What is Energy?
Energy is the ability to make things happen. It allows us to ride our bikes, sharpen a pencil, drive a car, or melt ice. Energy is needed for our brains to work and our bodies to develop. Most commonly in classrooms we define energy as the ability to do work. The first law of thermodynamics explains this further. The first law is that energy can be neither created nor destroyed. The energy of the universe is constant. This means that "work" is a process of energy transfer. When force is exerted it is the work of energy transferring from one source to another making it move or change. For example, the suns energy pours into solar cells, solar cells change radiant energy into electrical energy. Hydrogen and oxygen play a big role in the transfer of energy. "Most human energy requirements are met by forming bonds between hydrogen and oxygen, whether we are thinking in terms of metabolism, agriculture, industry, transport, building or domestic needs such as heating, cooking, refrigeration, or whatever," (Walker p 23).
Energy is measured in watts. A watt is a unit of power equal to one joule per second. In order to discuss energy globally, it is easiest to measure energy in terawatts. A terawatt is equal to one million (10
) watts (Wiktionary, 2007). In the year 2000, the global energy consumption rate was 13 terawatts (Lewis, 2006). With the rise of third world countries, the demand for energy will increase quickly. It is expected that in the year 2050 20 terawatts of power will be needed to supply the global demand (Lewis, 2006).
The Greenhouse Effect
There has been a huge push for "clean energy". "Clean energy" is energy that does not emit carbon dioxide. Renewable resources are sustainable and include all energy sources that do not lead to a net increase in atmospheric carbon dioxide when utilized. Nonrenewable resources, however, do emit carbon dioxide. Carbon dioxide is a gas that is emitted when burning fossil fuels. Carbon dioxide is considered a greenhouse gas (Royston, 2008). The carbon dioxide in the air acts like a blanket covering the earth in the atmosphere. Without any greenhouse gasses covering the earth, the sun's rays beat down to the earth, they bounce around and leave the atmosphere and travel back into space. When there are too many greenhouse gasses in the atmosphere, the sun's heat is trapped by the gasses and cannot escape the earth as easily. This causes warmer air to stay on earth and eventually creates a warmer planet. The Earth's temperature only increases a small amount each year but will continue to increase over time. It is probable that using fossil fuels is changing the climate (MacKay, 2009). Therefore, climate change caused by increasing amounts of greenhouse gasses in the atmosphere is a problem that can be fixed by using other energy sources instead of fossil fuels.
Energy sources can be categorized into renewable and nonrenewable sources. Renewable resources account for about 7% of our nation's energy use (U.S. Energy Information Administration, 2008). Renewable resources include wind, solar, tidal and geothermal. Solar energy is captured through solar panels, wind is captured through turbines, hydropower is captured through hydroelectric dams, and geothermal can be found deep within the earth's layers. These sources are more expensive to use because of the way they need to be captured. Building wind turbines, solar panels, and dams are expensive to first set up. However, once the power stations are created to capture these resources, there is little cost associated with obtaining the source. Renewable resources are plentiful and will not deplete. They are also "clean" energy and do not contribute to carbon dioxide pollution. Therefore, they do not add to the increasing problem of the greenhouse effect and global warming.
Nonrenewable sources include all fossil fuels. We get most of our energy from nonrenewable energy sources. Nonrenewable resources account for 93% of our nation's energy supply (U.S. Energy Information Administration, 2008). Nonrenewable energy sources are called fossil fuels and include oil, natural gas, and coal. They're called fossil fuels because they were formed over millions and millions of years by the action of heat from the Earth's core and pressure from rock and soil on the remains (or "fossils") of dead plants and creatures. We use fossil fuels to provide electricity to our homes, heat our buildings, and power our cars. They are the most widely used resource. They are heated or burned to create energy and when this occurs pollution is sent into the air. Burning fossil fuels causes carbon dioxide which is a greenhouse gas. By increasing the greenhouse effect in our atmosphere, the average global temperature increases. Not only do fossil fuels create pollution, but the supply is limited and cannot support our current energy demands without diminishing the supply for future generations. Globally there are between 40 and 80 years worth of oil reserves if we continue to burn at the same rate, and between 50 - 150 years of oil if the resource base is included (Lewis, 2006). It is possible that oil will run out in our lifetime or our student's lifetime. Fossil fuels can also be used for other reasons such as making plastic. We should be saving this finite resource to be utilized for a more creative reason (MacKay, 2009).
Solar energy is a renewable resource. The sun is our nearest star that gives our planet energy in many different ways. We can use the sun's energy to dry our clothes, plants use the sun's light to create food, and decaying plants when pressurized in the earth can produce fossil fuels.
Solar energy has been used since the late 1800's with solar water heaters. They became a very popular and cheap way to heat one's home. However, when large deposits of fossil fuels were discovered in the U.S. many people switched from solar water heaters to burning fossil fuels. Another way to capture the sun's energy is to use a highly curved mirror called a parabolic trough. This parabolic trough focuses the sunlight to strike the pipe and it gets so hot that it can boil water to create steam. The steam is used to turn a turbine to create electricity. A third way to collect the sun's energy is through solar cells called photovoltaic cells. These are the small cells that you might see on a calculator. When the cells come in contact with sunlight, electrons are knocked loose and begin to move toward the surface of the cell (California Energy Commission, 2010). Because of this, an electron imbalance is created and an electric current begins between the negative and positive sides. These same cells can be arranged in a larger model and used in a person's home or buildings. This type of solar collection provides immediate electricity.
