How much Energy do Humans use?
This turns out to be a complex question – the answer to which depends upon how and where we measure that energy. One way is to measure the potential energy in the raw materials like coal, oil and gas which we dig up and convert to energy.
We could measure how much natural gas, gasoline and electricity we use. That would give us a very different number from the number of raw materials we dug up.
What is taken out of the ground is called Primary Energy.
Crude oil and coal extracted from wells and mines are examples of primary energy. These primary energy sources are generally of little use to us in the raw form we extract them. For instance, we know that setting a light bulb on a pile of coal is not going to illuminate the bulb.
In 2012, the world consumed 524 EJ of primary energy, the majority of which came from fossil fuels. That number rose to 546 EJ (151550 TW/hr). in 2016 and continues to rise.
The following chart traces the growth of World Primary Energy Consumption from 1800 through 2016.
Figure 3-3 The History of World Primary Energy Production
This chart represents the history of primary energy consumption from 1800 through 2016.
To be useful, primary energy needs to be converted to a form called Secondary Energy.
In the case of oil, we refine it (see Figure 3-4). In the case of coal, we burn it in power plants. The resulting secondary energy is usable to humans. The process of mining these resources, moving them to where they are refined and then refining them requires additional energy.
Figure 3-4 Oil-based secondary energy products
Secondary energy needs to be distributed by pipeline, truck or via the power grid. These distribution systems deliver Final Energy to the consumer. The final energy in these two cases might be gasoline at the pump or electricity at the plug. Final Energy is used by end-use technologies to satisfy human needs such as transportation and lighting.
Primary energy is the first step in the path to useful energy used by consumers.
This chart shows the generic, cumulative path as well as a path based on crude oil and coal primary energy sources. Notice, the yellow, as described in the physics we discussed previously, all of the 496 EJ of energy taken from the ground, ultimately is turned into heat, described as waste and rejected energy.
Used with permission.
Energy Pathways
Oil
Primary – Refining – Secondary – Distribution – Final – End Use
Figure 3-5 Energy path of oil from well to end use
(Illustration by Heather Reed)
Coal
Primary – Power Plant – Secondary – Distribution – Final – End Use
Figure 3-6: Energy path of coal from mine to end use
(Illustration by: Heather Reed)
At each conversion stage, energy is lost in the form of heat.
Figure 3-7 below illustrates this point with the largest amount of potential energy (primary energy) gradually decreasing down to the smallest amount of useable energy (end use). The inverted triangle represents the energy lost at each stage of conversion. Ultimately, all the primary energy is converted to heat.
Figure 3-7 Energy Flow of Raw Resources
(Diagram by Heather Reed)
Arnulf Grubler of the International Institute for Applied Systems Analysis and Yale University, completed a study on the world’s energy flow and consumption using 2005 figures. This is the best analysis of the world’s energy flow I’ve seen and his work is used here with permission. It gives us a holistic template for the world’s energy consumption in 2005. At that time, our primary energy consumption was approximately 500 Exajoules (Figure 3-8). According to the International Energy Agency (IEA), that number had increased to 546 EJ by 2016.
The following chart is a Grubler’s breakdown of the world’s energy consumption in 2005, starting with Primary Energy mined from the earth through its end use.
| A Energy |
B C Examples of Energy’s Form |
D Available Energy |
E Energy loss |
F Conversion efficiency From Previous Step |
G Conversion efficiency from Primary Energy |
|
| Primary
Energy |
Crude Oil | Coal | 496 EJ | 1.00 | 1.00 | |
| Conversion | Refinery | Power Plant | 144 EJ | |||
| Secondary Energy | Gasoline | Electricity | 352 EJ | 0.70 | 0.70 | |
| Distribution | Truck | Grid | 22 EJ | |||
| Final Energy | Gasoline | Electricity | 330 EJ | 0.93 | 0.66 | |
| End Use Technology | Car | Light Bulb | 161 EJ | |||
| Useful Energy | Kinetic | Radiant | 169 EJ | 0.51 | 0.33 | |
| Services | Passenger-Miles/km | Light | 169 EJ | |||
| Total energy loss | 496 EJ | |||||
Figure 3-9 Energy System Schematic with examples
Adapted from Grubler figure 2.2 from page 6.
These numbers represent world energy consumption in 2005. They tell us the world extracted 496 EJ of primary energy, which was converted to 352 EJ of secondary energy.
When you read that primary energy must be converted to secondary energy to be useful, did the word “conversion” set off any bells? Remember what happens anytime energy is converted from one form to another.
Some of it is lost as useful energy.
| Notice in column F that the conversion from primary to secondary is 70% efficient, meaning that 30% of that energy is lost in the conversion. Our energy distribution system is 93% efficient, which when combined with the 70% conversion rate, yields an overall efficiency of 66% (.70 x .93 =.66). |
Each of these steps may represent opportunities for increased efficiency.
Finally, the remaining useful energy is used at a 51% efficient rate, meaning that only about one-third of every 100 units of primary energy is actually used to satisfy human needs (.66 x .51= .33).
After all was said and done, 496 EJ of primary energy provided a total of 169 EJ of useful energy to the world in 2005. Two-thirds of the potential energy in primary energy was unused. Some would say that energy was lost, but we know from our discussion of physics that this energy cannot be lost, it is dissipated to the atmosphere as heat. This suggests there is great opportunity for energy efficiency at each stage of the current energy conversion process, or perhaps we can develop new energy pathways with higher efficiencies.
