12 | Energy Production | IB Physics Content Guide |
Big Ideas
• Most energy sources can be traced back the sun, our ultimate primary source
• Energy sources must be compared based on many factors including energy density, cost, availability, politics, safety, and environmental impact
• No energy source can be converted to electricity with 100% efficiency
• All energy sources have advantages and drawbacks and it important to understand the complete picture
• Every object with a temperature above 0 K emits thermal radiation
• Radiation intensity is related to separation distance by the inverse square law (similar to force fields)
• The Earth’s climate relies on a delicate thermal energy balance where total energy in equals total energy out
Content Objectives
12.1 – Energy Sources Overview | ||||
I can list the top 6 most common sources in the global energy supply and general % of total |
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I can describe the different ways (sectors) that energy is used for |
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I can distinguish between primary and secondary energy sources |
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I can define power as a rate of energy usage in terms of watts |
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I can calculate the efficiency as the percentage of useful energy of the total |
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I can interpret energy flow from a Sankey Diagram |
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I can define specific energy and energy density with proper units |
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I can use specific energy to calculate the amount of fuel needed for a given amount of power |
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12.2 – Fossil Fuels | ||||
I can give an approximate number of years left in proved fossil fuel reserves |
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I can explain the Hubbert Peak and why it is important |
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I can discuss where the United States’ oil supply comes from |
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I can describe the process of fracking and how it is used to extract oil and natural gas |
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I can identify the primary uses for each of the primary fossil fuels |
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I can compare the transportation methods for the different fossil fuels |
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12.3 – Nuclear Power | ||||
I can describe the chain reaction that occurs to support a self-sustaining fission reactor |
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I can describe the concentration of U-235 as a sample is enriched into fuel-grade uranium |
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I can outline the process of enriching uranium |
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I can explain how a nuclear reactor transforms the energy of a fission reaction into electricity |
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I can describe the role of the moderator and control rods in a nuclear reactor |
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I can discuss the challenges of disposing of nuclear waste |
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12.4 – The Renewables | ||||
I can list examples of energy sources that are considered renewable |
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I can list examples of energy sources that are known carbon dioxide emitters |
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I can calculate the power produced by a wind turbine |
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I can compare the different styles of solar power and what each is used for |
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I can calculate the power from a solar panel from the panel area and solar intensity |
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I can describe the factors that affect the solar intensity in different locations on Earth |
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I can outline the operation of a hydropower generator |
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I can explain how a hydropower plant can incorporate pumped storage to store energy |
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I can list challenges that are facing a future of renewable energy |
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12.5 – Thermal Energy Transfer | ||||
I can provide examples of conduction, convection, and radiation |
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I can define black-body radiation in terms of absorption and emission of light |
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I can describe an object based on its emissivity |
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I can calculate the power emitted by a black body radiation using the Stefan-Boltzmann Law |
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I can describe the shape of the emission spectra in terms of radiation wavelength |
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I can mathematically relate peak wavelength and temperature using Wien’s displacement law |
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12.6 – Radiation from the Sun | ||||
I can define intensity with proper units |
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I can describe how intensity changes according to the surface area of a sphere |
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I can derive the Solar Constant from the sun’s power and distance from earth |
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I can calculate the average solar intensity on earth from the solar constant and earth’s radius |
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I can compare the properties of albedo and emissivity |
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I can list the gases that have the largest impact on the greenhouse effect |
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12.7 – Climate Change | ||||
I can describe the greenhouse effect as absorption and re-emission of thermal energy |
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I can describe the concept of thermal equilibrium and how it pertains to earth |
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I can recognize trends in the climate model based on different factors |
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I can describe the long term and seasonal trends in the carbon dioxide concentration |
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I can list examples of positive and negative feedback loops in terms of the climate discussion |
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I can engage in an evidence-based conversation about climate change |
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12 | Energy Production | Shelving Guide |
