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Tom Murphy

Tom Murphy

Tom is an associate professor of physics at the University of California, San Diego. This post originally appeared on Tom's blog Do the Math.

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A Few Easy Pointers to Increase our Energy Efficiency

I have described in a series of posts the efforts my wife and I have made to reduce our energy footprint on a number of fronts. The motivation stems from our perception that the path we are on is not sustainable. Our response has been to pluck the low-hanging fruit, demonstrating to ourselves that we can live a “normal” life using far less energy than we once did. We are by no means gold medalists in this effort, but our savings have nonetheless been substantial. Now we shift the burden off of ourselves, and onto our neighbours. You don’t have to run faster than the bear—just faster than the other guy. In this post, I summarize our savings relative to the national average, add a few more tidbits not previously covered, put the savings in context, and muse about ways to extend the reach of such efforts.

Setting the Scale

The U.S. energy budget—accounting for nearly a quarter of the energy consumption of the entire world—is about 100 quadrillion Btu (“Quads”, or QBtu) per year. A Btu is 1055 Joules, so that 100 QBtu/yr works out to about 10,000 W per person of continuous use, 24/7 (1 Watt is one Joule per second). That’s a nice round number worth committing to memory.

The 100 QBtu number refers to primary energy—before accounting for substantial efficiency losses in power plants, car engines, etc. It’s the raw (usually thermal) energy of the resource.

At 10 kW, each person therefore racks up about 240 kWh of energy in the course of each 24 hour day. We’ll cast everything into individual—rather than household—terms, so it is helpful to know that the 309 million people in the U.S. (2010 numbers) occupy 114 million households, for an average of 2.7 people per household.

I will evaluate the degree to which I have impacted my personal energy consumption by behavioural choices, and compare this to the full scale to see what sort of total effect I am having. Most of my energy statistics are derived from the 2010 Annual Energy Review put out by the U.S. Energy Information Agency.

I should say up front that San Diego offers some energy advantage over the rest of the country in relation to heating and cooling. But as I have shown in previous posts on natural gas and electricity use, I tend to tread a factor of five lighter than comparable residences in my area.

Household Savings

Let’s first look at the items directly associated with households, or residences. These represent direct purchases of energy, and are the easiest to tally.

U.S. residences used 4.95 QBtu of delivered electricity in 2010, at an overall efficiency of 37%. So each household claims 94 kWh of thermal input per day, corresponding to 35 kWh delivered. Per person, this is—coincidentally—also 35 kWh per day. In the second numerical coincidence of the paragraph, residences grabbed 37% of the total share of electricity in 2010.

Our own household use of utility electricity over the last year (750 kWh) averages 1.0 kWh per day per person, requiring 2.8 kWh of thermal energy each day.
So count me in for a daily 32 kWh of savings over the American average.

Man, the numerical coincidences just don’t stop! U.S. Residences used 4.95 trillion cubic feet of natural gas in 2010, or 20.5% of the total amount consumed. One hundred cubic feet delivers 1.02 Therms of energy, converting to 29.9 kWh. This makes for a daily 35 kWh per household, or 13 kWh per day per person.

Our household’s annual use of natural gas (66 Therms) works out to 2.6 kWh per day for each of us.
Add another 10 kWh of daily savings to the pile.

Don’t Touch My Shower!
As an aside, our main route to reducing natural gas usage has been by turning our thermostat down to 55°F (12°C), as described earlier. But the gas consumption in our house shot up in the Fall of 2010 when we had a house-sitter. It appears that this was notin the form of home heating, but rather in the form of hot water use. The fact that one person could more than double the gas consumption of two people in the hot water domain is noteworthy. In my quest to reduce energy, I have discovered that:

1.    I only need to shower about 3 times a week without anybody (including myself) noticing ill effect;
2.    I don’t need running water for much of the time I am in the shower;
3.    I don’t need tremendous flow;
4.    I don’t need piping hot water (just warm will do—especially in summer); and
5.    showers need not take very long, given focused effort.

Showers in our house routinely use something like 5 gallons of water (not all of this from the hot water heater, given mixing), and I know I could cut even this down by a lot if needed.

