Saturday, 14 January 2017

So how much energy does a person really use?

This post is a part of the series An Acre of Sunshine.

I've seen quite a number of different ways of calculating real world energy use, and the different techniques certainly have different merits. The simplest of them simply involves an estimate of the total amount of energy used by a group, such as an entire country, divided by the number of individuals in that group. This sort of estimate gives the average amount of energy that is used per person to keep society functioning. It has the big advantage of including all sorts of things that are outside of personal consumption such as the cost of building and maintaining infrastructure, running government, commerce, hospitals, manufacturing, etc., which are not easily visible to the individual. The downside of course is the lack of specificity to a given individual or family; some families may use vastly more or less resources than the average based on their wealth, geography, and their consumption habits.

Another pathway is to try to make specific estimates of a given individual's energy use, which allows a fine-grained analysis of the particulars of each situation. For the questions that prompted me to begin my investigation, it was these personal level energy considerations that I initially thought about. Of course this sort of approach leaves out everything outside of one's direct consumption, and can only measure those things that an individual comes into direct contact with.

One other form of energy that we should account for is the embodied energy in the major 'things' that we own, and there are existing estimates that I can piggy-back on of how much energy is needed to make things as well as how long they last. For my family's energy consumption, I will assume that each of the 4 individuals in my household, including two small children, each count as needing the same amount of energy. This is of course not entirely accurate, but provides a good first approximation.

What I've decided to do here is to follow multiple paths, to start with some rough calculations of the broader-scale averages, and then dig deeply into the situation of the family that I know best, my own. For the personal energy consumption, I need to make some caveats about what I am and am not including in this list. I'll look only at our personal consumption, of food, shelter, transport, etc., but to not even begin to account for the energy that was needed to grow and transport that food, or to refine and ship gasoline to my local station. It is absolutely true that this external energy use will be significantly greater than the amount of energy that reaches the end user. Likewise, for this first pass I will ignore the question of where this energy actually comes from, and discuss the sustainability of my energy use in a later section.

Overall energy usage estimates
In starting to write this section, I realized that I was just dipping a toe into an existing area of sustainability research. For instance, I found an entire book on energy usage by Dr. David MacKay, titled "Sustainable Energy - Without the Hot Air", which digs far deeper than I intend to on power sources and power usage. So rather than reinvent the wheel, I will suggest that you look at this book for a deeper analysis of these average energy estimates. The book is written about Britain, which uses less energy per person than Canada or the US, but other than that the analyses should be much the same. So without further ado, I will give his estimates of energy use per person, of 195 kWh/day for the British, and 250 kWh/day for Americans. Another analysis by the Economist puts together similar figures, giving 242 kWh/day for Canadians, and 233 kWh/day for Americans. It is no big surprise that the North American lifestyle is more energy intensive than the British, if only for the reasons of the larger distances that people must travel and the more severe climates that North Americans must deal with. As mentioned above, a given individual does not have personal control over a lot of this energy use, as it includes their share of the roads, government and commercial buildings, the military, and more.

Household energy use
Statistics Canada data shows that the average detached home in Canada uses about 40 kWh/day per person for such things as heating, cooling, and electrical loads. All home energy uses and sources are lumped together in this estimate, so this number includes the total energy used within the home by electricity, natural gas, heating oil, etc.

For my own family, we actually need to account for the household energy that we use both at our rental in the city as well as our place out at the farm. I have already run some analyses of our household energy use at our country house here, where I showed that this house consumed a total of 15,200 kWh for the year of 2014-15, giving a total of 10.4 kWh/day for each member of my family. This home was intentionally built to be highly efficient, and so it is good to see that this house needs only a fraction of the energy of a typical home.

