If I were a lightbulb, I’d be 4,200 watts*
(7) CommentsBy request, this is an attempt to make electricity, power and energy less abstract.
Does this Technical Definition of Watts, Joules, kW h work for you?
The kilowatt hour (kW h) is a unit of energy, equal to 1000 watt hours or 3.6 megajoules.
The standard unit of energy in the International System of Units (SI) is the joule (J), equal to one watt second.
Inversely, one watt is equal to 1 J/s.
From the top: The watt is 1 J/s, so a watt hour is one watt for an hour. An hour has 3600 seconds, so a watt hour has 3600 Joules. Thus a kilowatt hour is a thousand of those = 3,600,000 Joules = 3.6 megajoules.
Is that clear? No? Can’t relate it to your own life? OK, try this.
Be the lightbulb
Imagine that you are a giant lightbulb. You and all the appliances and heating systems in your home have merged into one giant heat lamp/light bulb. You are now Joe Lightbulb, burning away, day and night.
How many watts are you, Joe?
Before you can answer this, you need to know one thing:
The terms “power” and “energy” have different meanings.
Power is the rating that tells you how much energy can be consumed. You measure power in watts. All your appliances and light bulbs are rated to certain watts: a 1500 watt heater, a 60 watt light bulb.
The 60 watt light bulb is 60 watts, whether it is on or off. It’s not about consumption.
Energy, on the other hand, is about consumption.
Energy use kicks in once you turn the lightbulb on. Energy consumption is the watts multiplied by time. Your utility bill tells you how much energy you consumed in kWh’s.
Using a 60 watt light bulb for 1 hour consumes 60 watt hours, aka 0.06 kilowatt hours of electricity.
Using a 60 watt light bulb for 1000 hours consumes 60,000 watt hours, aka 60 kilowatt hours of electricity.
Got it? Great! (If not, leave a comment).
Calculating your wattage from your Utility Bill
So, here you are, Joe Lightbulb. How many watts are you? You can calculate this by figuring out how much energy you consume every day (your average kWh of consumption in a day) and dividing by 24 hours. Luckily, your utility company has done a lot of this work for you.
Electricity - 500 watts
My utility bill from PSE&G has an “Average daily electricity use” chart which shows that, on average, I consume(d) around 12 kWh’s of electricity every day in December.
12 kWh = 12 kilowatt hours = 12,000 watt hours.
What is 12,000 watt hours? One way to look at it is to imagine that I burned a 100 watt lightbulb. I’d have to burn that bulb - let’s see, 12,000 watt hours divided by a 100 watts = 120 hours. There you have it. 12 kWh means I can burn a 100 watt light bulb for 120 hours.
But I’m not burning some abstract 100 watt lightbulb. I’m the lightbulb, and I’m going to burn through 12,000 watt hours in one day - in 24 hours. So that’s 12,000 watt hours divided by 24 hours gives 500 watts.
Thus, if I were a lightbulb, I’d be 500 watts.
But wait! I consume more energy than that. Let’s add in the gas portion of the bill.
Gas - 3,700 watts
Gas consumption on my utility bill is measured in Therms. A Therm is 100,000 BTUs. A BTU is a ridiculous unit of measure.
a traditional unit of energy equal to about 1 055.05585 joules. It is approximately the amount of energy needed to heat 1 pound (0.454 kg) of water 1 °F (0.556 °C).
Pounds? Fahrenheit? You’re kidding me.
No, I guess not. So a BTU = 1,055.05585 joules, and a Joule is also 3,600 Wh. In order to convert from BTUs to watt hours, you multiply the BTUs by (1,055.05585 divided by 3,600) which is 0.293071 (seriously).
According to my bill, in January, our household used 8 Therms of energy a day, and in the summer, it was less than 0.5 Therms. It averages out to a daily energy use of around 3 therms per day (very rough averaging here).
3 therms x 100,000 BTUs per Therm = 300,000 BTUs.
Multiply that by 0.293071 Wh per BTU to get 87,951 watt hours. Then we divide by the 24 hours in the day to get 3,663 watts. Let’s round that up to 3700.
So, if I were a lightbulb, I’d be 3,700 plus 500 = 4,200 watts = 4.2 kW.
Peak power - 10 kW
Of course, my electrical consumption is not constant. The 12kWh of electrical energy I use throughout the average December day is used in various appliances and light fixtures. Between the 60 watt light bulbs, the 1500 watt space heater, the computer, printer, refrigerator, microwave - these things add up and are used or not used at various times of the day, going on and off. None of this makes that much difference compared to space heating issues, so we won’t worry about it.
Instead, let’s look at heat. In January, I’m cooking at 8 Therms a day. That takes a power equivalent of 9,769 watts - round up to 10 kW.