When I have queried students in energy/environment classes at UCSD about which of the five modifications above they would accept in their own lives, including a “none of the above” option, “none of the above” was the overwhelming favourite. When removing this option, I found that students would reluctantly acquiesce to showering less frequently—but few were willing to modify the other parameters of the experience. The message was clear: “Don’t mess with my shower habits—I like my showers long and hot, with water running full-blast all the time, even when I step aside and let it hit the floor while soaping up.” The barriers to personal change are rigid.

The average American household uses about 1050 gallons of gasoline each year to move their personal vehicles around. At 36.6 kWh per gallon, this comes to 105 kWh/day of energy per household, or 39 kWh/day per person.

In my household, we average 400 gallons of gasoline per year over the last four years, including a few atypical cross-country trips. This puts us at 20 kWh/day each. Even though most of this happens under my wife’s right foot, it is only fair that we split it evenly. Joint bank account, joint taxes, joint gasoline.

Compared to the 39 kWh/day average, I collect another 19 kWh per day of personal energy savings.

The only other major energy resources households may consume are fuel oil for heating and liquid propane mostly for rural applications. The U.S. used 0.55 million barrels per day of fuel oil in 2010, calculating to 2.7 kWh per person per day of energy expenditure.  Propane accounts for 1.139 million barrels per day of oil equivalent, resulting in 5.7 kWh/day.

Because I don’t take part in either of these resource, I’ll add 8.4 kWh to my pile of daily savings.

The typical American directly uses 95 kWh/day of energy supply in residential/personal applications. For myself, these same sources total 25 kWh/day (20 of which comes from gasoline!). Residentially speaking, then, I operate at 27% of the national average. Personal transportation is my undoing, for sure—even if it is half the national average.

Outside the Home

Recall that the average American lays claim to 10 kW of continuous power, or 240 kWh per day. Yet in the home, we only accumulated 95 kWh in our sum. That’s just shy of 40%, of the total. So if I did nothing else on the energy saving front, I would have to swallow my citizen’s claim to the remaining 145 kWh/day, bringing my total to 170 kWh/day, and therefore 71% of the average. That’s still a decent reduction, but not as dramatic as I would like.

What is all this other activity, and why should I have to lay claim to it?

Well, the bulk of our energy expenditures are not under our direct control, but rather support the economy in which we participate. Industries mine raw materials, transport them to factories, turn them into consumer goods, and ship them to stores—every step demanding energy, including the stores themselves. The government upon which we rely consumes energy to conduct its business, provide defense, and build/maintain infrastructure. Much of the demand is structural, determined by collective choices. Our jobs are a part of this collective demand, generally based on priorities within our society (although these priorities are skewed by aggressive advertising campaigns). As individuals, our control over such factors tends to be weak. But we’re all in the boat together, so we can’t easily release ourselves from claims to energy consumption outside of our personal realms.
We can, however, influence matters as consumers—in some domains more directly than in others. Depending on what and how much we buy, where and how often we travel, and what we do for entertainment, we can indeed shed responsibility for some portion of energy expenditures in the wider world. We can also try to steer society into less consumptive modes of operation. (See the excellent Story of Stuff video.)

For example, the U.S. spends about 11% of its total energy flow on the business of food (outside of refrigeration and cooking expenditures in the home). That’s about 27 kWh/day per person. Some foods are more energy-intensive than others. The way our food industry has evolved, we spend ten times as much energy producing our food as that same food provides to our bodies. Meats are particularly energy-costly, given the methods of meat production that prevail today. By modifying dietary choices so that meat is an occasional treat (or garnish) rather than a staple, we can change the amount of energy invested in food by something like a factor of two. I estimate my own dietary choices to save something like 10 kWh/day on my behalf.