I've also reviewed the electrical and natural gas bills for our rental in the city, which is a 3 bedroom duplex that we are in about half of the time. For our natural gas bill, we used 1480 cubic meters of natural gas over the last year, which with a bit of calculation puts us at 15318 kWh, or 10.5 kWh/day per person. Our electricity bill shows that we used 7075 kWh over the last year, and that adds up to 4.8 kWh/day per person. The total for this place is then 15.3 kWh/day per person, which is still quite a bit lower than the average. There are at least a couple of contributing factors here. One is that heating loads are much reduced over a typical detached home, because of a shared wall with the neighbor, as well as because of significant updates to the insulation and windows. Second, as we are not there all of the time, many energy uses are reduced when we are away.

Putting this all together, my family used a total of 25.7 kWh/day per person to run our household for all heating, cooling, and electrical loads for the year of 2015. While this is a reduction by almost half over the national average, but I would still like to bring down this number further into the future, or at least shift to most or all renewable energy sources.

Embodied energy in our homes

It takes a lot of energy to build a home, and it is also true that a building doesn't last forever. This means that one should consider the amount of energy that is 'used up' each year due to the slow and steady aging and decay of a home. Some homes may end up lasting hundreds of years if someone takes the time and invests the energy to do regular updates and maintenance, whereas some others, if poorly cared for or if someone decides the land should have a different use, may not even last a decade. Putting these together, it is a reasonable rough assumption to say that a house lasts 100 years. While it is beyond the scope of this piece to go into the ins and outs of calculating this embodied energy, some analyses that I found here, here, and here all point to figures that are in the ballpark of 300,000 kWh for a 2000 square foot home. Spaced out over 100 years for a family of 4, this means that each of the homes that we occupy are consuming 2.1 kWh/day per person for each of the two buildings that we inhabit, due to the slow process of aging, decay, and obsolescence.

Gasoline used in our automobiles
Transportation is another large source of energy consumption. Americans, in 2013, used 392 gallons of gas per capita. Put into our terms, this is 36 kWh/day per person. This is a lot of energy. So how does my own family stack up? We have 2 cars, one that is a 2003, the other is a 2015 model, they both happen to be Subaru Outbacks. Fortunately, my wife has a commute of only 4 miles, and my commute is short enough that I can usually walk or bike. We do often go from the city to the country, but usually take only one car, and the trip is about 50 miles each way. In 2015, we put 8000 miles on the 2015 car, and only 1000 miles on the 2003. While I don't have gas receipts, I can calculate our total energy use based off of the odometers and the published mileage estimates for our cars. Our 2003 Outback should get a combined 22 miles per gallon, while the 2015 car gets 28 miles per gallon. This gives us a total of 331 gallons of gasoline containing 11,155 kWh, or 7.6 kWh/day per member of my family to get us around in our cars. This is again a pretty dramatic reduction over the American per capita use. However, do keep in mind that the overall American figure does include all sorts of commercial traffic, as well as all those poor souls who have daily long commutes in gridlocked traffic to deal with.

The 'typical' American driver drives for 13,476 miles per year. The average gas mileage of the American passenger car fleet is in the same ballpark as our own vehicles, so if our family drove the typical mileage, this would consume 1077 gallons of gas for 35972 kWh, or 24.6 kWh per day per family member.

Embodied Energy in our cars
Just as with homes, cars have a finite lifespan and require considerable energy to manufacture. In looking around, I found various figures (here, here, and here). None of these analyses are for our vehicles in particular, so I will approximate our cars as having about 40,000 kWh of embodied energy in each of them. Considering a car lasts about 15 years and that we have two of them, this means that car aging accounts for about 3.7 kWh/day for each of our family members.

Embodied energy of other possessions
On top of the big items of home and car, we of course have all the other trappings of modern life, including appliances, furniture, electronics, clothing, and more. I wasn't able to easily track down good estimates of the embodied energy of each of these myriad items, so for the sake of argument, I will simply say that we have an amount of 'other stuff' that is about the equivalent of our cars, which a quick run through my imagination suggests is roughly reasonable both to the amount of stuff that we have as well as how long things last. With that estimate, we then have an additional 3.7 kWh/day to account for.