Average solar panels have an efficiency of about 10% and more expensive panels have about 20% (MacKay, 2009). Therefore, covering your roof with solar panels will not be enough to power your home year round. Solar power plants that send power through lines would also be expensive but would be able to produce enough energy to power our homes. Also, keep in mind that some energy is lost in transportation.
The best places to capture the sun's energy are places that get direct sunlight for most of the day. Because deserts very rarely rain, they are a great location for solar power plants and can produce a lot of electricity. The Mojave Desert in Southeastern California is one example of utilizing a desert for solar power. Solar power plants would not be very efficient in a place with a lot of clouds or with short days. Solar power cannot be collected at night. The mirrors also take up a large amount of space covering land. Lastly, they are expensive to build and would not be cost effective unless constant direct sunlight was supplied near your home.
Building solar power plants is currently expensive. However, there is ample solar energy potential. Once the power stations are built, there is very little cost thereafter and they supply a great amount of energy. Solar energy is the only renewable resource that has enough potential energy to satisfy the future needs of 10-20 terawatts of carbon-free energy in the year 2050 and only 0.16% of the earth's surface is needed to collect this is energy (Lewis, 2006). No other source has the potential to supply such a great amount of energy for the demand our earth will face in the year 2050.
Hydropower is another renewable resource. Hydropower is harnessed from flowing water. Students have probably seen river mills where water can either go over the top of the wheel or can push past the wheel. These mills have been used for hundreds of years to grind flour or corn.
Today we use a similar concept to generate electricity. The three different ways of using water to generate electricity are hydroelectric, tidal, and wave power. The most common way to generate electricity is with hydroelectric. Hydro means water, so hydro-electric means making electricity from water. Moving or falling water can be used to do work. Hydroelectric power is when a large amount of water tries to squeeze through a narrow gap and produces a strong force. This strong force is harnessed and turned into electricity. To do this, a dam is built across a river to stop the flow of water. This forms a reservoir lake to fill up behind the dam. The dam has to be built very strong to make sure it can hold the water back from spilling over into the river. The dam is also constructed with a small tunnel. Water from the lake is able to stream through the tunnel with great force. The water has so much force from all the pressure of the lake that it spins a turbine and generates electricity (Royston, 2008). Hydroelectric power stations are very efficient at converting the water's energy into electricity. States with high mountains and a lot of rivers are great for generating hydroelectricity.
Hydroelectricity is a very reliable resource for energy and appears to be a model energy source. For example, once the dam is built the lake is so big that even when there is a drought the water is not depleted. Water is a renewable resource so it is very sustainable. The water cycle is a great example to show students how it will not deplete. Collecting the energy and turning it into electricity does not emit carbon dioxide. However, with every resource there are also some negative reasons for harnessing its energy. Hydroelectricity does not contribute to the greenhouse effect when it is being harnessed but it does contribute to the greenhouse effect through the building of the dam. It does take a lot of concrete to build the dam which releases tons of carbon dioxide into the atmosphere (Royston, 2008). There are also some environmental concerns once the dam is built in rivers. One issue is the impact dams have on ecosystems. Fish are blocked from swimming up and down the river to reproduce. The river also floods creating a large lake behind the dam and people and other animals have to relocate from their homes.
Hydroelectric is a very attractive renewable resource. It should be captured in locations with large flowing rivers if possible. The plants are also efficient at harnessing the energy of flowing water and in 1997 it produced 0.3 terawatts globally (Lewis, 2006). Although this is a lot of clean energy produced, this is not nearly enough energy to reach the global need of 10-20 terawatts of carbon-free power in the year 2050. Hydropower alone will not be enough to power our planet.
Fossil fuels are a nonrenewable resource. Fossil fuels include coal, oil, and natural gas. They were formed from decaying plants and tiny sea creatures that lived hundreds of millions of years ago (Royston, 2008). When the plants and tiny sea creatures died they were covered by layers of silt. As the silt piled up, the plants became pressurized and over millions of years became coal and natural gas. The sea creatures became oil and natural gas.
Coal is often found underground and the seabed. A lot of coal is cut from mines near the surface. Some coal mines are dug by putting shafts under the earth surface. Coal miners then travel deep underground by elevators or trains and dig the coal out. Another way coal is mined is in strip mines. In these mines, huge steam shovels strip away top layers above the coal. Once all coal is removed, the earth's layers are restored back (California Energy Commission, 2010). After coal is removed, it is shipped by train, boats, and pipelines. For shipment through pipelines, the coal is ground and mixed with water until it turns into a slurry. It is then pumped through pipelines until it reaches power plants.
