Energy use: boring numbers tell the real story much better than sound bites

One danger modern politics and media has produced, is the tendency to convey complex global issues in very short sound bites. While scientists and engineers would know, to understand anything large scale of consequence, one has to look at the underlying numbers.

For example, even simple questions like "how much energy do we exactly use, in which form, for what functions" - the answer is poorly known among most of the public. The problem is, without knowing the answer to this simple question, it is very hard to decode where exactly CO2 emissions (and many other forms of environmental impact) come from and why.

In this second bite, I'll give some answers. To make it a little bit simpler, I'll only give the answer in terms of the USA household average.

1. Electricity

The unit of electricity comes from James Watt.

A light bulb, for example, may be 15 watt (dimmer), or 50 watt (brighter), etc.

There can be many appliances using electricity in a modern home. Some are less power thirsty, some are more, as shown in the table below.

It may be surprising that some physically "little" appliances such as mobile electric stove, tea kettle and hair dryer can be so power thirsty (high watt numbers).

When I was in college in 1992-1997, I lived in the typical old fashioned multi-story college dorm in China. There were no kitchens in these dorms; but some students attempted to use mobile electric stoves to cook some food anyway and often caused a blackout for the entire building because the electricity connection was so weak at the time. Any time it happened, it was almost guaranteed someone would shout in the dark corridors "who is so immoral and using the electric stove again?"

Not all appliances are used continuously all the time in a household. If the uses are averaged out and smoothed out, the typical US household electricity use is as if a 1.22 kw (1220 watt) appliance is used continuously 24/7.

In other words, the average US household monthly electricity use is approximately

1.22 kw * 24 hours/day * 30 days = 880 kw * hour

the average US household monthly electricity use: 

880 kwh        

What is the concept of 880 kwh /month? It turns out to be a very large number for most people in the developing world - for whom the number can be well below 100.

A fun fact: according to some Princeton researchers, the average power use of an adult human brain, is equivalent of ~12 watt.

That is to say, the human brain is a very efficient "appliance" made by the nature.

2. How much more electricity use per US household, if they own two EVs?

First of all, some basic numbers:

In the US, there are approximately

• 330 mln people
• 120 mln household
• 250 mln cars

Typically,

• 2 cars / household
• a typical car drives 1000 miles / month

Today, the great majority of these cars use gasoline. What if every household use two EVs instead?

It turns out, a typical EV can be charged weekly, to store 80 kwh electricity and run 250 miles. In other words, if we assume it is still being driven 1000 miles/month, then it will use about 320 kwh/moth.

Therefore:

If a US household owns two EVs, 
the monthly electricity use will likely be

640 kwh/month        

This is to say, compared to the average monthly use of 880 kwh/month currently, each household will need slightly less than twice the amount of electricity if they own two EVs.

A natural extension of the above, is the following critical factors for more EV adoption (compared to the current 8% EV among new car sales in the US):

• Build more EVs (esp. Lithium batteries)
• Build more fast charging network and home charging
• Provide (A LOT) more electricity - aka “grid capacity expansion”
• Consumer behavior change into EV preference

3. Beyond electricity: the household use of natural gas and gasoline

The average monthly US household use of the three most common forms of energy are:

• Electricity: 880 kwh
• Natural gas: 5500 scf (standard cubic feet)
• Gasoline: 100 gallon

How do we make sense of these vastly different forms of energy and their units (kwh, scf, gallon)?

The problem was solved by someone with the name of James Joule.

1 Joule is the energy of an 1 watt appliance used for 1 second, i.e.

• 1 joule = 1 watt * second

Therefore, with arithmetic, we know

1 kwh = 1000 watt * hour = 1000 watt * 3600 second = 3.6 mln watt*second

or

• 1 kwh = 3.6 mln joules

Similar measurements/calculations have been made for natural gas and gasoline:

• 1 gallon gasoline = 120 mln joules
• 1 scf natural gas = 1 mln joules

With the above, we can calculate the total energy use of a US household per month:

The average US person consumes 85 GJ/year, IN their household. Combined with those OUTSIDE the household (e.g. road construction, cement and fertilizer manufacturing, etc.), and minus the energy wasted due to "machine efficiency", the average US person consumes about 150 GJ/year.

Recall in the previous post, the world average is 34 GJ/person/year - the US uses about 4~5 times of the global average per person (source: Vaclav Smil).

the average US person consumes about 

150 GJ/year of "useful" energy

compared to the global average of 

34 GJ/year        

Another important observation:

Note that the average US household uses per month:

• 3.2 GJ of electricity
• 5.5 GJ of natural gas
• 12 GJ of gasoline

This means on average, the US household uses only about 15% (3.2 GJ electric energy out of 20.7 GJ total energy) of the energy in the form of electricity.

the US household uses only about 

15% of the energy 

in the form of electricity.         

Therefore, there is a significant gap to potential in reducing household CO2 emissions if we can do two things:

• Consume more electricity instead of natural gas and gasoline.
• Generate electricity from more renewable sources (such as solar, wind, hydro, nuclear, etc).

Also let's not forget the third thing we can do:

• Consume less of any forms of energy by being a bit more "frugal" if one chooses to (not passing any judgement here!). For example, smaller houses, less driving, less cold AC in the summer, turn off lights when not using them, and certainly consider not building a giant heated outdoor swimming pool ...

If more people can do the above, it will make a meaningful impact on average household CO2 emissions. There is no reason why most of household energy use cannot be provided by green electricity, if the citizens, the market and government can put their efforts into it. But it also means:

• Can the government create the conditions for building more transmission lines for electricity?
• Will the citizens not say "don't go through my backyard" if a transmission line needs to go through it?
• Will the market enable some reasonable profit for those who wants to build electricity generation?
• Will the minerals supply (such as lithium) be secure and sustainable to provide for EV manufacturing?
• How do the market and the government make sure those land owners who allow their own or neighboring areas to be used for transmission lines, lithium mining, or solar and wind generation, to be properly compensated and the land be used for its intended purposes responsibly?

Everyone has a role and responsibility if we are serious about effecting material changes.

I hope you get a sense of the scale of the energy we use in a household! In the next bite, I'll outline the pros and cons of some of the most common forms of energy.

Appreciate your feedback, and please pass it on to your network!