustive [4]:
Figure 2: Some additional blackout examples of the past 10 years
Figure 3: Pre-Event Oscillations in the Iberian Grid [11]
What are oscillations and what happened in Spain? Power oscillations happen when electricity in a system starts to fluctuate or “wobble” instead of flowing smoothly. This can occur when there are sudden changes, like a big power plant turning on or off, an unexpected spike in demand, or unexpected clouds appearing over large solar fields. Think of it like a swinging pendulum: if the swings get bigger instead of remaining constant, it can lead to unwanted events like blackouts.
Engineers use special devices to keep these swings under control and ensure the power stays stable. Without them, the system could become unstable, leading to power outages.
What happened in Spain?
Here is what we know [5, 6, 7] The power outage took place during a time when solar, wind, and hydro sources generated more than 100% of Spain’s electricity needs. In the moments leading up to the blackout, Spain was exporting 4.3 GW of excess power to France, Portugal, and Morocco, while also using an additional 3 GW to replenish pumped hydroelectric reserves. Over 70% of generation came from weather dependent, unpredictable wind and solar.
The initial frequency drop (N-1) appears to have been caused by two large solar farms going offline in Southwest Spain [8].
The initial loss of power originated with solar farms in the southwest of Spain. What then happened?
We don’t know yet exactly, but have a look at the short video from Practical Engineering [9] or Figure 5 in the next section, which could give a hint. Officially, the Spanish grid operator informed that three “successive” loss of generation in Granada, Badojuz, and Seville totalled 2.2 GW. Over voltage triggered a “cascade of generation losses” and a “large scale” drop in generation triggered a “loss of synchronization” between the Iberian Peninsula and the rest of Europe [5].
Figure 4: Wood Mackenzie on the Spain blackout [7]
On 16 May the news came out that Spain adopted a temporary solution to address the energy security challenges during the “hellbrise” at midday. “Hellbrise” is the new term opposite of the now famous “Dunkelflaute”
Spain’s grid operator, Red Electrica REE, transitioned the national grid into a “strengthened mode” of operation. Prof Noland writes on LinkedIn that this “strengthened mode” essentially involves partially suspending normal electricity market operations by curtailing wind and solar at peak times, making space for more synchronous generation from hydro, nuclear, and gas plants. These conventional plants provide essential stability services. As we discussed, the large spinning turbines offer critical system inertia, absorbing shocks and smoothing power fluctuations, thus creating a robust buffer against disturbances as synchronous generators significantly enhance frequency regulation and voltage support, while also boosting system strength through short-circuit capacity and power system stabilizers (PSSs).
These adjustments in Spain confirm what we cover in this article on the importance of system inertia and the negative influence on grid reliability of inverter based resources (IBR) such as wind and solar.
2. Blackouts vs Brownout or “Loadshedding”
When South Africa experienced “loadshedding” or scheduled outages for up to 18h each day during 2023 and 2024 these were not blackouts. There we scheduled, planned for, announced “grid cut-offs”, affecting certain areas, to ensure that power demand will not supersede power supply keeping the frequency in the grid stable. These “brownouts” are likely to become more common in the coming years across Europe, Australia, California, and Texas…driven by a lack of reliable, weather-independent, dispatchable power sources that can handle extreme weather or grid disruptions.
When demand is higher than supply, the frequency in the grid will drop from the desired 50 Hz (60 Hz in the US and certain other countries). When supply is too high, the frequency increases. A frequency drops of 2,5 Hz immediately leads to a blackout, see Figure 5 below. So, when possible, system operators may plan scheduled load shedding once a 1 Hz frequency deviation is detected to help stabilize the grid during times of high demand or insufficient power supply.
You may remember that America decided on alternating current (AC) for basically the whole world, in the “War of the Currents” over 130 years ago (Tesla for AC vs Edison for DC). This we can still feel today!
Solar and wind need inverters… (This section refers on our book “The unpopular Truth… about Electricity and the Future of Energy” that can be purchased right here)
Wind turbines produce intermittent alternating current (AC) electricity that needs to be converted and “conditioned” or rectified before the power can be fed into the grid. The alternating current from a wind turbine is not produced at a sufficiently stable voltage, frequency, or phase to insert directly into our alternating current grid. Solar generates direct current (DC) power. Batteries also “store” DC power.
The primary function of inverters is to convert direct current (DC) electricity, which is generated by solar panels and some wind turbines, into alternating current (AC) electricity, those 50 Hz in Europe or 60 Hz in North America.
Why Wind and Solar need inverters:
- Solar power: Solar panels produce DC electricity, but household appliances and the electrical grid operate on AC. Inverters ensure that solar energy can be used efficiently and safely and fed into the power grid.
