Shift Key – “What Is a Watt?”
Podcast: Shift Key with Robinson Meyer and Jesse Jenkins | Host: Heatmap News
Date: July 2, 2025
Overview
In this launch of "Shift Key Summer School," Heatmap News Executive Editor Robinson Meyer and Princeton energy systems expert Jesse Jenkins break down the core concepts that underpin the energy transition: what energy is, how it’s measured, and how to make sense of commonly used energy and power units. The discussion serves as a back-to-basics explainer for anyone who encounters kilowatts, megawatts, or gigawatts in the news, policy, or daily life—helping listeners orient themselves as the world shifts away from fossil fuels. Throughout, Jenkins answers fundamental questions posed by Meyer and dispels confusion between terms like power and energy, anchoring each with tangible analogies.
Key Discussion Points and Insights
1. Defining Energy and the Joule
- Energy’s Many Forms: Jenkins explains that energy can be confusing since it comes in many forms and units, but in all cases, energy is “the ability to do work” (03:07).
- The Joule Explained:
- Joule is the SI unit for energy, defined as moving 1 kilogram over 1 meter with an acceleration of 1 meter per second squared.
- Jenkins offers a relatable analogy:
“If you want to throw your [1 kg] laptop over a meter, accelerating at a pace of 1 meter per second squared, that's about a joule.” (05:40, Jenkins)
- Joules Are Small: Everyday activities use far more than a single joule, highlighting how small this unit actually is.
2. Power vs. Energy: Watts, Watt-Hours, and Analogies
- Energy Is Quantity; Power Is Rate:
“If energy is a quantity, it’s something that we’re consuming or producing... Power is the rate at which we’re doing that.” (05:40, Jenkins)
- Watts as Rate: A watt measures the rate of energy use—one joule per second.
- Bathtub Analogy:
“The amount of water in the tub, the volume, that's the energy; and the size of the faucet, or the rate at which the faucet is adding water, that’s power.” (05:40, Jenkins)
- Frequently Confused Terms: The hosts highlight how, especially in media, ‘power’ and ‘energy’ are often used interchangeably—but they shouldn’t be.
“Especially writing about the power grid, referring to electricity, energy and power... are basically treated as interchangeable, even though from a physics perspective, they aren’t.” (16:02, Meyer)
3. Making Energy Relatable: Calories, Kilowatt-Hours, and Human Consumption
- Food energy:
“If you think about people eating 2,000 calories a day, that means the human body’s expending like 8.3 million joules a day.” (14:09, Meyer)
- Jenkins translates this for household energy use:
“A typical household in the US...consumes a little bit over a kilowatt of average power... That’s about 28, 29 kilowatt hours a day…” (14:47, Jenkins)
- Comparison:
“Weird how a house is using 10 times as much energy as your body is at any through the day.” (15:17, Meyer)
4. Energy Unit Conversions and Contexts
- Joules, Calories, BTUs:
- The show describes how energy units proliferate—joules (physics), calories (food), BTUs (heating).
“It can come in so many different forms, and we often use different units when we’re talking about a different form.” (11:31, Jenkins)
- Physical Examples:
- 1 calorie ≈ 4.186 joules
- Gallon of gasoline ≈ 40.5 kilowatt-hours
- “A tank of gas, 10 gallons...400ish kilowatt hours. That’s actually quite a lot. This is why fossil fuels are so amazing.” (25:58, Jenkins)
5. Understanding Kilowatts, Megawatts, Gigawatts, and Terawatts
- Household and Device Scale:
- Light bulb (incandescent): ~60W; LED: ~10W (23:50, Meyer)
- Laptop: ~60 watts; Air conditioner overnight: ~4 kWh
- EV Charging: “EVs are the scale of kilowatts.” (24:37, Jenkins)
- Power Plants and Grids:
- “A large nuclear reactor is typically on the scale of about a gigawatt or a billion watts.” (26:32, Jenkins)
- National US electricity consumption: ~4,200 TWh annually
- Memorable Visual: Empire Wind offshore project = 810 MW (30:03, Meyer)
- Context Matters:
“[When] talking about renewables...we’re usually talking about in the world of megawatts … Only when you’re talking about these giant generating sites ... then we’re talking about gigawatts.” (28:20, Meyer)
6. Beware Conversions to “Households Powered”
- Ambiguity and Regional Variation:
- Many projects are described as “powering X homes,” but this can be misleading due to embedded assumptions: capacity factor, average home use, and regional consumption.