There are two quick-and-dirty methods for estimating the energy content of consumer goods. One simple way is to guess that the energy value is approximately equal to the equivalent weight (or mass) of the product in the form of gasoline—working out to about 40 MJ/kg, or about 11 kWh/kg. This is a very approximate scheme, but can sometimes be helpful if you have no other handle on the problem. It works well for most metals and plastics (although aluminium is over 4× more), but many building materials (glorified dirt/rock) come in much lower. Intricate items, like automobiles, laptops, and iGadgets may take at least an order-of-magnitude more energy than the gasoline-weight-equivalent estimate.

The other—arguably more reliable—handle we can employ is to note that energy accounts for something in the neighbourhood of 5–10% of GDP (on the higher end, recently). So we can divide the purchase price of an item by ten, and relate this to the cost of industrial energy (say $0.05/kWh) to guess that each dollar spent on an item requires 2 kWh of energy investment. Again, it’s not a universal law, but might get you in the ballpark.

Let’s test this on a few cases. A new car might have a mass of 1000 kg and cost $25,000. The two methods would suggest an energy cost of 1,100 kWh and 50,000 kWh, respectively. Because it is an intricate device, we should lean toward the higher number, one study suggests 75,000 kWh is about right). A large flat-panel television may have a mass of 20 kg and cost $1000. We’d compute 220 kWh and 2000 kWh for the two methods, again favouring the higher price. How about a ladder from Home Depot: mass of 15 kg, costing $60. We get 165 kWh and 120 kWh for the two methods, respectively. The two estimates reach parity when the item costs $5.5/kg, or about $2.50/lb.

The whole point of these estimates is that we can reduce our energy footprint by deciding to buy less stuff. Make things last longer. Repair when possible. Forgo some pleasures. Adopt a gift-draw for occasions like Christmas, rather than buying something for everyone. For every $1000 not spent on a consumer purchase, you’ll save about 2000 kWh. So each $1000/year you don’t spend turns into about 5 kWh/day that you do not incur.

It is hard to assess something you don’t do. I can’t seem to find the receipts for all those things I did not purchase! But I know my energy-influenced attitudes have resulted in less material expenditure than I witness in my peers. I’m going to guess I get another10 kWh/day out of this mode, at least.

Out of the total petroleum flow, 1.42 million barrels per day went to jet fuel in 2010 in the U.S. Each person’s share works out to 7 kWh/day, amounting to about 3000 air miles per year (figured at 40 passenger-miles per gallon). This is approximately what I rack up for personal travel (mostly due to familial dispersion), so I get no points on this front. In fact, considering that much of the aggregate is for business rather than personal travel, and I lump this into the collective societal mode, perhaps I should take a 10 kWh/day hit for the personal travel I do perform.

The Net Effect

I can likely justify shaving off a bit more in the way of energy expenditures tied to personal choices. My energy-conscious mentality carries over into reducing energy demands imposed by my profession. So I could easily believe that I am down to 150 kWh/day by my choices and actions. That’s 63% of the average. I’d like to be able to claim I’m at 50%, but I probably can’t stretch that far, and this is an arbitrary target anyway.

To reiterate: the bulk of energy expenditure on our behalves is beyond our direct and immediate control. We make choices as a collective that influence us all. I can’t deny my share of that responsibility, even if I don’t agree with all the choices we make.

Meanwhile, I can at least exercise substantial control of my personal share (for which I operate at about a quarter of the average). And I can share these concepts with a broader audience and maybe have some indirect impact that way. Hmmm. Will I get credit, or will you, for any energy savings you employ as a result of reading Do the Math? No question: it belongs to you!


I can also advocate for a society that is less dependent on energy-intensive activities. When we collectively realize that we need to invest in a new energy infrastructure, we will need a fresh supply of energy to pull it off—threatening to tip us into the Energy Trap. Shaving personal energy use could be a potent tool.

In the end, it’s more important for me to know that we can trim energy use by a large factor while still engaging in important pursuits than it is that we all do reduce our energy right now. Of course, immediate widespread reduction would be my preference, being the most conservative approach to the possible energy precipice ahead. We could let off the gas and take stock of our future rather than barrel ahead under the assumption that our energy resources are guaranteed. Being wrong on the cornucopian gamble could be far more ruinous than easing off ahead of time.

Can I Blame the Neighbours?

