Lesson Objectives
- 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.
Vocabulary
- energy efficiency
- net energy
- net-energy ratio
Introduction
The Earth’s Energy chapter deals with many aspects of energy and energy use. It would be good to review it before embarking on this lesson on energy conservation. Getting and using natural energy sources is a lot like spending money to get money. To get energy, we must use a lot of energy. Finding an energy source, extracting it, refining it, and transporting it to where it will be used all require energy. One way to keep the energy costs of energy down is to use energy more efficiently: to conserve energy.
Obtaining Energy
Net energy is the amount of useable energy available from a resource after subtracting the amount of energy needed to make the energy from that resource available. For example, every 5 barrels of oil that are made available for use require 1 barrel for extracting and refining the petroleum. What is the net energy from this process? About 4 barrels (5 barrels minus 1 barrel).
What happens if the energy needed to extract and refine oil increases? Why might that happen? The energy cost of an energy resource increases when the easy deposits of that resource have already been consumed. For example, if all the nearshore petroleum in a region has been extracted, more costly drilling must take place further offshore (Figure below). If the energy cost of obtaining energy increases, the resource will be used even faster.
Offshore drilling is taking place in deeper water than before. It takes a lot of energy to build a deep drilling platform and to run it.
The net-energy ratio demonstrates the difference between the amount of energy available in a resource and the amount of energy used to get it. If it takes 8 units of energy to make available 10 units of energy, then the net-energy ratio is 10/8 or 1.25. What does a net-energy ratio larger than 1 mean? What if the net-energy ratio is less than 1? A net-energy ratio larger than 1 means that there is a net gain in usable energy; a net-energy ratio smaller than one means there is an overall energy loss.
Table below shows the net-energy ratios for some common energy sources.
| Energy Source | Net-energy Ratio |
|---|---|
| Solar Energy | 5.8 |
| Natural Gas | 4.9 |
| Petroleum | 4.5 |
| Coal-fired Electricity | 2.5-5.1 |
Notice from the table that solar energy yields much more net energy than other sources. This is because it takes very little energy to get usable solar energy. Sunshine is abundant and does not need to be found, extracted, or transported very far. The range for coal-fired electricity is because of the differing costs of transporting the coal. What does this suggest about using coal to generate electricity? The efficiency is greater in areas where the coal is locally mined and does not have to be transported great distances (Figure below).
Obtaining coal for energy takes a lot of energy. The coal must be located, extracted, refined, and transported.
This is not to say that solar energy is less expensive than other types of energy. The cost of energy is dependent on lots of different factors, such as the cost of the equipment needed to harness the energy. If solar power cost less to use, it would be more widespread.
Energy Efficiency
Energy efficiency describes how much useful work is extracted from one unit of energy. Remember that although energy is not created or destroyed, it’s just transferred from one form to another, some energy is nearly always lost in the transfer as heat. By saying that the work must be useful subtracts the energy that is lost to non-useful work. For example, some energy may not be doing useful work if the equipment is not running well (maybe a piston is moving sideways a bit rather than just up and down).
Higher energy efficiency is desirable because:
- Less energy is being wasted.
- Non-renewable resources will last longer.
- The cost is kept lower.
Because so much of the energy we use is from fossil fuels, we need to be especially concerned about using them efficiently. Sometimes our choices affect energy efficiency. For example, transportation by cars and airplanes is less energy-efficient than transportation by boats and trains. Compact fluorescent light bulbs are more efficient than incandescent light bulbs (Figure below).
(a) A compact fluorescent light bulb. (b) Compact fluorescent bulbs use less electricity to produce light than incandescent or halogen bulbs.
Energy Conservation
What benefits are there from energy conservation? Conserving energy means that less energy is needed, which reduces costs, ensures that non-renewable energy sources will last longer, and reduces political and environmental impacts.
What are the two ways that energy can be conserved? (1) Use less energy, and (2) use energy more efficiently.
The pie chart (Figure below) 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 individual choices can make a big impact on energy conservation.
Table below shows some ways that people 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 |
|---|---|---|
| Transportation |
Ride a bike or walk instead of taking a car. Reduce the number of trips you make. Use public transportation. |
Increase fuel efficiency in cars. Buy and drive smaller cars. Build cars from lighter and stronger materials. Drive at speeds at or below 90 kilometers per hour (55 miles per hour). |
| Residential |
Turn off lights when not in a room. Only run appliances when necessary. Unplug appliances when not in use. Wear a sweater instead of turning up heat. Use fans instead of turning down air conditioner. Engage in activities that do not involve electronics. Rely on sunlight instead of artificial light. |
Replace old appliances with newer more efficient models. Insulate your home. Make sure windows and doors are well sealed. Use LED bulbs if available, or compact fluorescent light bulbs (and dispose of properly!). |
| Industrial |
Recycle materials like soda cans and steel. Reduce use of plastic, paper, and metal materials. |
Practice conservation in factories. Reuse materials. Design equipment to be more efficient. |
| Commercial (businesses, shopping areas, etc.) | Turn off appliances and equipment when not in use. |
Use fluorescent lighting. Set thermostats to automatically turn off heat or air conditioning when buildings are closed. |
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.
Energy saving tips from the U.S. Department of Energy: http://www.energy.gov/energytips.htm.
The U.S. Department of Energy has a video to let you know how a home energy audit will help you to make your home more energy efficient. Be sure to follow links to the Do it yourself page. http://www.energysavers.gov/your_home/energy_audits/index.cfm/mytopic=11160
Lesson Summary
- It takes energy to get energy. Net energy refers to the amount of energy left for use after we expend energy to get, transport, and refine other forms of energy.
- Energy resources can be conserved by reducing energy use.
- Energy can be used more efficiently by getting more work out of each unit of energy.
- There are many ways for an individual to conserve energy.
Review Questions
1. Define net energy.
2. Why does solar power have a higher net-energy ratio than coal-fired electricity?
3. Some coal-fired electricity has a net-energy ratio of 2.5. Explain what this means. When is coal a good choice for generating electricity? When is coal not a good choice for generating electricity?
4. What are two ways you can use less energy in your home?
5. What are two ways that energy can be conserved?
6. Why is it especially important to not waste energy from fossil fuels?
7. Why are trains much more efficient than trucks for transporting items? Why are boats more efficient than airplanes or cars for travel?
8. If you were to replace a 240V incandescent bulb with a compact fluorescent bulb with an initial luminous flux of about 1500 lm, how much would you decrease electrical consumption?
Points to Consider
- 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?