Notice that after we’ve performed all the services for which the energy was used, the 496 EJ of primary energy became 496 EJ of waste heat as represented in the energy loss column. Consider that there is no energy left over when you run your gas tank dry or shut off the light. This is exactly as the laws of thermodynamics state.
Changing Primary Energy Sources and Advancing Technologies
Not only has energy consumption grown over the years, but the sources of our energy have changed.
The following chart shows a history of the world’s primary energy usage since 1850 in EJ and the corresponding technologies sustained by that usage. Figure 3-10. History of world primary energy use, by source (in EJ). Source: updated (IEA, 2012, BP, 2014) Grubler et al., 2012.
Figure 3-11: Primary Energy Sources as a percentage of total (1850-2010). Source: Grubler, name of doc, yr., p. 25, Figure 3.9.
The relative usage amounts of each of these primary energy sources has changed. In 1850, wood was the predominant fuel and source of biomass.
Since 1850, we have supplemented our biomass use with coal, oil, gas and other primary energy sources. The above chart (Figure 3-11 above) quantifies the relative percentage of the varied primary energy sources over time.
Figure 3-11 tells us that in 1850, about 95% of our energy came from biomass and 5% from coal. Notice that today only about 10% of the world’s energy comes from biomass. We are still using roughly the same physical amount as before, but now the world uses a greater proportion of other primary energy forms, thereby changing the ratios. Between 1850 and 1900, the percentage of our primary energy obtained from biomass (wood) declined dramatically. With the introduction of oil into the market, both the coal and biomass shares of the market continued to decline.
Our primary energy has come from a variety of sources since 1900 – predominantly oil, coal and gas. Around 1975, we see the emergence of what the chart labels “New Renewables”, which include wind, solar and geothermal energy sources.
Oil as a percentage of total primary energy peaked around 1975. This may be evidence for the peak oil theories that we will discuss in the next chapter. This graph suggests it takes a significant amount of time for a primary fuel to be adopted after it has been introduced. Part of the reason for this is the length of time and the large capital costs it takes to establish new infrastructure.
For example, when we build a new power plant, we are making a large investment with the expectation that the new plant will last a long time.
The Fate of Primary Energy
It is hard for any individual to comprehend what 496 EJ means.
It’s a large number for sure, but beyond that, it is rather abstract. One way of making it a little less abstract is to break that number down into average person’s use of primary energy. In 2005, there were 6.5 billion people on the planet. Dividing the amount of energy used for each sector by 6.5 billion provides us with an average of how much primary energy per capita we used.
TRANSPORT – Primary energy used for transport provides an average mobility of 13km/day/person, and moves another 1 tonne/20 km/day/person
INDUSTRY – About 10 GJ of primary energy used in industry provides 50 Gt of materials yearly, which works out to an average of 9 tonnes/yr/person.
BUILDINGS – Grubler estimated that we condition around 150 billion m2 of space. This works out to conditioning about 20 m2 per person on average.
A group called Architecture 2030 analyzed US Energy Information Administration energy consumption data from 2013 in a different way. They asked the question, “How much of the energy we use is associated with buildings?” What they found was significant! According to their analysis, 47.6% (45.2 QBtu/47.7 EJ) of final energy went to energy services associated with buildings. Of the energy not used in relation to the built environment, 28.1% (26.7QBtu/28.17 EJ) was used for transportation and 24.4% (23.2 QBtu/25.74 EJ) was used for industry. Based on this information, Architecture 2030 focuses its resources on energy efficiency in buildings as the fastest, most cost-effective means of saving energy and cutting carbon emissions.
Another way we can examine energy consumption is based on the human needs we want to satisfy. We know that approximately 496 EJ of primary (raw) energy were mined across the globe in 2005.
How was all that energy used?
Figure 3-12 World Primary Energy Consumption by Service (2005)
The pie chart above illustrates how primary energy resources were used, as well as the amount of heat energy lost in the conversion from primary to secondary, final and useful energy.
We can easily see that thermal comfort and food comprised the greatest consumption of energy resources. Also note that roughly two-thirds of the original energy was lost in conversion!
Primary energy can give a somewhat distorted picture of our energy usage. Each pathway from primary energy to useful energy involves a series of energy conversions, each with different efficiencies. The end product includes varied sources of useful energy: thermal, fuel and electric, which are generally not interchangeable. As we saw in Figure 3-8, the amount of primary energy extracted from the ground (496 EJ) is equivalent to the total energy loss after final energy has been consumed (496 EJ).
It is instructive to look at final and useful energy because they best reflect what we, as energy users, care most about the cost of final energy and the actual services it provides. Final energy and its conversion to useful energy are the real currencies of the energy processing system. If we found a way to eliminate the first steps and the associated energy loss from the process and provide energy for the service, we would have the needed energy to meet human demands without the significant loss from conversions. Distributed energy generation systems using wind turbines or photovoltaic panels installed where the energy is being used might provide the needed energy without the current energy losses from transmission.
For sustainable energy to be adoptable, it must provide the service at a competitive price, part of which might come from the savings associated with the added efficiency of providing final energy locally.
We’ll discuss this economic component further in Chapter 6 and again in Section 3.
Next week, we’ll discuss further how much energy humans use.
What are your thoughts on this week’s post?