Oil is also found under the ground and the seabed. Some scientists believe that tiny diatoms are the source of oil (California Energy Commission, 2010). Diatoms are tiny sea creatures. These organisms are similar to plants because they use photosynthesis to convert sunlight into stored energy. When the diatoms died their remains fell to the seafloor and were buried under rocks. The rock pressurized the diatoms and the stored energy could not escape. This stored energy eventually turned into oil. Native Americans living in North America skimmed oil off the top of streams and lakes. This technique was used where oil could be found on the surface of water. Then, in 1859, a man named Edwin L. Drake found oil under ground and invented a way to pump it to the surface (California Energy Commission, 2010). Today companies drill through the earth to find oil and natural gas deposits pocketed in the earth's layers. Oil and natural gas are then pumped to the surface by oil rigs. They are then usually transported through pipelines or by ships. Oil must be refined before it can be used. Oil can be found in many parts of California and Alaska. More than 50 percent of the U.S.'s oil supply comes from outside our country. Most of the outside suppliers are from the Middle East.
Oil can be used for more than just energy. Oil is made into fertilizers for farms, fibers for clothes, and plastic. Almost all plastic comes originally from oil (California Energy Commission, 2010). If we use all the oil resources for energy, we will not have it for other uses.
Natural gas is mostly made of methane. Methane is a chemical compound made up of carbon and hydrogen. Methane is one atom of carbon combined with four atoms of hydrogen (California Energy Commission, 2010). It was formed millions of years ago at the same time that coal and oil were formed. It was also trapped between layers of the earth's surface with oil. At first, people burned natural gas off of oil because they thought it was a waste. Today people use it in power plants because they realize it produces less carbon dioxide then oil. Natural gas is very flammable so when it is sent to storage tanks it is mixed with a chemical to give it a potent odor so that it is easily detected if there is a leak. This is done for safety reasons.
Fossil fuels are a great resource because they are so cheap to use. They are a material that burns very easily. Because these resources derive from living things, they are composed mostly of carbon and hydrogen. Most living things that die release these chemicals, but since these living things were trapped underground the carbon became trapped and could not release itself. Carbon makes good fuel because it burns well. However, when it combines with oxygen from the air it makes carbon dioxide. As described earlier, carbon dioxide is a greenhouse gas that acts as a blanket surrounding the earth and traps in heat from the sun's rays. This trapped heat is warming the earth's surface. Not only are fossil fuels bad because they pollute the earth and create a warmer climate when burned, but they are also limited. If we assume that the consumption of coal grows 2% each year as it has in the past, then coal will be gone by the year 2096. If the growth rate is 3.4% per year, then we will run out of coal before the year 2072 (MacKay, 2009). Fossil fuels not only produce carbon dioxide and other pollutants when burned, they also are finite and will not last long enough for our global demands. Since they were made hundreds of millions of years ago, they cannot be made again in our lifetime. Once they are gone, they are gone.
Wind is a natural renewable resource that can be harnessed as energy. Wind is a resource that is derived from the sun. The sun's rays heat the earth's surface. Some parts of the earth become hotter than other parts. The difference in temperature creates wind (Royston, 2008). The kinetic energy of the wind can be changed into mechanical energy or electrical energy. When a sailboat moves through the water the wind is doing work by pushing on the sail and moving the boat. In the past, windmills were used to pump water or grind wheat or corn. Today wind can be used to make electricity. The wind offers a free sustainable source of carbon-free energy.
Wind is now utilized through wind turbines. When wind blows at the blades of a wind turbine, the blades spin. Wind turbines have three blades that reach up to 300 feet long. The blades are connected to a hub that is mounted at the top of a tall hollow tower. When the hub spins the connected shaft spins as well. The shaft goes through a gear transmission box where the speed of the turning is increased. The transmission is attached to the generator that turns the spinning motion into electricity. A computer inside the hub monitors the motion of the turbine and will change the direction of the blades to get the best speed. If the speed is too strong, the computer will slow the blades down so that they do not get damaged. The electricity is transported through cables and sent through a transformer. The transformer increases the voltage to send the electricity farther through power lines.
Wind farms consist of several wind turbines. The farms can produce enough electricity to power communities. Wind farms work best in places that are windy. In order for a turbine to work efficiently, the wind's speed usually must be above 12 to 14 miles per hour. The wind must reach these speeds in order to generate electricity. Each turbine usually produces about 50 to 300 kilowatts of electricity (California Energy Commission, 2010).
Wind is a resource that will never run out and it will always cost nothing. In places where it is very windy like off the coast of an ocean or flatlands like prairies, wind farms can generate a lot of electricity. However, many communities complain that they are too large and take up too much space. People also complain that they are an eyesore and take away from the skyline view. Neighboring homes proclaim that these farms create too much noise and are a nuisance to live near. The global demands in the year 2050 will not be met through wind power only (Lewis, 2006). To generate enough electricity through wind would involve large windmill installations far offshore and the issue of transporting electricity becomes a factor. When electricity is transported long distances energy is lost. Lastly, it is uncertain if wind turbines would affect regional weather. Wind energy should be harnessed in places that have a large amount of wind. However, putting wind turbines all over the earth to capture energy will not provide a global solution to meet our energy demands.