How much energy is lost along the way as electricity travels from a power plant to the plug in your home? This question comes from Jim Barlow, a Wyoming architect, through our IE Questions project.
To find the answer, we need to break it out step by step: first turning raw materials into electricity, next moving that electricity to your neighborhood, and finally sending that electricity through the walls of your home to your outlet.
Step 1: Making Electricity
Power plants – coal, natural gas, petroleum or nuclear – work on the same general principle. Energy-dense stuff is burned to release heat, which boils water into steam, which spins a turbine, which generates electricity. The thermodynamic limits of this process (“Damn that rising entropy!”) mean only two-thirds of the energy in the raw materials actually make it onto the grid in the form of electricity.
Energy lost in power plants: About 65%, or 22 quadrillion Btus in the U.S. in 2013
This graph shows the heating efficiency of different types of power plants. All types of plants have roughly the same efficiency, with the exception of natural gas, which has seen recent improvements in efficiency in recent years with the addition of combined cycle plants. (The coal efficiency line is nearly identical with nuclear energy, and is swallowed up in the purple).
Step 2: Moving Electricity – Transmission and Distribution
Most of us don’t live right next to a power plant. So we somehow have to get electricity to our homes. This sounds like a job for powerlines.
Transmission
First, electricity travels on long-distance, high-voltage transmission lines, often miles and miles across country. The voltage in these lines can be hundreds of thousands of volts. You don’t want to mess with these lines.
Why so much voltage? To answer this question, we need to review some high school physics, namely Ohm’s law. Ohm’s law describes how the amount of power in electricity and its characteristics – voltage, current and resistance – are related. It boils down to this: Losses scale with the square of a wire’s current. That square factor means a tiny jump in current can cause a big bump in losses. Keeping voltage high lets us keep current, and losses, low. (For history nerds: This is why AC won the battle of the currents. Thanks, George Westinghouse.)
Jordan Wirfs-Brock / Inside Energy
The sagginess of power lines is actually the limiting factor in their design. Engineers have to make sure they don’t get too close to trees and buildings.
When that electricity is lost, where does it go? Heat. Electrons moving back and forth crash into each other, and those collisions warm up power lines and the air around them.
You can actually hear those losses: That crackling sound when you stand under a transmission tower is lost electricity. You can see the losses, too: Notice how power lines sag in the middle? Some of that’s gravity. But the rest are electrical losses. Heat, like the kind from lost electricity, makes metal power lines expand. When they do, they sag. Powerlines are saggier, and leakier, on hot days.
Distribution
High-voltage transmission lines are big, tall, expensive, and potentially dangerous so we only use them when electricity needs to travel long distances. At substations near your neighborhood, electricity is stepped down onto smaller, lower-voltage power lines – the kind on wooden poles. Now we’re talking tens of thousands of volts. Next, transformers (the can-shaped things sitting on those poles) step the voltage down even more, to 120 volts, to make it safe to enter your house.
Generally, smaller power lines mean bigger relative losses. So even though electricity may travel much farther on high-voltage transmission lines – dozens or hundreds of miles – losses are low, around two percent. And though your electricity may travel a few miles or less on low-voltage distribution lines, losses are high, around four percent.
Energy lost in transmission and distribution: About 6% – 2% in transmission and 4% in distribution – or 69 trillion Btus in the U.S. in 2013
Jordan Wirfs-Brock
This graph shows the average percent of electricity lost during transmission and distribution, by state, from 1990 to 2013. With the exception of Idaho, the states with the lowest losses are all rural, and the states with the highest losses are all densely populated.
Fun fact: Transmission and distribution losses tend to be lower in rural states like Wyoming and North Dakota. Why? Less densely populated states have more high-voltage, low-loss transmission lines and fewer lower-voltage, high-loss distribution lines. Explore the transmission and distribution losses in your state on our interactive graphic.
Transmission and distribution losses vary country to country as well. Some countries, like India, have losses pushing 30 percent. Often, this is due to electricity thieves.
Step 3: Using Electricity Inside Your Home
Utility companies meticulously measure losses from the power plant to your meter. They have to, because every bit they lose eats into their bottom line. But once you’ve purchased electricity and it enters your home, we lose track of the losses.
Your house, and the wires inside your walls, are kind of a black box, and figuring how much electricity gets lost – electricity that you’ve already paid for – is tricky. If you want to find out how much electricity gets lost in your home you’ll either need to estimate it using a circuit diagram of your house or measure it by putting meters on all of your appliances. Are you an energy wonk attempting this? Let us know, we’d love to hear from you!
Energy lost in the wiring inside your walls: We don’t know! It could be negligible, or it could be another few percent.
The Future Of Transmission and Distribution Losses
Grid engineers are working on technologies like superconducting materials that could essentially reduce electricity transmission and distribution losses to zero. But for now, the cost of these technologies is much higher than the money lost by utility companies through their existing hot, leaky power lines.
A more economical solution to reduce transmission and distribution losses is to change how and when we use power. Losses aren’t a constant quantity. They change every instant based on things like the weather and power consumption. When demand is high, like when we’re all running our ACs on hot summer days, losses are higher. When demand is low, like in the middle of the night, losses are lower. Utilities are experimenting with ways to spread out electricity use more evenly to minimize losses.
The same principle applies to your house, which is basically your own personal grid. You can reduce losses in your home by spreading out your electricity use evenly throughout the day, instead of running all your appliances at once.
Adding Up The Losses
- Generating electricity, we lost 22 quadrillion Btu from coal, natural gas, nuclear and petroleum power plants in 2013 in the U.S. – that’s more than the energy in all the gasoline we use in a given year.
- Moving electricity from plants to homes and businesses on the transmission and distribution grid, we lost 69 trillion Btu in 2013 – that’s about how much energy Americans use drying our clothes every year.
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