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Understanding Inertia without the Spin (Text Version)

This is the text version of the video "Understanding Inertia without the Spin."

The video opens with an image of a spinning top on a table and the title “Understanding Inertia without the Spin.” Then, it moves to a shot of a hand pulling a light switch to turn on a light.

Narrator: Everyone wants reliable power.

Shot of a busy city at dusk, with cars moving on freeways and skyscrapers lit up. Shot of transmission lines followed by an image of a large conventional power plant.

Narrator: And one reason why today’s grid is so reliable is its inertia, which basically helps the whole system keep running even when a power plant fails.

Aerial shot of a large utility-scale solar photovoltaic array, followed by a large wind farm.

Narrator: But the grid is evolving to include ever-higher levels of solar and wind—which don’t provide inertia.

Shot of two people running through the woods, then the word "NO."

Narrator: Should we all panic? No.

Images of equations written on a chalkboard, followed by a hand moving a Newton’s cradle.

Narrator: Here’s why. You don’t have to be able to cite Newton’s Laws of Physics to understand inertia.

Shots of cars on a busy highway, followed by a parrot riding a bicycle, a hamster in a wheel, and a man spinning a basketball on his fingertips. The video then moves to a shots of a car driving a rural highway, then two people riding bicycles.

Narrator: Anyone who has driven a car or ridden a bike is familiar with it. It’s the tendency of an object in motion to remain in motion—and it keeps your vehicle moving forward when you stop pressing on the gas pedal, or keeps your bike from falling over if you stop pedaling.

Shot of a bicycle wheel, followed by a spinning power plant turbine.

Narrator: Spinning objects, like wheels or power plant turbines, have rotational inertia.

Shot of a car coasting down a mountain highway, followed by a city skyline at night.

Narrator: And this inertia is useful whether driving a car or operating the power grid.

Animated sequence showing a simulated grid of several power plant generators. The video zooms into one of these power plant generators spinning. A frequency wave appears with the label “60 Hz.”

Narrator: Here’s how it works. The grid consists of hundred of generators rotating in lock step, each synchronized to a grid frequency of 60 cycles per second in the U.S.

Animation of a pulse monitoring screen, creating the line of a heart to convey the idea of health.

Narrator: This frequency is used as a measure of the health of the grid.

The simulated grid of several power plant generators appears again, with energized lines appearing between plants to connect them electrically. The words “Supply of power = demand for electricity” appear at the top of the screen.

Narrator: During normal operation, the supply of power from all the generators equals the demand for electricity, and the frequency remains nearly constant.

One of the simulated power plant generators starts to smoke and loses the energized connection from the rest of the grid.

Narrator: But just like how a vehicle slows when you take your foot off the gas, if there is a loss of a power plant, the supply of power will drop almost instantly. But the demand for electricity hasn’t changed.

Animated images of a lightbulb, air conditioner, and TV appear, drawing power from the grid.

Narrator: The lights and air conditioners and TVs will continue to extract the same amount of power from the system.

The animated image of the individual power plant generator returns, with a flyball governor connected to it. An inset image shows a close-up of the animated generator blowing steam from a valve. An animated speedometer also appears, showing a green “healthy” zone at 60 Hz at the top of the wheel, with yellow and red zones on either side to denote ranges of low or high frequency. The dial moves from 60 Hz to the red zone on the left, indicating a drop in frequency.

Narrator: As this energy is extracted from the inertia of the spinning generators, the grid will begin to slow down, so the frequency will drop.

An arrow and the text label “Governor” appears to call out the flyball governor. The dial on the speedometer moves back to 60 Hz.

Narrator: Devices called governors located on the generators detect these changes in frequency. They measure how fast the generators are spinning, and tell power plants to speed up or slow down.

Shot of a person’s hands on the wheel of a moving car.

Narrator: This is essentially the “cruise control” for the power grid.

Close-up of a wristwatch ticking down the seconds, followed by a Rube Goldberg machine.

Narrator: But it takes time—up to several seconds—for all these levers and valves to work and the power plant to increase output.

Shot of a spinning top, followed by gears, an aerial image of a hurricane, and a busy city street at night.

Narrator: That’s where inertia comes in. It gives the system time for all these mechanical systems to react to an emergency—while keeping the lights on.

Aerial shot of a conventional power plant, followed by wind turbines on an oceanside cliff, and a close-up of a sunlit solar photovoltaic panel.

Narrator: So that’s how inertia works to make the current grid reliable—but how we operate that grid is changing as more renewables are added to it.

Animated image of a conventional power plant turbine. As they are described in the audio, a geothermal, hydropower, biomass, and concentrating solar power plant appear onscreen.

Narrator: We can still get inertia from renewables that use traditional generators, including geothermal, hydropower, biomass, and concentrating solar power.

These images move to the background. Animations of a large wind turbine and solar array appear in the foreground. An animated inverter appears between the wind and solar images.

Narrator: But variable-generation renewables like wind and solar PV don’t use traditional generators—instead, they use inverters, which have electronic controls that do not provide inherent inertial response.

The conventional power plant turbine in the background disappears.

Narrator: And when we add inverter-based renewables and start turning traditional generators off, we have less inertia on the system.

Shot of a man making a panicked expression.

Narrator: Does this mean doom for the grid?!

The word “NO!” appears onscreen.

Narrator: No!

An image of three children with lightbulb hats.

Narrator: Grid operators have figured out how to address this without affecting reliability.

The animated power plant generator returns to the screen, and is then “wiped away” by a hand.

Narrator: If we replace the slow mechanical systems in conventional generators with something faster, we simply don’t need as much inertia.

The hand adds the wind, solar, and inverter animation back to the screen. Images of lines of electronic code appear, running across the screen.

Narrator: Fast frequency response replaces some of the mechanical processes with electronic sensors that that can quickly measure frequency and respond in fractions of a second.

Shot of a hand pushing an emergency stop button on a control panel, followed hands flipping power switches off.

Narrator: This response can be derived from non-critical loads that sense low frequency and disconnect in less than half a second.

Montage of different shots of wind turbines, solar arrays, and transmission lines. Shot of a rooftop solar array followed by a wind farm.

Narrator: You can also get fast frequency response from renewables by controlling the output of wind and solar plants, or extracting the stored kinetic energy from rotating wind turbines.

Shots of battery storage technology.

Narrator: Many storage technologies—like batteries—can also provide very rapid frequency response.

Time-lapse shot of a fast-moving assembly line, followed by a time-lapse shot of a set of wind turbines spinning, then a quick pan over a solar array.

Narrator: And when we say fast frequency response, we mean fast: wind plants can respond 10 times faster than traditional generators, and solar plants can be more than 50 times faster.

Shot of a child in a laboratory holding beakers.

Narrator: And these aren’t just lab experiments. This is already happening in real systems.

Shot of rotating wind turbines at sunset, followed by fingers scrolling down a screen of data.  

Narrator: In Texas, wind plants have been required to provide frequency-responsive services for years.

Shots of renewable energy workers wearing hard hats in the field.

Narrator: And since 2018, it’s been a requirement for all new utility-scale wind and solar plants in the U.S. 

Shot of a woman wearing headphones and meditating as fast-moving activity surrounds her, followed by shots of wind and solar, and a dog riding a skateboard down a sidewalk.

Narrator: So we don’t need to panic: there are many solutions to help wind and solar “play nice” with the grid—even without traditional inertia.

Animated data, followed by a shot of a dog cocking its head in bewilderment. Shots of researchers looking at data on computer screens, followed by a close-up aerial shot of a wind turbine with the National Renewable Energy Laboratory and U.S. Department of Energy logos prominently displayed on it.

Narrator: Although how far we can go with inverter-based resources remains an open question, researchers at NREL and around the world are exploring this challenge, and ways to make our grid more reliable, stable, and cost effective as it continues to transform.

The video closes with the NREL logo and the words “Read the full report at This video was supported by GridLab.”