Adding gas to electricity, at peak power I could be running at 10,500 watts.
What a big light bulb I am! Does that make me a kleig light?
* Disclaimer
If I were a lightbulb, on average, I’d be a 4,200 watt bulb. At peak demand, I’d morph like the hulk into a 10,000 watt bulb.
Then again, I haven’t added up all my other energy consumption activity, so this number is low. According to some reports, the average New Jersey resident runs at least 10,000 watts on average (see below). That’s 10 kW every moment of every day - not just at some peaks.
For a more thorough estimate of total wattage we’d need the following:
- Calculate your electricity and gas consumption as we’ve just done here
- Divide by the number of people in the household. (Hey! I forgot to do this! Just dropped my watts in half!)
- Add in transportation energy - how to calculate? This requires an algorithm, a function of gallons or miles or mode of transport…
- Add in your share of societal and commercial energy use. The energy that goes into agriculture, infrastructure, the products you consume, the places you work at, government offices, services you use.
New Jersey residents each consume an average of 300 to 374 million BTUs of energy a year. New Yorkers consume 224 million BTUs a year each. Their number is lower due to public transport use.
Because I don’t use a car much, I’ll take the low end for a New Jersey resident. 300 million BTUs x 0.293071 Wh per BTU = 87,921 kWh per year. Divide that by 365 days per year and 24 hours per day to get 10 kW (that is, 10,000 watts) - as an average.
It’s all crudely rounded. To get an actual number for each individual would be pretty tough. One of these days we may have apps that keep track of our watts.
5 MW Focus Fusion Reactor
If LPP shows proof of concept for the Focus Fusion reactor, they envision developing easily distributed 5 megawatt power plants. That’s 5 million watts or 5,000 kW. Now that you know the average NJ rate is 10 kW, one plant could handle the complete energy needs of 500 households. Does that sound right to you?
It wouldn’t quite work out that way. The power plants would be hooked up to thousands of homes and businesses because they supply electricity. At this point, most homes only have some of their energy use coming from electricity (500 watts for me, as noted above). It will take quite a while before heating and transport switch over to electricity rather than gas or oil.
The continuing adventures of Joe Lightbulb
Now that we’re starting to get a sense of Joe Lightbulb and his energy needs, it would be fun to do an animation with him. He could be a useful character to explain energy concepts with. This essay might work better as an animation.
FoFu-1 Design
Switches and Sparkplugs
Comments
For a more in depth discussion, start a thread in the forums.20MW? Wasn’t the goal a 5MW plant of FoFu? Of do you mean simply put 4 FoFu together?
“That’s 5 million watts or 5,000 kW. Now that you know the average NJ rate is 10 kW, one plant could handle the complete energy needs of 500 households.”
Nope. Persons, not households.
My handy-dandy converter software tells me a Therm = 29.3 kwh. Much easier.
Interesting historical note: When James Watt was first promoting his steam engines to mine owners, he set the unit “horsepower” to be about twice what actual horses put out. Then when the miner guys tested and found this out, they would think they were pulling a fast one on him, and snap them up. It seems to have worked.
Yes Brian. I could have kept this a lot simpler, stuck with the New Jersey average. Not brought up my utility bill. I say “households” because it occurs to me that my heating bills can be divided by myself and house-mates. So only half of that 4200 watts is on me. That’s 2,100 watts. So I need about 8000 watts more to cover my average individual consumption in New Jersey. And that means there’s a lot of unaccounted for energy consumption for my personal number.
So now I’m wondering where the 10,000 watts aka 300 million BTU’s per person estimate comes from, how much of that really belongs to me, and how much is a societal average on something that I don’t even use. It’s like being at a restaurant where you all agree to split the bill, but you just got an apple pie and dude over there is eating lobster and libations.
Writing this post makes me long for a better audit of these numbers. Is part of the problem that the utility companies charge you for energy delivered to your home, but the power plant itself is losing a lot of energy from inefficiency and for every Joule you get, they use up a lot more, say by burning coal and converting it to electricity?
Well, those losses are certainly priced in. Their amount probably varies in a fairly wide range, as plant efficiencies differ. Same with transmission; depends how close you are to the (a) source!
I’m sure they are priced in. At the same time, the meter on the house is reading just what comes into the house, correct? And it reads 4,200 watts for the household, not individuals. But per statistics, we’re burning at 10,000 to 15,000 watts as individuals. I’m curious as to how much of those additional watts are from power plant inefficiency, and how much is other stuff: my share of commercial space heating costs; of office and place of business heating; etc.
It would be cool if the bills gave you that additional information. “You live ___ miles from the power source. Transmission line loss was ___%. Your rate in this area is thus ____.
I’m not all that sure what it would achieve.
Anyhow, FF resolves all those problems.
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