“There’s some embedded assumptions in there. The most important of which is the average power output of the facility versus its maximum and then what you assume for how much electricity a household uses.” (32:24, Jenkins)
- Rule of Thumb:
- 1 GW of average consumption ≈ 800,000 homes (two people per home = 1.5 million people)
- Jenkins walks through how to do the calculation at (32:35)
- Sector Usage: Only about a third of US electricity goes to residential; the rest goes to commercial and industrial uses.
“Just over a third of US electricity production goes to residential usage … about 35% to commercial buildings … about 26% to industry.” (35:01, Jenkins)
7. Average, Maximum, and Annual Use
- Critical Distinctions:
“When you’re looking at what energy use is for a geographic area or for a system, you have to be careful between maximum use, average use, [and] annual use… you just have to be careful that you don’t allide them.” (36:17, Meyer)
- Jenkins underscores the importance of not conflating these, as reporters sometimes do.
8. End-Use Breakdown in Homes
- Where the Electricity Goes:
- “There are just a few really large consumers of electricity in a typical home. That is space heating and cooling... water heating ... then refrigerators ... EVs would be on the scale of your heating and cooling, too. Lighting used to be part ... but it’s not anymore because of LEDs.” (37:07, Jenkins)
Notable Quotes & Memorable Moments
-
On How Energy Is Experienced:
“Unless you’re shocking yourself, you’re not really feeling electricity on a regular basis, right?”
(03:07, Jenkins) -
On Energy vs. Power:
“Power is the rate at which that energy is consumed or supplied ... If you have a 10 watt bulb on for an hour, that’s 10 watt hours.”
(09:12, Jenkins) -
On Why Horsepower Is Weird:
“I have questions about this horse.”
(09:25, Jenkins, on using horsepower instead of watts to rate engines) -
On Physical Intuition:
“A gallon of gasoline contains about 40 and a half kilowatt hours … This is why fossil fuels are so amazing. You can fill 10 gallons ... and have an enormous amount of energy.”
(25:58, Jenkins) -
On 'Homes Powered' Calculations:
“I think the best thing to do is just get a feel for the round numbers … several hundred thousand homes … That’s probably as accurate as we can get in these kinds of conversions.”
(33:59, Jenkins) -
On the Evolution of Grid Demand:
“The fact that we’ve now basically finished converting most light bulbs ... to LEDs and [we] are still adding new capacity—no wonder demand growth is back.”
(23:50, Meyer)
Timestamps for Major Segments
- Intro & Purpose of ‘Summer School’: 00:00 – 03:07
- What Is Energy, Joules Explained: 03:07 – 05:40
- Power vs. Energy; Watts, Bathtub Analogy: 05:40 – 09:12
- Energy in Daily Life; Calories, Kilowatt-Hours: 13:38 – 16:53
- Units in Reporting, Power vs. Energy: 16:53 – 18:38
- Scale: Kilowatt, Megawatt, Gigawatt, Terawatt: 18:38 – 27:58
- Case Studies: Solar, Wind, Nuclear: 28:04 – 32:24
- ‘Homes Powered’ Conversions and Caveats: 32:24 – 36:17
- Who Uses Electricity? Economic Sectors: 35:01 – 36:17
- Peak/Average/Annual Use Distinctions: 36:17 – 37:07
- Household Device Consumption: 37:07 – 37:56
- Wrap & Preview of Next Episode: 37:56 – End
Conclusion
This episode serves as a clear, jargon-busting primer for anyone wanting to understand the numbers behind the energy headlines—from the basic definitions of joules and watts, to what it means for a wind farm to power “300,000 homes.” Robinson’s questions and Jesse’s explanations are relatable and candid, equipping listeners to make sense of the torrent of energy metrics driving the energy transition debate. Next week, the focus will turn to how various power plants actually work.