This brings me to tactics. How might we accomplish a ramp-down in energy, in a time of need? Even if just on the household front, I have demonstrated that it’s possible to reduce one’s total energy share by significant amounts (of order 30%) without even touching the aggregate system. That’s more than chump-change.

But how does this sort of thing grow large enough to have an impact? How would we achieve buy-in? No one wants to feel like they are part of the problem. We instinctively become defensive. And my standing here parading my own accomplishments in this realm may in fact have a souring effect on people: “look at this goodie-two-shoes, boasting of his righteous ways.” So I have an idea that, admittedly, is not all that well thought out yet.

Rather than tell people that they use too much energy (which they will A: not want to hear; B: deny; or C: rationalize), maybe we can make the case that their neighbours use too much energy. People are much less likely to object to that. They may not like the neighbours all that much anyway. But if enough people are hearing this message, everyone is someone’s neighbour. And to the extent that people are willing to buy the message, they internalize a value for lowering energy without ever feeling personally challenged. Get it? We are the neighbours, but we never feel that way.

So if we start noticing instances of neighbours using more energy than we think they should, we’re more likely to tone down similar activities that we might otherwise do. Of course this scheme only works if the larger context suggests energy scarcity. We’re not there right now. But perhaps we are inching (ahem, centimetering) our way toward such a condition.

In much the same way, racism is well-understood today to be shameful in today’s America.  Even those who rail against political correctness know better than to embrace openly racist attitudes.  Such a values shift is possible in attitudes toward wasteful energy use as well.

For what it’s worth, the electricity meters on my street were all replaced with digital meters at the same time. A number of them are easily visible from the sidewalk. A quick walk-through confirmed that our utility electricity usage tends to be 4–14 times lower than our cohort, 9× being typical. So my assertion that the neighbours use too much energy is more than hypothetical, in my case. About half of this factor comes from my hobby photovoltaic setup, but even without this, we’re looking at substantial reduction.

A Word on Energy vs. Growth

Before signing off, I should comment that part of the message in this post validates the conflict between energy reduction and economic growth—which has been the focus of a number of Do the Math posts. Part of the recommended strategy is to buy less stuff and do less stuff as a way to cut back on energy. This would have a recessionary influence on the economy: slowing, stalling, or even reversing growth.

In our imaginations, we can concoct economic exchanges that involve little energy (Fred pays Ralph to sing a song; I pay Ralph not to sing; money is exchanged, nothing is done, little energy is exerted), but the fact is that we place too much value the energy-intensive things for them to melt to economic insignificance relative to the frivolous stuff. Someone may be willing to pay an obscene amount of money for a Picasso painting involving negligible energy, but not if their basic energy needs are as yet unmet (e.g., sitting in a cold or hot shack with inadequate food, no car, and no computer).

The point is that our economy is tied at the hip to energy. We can’t expect to lower substantially the rate of energy use (especially not arbitrarily low) and keep our economy humming. Likewise, in a steady energy scenario, we cannot expect indefinite economic growth (even if defined as utility, which runs into subjective ambiguity and diminishing returns before very long). Practically all of the methods I have used to scale back energy use have resulted in fewer dollars spent in the economy. You can see why my reduction recommendations will encounter stiff headwinds, suggesting that energy reduction is unlikely to be voluntary—more likely being forced on us by physical realities. The dream case is that we don’t have to make this choice, because our energy supply will never be unable to satisfy demand/desire. It’s a good dream. I could root for it, but also realize that we can’t always get what we want in this physical world.

By. Tom Murphy

This is a guest post by Tom Murphy. Tom is an associate professor of physics at the University of California, San Diego. This post originally appeared on Tom's blog Do the Math.

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  • dave trentlage on May 08 2012 said:
    I'm doing energy remediation work in memphis, tn. "Easy Pointers" is a great article. Options are limited here--we would buy Ford Ranger Hybrids as our pickups--they don't exist. WE recycle paper etc but large scale recycling of residential construction material is not available. Our focus has always been remodeling not new homes.
    Thanks for all you do I'll read the other articles.

    Dave t

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