Key Energy Demand Sectors

The six stages of the energy system described above lay the foundation for the current economy of much of the world, more or less broken down into four key economic sectors: electricity generation; transportation; industry and manufacturing, and residential and commercial end-use.

The electricity generation sector often is the largest consumer of primary energy in Developed Nations, and influences all of the other economic sectors except for transportation, at least, directly. As such, electricity generation is distinguished because it is not an end-use sector of the economy, but a necessary energy service sector, for which the rest of the (nontransportation) economy depends. As an example, the United States Lawrence Livermore National Laboratory (LLNL, 2014) reports that total national primary energy consumption in the United Sates in the year 2013 amounted to 97.4 quadrillion BTUs, or Quads for short.^[1] Of that, 38.2 Quads, or 39% of total consumption, was diverted to electricity generation. Coal, natural gas, and nuclear fuels represent the majority (86.6%) of primary energy used for generation. (The primary energy sources that fed into the electricity sector are broken down in Table 1.1.)

Note that of the 38.2 Quads entering the electricity sector, only 12.4 Quads actually flowed into the other demand sectors, with 25.8 Quads leaving as rejected, or waste energy. The reason is: there is a high cost associated with electrical energy conversion efficiency, as much of the primary energy conversion processes involve combustion, resulting in heat losses that cannot be tapped. This is often referred to as being “lost out the stack” although significant thermal pollution into nearby rivers and

Table 1.1 Energy sources fed into the U.S. electricity generation sector, 2013.

Source: LLNL 2014

streams also occurs. This reality offers some advantage to hydro-, solar-, and wind-based energy resource systems, at least from a fuel’s accounting perspective. A megawatt of hydro, solar, or wind electricity generation already accounts for inefficiencies. That is, we do not bother to discuss the inefficiency of the wind or water turbine, or of the concentrating solar power system at the point of conversion, because we consider water, wind, and solar radiation to be “free” sources of energy, as opposed to coal or natural gas, which are priced in the market before they are converted into electricity. Taking this into account, solar’s contribution to the electric power sector actually jumps from 0.2% of energy input for electricity to roughly 0.7% of electricity used, since none of it is rejected. Regardless, the share of energy generated from direct solar radiation remains a dismally small contribution toward our energy system. Even the resulting electricity production from solar energy is barely on par with the effective energy flow from petroleum into the sector, which is only used as a backup fuel when local grids are approaching peak electrical loading. Furthermore, solar and wind remain small contributors to the only sector in which they are directly used.

The transportation sector is another large consumer of primary energy. The scale of its influence on a particular national economy is often a function of the physical size of the country, the size of the national economy, and the primary modes of transportation chosen to move people and goods into, out of, and around it. In the United States, a country that spans a substantial land area, there is a heavy dependence on road and air transport. In fact, in 2013, 27 Quads of primary energy was diverted to its transportation sector, which is about as much total primary energy consumed by all of Central and South America combined. Primary energy and electricity fed into the sector, but the mix is very much lopsided to one primary resource: petroleum. (A breakdown is given in Table 1.2.)

Table 1.2 Energy sources fed into the U.S. transportation sector, 2013.

Petroleum dominates the U.S. transportation sector, as it does every other country. It will be challenging to displace it in this sector, because petroleum products have remarkable energy and power densities. In other words, a relatively small volume or mass of gasoline or diesel provides for long cruising range and rapid acceleration: critical values for transportation. Biomass, almost entirely ethanol from corn crops, is in a distant second place in the United States energy mix, which is a heavily subsidized endeavor. Compressed natural gas may be able to take some noticeable market share, where the shale plays have made gas much more abundant in the United States. For electricity to take a much larger share, batteries or other storage technologies will need to advance dramatically. Liquid fuels will remain valuable to consumers for the foreseeable future.

The industrial/manufacturing sector is yet another large consumer of primary energy. In a massive economy such as the one in the United States, there exists a large demand for fuels, materials, and other manufactured goods. Primary industries include petroleum refining, and steel and aluminum processing, while secondary industries (i.e., industries that depend on the primary industries to function) comprise cement, paper, and chemicals industries. All of these industries require healthy amounts of primary energy and electricity to make them operate; thus, it should not be surprising that manufactured goods contain a large degree of what is called embedded or embodied energy: energy that is required to produce all of those manufactured products. The U.S. industrial sector consumed 24.7 Quads of energy in 2013. (The breakdown of energy sources fed into the sector is shown in Table 1.3.^[2])

Table 1.3 Energy sources fed into the U.S. industrial/manufacturing sector, 2013.

Source: LLNL 2014

It is obvious from viewing Table 1.3 that natural gas, petroleum, and electricity are vitally important to the U.S. industrial sector, since petroleum refining and chemicals manufacturing are the two dominant industries in the country. Coal’s contribution is somewhat obscured by two factors: electricity and China. Since 43% of all electricity generated in the United States comes from coal, the total contribution to the industrial/manufacturing sector will obviously rise if we count the embedded “coal energy” in electricity. Also, much of the metal processing that the United States used to perform, which requires large quantities of coke, now is outsourced to other countries, primarily China. This means they use the coal and produce the emissions, while the rest of the world benefits from just using the steel they produce and sell to us. This is another form of embedded energy, and deferred local pollution, that does not get accounted for in our total consumption tally.

Finally, the residential and commercial sector rounds out the energy system’s demand component. Homes and office buildings, combined, represent yet another substantial fraction of energy use in modern economies. These are end-use sectors that depend heavily on electricity, which is already processed from primary energy, and that also depend on natural gas. Common activities, of course, include: lighting, heating, operating appliances, and also communication, and entertainment. As such, the energy sources fed into these sectors are varied, and in the United States, amount to 20 Quads of primary and electrical energy (broken down in Table 1.4).

Table 1.4 Energy sources fed into the U.S. residential/commercial sector, 2013.

Electricity and natural gas are the two energy-feed sources that dominate end-use sectors, because they are the cleanest and most flexible of the fuels for lighting, cooking, and space heating. In certain areas of the country, petroleum is still used directly in domestic and commercial buildings as heating oil for space heating. Some firewood and tiny amounts of coal are still used for space heating, even in the United States. Geothermal applications in buildings remain small, and would generally consist of tapping moderate enthalpy heat such as those found in the western part of the country for municipal heating.

• [1] A Quad is such a large number (one with 15 zeroes after it) that it is rather difficultto conceptualize. Syracuse University’s Maxwell School of Citizenship and PublicAffairs (2014) offers a little less abstract analogy of it being equal to 45 million tonsof coal, or a pile of coal that is 10 feet tall, 1 mile wide, and 3.3 miles long. By theirestimates, it would take 9 minutes to drive around it, if you traveled at a speed of 60miles per hour.
• [2] Though electricity is an energy carrier, not an energy source, it is often accountedfor in energy analysis as a feed source into a sector.