Imagine that someone offers you a $100 bill that you can use for whatever you want. That would be a pretty good deal, wouldn’t it? Now imagine that the person attaches a condition to their offer: in order to get the $100 bill you have to pay them $75. You would still come out ahead, but this time you would only be getting $25. Does it make sense to spend money to get money? That depends on how much you get back for what you spend.
Getting and using natural energy sources is a lot like spending money to get money. We use a lot of energy just to get energy (Figure 20.8). We have to find an energy source, extract it from the Earth, transport it to the places where it will be used, and often process or convert it into a different form of energy. All of these steps of getting energy require energy use themselves. For example, we use petroleum to make fuel for our cars. To get the petroleum, we often have to build huge drilling facilities and drill down hundreds of meters into the Earth. It takes energy to do this. We then use trucks or ships to transport the oil all over the world, which also takes energy. We then have to heat the petroleum to its boiling point to make different products from it, like fuel and automotive oil and this takes even more energy.
In this lesson, you will learn that different sources of energy all require adding some other energy before they can be made useful. You will be able to compare various sources of energy in terms of their usefulness. You will also learn some ways that we can conserve energy or use it more efficiently.
- Discuss why it takes energy to get energy and why some forms of energy are more useful than others.
- Describe some ways to conserve energy or to use energy more efficiently.
It takes energy to get energy. Net energy is the amount of usable energy available from a resource after subtracting the energy used to extract it from the Earth and make it usable by humans. We just discussed someone giving you $100 but requiring you to pay them back $75. In this case, your net pay would be $25, or $100 minus $75. Net energy is calculated the same way. For example, for every 5 barrels of oil that we take from the Earth, we have to use 1 barrel for the extraction and refining process. This leaves us a net supply of only 4 barrels (5 barrels minus 1 barrel).
Remember that oil is a non-renewable resource. Imagine what would happen if the energy needed to extract and refine oil increased. What might happen if it took 4 barrels of oil being used to get 5 barrels of new oil? Then our net supply would only be 1 barrel. Our supply of oil would begin to dwindle away even faster than the current rate.
We sometimes use the expression net energy ratio to demonstrate the difference between the amount of energy available in a resource and the amount of energy used to get it. If we get 10 units of energy from a certain amount of oil, but use 8 units of energy to extract, transport, and refine the oil, then the net energy ratio is 10/8 or 1.25. A net energy ratio larger than 1 means that we are still getting some usable energy. A net energy ratio smaller than one means there is an overall energy loss. Table 20.2 shows several energy sources commonly used for heating our homes and schools. It shows their net energy ratios. Higher ratios mean that the source provides more usable energy than those with lower ratios.
|Energy Source||Net Energy Ration|
Notice from the table that renewable solar energy gives you much more net energy than other sources and that coal-fired electricity actually consumes more energy than it produces. Why do you think this is so? Burning coal for electricity requires a large input of energy to get energy. We have to find the coal, mine the coal, transport the coal, and build power plants to burn the coal (Figure 20.9). All of these take energy and reduce the net energy available for us to use. Solar energy, however, requires very little energy to get in the first place. We don't have to mine it or transport it in trucks. Sunshine is abundant globally and can be used in the same place where it is collected.
The discussion above on net energy shows you that it takes energy to get energy and that some sources of energy require more input than others to get usable energy. After we get the energy, we then use it for some purpose. Energy efficiency is a term that describes how much usable energy we have available to do work from every unit of energy that we use. Higher energy efficiency is desirable because it means we are wasting less energy and getting more use out of the energy sources that we take from the Earth. Higher energy efficiency also lets us extend our non-renewable sources and make them last longer.
Nearly 85% of the energy used in the United States comes from non-renewable fossil fuels. Since these exist in limited supplies, we need to be especially concerned about using them efficiently. Sometimes our choices affect energy efficiency. For example, transportation needs require huge amounts of energy. Forms of transportation such as cars and airplanes are less efficient than transportation by boats and trains. Fluorescent light bulbs are more efficient than regular, incandescent light bulbs. Hydroelectric power plants are more efficient than nuclear fission reactors.
Energy conservation involves reducing or eliminating the unnecessary use of energy. This improves energy efficiency. Energy conservation saves us money and it also ensures that our energy supplies will last longer. There are two main ways to conserve energy: use less energy and use energy more efficiently. The pie chart (Figure 20.10) shows how energy is used in the United States.
Almost one-half of the energy used in the United States is for transportation and home use. This means that individual people can do much to conserve energy on a national basis. Table 20.3 shows some ways that we can decrease energy use and use energy more efficiently in transportation, residences, industries, and office settings.
|Where Energy is Used||How We Can Use Less Energy||How We Can Use Energy More Efficiently|
|Commercial (businesses, shopping areas, etc.)||
Using less energy or using energy more efficiently will help conserve our energy resources. Since many of the energy resources we depend upon are non-renewable, we need to make sure that we waste them as little as possible.
- It takes energy to get energy. We use the term 'net energy' to refer to the amount of energy left for use after we expend energy to get, transport and refine other forms of energy.
- Once the energy is available, we use it for some purpose, but sometimes do so inefficiently.
- We can conserve energy resources by reducing energy use.
- We can also use energy more efficiently by getting more work out of the energy that we use.
- Examples of this include driving smaller cars and using fluorescent light bulbs.
- Define net energy.
- Why does solar power have a higher net energy ratio than coal-fired electricity?
- Coal-fired electricity has a net energy ratio of 0.40. Explain why this means that getting electricity from burning coal is an undesirable option for energy use.
- What are two ways you can use less energy in your home?
- Why is it especially important to not waste energy from fossil fuels?
- Trains are much more efficient than trucks in transporting items around. Why do you think this might be so?
- The ability to do work which we can get from a fuel.
- The process of taking oil out of the Earth.
- A type of lighting that uses less energy than regular light bulbs.
- net energy ratio
- The ratio between the useful energy present in a type of fuel, and the energy used to extract and process the fuel.
- The process of removing impurities from oil and to make it usable.
Points to ConsiderEdit
- If it takes energy to get energy, then what are the best choices for types of energy?
- Put each of these actions in order from most important to least: choosing a sustainable form of energy, increasing energy efficiency, conserving energy use. Explain the order you chose.
- Could everyone in the world use as much energy as a person in the United States does each day? Why or why not?