- Wind power: Some small wind turbines also generate DC electricity, requiring an inverter for conversion. Larger wind turbines typically produce AC directly, but still use inverters for grid compatibility and voltage regulation.
- Grid integration: Inverters help synchronize wind and solar power sources with the grid, ensuring stable voltage and frequency levels.
Figure 5: Grid frequencies and its impact [10]
Figure 6: YouTube – Practical Engineering: A lot of the interesting challenges with wind an solar are happening behind the scenes [9]
It is understandable that electricity generation from wind and solar is subject to significant fluctuations and can vary from one second to the next. Accordingly, balancing must be done quickly via controlling power (German: “Regelleistung”). The more wind and PV plants are operated in the grid, the higher the demand for controlling power. Controlling power is always provided by power plant types or consumers that are not dependent on fluctuating factors and are fully dispatchable, such as coal, gas, or hydropower.
Even after conditioning, wind and solar power (or inverter-based resources IBR) in the grid they do not have the same quality as rotating turbine-generated power and is considered “unclean” by network specialists.
Since wind and solar power get prioritized in the grid, more electricity requiring conditioning enters the grid. This conditioning happens with the help of rectifiers and inverters. In the process, uncontrollable “harmonics” can occur in addition to or above the standard frequency of 50 Hz (for Europe), which can lead to power losses, due to heat generation, and to other undesirable or even catastrophic side effects. On the other hand, uncontrollable amplifier effects can also occur due to resonances, which can lead to short circuits and fires.
Destructive resonances can only be avoided if the proportion of “unclean” electricity in the grid is kept as small as possible. In Germany or Spain, on the other hand, the sources of “unclean” alternating current have been systematically increased for decades, resulting in “alternating current chaos” and in the end to blackouts as experienced on 28 April 2025.
For the technically interested, the video linked under Figure 6 will explain to you what is required to connect solar to the grid.
3. Inertia in the Grid and Inverters
Size DOES matter. The true stabilizers of our alternating current (or AC) grid system are large rotors, each 100MW or more. Their substantial rotational mass ensures inherently stable rotation, RPM, allowing them to endure major grid AC waveform faults without disruption. Even when separated by 100 miles, these large rotors, for instance in nuclear, coal, or gas power stations, remain synchronized for 1 to 5 seconds, maintaining their motion without any electrical connection, even in the presence of a dead short.
In Spain, the proverbial straw that broke the camel’s back was that last increment of solar/wind which seemed enough to cause the system to oscillate and to collapse. Not “wind nor solar” per se, but probably too many non-synchronous inverters feeding noise into the grid AC waveform caused this. It was like “an orchestra without a conductor, trying to play a symphony by ear” [11].
The problem of random intermittency, be it from solar, wind, or anything else, is actually a separate issue and has nothing to do with system inertia. It is a load balancing problem.
Historically, intermediate generation was dispatched ahead of time, to meet 100% of anticipated load demand when running at 80% of nameplate capacity, leaving 20% headroom for contingencies (reserve margin).
Ultimately, the math is straightforward: if 60% of total system generation suddenly drops within a single second, the remaining 40% simply cannot keep the grid stable. That’s just basic logic.
The risk of large-scale blackouts in electricity systems with high shares of wind and solar is well-identified. However, the Iberian blackout of April 28 brings these long-recognized vulnerabilities into sharp focus [12].
Solar and wind installations generally use grid-following inverters, which align with the grid’s existing frequency and voltage rather than setting those parameters themselves. These systems rely on a stable grid (and electricity actually forms the grid) for proper operation and lack the ability to independently maintain grid stability during disruptions.
Inverters function as rapid switches that introduce considerable noise into the “grid AC waveform”, potentially leading them to either chase each other unpredictably (grid-following mode), clash aggressively (grid-forming mode), or even do both simultaneously. This interference represents wasted power. As this noise accumulates, inverters can become overwhelmed, eventually losing synchronization with the grid AC waveform. At that point, a minor disturbance can trigger a cascading failure, much like rats abandoning a sinking ship all at once, causing the entire system to collapse.
Figure 7: Synchronous generators delivery grid AC waveform
Figure 8: Siemens Ad for “Flywheels” or “Synchronous Condensers” [13]
It’s akin to an orchestra without a conductor attempting to perform a symphony by ear, inside a large shed with a tin roof, during a thunderstorm.
The performance is bound to start off poorly, and a complete breakdown is inevitable [11].
Grid operators acknowledge these risks, with some setting a minimum requirement of 65% or more of the system’s spinning rotor generators remaining online. Additionally, sufficient reserve margin is necessary to compensate if all the inverter-based generation fails at once.
