It is important to look at the big picture. The way I see it, few people are aware of the sources of energy they utilize each day. Some energy is paid for directly such as gasoline for our cars. Gas for home heating, electricity for lights and air conditioning, etc. are often seen only as utility bills that come each month. What are the various energy sources we use?
Energy utilization was always an important topic in my physics classrooms. I wanted the students to know where their energy came from and how it was consumed by them and the general public. We discussed why efficiency was important. They were going to face and decide the actions on many complicated, technical, and politically charged issues in their future such as climate change. Those decisions would affect their quality of life and that of future generations.
We started with a simple flow diagram like the one below. The diagram shows how sources of energy are delivered to systems and devices that convert it into forms useful to the consumer. In the process, a useful amount of energy is delivered. But the conversions are never 100% efficient. As a result, much useless energy is wasted to the environment. We discussed examples of some common systems and how efficient they were. They soon got the point that increased efficiency and efforts to reduce wasted energy were actually very important issues. If we are unable to come up with more cheap sources, there are ways to reduce inefficiency and waste. Improved efficiency can be considered a source of energy and a lot of it. The diagram shows the gray box of Useless Wasted Energy quite large. It is actually much larger than the Useful Energy Output.
Energy Flow in the U.S.
Lawrence Livermore National Laboratory publishes energy consumption flow charts each year like the one shown below for 2016. Their archive goes back as far as 1950. This chart needs to be seen larger in order to appreciate the details within it. Click it to embiggen. It is arranged in the same way as my classroom chart above. Sources are on the left. Conversion systems are in the center. Output of energy is on the right. Below I will provide a closer look at each part.
Quads of Energy
The title of the chart says the U.S. used 97.3 Quads of energy in 2016. What is a Quad of energy?
1 Quad = 1,000,000,000,000,000 BTU (British Thermal Units)
1 Quad = 1,055,000,000,000,000,000 joules
Suppose an average sized apple fell from the countertop to the floor. About 1 joule of motion energy was gained by the apple as the force of gravity sped it up during the fall. If the apple fell into a bucket of water on the floor, it stirred the water as it lost its motion energy. The stirred water became very slightly warmer. The motion energy of the apple was converted into heat energy.
Imagine 1055 apples dropped the same distance into a container of water so 1055 joules of motion energy was delivered to the water. The cumulative effect caused a larger increase in the heat energy of the water. Under carefully controlled conditions, 1055 joules of energy raises the temperature of 1 pound of water 1 Fahrenheit degree. That amount of heat energy is called a British Thermal Unit or BTU. Therefore, 1055 joules of energy = 1 BTU of energy.
Sources of Energy
Nine primary sources of energy appear in the image at the left. Petroleum, natural gas, and coal are the largest suppliers in that order. They have been part of the energy flow for many years. The U.S. imports about 25% of its petroleum from foreign sources: Canada (38% of the imports), Saudi Arabia (11%), Venezuela (8%), Mexico (7%), Columbia (5%)
More recent additions growing in size are solar and wind. Some regions of the U.S. are well suited to utilizing these. For example, the great plains states are more windy than most others. Iowa where I live is heavily invested in wind energy. Iowa currently produces about 34% of its electrical energy from wind. It might reach 40% by 2020.
Natural gas production has increased in the U.S. due to the increased use of fracking. Such practice is not without controversy.
Energy Conversion Systems
Energy from the sources is delivered to 5 primary systems in order to convert it into a useful form. In order of size they are electricity generation, transportation, industrial, residential, and commercial. Note how electricity generation is done using all 9 sources of energy. The largest is coal followed closely by natural gas and nuclear. Wind and solar are growing sources. Hydro has maxed out as there are no new rivers to dam.
Transportation uses almost entirely petroleum. Note the tiny amounts of natural gas, biomass, and electricity feeding energy to a small number of vehicles.
Industry uses a broad mix of energy sources with petroleum and natural gas about evenly split. Residential and commercial areas uses about equal parts of electricity and natural gas. The electric energy supplied to them was previously converted from other forms of energy at a power plant.
This figure is the rightmost part of the Livermore chart showing the ultimate fate of the energy utilized by the U.S. Rejected Energy is not useful in any way. It appears in our environment as heat. Energy Services is energy useful to us in some way. We move vehicles, make things in factories, operate businesses, run our coffee makers and toasters, etc.
Of the 97.3 Quads of energy sourced for the U.S., 30.8 Quads (32%) is put to use. The rest (68%) is waste heat energy.
Roughly 2/3 of the energy delivered to the orange Electricity Generation box is wasted. The gray bar out of the orange box is 24.9 Quads compared to the 37.5 Quads delivered to the box. Transportation wastes 22.0 of the 27.9 Quads and Industrial wastes 12.5 of the 24.5 Quads.
Consider the operation of an incandescent light bulb in your home. Such bulbs get hot. They waste 75% of their electric energy to heat and produce 25% of their energy as the useful energy service of light. Energy from a source delivered to an electric generation plant is needed to light the bulb. The plant is only 33% efficient at doing so. The bulb is only 25% efficient at making light. Overall efficiency is 0.33 x 0.25 = 0.0825 or barely 8%. Consumers can improve on that by using compact fluorescent and LED bulbs.
Running a 100 Watt bulb continuously 10 hrs a day for a month uses the equivalent energy of burning nearly 4 kg or 10 pounds of coal. Three quarters of that energy makes heat. The power plant supplying the electric energy needs to burn about 12 kg or 30 pounds of coal since it is 33% efficient.
It might seem futile to think we can do much to change this picture of energy consumption. Our individual impacts seem small compared to the big picture. Collectively the billions of people worldwide can act to make changes. In our home, we took measures to add insulation and weather stripping, replaced incandescent bulbs in high use areas, adjusted our thermostat in summer and winter, use efficient appliances, etc. Our utility bills are down to nearly half the typical household.
Science and Technology can be of great help. Research and development dollars need to be invested into finding ways to improve efficiency of energy conversion systems. There is a huge amount of wasted energy there to be harvested. Investment should be encouraged into renewable sources of energy such as wind and solar.
Nations need to continue efforts at cooperation such as with the Intergovernmental Panel on Climate Change IPCC. Climate change is a problem faced by the entire globe. We need to fully understand the impact of continued heavy fossil fuel use. The 195 member nations need to work together to mitigate the negative impacts. Cooperation is necessary.