Air travel
In recent years I have heard rumblings about the sheer amount of energy is needed for air travel, and there appears to be a considerable literature on the topic (e.g., here). Fortunately I was able to find a source that lists the FAA estimate of energy expended per passenger mile traveled, at .778 kWh/mile. A look at the US Department of Transportation data shows that there were 607,772,000,000 passenger miles flown domestically in the US in 2014, and there were 318,900,000 Americans at that time. This works out to an average of 1906 miles flown per person in 2014. In energy terms, this is 1483 kWh/year, or 4.1 kWh/day.

A few minutes with our calendar and a map show that my family traveled 2714 miles by air in 2015 with a couple of trips to visit friends and family, which puts us at a total of 8446 kWh for the year, or 5.8 kWh/day per person. Not as much energy as we burned in the car engines, but still quite considerable, and a bit above the national average.

Food is easy to account for if you simply estimate that each member of my family ate the typical recommended 2000 calories per day. Again, this doesn't account for a lot of things, like any food that we may waste, or the fact that my young kids certainly don't eat this much, but it is close enough for our needs. There is also the consideration that meat requires much more energy to produce than fruits, grains, and vegetables, but we will for now leave that outside of our calculations. 2000 calories per day means that my family consumes about 3360 kWh worth of food per year, or 2.3 kWh/day per person.

Table summary
First, keep in mind that the figures for my family and the averages aren't directly comparable, as they were calculated in different ways in the descriptions above. That said, the table above summarizes most of the energy that my family is in direct control of, we get to decide where we live, how much and how we travel, what sorts of goods we buy, etc. It is also easy to see here that of the energy that we have direct control over, most of it is for transportation and home energy needs, and that a smaller proportion is for all of the 'stuff' that we have.

You can also see that the estimate of personal average energy use is 80.5 kWh/day, while the total national energy use is 233 kWh/day. This means that the average individual only has direct control over about 1/3 of the energy that is being used 'on their behalf'. Two thirds of the energy is from all of the infrastructure and services that surround us, the roads, the stores, the hospitals, the police, inputs to food production, all of it. All of this other energy being used on your behalf is a part of what it means to be an American, or a Canadian, or whichever nation you may live in.

A later section of this blog will look more deeply at my ideas about what we could aspire to do in terms both of reducing total energy usage as well as to make the energy that we do use to be truly sustainable in the long term. However, I'll give you a hint of where I'm going, and suggest that I think that my family may over time be able to reduce our energy usage by as much as one half. This still leaves a big job to provide for enough energy to run our busy household. Now we have to hope that sustainable and renewable sources can provide for those needs, and will begin to look at those numbers next.

Family energy use and the amount that our farm would need to produce

So these final numbers in this section are the numbers that we need to shoot for, if we were going to produce enough energy from our farm to provide for my family. My original question was, "Does our farm property produce enough usable energy to sustainably provide for all of my family's energy needs?" In the table above are three different statements of the same information, and all three scales make different kinds of sense. Energy use per day makes sense when thinking about all of the things that we do on a daily bais, from commuting to work, eating meals, watching TV, sleeping, and more. It is a scale that is very human. Then, there is the much larger number of annual energy consumption. This makes sense in light of yearly cycles. Plants only grow in the summer, home heating is only applicable to the winter season, and all of the ups and downs of daily activities and energy use are smoothed out when looking at the course of a full year. Finally, there is average continuous energy use, watts. When you get right down to it, this is still energy use per unit time (joules/second), but we often think of watts as 'instantaneous' usage. 8500 watts, this would be like constantly supplying the needed power for 85 laptops, or 8 drip filter coffee pots, or 2 large domestic hot water tanks. It is a lot of energy, but by no means unimaginable. Following sections will examine how much energy different land use decisions could actually generate.

Previous page: Measuring energy
Next page: Insolation (aka Sunshine)

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