A proposed strategy for reducing the risk of grid destabilization from large wind and solar shares is to invest in grid-forming inverters. These inverters are supposed to allow wind and solar installations to replicate the operational characteristics of traditional power plants by providing a stable voltage and frequency reference, which could help maintain grid stability during disruptions. However, grid-forming inverters have been used only in microgrids and isolated systems, like those in Australia and Hawaii. Their application in large, interconnected grids remains untested. Most importantly, grid-forming inverters cannot replace rotating mass as I explained above and will provide more detail below.
Batteries? … In theory yes, but practically no. To date, there are no proven models for large-scale deployment of battery-based grid stabilization in complex, interconnected systems, in which a large amount of storage capacity will be needed [12]. Again, a battery, if not drained during a blackout, could in theory turn a flying wheel (or flywheel) that Siemens produces for this purpose. Thus, Siemens suggests to use “green” energy to build and operate large flywheels, mimicking conventional power plants to provide rotating mass inertia in the grid… imagine how energy and raw material (in)efficient this is (Figure 8).
To understand the problem of inverters properly, we need to go back to “first principles” and understand how the rotational inertia within a spinning mass (i.e. a flywheel) maintains the grid AC waveform and more importantly, when.
The correct answer is NOW, and ALWAYS.
Inertia is a brute force of nature that correlates with mass, alone. And in this case, we are referring to the form of inertia called momentum. And momentum can’t change directions unless it is acted upon by an equal and opposite force. So, if you are not working with the momentum, you are most definitely working against it (i.e. inverters connected to wind and solar). Because if the inverter’s AC waveform is not working with the grid AC waveform at every moment, in every possible direction, it is most definitely working against it literally at every possible instant, in every possible direction. And this is the problem with inverters that no computer can overcome. (my thanks goes to Tom Troszak for his insights and support [11])
Inverters are also an easier target for cyberattacks, they are in fact critical infrastructure and I covered this subject in a recent blog post. The fact that most countries purchase critical infrastructure from other countries that may have geopolitical significance should be a concern when looking at energy security.
4. Blackstart capability, Short Circuit Levels (SCL), and Energy Security
Ok, we are almost done, two more important points about the grid… but you can skip over this if you want to.
Blackstart: Every power plant, every wind turbine, and every solar panel requires electricity to be able to “start up”. The ability to start up without power from the grid, i.e. completely self-sufficient as an island, is referred to as “blackstart capability”. This capability is especially important in the event of brownouts or blackouts (see Balkan blackout in June 2024). The blackstart capability of larger power plants is provided by batteries that then start diesel generators, which are then used to ramp up power plants. In the case of wind and solar, batteries and diesel generators are also typically required. Hydroelectric plants and pumped hydro reservoirs usually require only a smaller amount of electricity to start up, for example, to open locks.
In Germany, during the first half of the 20th century, and also historically before that time, and in the former East Germany, every power plant had black-start capability for good reason. Since the 1980s, for economic reasons, this capability was not always planned for in newer power plants. In Germany and other parts of the world, the black-start capability of power plants has thus been significantly reduced over the years. In the case of wind and solar, black-start capability, although it is theoretically possible, is rare to non-existent.. As grid stability decreases with increasing wind and solar penetration, the risk of blackouts also increases.
When blackouts occur, the electricity grid must be carefully “ramped up” again. This is done in so-called grid islands, i.e., limited power consumers are connected to the grid together with a restarting power plant and the 50Hz power frequency stability has to be built up. Remember that demand and supply must always be exactly equal for the grid to be stable. If the grid island runs constant at 50 Hz, it must be connected or merged to another grid island. This can only happen if both grids run completely synchronously. This synchronization of subnetworks can in some cases take days, but Spain managed in less than a day.
If the synchronism between sub-grids to be merged is absent, generators and turbines can not only be damaged, but blow up. Large turbines are very sensitive when the frequency drops or rises, mechanical resonances can occur, which can cause irreparable damage. In Spain, Morocco and France helped by providing the power to restart the grid… with amazing speed, congratulations to the engineers!
As always, you can read more in our recently updated book “The unpopular Truth… about Electricity and the Future of Energy” that can be purchased right here)
Short Circuit Levels (SCLs): Now getting to Short Circuit Level (SCL) vs Short Circuit Current – (Kurzschlussfestigkeit vs Kurzschlussstrom). Think of Short Circuit Current as the gushing water when a dam breaks. It’s the immediate and intense flow. It is the actual current that flows through an electrical circuit when a short circuit (disturbance) occurs. Short Circuit Level SCL is like the dam’s capacity to withstand and control such a sudden influx without failing. It is the maximum current that an electrical grid or system can handle during a short circuit without causing significant damage.
