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- Distinguish between renewable and non-renewable sources of energy.
Non-renewable energy sources are sources of energy that are available in limited supply. Examples include fossil fuels (like coal, oil, natural gases, etc.) and nuclear energy. This is usually because it takes a long time (often millions of years) for these resources to be replenished.
Renewable resources are replenished naturally and over short periods of time, so are in a virtually unlimited supply. Examples include the solar energy, hydraulic energy, wind, geothermal energy (heat from the Earth’s mantle), etc.
- Know that the Sun is the source of energy for all our energy resources except geothermal and nuclear.
This works because almost everything exists because of the Sun:
Fossil fuels are made from remnants of life that existed millions of years ago – life that relied on energy from the Sun to grow the plants that they eat or life that was these plants themselves. (Remember how in unit B10.0 – Energy Flow in Ecosystems, we discussed how the Sun is the principal source of energy input to all biological systems). Wind is produced by the uneven heating of the air by the Sun (cold air is heavier than warm air, causing them to flow over each other). The uneven heating of water in the ocean causes ocean currents, which can be used as a source of energy. The wind blowing across the ocean can cause waves, too.
Solar energy heats up and evaporates water, allowing it to build up in dams, which allows us to generate hydraulic energy, etc.
Geothermal energy is when we use the heat from beneath the surface of the Earth to generate power and nuclear energy is when we use the energy released by nuclear fission to generate power.
- Demonstrate understanding that energy is released by nuclear fusion in the Sun.
We’ve already discussed how nuclear fusion works in Section P3.1 – Energy, but we haven’t yet explored how nuclear fusion powers the sun.
The Sun is basically a giant ball of gas. At its core, it has mostly Hydrogen and Helium atoms. Because of the humungous mass of the Sun, its gravity is very strong, causing all those atoms to be compressed together and travel at very high accelerations towards each other. They travel fast enough to allow fusion to occur. Generally, two hydrogen nuclei collide to form a Helium nucleus, and they release a large amount of energy. Numerous reactions like these occur, allowing the Sun to release large amounts of light energy, heat energy, sound energy, etc.
- Describe how electricity or other useful forms of energy may be obtained from:
- Chemical energy stored in fuel
- Water, including the energy stored in waves, in tides, and in water behind hydroelectric dams
- Geothermal resources
- Nuclear fission
- Heat and light from the Sun (solar cells and panels)
First, I’m going to explain how a generator works, because a generator is involved in the production of electricity in almost every single one of these methods.
When a generator turns, it generates a current. This is because the turning of the generator causes a magnet to move in an electric field. This is what causes the induction of current. We learn more about this in Unit 14.1.
In some cases, the generator is turned directly.
In wind turbines, the wind causes the generator to turn. Here, kinetic energy is converted to electrical energy.
In hydroelectric dams, the water is held behind a dam, forming an artificial lake or reservoir. The force of the water being released through the dam spins the blades of a giant turbine, which turns the generator, as shown in the diagram. Here, potential energy is converted to kinetic energy, which is then converted to electrical energy.
Next is wave energy. This can be used to generate electricity in many different ways. One of them is the method shown in the diagram. Here, the waves force the water to move up and down inside the chamber, which in turn forces the air in the chamber back and forth through the turbine. This causes the turbine to turn, and thus the turbine turns the generator. In each method of using wave energy to generate electrical energy, the kinetic energy of the wave is used to generate this energy.
The most common method of harvesting tidal energy is called a Tidal Fence. Here, there is a long row of vertical axis turbines (like wind turbines), that span across a channel or a long straight. The water is forced through the turbines, turning them. This turns the generator, which produces electrical energy. Here, the kinetic energy of the water is used to produce electric energy.
In the next few examples, generators are turned indirectly.
In the case of fossil fuels, these fuels are burnt. This produces a lot of heat energy, which is used to heat a reservoir of water. This produces steam, which expands against the blades of the turbine, causing it to turn. This turns the generator, and electricity is produced. In the diagram, the object under 4 is a transformer – this adjusts the voltage of the electricity to the correct voltage to be transported. Here, chemical energy is converted to heat energy, to kinetic/ mechanical energy, to electric energy.
Geothermal resources are used to generate electricity in the same way – their heat is used to heat water, which creates steam, which turns a turbine, which turns a generator. Heat energy is converted to kinetic energy, which is converted to electric energy.
Nuclear fission uses the same method: an accelerated neutron is fired at a Uranium-235 nucleus, which splits into two similar sized neutrons and releases more neutrons. These neutrons collide with and split more Uranium-235, and so on, in a large chain reaction. As a result, an enormous amount of nuclear energy is released, and this energy turns into heat energy. The heat is used to heat water to produce electrical energy in the same method as geothermal energy and fossil fuels are used to generate electricity.
Now we’re going to discuss a type of electricity generation doesn’t require a generator:
Solar panels. Solar panels comprise of many, many smaller units called photovoltaic cells. When light energy strikes a photovoltaic/ solar cell, electrons are knocked loose from the atoms in the semiconductor material. If electrical conductors are attached to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current — that is, electricity. This electricity can then be used to power a load, such as a light or a tool. Here, light energy is directly converted to electric energy.
In newer solar panels, which have the STPV solar cells, there is a layer that absorbs light and heat from the sun and reflects it back as light. This light is captured by a nearby solar cell and converted to electricity. Here, heat energy is turned to light energy, which is then turned into electric energy.
Alternatively, there are solar panels that absorb the sun’s heat and use it to heat water. These do not provide electricity – they just heat water.
- Give advantages and disadvantages of each method in terms of reliability, scale and environmental impact.
- Low-tech equipment required
- Easy to transport
- In abundant supply
- Harmful wastes – greenhouses gases, pollutant gases, radiation
- Is non-renewable, so will run out at our current rate of consumption
- No pollution
- No greenhouse gases
- Is a renewable resource
- Reasonably reliable
- Must be built on bodies of water – can’t be built anywhere
- May not be able to be used during periods of drought, when water levels run low
- No greenhouse gases
- No pollution
- Difficult to build, so can’t be used very large scale
- Not reliable – there aren’t always waves.
- No greenhouse gases
- A reliable resource
- Deep drilling is expensive and difficult
- Produces a lot of energy from very little resources
- Produces radioactive waste
- Potentially dangerous
Solar panels and cells:
- No greenhouse gases
- No pollutants
- Sunshine is not constant, so not reliable
- Expensive to install.
- Demonstrate a qualitative understanding of efficiency.
Efficiency is a measure of how much useful work is done with the energy supplied.
- Recall and use the equation: efficiency = (useful energy output/energy input) x 100%
Use this equation in your questions to calculate efficiency, useful energy output or energy input if you have two of these values.
Notes submitted by Sarah.
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