Global Energy Usage
Rank | Energy Source | % |
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1 | Oil | 32% | |
2 | Coal | 28% | |
3 | Natural Gas | 22% | |
4 | Biomass | 10% | |
5 | Nuclear | 5% | |
6 | Hydropower | 2.5% |
Efficiency
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Sankey Diagram Rules: Width of the arrow proportional to the amount of energy |
Energy Density
Definition | Units | |
Specific Energy | Energy transferred per unit mass | J kg-1 |
Energy Density | Energy transferred per unit volume | J m-3 |
Primary and Secondary Sources
Primary Energy Sources | Secondary Energy Sources |
Energy sources found in the natural environment (fossil fuels, solar, wind, nuclear, hydro, etc.) | Useful transformations of the primary sources (electricity, pumped storage for hydro, etc.) |
Fossil Fuels
Number of years left in global reserves |
| Describe the process of Fracking: | |
Coal | ~100-150 years |
| 1. Drill hole into shale rock 2. Inject fracking fluid at high pressure to create cracks 3. Extract newly released natural gas 4. Seal fracking fluid in the hole |
Oil | ~50 years |
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Natural Gas | ~50 years |
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Nuclear Power
| % of U-235 |
| Why is the concentration of U-235 important? Only U-235 can undergo a fission chain reaction |
Uranium Ore | 0.7% |
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Fuel-Grade | 3.5% |
| What is done with the nuclear waste? Stored on-site in spent fuel pools and/or concrete dry cask storage |
Weapons-Grade | 90% |
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Moderator | Control Rods |
Slows down neutrons to be absorbed by U-235 Made from Water or Graphite (carbon) | Absorbs neutrons to limit number of chain reactions Made from Boron |
Renewable Energy
Variable Symbol | Unit |
| Data Booklet Equations: | |
Power | P | W |
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Cross-Sectional Area | A | m2 |
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Air Density | ρ | kg m-3 |
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Air Speed | v | m s-1 |
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Photovoltaic Cells | Solar Concentrator | Solar Heating Panel |
Converts solar energy directly into electricity. Useful in solar panels on top of building or solar farms connected to the energy grid | Mirrors focus sunlight onto a central tower. The high thermal energy is converted to steam and runs turbines to produce electricity | Sun’s radiation is absorbed by black pipes that transfer thermal energy to the water flowing through them. Replaces hot water heater. |
| Biomass | Coal | Geothermal | Hydropower | Natural Gas | Nuclear | Petroleum | Solar | Wind |
Renewable | ✓ |
| ✓ | ✓ |
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| ✓ | ✓ |
Produces CO2 | ✓ | ✓ |
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| ✓ |
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Thermal Energy Transfer
Conduction | Convection | Radiation |
Energy is transferred through molecular collisions | Energy circulates through the expansion and rising of hot fluids | Energy is transferred through electromagnetic radiation. Can travel through a vacuum |
| Emissivity |
| Black Body Radiation |
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Sun | ~1 |
| An idealized object that absorbs all the electromagnetic radiation the falls on it | |
Earth | ~0.6 |
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Black-Body | 1 |
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Power Emissivity | Variable Symbol | Unit |
| Data Booklet Equations: |
Power | P | W |
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Emissivity | e | — |
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Surface Area | A | m2 |
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Temperature | T | K |
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Max Wavelength | λmax | m |
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Solar Radiation and Climate Change
Intensity | Variable Symbol | Unit |
| Data Booklet Equations: |
Intensity | I | W m-2 |
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Power | P | W |
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Area | A | m2 |
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Greenhouse Gases |
| Positive Feedback Loop | Negative Feedback Loop |
Water Vapor (H2O) |
| Melting ice (decreases albedo) | Cloud formation (increases albedo) |
Carbon Dioxide (CO2) |
| Melting permafrost (releases methane) | Increased photosynthesis (uses CO2) |
Methane (CH4) |
| Rising ocean temp releases methane | Climate Change leads to renewables |
Energy measurements
Specific energy (ES): “Amount of energy a fuel releases per unit mass”, in J kg^-1.
Energy density (ED): “Amount of energy a fuel releases per unit volume”, in J m^-3.
Both useful in the choice of a fuel, but other factors must be taken into account, such as transportation, availability, safeness etc.
Energy classifications
Primary energy: Found in nature, which has not yet been transformed or converted.
Examples: Fossil fuels (oil, coal and natural gas), Solar energy, Kinetic energy of air.
Secondary energy: Resultant from the transformation of a primary source.
Examples: Electricity and Kinetic energy from wheel.
Transformation process: From primary energy form into secondary energy form.
Renewable sources: “Rate of use is less than the rate of production of the source”.
Examples: Biomass, solar, hydroelectric, wind.
Non-renewable sources: “Rate of depletion is greater than the rate of production”.
Examples: Fossil fuels and nuclear.
Energy sources
Fossil fuels (oil, coal and natural gas): Burning fossil fuels in thermal power plants.
Process:
Initial chemical potential energy (decomposition of dead animals and plants)
Kinetic energy of moving steam
Kinetic energy of turbines
Electrical energy (generator).
Nuclear power (uranium and plutonium): Induced fission in thermal fission reactors.
Fission reaction
Uranium enrichment: U-238 absorbs neutrons. Hence, uranium needs to be enriched, i.e. the percentage of U-235 needs to be increased to up to 3%, producing yellow cake, thus achieving critical mass and being able to have a chain reaction.
moderator
Moderator (graphite or H20): reduce the speed of neutrons, because very fast moving neutrons do not induce fission.
Heat exchanger: allows coolant (H20 or C02) to transfer heat from reactor to water.
Control rods: absorb neutrons, so that the reaction does not go out of control.
Safety issues:
Radioactive waste: buried deep underground in containers, supposed to avoid leakage
Fukushima: reactor explosion.
Chernobyl: thermal meltdown of the reactor.
Solar power
Solar heating panel: sunlight directly used to heat up water.
Photovoltaic cells: sunlight directly converted into direct electrical current (dc), as the light incident on the panel releases electrons and establishes a pd across the cell.
