Because I write about infrastructure, and there’s an enormous amount of energy infrastructure that needs to be built for the US to decarbonize, I’m spending an increasingly large amount of time writing about energy and energy-related topics. One challenge I have with this is that thinking about energy doesn’t come especially naturally to me. I have an engineering background, but it’s in structural engineering, which only requires analyzing things that are sitting perfectly still. To improve my thinking around energy and to try and build some better intuitions around it, I put together a little “cheat sheet” of various energy infrastructure facts.

If you’re not a physicist, it’s actually not amazingly straightforward to precisely define energy. Wikipedia describes energy as “the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat and light.” But a reasonable working definition is “the capacity to get stuff done:” move things around, change their state, and so on. Everything we want to do — whether driving to the grocery store, turning iron ore into steel, or boiling a pot of water — requires energy; the more stuff we want to do, the more energy we require.

Per the first law of thermodynamics, we can’t create or destroy energy, but we can change its form. “Energy generation” is something of a misnomer — it really means changing energy from one form to another. A gas turbine, for instance, transforms the chemical energy of natural gas into the kinetic energy of rotating turbine blades. When we’re talking about energy or energy infrastructure, we’re usually talking about either a) moving energy around, b) changing the form it takes, or c) storing it while we wait to do A or B.

For a clearer picture of energy transformation, let’s dive a few miles below the Earth’s surface to a natural gas reservoir beneath the Permian Basin. Natural gas stores energy in chemical bonds between hydrogen and carbon. The gas travels to the surface through a natural gas well and then moves to a processing facility, where contaminants are removed. After processing, the gas moves to temporary storage in a large underground cavern, then travels by pipeline to a natural gas export terminal. In the terminal, the gas is cooled, transformed into liquified natural gas, and loaded onto a liquified natural gas carrier for transport across the Atlantic. When it arrives at its destination terminal, it’s turned back into gas and sent by pipeline to a gas turbine power plant.

In the power plant, the gas is burned in a gas turbine. The burning converts the energy in the chemical bonds into heat and then turns that heat into kinetic energy of the rotating turbine blades. A generator connected to the turbine turns this kinetic energy into electrical energy, which takes the form of electrons moving back and forth in an alternating current. This electrical energy then moves through the transmission and distribution system, its voltage and current being modulated along the way by transformers to minimize distribution losses, until it eventually reaches someone’s home.

Inside the home, the electrical energy flows through the house’s wiring and into a phone charger, where it’s used to force lithium ions from a nickel-magnesium-cobalt cathode through an electrolyte and into a graphite anode, converting the electrical energy into chemical energy. When the phone then gets used, the ions will flow back from the anode to the cathode, creating an electrical current and converting the chemical energy back into electrical energy. This electrical energy then flows through various electrical components and is ultimately discharged as heat.

We’ve just followed a small amount of energy thousands of miles, from deep within a natural gas reservoir to a slightly warmed-up cell phone, and over a dozen transformations.

Of course, there are innumerable paths for a given quantity of energy to take. Natural gas alone could get piped directly to consumers to burn in stoves or water heaters get piped to a chemical factory that uses it to generate heat, or get flared directly at the well, where it turns straight into heat.

The purpose of our energy infrastructure is to create paths for the mass movement of energy and to change its form depending on what makes it easiest to move and what sort of work needs to be done at its destination.

The range of different units we use to quantify energy can make it hard to build intuitions about energy. Different industries and sectors use their measurements of choice: joules, kilowatt-hours, British thermal units, and so on. Sometimes even the same type of device will use different units in different places. In electric vehicles, lithium-ion batteries give their capacities in kilowatt-hours but in smartphones, they use milli-ampere hours. Other times, the energy content will only be implicit: a barrel of oil, a cubic foot of natural gas, and a gallon of gasoline are all volumes of a particular substance, but they’re also acceptable measures of energy content.

One way to help our energy intuition is to do some simple unit conversions and review some reference values of what various amounts of energy represent

The basic metric unit of energy is the joule, which is the amount of energy needed to accelerate a 1-kilogram mass at 1 meter/second^2 over a distance of 1 meter. Wikipedia gives some nice examples of how much energy a joule is:

• The typical energy released as heat by a person at rest every 17 milliseconds

• The kinetic energy of a 2-kilogram mass traveling at 1 meter per second

• The energy required to lift an apple 1 meter

• The heat required to raise the temperature of 0.239 grams of water from 0 °C to 1 °C

• The kinetic energy of a 50 kg human moving very slowly (0.2 m/s or 0.72 km/h)

• The kinetic energy of a 56 g tennis ball moving at 6 m/s (22 km/h)

• The food energy (kcal) is slightly more than half of an ordinary-sized sugar crystal (0.102 mg/crystal)

Related to energy is power, which is the rate at which energy gets transferred. The metric unit of power is the watt, where 1 watt is energy transferred at a rate of 1 joule/second.

One problem with using joules is that a joule is a tiny amount of energy, and using it to describe quantities of energy used in everyday life results in huge figures: burning a gallon of gas releases about 121 million joules. For intuition building, it’s useful to use a unit that doesn’t have so many trailing digits.

One common unit is the kilowatt-hour (kWh), the quantity of energy moved by a 1000-watt power source over an hour (ie: 1000 joules a second, or 3.6 million joules). A kilowatt-hour is an aesthetically unpleasing unit since it defines energy in terms of power, which is itself defined in terms of energy — but it turns out to be a nice unit for working with sort of “everyday” quantities of energy. The numbers ar