Day 5: Energy Efficiency and Conservation by 2/21(A) 2/24(B)
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.
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.
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.
The table below shows the net-energy ratios for some common energy sources.
The table below shows the net-energy ratios for some common energy sources.
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).
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:
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.
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.
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.
The table below shows some ways that people can decrease energy use and use energy more efficiently in transportation, residences, industries, and office settings.
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.
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 is energy efficiency?
5. What are two ways you can use less energy in your home?
6. What are two ways that energy can be conserved?
7. Why is it especially important to not waste energy from fossil fuels?
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 is energy efficiency?
5. What are two ways you can use less energy in your home?
6. What are two ways that energy can be conserved?
7. Why is it especially important to not waste energy from fossil fuels?