(MINNEAPOLIS) – If we are going to make fundamental changes in the way we use energy, we have to understand how we use it now. We use a lot of energy. The numbers for annual U.S. consumption seem like made up words: 98 quadrillion Btu a year. “Btu”, or British Thermal Unit, is hardly a term we use every day and talking about “quadrillion” – another term we seldom use – hardly helps.
If you use a thousand watts (ten 100 watt incandescent light bulbs) for an hour you’ve used 3,400 Btu. One kilowatt hour is 3,400 Btu. And a quadrillion is what comes after “million, billion, trillion … quadrillion.” So, do the math and you get 29 trillion kilowatt hours. That probably isn’t any easier to grasp.
Use ten gallons of gasoline and you’ve used over a million Btu. So the annual U.S. consumption of energy is roughly equal to one trillion gallons of gas or 3,200 gallons per person. However you look at it, it’s a big number.
What do we use energy for?
A better way of getting a handle on our energy use is to divide up where we use energy. A standard way is to do that is in terms of four sectors: industrial, commercial, residential and transportation.
Industrial uses include manufacturing in various forms, including agricultural, construction and related uses. Thirty one percent of our energy is consumed here. What is perhaps the most surprising aspect of this is that fully half of the energy use within this sector is concentrated in two industries: petroleum refining and chemical production. It takes energy to make energy and the refining of oil is itself a major consumer of energy. Other industry groups that consume significant power in this sector are metal producers, paper and agriculture. We use twice as much energy making paper as growing food.
Another unexpected aspect of this sector is that its use of energy is not growing. From 1970 to the present, the amount of energy used for industry has remained the same. Part of that must be due to a shift away from manufacturing industries, but part is also due to increased efficiency.
Commercial uses are buildings of all kinds used for retail activities. Hospitals, hotels and places of worship are also included here. Nineteen percent of our energy use is in this sector. No single occupation dominates use here, but one of the ones that has grown the fastest is lodging which used twice as much energy in 2003 as it did in 1979.
Commercial energy use has been getting more efficient, with energy consumption per square foot of building declining over 20 percent since 1979.
Residential use we understand: heating, cooling and lighting our houses and running our appliances. Twenty three percent of our energy use is here. So we use more energy in our homes than we do in our retail buildings. The biggest area, 40 percent of our residential use, is heating our homes. Twenty percent goes to heating water and 26 percent to lighting and appliances. Only 8 percent of residential energy use is air conditioning, even though more than 85 percent of homes have some form of air conditioning installed, and air conditioning seems often to be a symbol of excess energy use.
Home energy use has become more efficient, offsetting the increased number of homes. There has been a 31 percent drop in energy consumption per home between 1978 and 2005. While insulating and better windows have reduced heating use, our entertainment and other electronics uses have increased rapidly. About half the homes in the U.S. now have three or more televisions and 40 percent have two or more computers.
Transportation uses 29 percent of our energy with 60 percent of that coming from cars, motorcycles and light trucks.
Fuels and uses
We get our energy mostly from coal, natural gas, petroleum and to a lesser extent from nuclear power and renewable energy. Certain fuels are associated with certain types of energy use. The transportation sector gets almost all of its energy from petroleum, and that is where most of the petroleum use is. So, from that perspective, the issue of energy imports and our dependence on them hits the transportation sector disproportionately.
Natural gas is associated with home energy use, but not as extensively as petroleum is.
Another key energy connection involved electric power production.
Electricity: an intermediate use
Most coal, all of nuclear and half of renewable energy production is used to generate electricity. But electricity is not an end use in itself, rather it is an intermediate use because it is sent over transmission lines to end users.
Electricity is used in three of the four sectors we mentioned; only a very small fraction of electricity is used in transportation, and that mostly for subways and commuter trains.
Why so little electricity use in transportation? Why are electric cars taking so long to catch on? The ‘elephant in the corner’ regarding electricity is that it is very hard to store. Aside from batteries in flashlights, cameras, computers and other electronics, electricity is almost never stored. Failure to balance in real time the production and use of electricity is the key reason for many summer brownouts and power outages in our cities.
The term “energy density” captures the concept of how hard it is to store energy. This measures how much energy can be extracted from the same weight of various substances. Gasoline has an energy density nearly 80 times that of an alkaline battery. That’s the problem with cars: to run them on batteries now would require far too much weight. The most dense energy storage involves converting mass to energy in nuclear reactions (millions of times more energy-dense than even gasoline) and in matter – anti-matter collisions (which is presumably why Star Trek and many science fiction stories rely on it).
In fact electricity is often stored in ways other than as electricity. One oft-discussed approach is pumped hydro: surplus electricity production (at night, for example) is used to pump water uphill to a storage reservoir. Then, during times of peak demand, that water is allowed to run downhill and used to produce electricity.
Efficiency
At a couple of points we’ve discussed how the U.S. has increased its energy efficiency. There seems general agreement that there is much more to be done.
Replacing incandescent light bulbs with compact fluorescents (probably an intermediate step on the way to using LED lights) was motivated less by a desire to spread socialism or destroy personal freedom than the undeniable fact that incandescent light bulbs are horribly inefficient. Our homes and cars can get much more efficient.
And by the way, this “ban” on old style light bulbs? It was already on the way in Europe, was supported by lighting manufacturers, signed into law by George Bush, and really doesn’t ban incandescent bulbs, just any bulb that isn’t at least 25 percent efficient, unless they are for a variety of special uses, in which case they aren’t banned at all.
Changing energy policy
This overview of energy use suggests four implications for our energy policy debates. First, that improving efficiency can pay benefits. Being efficient has already paid off for many and doesn’t generally involve massive changes to our lifestyles.
Secondly, we often are told about ‘going green’ solely in terms of our houses, but most of our energy use is in commercial activities. We need to focus on this area as well.
Third, the “energy independence” problem is really a transportation problem since petroleum is used primarily for that. If we want independence, or less dependence, we need to zero in on energy use in transportation.
Finally, you want to become a billionaire? Be as rich as Bill Gates? Well then, invent a really efficient battery. But hurry, others have that idea also.