Sir Isaac Newton published his magnus opus, titled Principia Mathematica, in 1687. In Principia, Newton introduced his three laws of motion — the law of inertia, the law of acceleration, the law of action-reaction — and the law of universal gravitation. It is arguably the greatest scientific work ever published.
Principia set the stage for the “Age of Enlightenment” and paved the way for the Scientific Revolution. However, it seems that almost 350 years later, the operators of electric power generation systems utilizing wind turbines and solar voltaic cells in Spain and Portugal neglected to consider the law of inertia in the design of their power grids.
Europe continues to pursue a “net zero climate strategy” with the goal of “becoming climate neutral by 2050.” The net-zero strategy envisions “net-zero greenhouse gas (GHG) emissions across the E.U. economy.” The term “net-zero” refers to a balance between GHG emissions and the removal of CO2 from the atmosphere by various means, including natural carbon sinks such as the ocean (which is by far the largest carbon sink) and green plant matter during photosynthesis as well as carbon sequestration projects. The net-zero strategy is legally binding on E.U. countries under the European Climate Law that was enacted in July 2021.
A major part of the net zero strategy involves the elimination of fossil fuel–powered generation plants in the E.U. and their replacement with wind turbines (wind), solar voltaic cells (solar), and hydroelectric plants (hydro). In 2024, around 29% of E.U. electricity was generated from fossil fuel-powered electric generation plants, down from around 56% in 2000. The various E.U. countries differ in their percentage use of wind, solar, and hydro generation to power their electric grid. In 2024, “Eurostat” estimated the following percentage of wind and solar used by each country: Greece (50%), Denmark (60%), Germany (65%), Spain (80%), and Portugal (85%). At times, that percentage can go much higher.
On April 28, 2025, at 12:33 CEST, a blackout (total loss of electricity supply on the grid) occurred across the Iberian Peninsula, affecting mainland Portugal and Spain. The Spanish electrical power grid experienced a sudden and unexplained loss of 15 gigawatts (billion watts) of power, equivalent to about 60% of the country’s electricity demand at the time. This caused a “synchronous area separation,” where Spain’s grid disconnected from the European system, leading to a collapse of the Iberian electricity network. The Spanish grid operator found two “disconnection events” in the southwest, involving solar plants, which destabilized the grid. These events caused oscillations in high-voltage lines, disrupting synchronization between systems.
To understand what happened on April 28 in Spain, it will be necessary to engage in a short primer in terms used in the electric power generation industry and physics.
The “load” on an electric power grid is a general term that refers to the power draw of all of the electric devices connected to the grid, including residential (lights, air-conditioners, electric heat pumps, etc.), commercial (stores, entertainment venues, restaurants, etc.), and manufacturing operations (steel mills, paper mills, automotive plants, etc.). The “demand” on an electric power grid is the measure of the load at any one point in time, usually expressed in billions of watts, or gigawatts (GW). An “inter-connector switch” is a device designed to separate the connection between two adjacent power grids when demand for electricity in one or the other grid exceeds the ability of the combined system to supply it. A “system generator” is a device used to produce electricity, and it is connected to the power grid by switches. System generators usually include steam-powered turbine generators (coal, oil, and nuclear), gas turbines, wind turbines, solar voltaic cells, and hydroelectric plants. The “frequency” in a power grid is based on the design parameters of the load, usually expressed in cycles per second or Hertz (Hz). In the U.S., the frequency of the power grid is 60 Hz; in the E.U., the frequency of the power grid is 50 Hz. The frequency in a power grid has to be maintained to a very close tolerance in order to protect the system generators and load devices, such as electrical motors, transformers, and electronic devices, from being damaged. In the E.U., the critical minimum frequency is 49.8 Hz; below that level, the grid system automatically begins to “shed” load — that is, separate the load from the power grid by inter-connector switches.
When the demand on a power grid suddenly increases, or the output of system generators suddenly decreases, the load on the remaining system generators in the grid suddenly increases. The increase in load results in a force (torque) at each system generator that acts to resist the rotation of the generator shaft in the system generators. The ability to withstand a sudden increase in torque that opposes generator rotation is called kinetic energy. The kinetic energy of a rotating object is a function of its moment of inertia and its angular velocity: The formula to calculate the moment of inertia of a rotating shaft is I=1/2 MR^2, where I = moment of inertia, M = mass of the rotating shaft, and R = radius of the shaft. The formula for calculating the kinetic energy of a rotating shaft is KE = 1/2 * I * ω², where KE is the kinetic energy, I is the moment of inertia, and ω (omega) is the angular speed.
Interestingly, the combined mass of the wind turbines in a 100 MW (million watts) wind farm is approximately 19,800 tons; the mass of a 100 MW steam generator is about 200–300 tons. So the combined mass in a 100 MW wind farm is 66 times greater than a 100 MW steam generator. However, the kinetic energy of a 100 MW wind farm is around 405 megajoules, whereas the kinetic energy of a 100 MW steam generator is 7,105 megajoules, or about 17.5 times greater. The reason why a steam turbine has a much higher kinetic energy than a wind farm with the same capacity is that the shaft in a steam generator rotates at a much higher speed (3,000 rpm) vs. a wind farm (15 rpm). By contrast, a solar voltaic cell (solar panel) has no rotating inertia since it has no moving parts. It can contribute no inertia to the power grid.
So what does all this mean as regards the Spanish blackout and power grid stability when using wind and solar generators? Immediately preceding the blackout, the generation mix on the Spanish grid was 59% solar (no inertia), 12% wind (low effective inertia), and 15–20% steam turbine (nuclear and gas). The steam turbines had a much higher inertia component than wind and solar but a low overall contribution to total grid inertia since they supplied only 20% of the grid demand. A frequency disturbance (probably a transmission fault) caused a rapid frequency drop. Low system inertia allowed the frequency to oscillate, which then tripped out the solar generators, which have tighter frequency tolerances than steam generators. A 15 GW loss of power supply immediately resulted. The loss of power supply caused the system voltage to plummet, which tripped the inter-connector switches between the Spanish and French grids.
The black-start process took 18 hours to restore power to the approximately 60 million people in the affected areas of Spain and Portugal. Thirty-five thousand train passengers were stranded; 500 flights were canceled, affecting 80,000 passengers. An estimated 3 billion euros was lost when ATMs and electronic payments systems failed to operate and stores shut down. Industrial plants shut down. It was estimated that 4.5 billion euros was lost due to production outages.
Neither wind nor solar power can be used to black-start a grid because of lack of inertia and inability to control generation frequency during system start-up. Portugal used a hydro dam and gas turbine plant; Spain used hydropower and gas turbines. France supplied 2 GW via inter-connectors, and Morocco supplied 900 MW.
A properly designed power grid uses nuclear power and fossil fuels (coal and oil) to generate a high percentage of the base load. Hydro, wind, and solar (in that order) should be layered on the base load generation as conditions permit. Gas turbines are employed to supply peak load demands and respond to unexpected generator outages. System inertia must be maintained to control system frequency when demand fluctuates. The load mix (heavy manufacturing vs. residential) must be considered in grid design.
Politics and pseudoscience based on the fraudulent global warming hypothesis should play no role in designing a nation’s power grid. Excessive deployment of wind and solar generators can reduce the reliability of the power grid by decreasing system inertia.
Guy K. Mitchell, Jr. is the author of a book titled Global Warming: The Great Deception — The Triumph of Dollars and Politics Over Science and Why You Should Care. It placed #3 on the Wall Street Journal’s Top Ten Best Selling Book list in April 2023. www.globalwarmingdeception.com
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