Wind power
Formula: maximum theoretical value of the available power = ρAv3.
Assumptions: all wind is stopped, no friction or turbulence.
Ideal places: off-shore and top of hills, due to higher wind speeds.
Hydroelectric power
Process: potential energy of a mass of water transformed into electricity.
Formula: P = mgh/∆t = ρ∆Vgh/∆t = ρQgh, where Q = volume flow rate and ρ the water density.
- Reverse process (pumped storage system): storing energy in large scale in the case of necessity (emergency), what requires more energy than it will be gained.
Sankey diagram
Use: represents energy and power flow, from left to right.
Representation: each energy source and “loss” is represented by an arrow.
Arrow drawn to scale (both vertical and horizontal).
Energy flow always from left to right.
Degraded/”lost” energy to the bottom.
8.2 Thermal Energy Transfer
There are three types of thermal energy transfer: conduction, convection and radiation. While conduction and convection will only occur if there is a difference in temperature, radiation will always occur. Temperature will be constant if radiant heat from surroundings equals heat lost by radiation.
Conduction
Definition: moving electrons collide with neighboring molecules, transferring energy to them and so increasing their average kinetic energy, and, consequently, the temperature.
Occurrence: normally in solids, because fluids have weaker inter-atomic bonds and their atoms are further apart.
Materials: good thermal conductors are normally good electrical conductors (e.g. copper), since the mechanism is similar.
Convection
Definition: movement of groups of atoms or molecules within fluids that arise through variations in density, leading to thermal energy transfer.
Movement direction: Mass of fluid is bottom heated, what decreases density, causing mass to go up, while mass that goes down is heated, leading to the formation of a convection current.
Thermal radiation
Definition: transfer of energy by means of electromagnetic waves, and so, it does not require a medium, like conduction and convection do.
Black body: at a certain temperature, black bodies absorb all incoming energy, while at other, it emits great amount of radiation.
Intensity (I) definition: “The power received per unit area from a radiating source”.
I = P/A
Stefan-Boltzmann’s law: P = eσAT^4, where σ = Stefan-Boltzmann’s constant = 5.67 x 10^-8 W m^-2 K^-4 and e = emmissivity of a body.
Emmissivity:
For a black body: e = 1.
Grey bodies: all other bodies, 0 < e < 1
Albedo (α): the ratio of the power of radiation scattered from the body to the total power incident on a body
Relationship between albedo and emissivity: α + e = 1.
Albedo of a planet depends on cloud cover, ice, water, color and nature of the soil and latitude.
Solar constant (S): the solar radiation per second per m^2 at the top of the Earth’s atmosphere (= 1400 W m^-2).
Tip: Although the intensity of the Sun’s radiation at the position of the Earth is approximately 1400 W m^-2, the average power received per unit are on the Earth is 350 W m^-2. This occurs, because the solar radiation is captured by a disc of area πR^2, where R is the radius of the Earth, but it is distributed (when averaged) over the entire Earth’s surface, which has an area four times as large (4πR^2). The power received per unit area on the Earth may be further reduced if we take the effect of the albedo into account.
Graph: Radiation distributed over a range of wavelengths.
Wien’s displacement law: T x λmax = 2.90 x 10^-3 K m.
Greenhouse effect
Definition: the warming of the Earth caused by infrared radiation, emitted by the Earth’s surface, which is absorbed by various gases in the Earth’s atmosphere and is then partially re-radiated towards the surface.
Greenhouse gases: The gases primarily responsible for this absorption are water vapor (H2O), carbon dioxide (CO2), methane (CH4) and nitrous oxide (NO2).
Temperature balance: energy input to Earth must be equal to energy output by the Earth.
Natural balance on the Earth, due to naturally occurring greenhouse gases.
Enhanced greenhouse effect: increased level of greenhouse gases, commonly attributed to human cause:
Water vapor (H2O): irrigation.
Carbon dioxide (CO2): burning fossil fuels in power plants and cars.
Methane (CH4): flooded rice fields, farm animals, processing of coal.
Nitrous oxide (NO2): burning fossil fuels, manufacture of cement, fertilizers.
The wavelength at which the curve peaks can be associated with temperature through Wien’s law
Earth’s Energy Balance
Unit 8. Energy production Questions and Answers
Sankey diagrams indicate how much energy remains after a series of transformations. The arrows pointing upwards indicate exhaust while the arrows pointing downwards indicate loss due to heat, friction or other factors. The thickness of the lines should be proportional to the percentage of energy being represented. Exercises with Sankey diagrams include identifying where energy is degraded, calculating overall efficiency and drawing diagrams to represent energy conversions.
Using Sankey diagrams, we can calculate the efficiency of a process. Efficiency can be calculated by:
(Useful Energy Output ÷ Total Energy Input) x 100
It is a percentage value with no units.
Electricity can be produced mechanically, chemically or through photovoltaic cells. It can also be stored chemically in the form of batteries.
Mechanical energy is converted to electrical power through an electric generator. Electric generators are powered through steam, water or air. