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You toss some bananas and milk into a blender. Then you plug it into the wall and press start. Soon, you have a delicious smoothie. While you’re sipping and scrolling through TikTok, you notice your phone’s battery is low. So you plug that into the wall and the battery charges.

We use electricity to cook, to connect with friends and family, to keep warm, to shop, to work, and so much more. Electricity is so essential in the modern world that it has spread to nearly every corner of the planet. Approximately 87 percent of the world’s population has access to electricity. In North Korea, Haiti, and parts of Africa, though, the rate of access is just 10 to 50 percent, while in the United States, China, Brazil, and Europe, 100 percent of the population has access. If you live in a place with reliable electricity, you don’t think about it much. Like air or water, electricity is there when you need it.

Electricity is not like water, though. Water can sit inside a reservoir or a pipe, waiting for someone to turn on the faucet and start the flow. As soon as electricity is produced, it must flow somewhere. That’s because electricity is not a physical thing, like water. It is a physical phenomenon. It can be used as a way to supply energy . It is a way to transfer energy from one place to another. Electricity can flow in a complete circuit or a complete loop from a source and back again. There is no flow if the circuit is interrupted or broken. People can get electrocuted if they touch live wires or outlets because the electrical energy uses the human body to complete the circuit and reach the ground.

A vast network called the grid carries the electricity you use every day. The grid acts a bit like your heart and the vessels that carry blood through your body. In your body, your heart pumps fresh, oxygen-filled blood out into arteries. These arteries branch into smaller and smaller channels that carry the blood to each and every cell in your body.

The electrical grid has many hearts. They are power plants, solar panels, wind turbines, hydropower dams, and other power generators. Each has its own way of turning one form of energy (such as sunlight or rapidly moving water) into another— electricity. They push this electricity out into the grid, just like the heart pushes blood out into the body.

Most power plants produce three-phase AC electric power . AC stands for alternating current, which means that the electricity comes from the motion of electrons jostling back and forth in alternating directions, creating a wave-like pattern in the flow of the electricity. At peaks in this wave, a lot of power is available. The amount of time between peaks in this wave is called the frequency of the current. (Light bulbs actually flicker on and off because electricity fluctuates like this. But the flickering is so rapid that we don’t notice it.)

In three-phase power, plants send out electricity traveling in three separate waves with the peaks of each wave evenly spaced. These waves travel along three separate wires. One spinning turbine can generate all three phases of power at the same time.

Most people don’t want to live right next to power plants or even right next to solar or wind farms. Power plants and other generators may be located up to three hundred miles away from the homes and businesses that will use their electricity. Electricity loses energy as it travels over long distances. However, these losses will be much lower if the electrical current traveling through a certain thickness of wire is lowered. Current is the amount of electrical power flowing through a wire. In order to make sure customers get the power they need at a lower current level, the grid increases the voltage of the current. Voltage is, essentially, how hard electrons get jostled back and forth. It acts a lot like the water pressure in a water pipe. The harder the push, the more rapidly and forcefully electricity moves through wires . So even at a low current, the correct amount of power will be transmitted, and less will be lost along the way.

A step-up substation located next to a power plant or other power source increases the voltage of the electricity. Typically generated at around 1,000 volts, electricity gets boosted up to between 155,000 and 765,000 volts for transmission! For comparison, the outlets in North America operate at 120 volts, while European outlets supply 220 or 240 volts.

At hundreds of thousands of volts, electricity is powerful enough to jump across a space of several feet of air to find a path to the ground. This is called arcing. (Birds can safely perch on a single wire because their bodies do not offer any path to the ground or to another wire, so the electricity doesn’t travel through them.) For safety, most high-voltage wires are hoisted high up onto very tall steel towers arranged across the landscape like statues. Workers who service the lines are warned to stay at least twenty-five feet away from the highest voltage wires, and any trees growing near the wires must be cut back to prevent electricity from jumping to their branches.

High voltage transmission towers carry three main wires, one for each phase of electric power. They usually also carry extra wires on top to attract lightning so it doesn’t hit and destroy the active power lines. In the United States, around seven thousand power plants feed into approximately 180,000 miles of high-voltage transmission lines. But that’s not the entire grid. The electricity still has to get to homes and businesses . A total of around 360,000 miles of wires makes up the entire grid in the United States.

High voltage power lines carry electricity very close to a city or town. From there, a step-down substation lowers the voltage to 66,000 or 115,000 volts. A substation is not a building. Rather, it is a collection of electrical equipment. Some of this equipment converts the voltage. Regulator banks help keep the voltage from getting too low or too high. Other equipment switches electricity on or off, helping to control the flow of electricity. Switches can also turn off electricity to small sections during repairs or maintenance.

Once the voltage has been lowered, smaller wooden or steel poles can safely carry the electricity through a city or town. In some places, subtransmission lines travel underground. Some factories or businesses that use high amounts of electricity may connect directly to these lines . But most people don’t need such high voltages . So these lines feed into still more substations, called distribution substations.

A distribution substation lowers the voltage even further, to 16,000, 12,000, or 4,000 volts. Afterwards, a structure called a distribution bus splits the electricity so it can travel out in multiple directions, through neighborhoods or business districts. Having wires and wooden poles all over a city doesn’t look very nice and the poles and wires often get damaged during storms, so many areas now run these distribution wires underground instead
The voltages in distribution wires are still too high for most homes and businesses . So metal boxes called transformers drop the voltage even farther before sending the electricity along wires that connect to a building and its outlets (which operate at 120 volts or 220-240 volts). A transformer may hang on a telephone pole, sit on a concrete pad, or be buried underground. Distribution lines along main streets typically carry three wires with the three phases of electricity. Phase converters carry a single phase of this power down side streets or directly to homes and businesses. Most outlets and electrical devices only take single-phase power.

The electrical grid is an incredibly complex system . And many of the wires and towers and substations that make it work are located outside in the open. Lightning, hurricanes, ice storms, and many more problems can lead to broken or damaged wires and structures . A small problem in one part of the grid could rapidly spread to other parts, leading to fires, blackouts, or other major problems . To help avoid this, the grid is peppered with fuses, circuit breakers, and switches. Fuses burn out when the power rises above a certain amount, automatically switching off the flow of electricity. A burnt fuse has to be replaced with a new one . Circuit breakers and switches can cut off or turn on the flow of electricity. Workers can operate circuit breakers and switches from afar using a computer.

The journey from power plant to power outlet has many steps with many changes in voltage . Sometimes the voltage will get stepped up and down multiple times before the current arrives at an outlet. Yet this journey happens almost instantly since electricity travels at close to the speed of light.

The amount of electricity that power plants and generators feed into the grid must match the amount of electricity that people are using at all times. For example, power plants increase their production and feed more power into the grid during the day, when people are awake and working and using devices. At night, when most people are sleeping, power plants lower production and make less electricity. During hot summers, when people run air conditioners, they need more power than when the weather is mild in the spring or fall.

Maintaining the grid is an incredible balancing act between supply and demand. The demand, also called load, is the amount of electricity people are using. The supply is the amount of electricity power plants and other generators are making. A typical power plant heats steam to turn turbines to make electricity, so it can usually add more steam into the system to increase the amount of electricity or reduce the amount of steam to make less. However, it can’t increase or decrease production too much or its equipment might get damaged.

When load and supply are balanced, turbines turn at a steady rate, producing electricity with a constant frequency. That frequency is 50 Hertz in Europe and 60 Hertz in the US. If the load increases—meaning people are using more energy than expected—the power plant must generate more electricity to match. If it can’t, then the extra load creates a magnetic field that acts in the opposite direction of the magnetic field the turbine uses to make electricity. The opposing magnetic field slows the turbines down. This process is similar to what happens when a car starts to drive up a hill. Unless the driver presses down on the pedal to add more gas, the car will slow down because it needs extra energy to drive uphill. Slower turbines make electricity with a lower frequency.

If the frequency drops too low, some turbines will slow down so much that they stop spinning and fail, leading to an even larger imbalance because even less energy will be available. This can trigger a cascade in which many power plants shut down and cause a blackout.

If the load decreases—meaning people are using less energy than expected—the power plant must generate less electricity. If it doesn’t, the opposite problem will occur. The turbines will spin faster, just like a car speeding up when it reaches a downhill slope. This will produce electricity with a higher frequency that may damage the power plant or electrical equipment in the grid. Power plants will disconnect from the grid if they are producing too much electricity.

The easiest way to maintain balance is for power plants to increase or decrease the amount of electricity they make. But this isn’t the only way. Power companies may charge higher amounts for electricity during times when lots of people want it to try to reduce the demand. If that doesn’t work, the power company may have to do something called load shedding. This means they cut off the power to some customers to avoid a larger blackout.

Renewable power generators such as solar panels and wind turbines aren’t as flexible as power plants. A solar panel produces lots of electricity when the sun is shining brightly, only a little when it is cloudy, and none when it’s night time. A wind turbine produces more electricity as the wind blows harder. A grid operator can’t change how the sun shines or how the wind blows to match the load on the grid. So renewable energy sources actually cause a problem for the grid. Grid operators must adapt to how much power these sources are adding, usually by increasing or decreasing how much electricity power plants make.

In order to switch entirely to renewable energy sources, we will need a better way to keep unpredictable energy sources balanced. It would help a lot if the grid could store extra electricity when the load is low and release this stored electricity when demand is high. Batteries make it possible to store electricity for later. It’s very difficult and expensive to build batteries large enough to store the huge amounts of electricity the grid shuffles around. But engineers have taken on the challenge. In early 2021, the world’s largest battery storage facility connected to the grid for the first time. It is located in Monterey Bay, California. The racks of batteries take up a space the size of three football fields.

Smart sensors and networks can also help keep the grid balanced and distribute energy more efficiently. Right now, human experts are mostly responsible for figuring out how to match the load and supply of electricity. Sensors could respond much more rapidly to changes in load or supply and could automatically detect problems in the grid before they spread and become large blackouts. The smart grid is growing over time. In the future, keeping the grid balanced and maintained may be as easy as it is for you to make that banana smoothie.