The short circuit level reduces the more wind and solar (inverter based resources IBR) we add to the system – risk increases. For example, compared to a coal turbine, a 100 MW solar installation might only provide roughly one-fifth of the short circuit capacity (on the order of 100–150 MVA). The consequence is that in regions with high solar (or other inverter-based) penetration, the overall SCL of the grid is lower, which can make the network more “weak.”
Energy Security: How do we ensure our energy security? All sources of power have advantages and disadvantages. Every country has its own unique position, but here are a few things to consider.
The fact that wind and solar do not provide any energy security is logical. The famous “Dunkelflaute” means there are days, sometimes even weeks of little to no wind and solar across continental Europe. Such prolonged periods of lacking wind and sunshine cannot be overcome with batteries nor with Siemens flywheels. Hydrogen for power storage is an economic and environmental non-starter due to the 80% of “lost energy” when producing, storing, transporting, and repowering hydrogen. Wind and solar also have no rotational inertia, which was the problem in Spain, hence reducing grid resilience.
Conventional fuels?: Coal vs gas, seems clear-cut… Coal is generally safer as it can withstand extreme weather conditions and you can, for instance, store four months of “fuel” supply in your backyard, which is not possible with gas. Coal-fired power is dispatchable, and power plants can easily be fired up and shut down (fast, but not as fast as gas). Coal is environmentally generally not as good as gas, but for the “climate” they are more or less the same when including methane (see here for more details). Nuclear is also safe and easy but of course more expensive and not as flexible. Gas is fast, generally more expensive than coal, burns cleaner but requires more complex LNG or pipeline infrastructure. I would call it impossible for a gas-fired power plant to have four months supply in its backyard.
Keep in mind, in my opinion, we need all, coal, gas, and nuclear we can get to power our world!
I recommend you to read this interesting article from 2015 “Zombie Coal Plants Reanimated to Stabilize the Grid” [14].
5. Summary
Ok, the “energy transition” is supposed to lead us to an electrified world using only “clean power” from wind, solar, hydro, biofuels, and geothermal. Since geothermal is insufficient, hydro is limited, biofuels are not sustainable, (see my recent article on biomass here) only wind and solar remain. But they have many issues, and one important point is that wind and solar destabilize the grid… the Iberian blackout was a drastic reminder.
The fact remains that the “old” AC based power system was not broken, but it is now being broken by adding wind and solar to it. Today’s inverters do not solve this problem, although that is the intended solution. Wind and solar are not the issue for grid resilience per se, but rather too many non-synchronous inverters feeding noise into the grid AC waveform.
To be fair, the power could be coming from solar, wind, unicorns, or aliens (I just love to quote from Tom Troszak). The inverters needed for wind and solar are the source of grid instability, not the actual type of power. The problem of random intermittency is a completely separate issue and will cost a lot of money to overcome. Intermittency has nothing to do with system inertia which we discussed here.
The higher the penetration of wind and solar in the system and the more power plants with rotating turbines we blow up (like in Germany the Hamburg coal-fired power plant in March 2025) the higher the risks of blackouts.
I was asked last week… What do we do now? Well, here are some simple suggestions…
- Personally, prepare for 3-5 days of blackouts, water, batteries, candles, canned food… and if possible a generator (the EU put this recommendation online in March 2025 [15])
- Lobby for stable, reliable, predictable power systems and avoid wind and solar
- Educate yourself and stay away from political statements or political bias
Links and Resources
[1] Reliability First Movie on YouTube commemorating the 20th Anniversary of the big New York or Northeast blackout in 2003, (link)
[2] August 2003 Blackout | Department of Energy, (link)
[3] Reuters: Indonesia’s Bali Island Hit by Power Outage.” May 2025, (link)
[4] List of major power outages and subsequent research (link)
[5] Javier Blas quoting the official explanation from Red Electrica, (link)
[6] Spanish generation from Red Electrica website on 28th April 2025 (link)
[7] Wood MacKenzie on Spain blackout (link) and (link)
[8] EPRI, based on UTK Fnet Grideye, 20min into video (link)
[9was 14] YouTube: Connecting Solar to the Grid Is Harder Than You Think, 2024, (link)
[10] netzfrequenz.info: Sep 2022, (link)
[11] with the support of Tom Troszak and Prof Bill Smith, USA, email exchanges May 2025
[12 The Iberian Peninsula Blackout — Causes, Consequences, and Challenges Ahead, Baker Institute, May 2025. (link)
[13] Siemens flywheels to provide rotating mass inertia (link)
[14 was 15] “Zombie Coal Plants Reanimated to Stabilize the Grid – IEEE Spectrum,” 2015, (link)
[15] EU 72h emergency kit; Brussels asks EU citizens to put together a 72-hour emergency kit to face crises | Euronews (link)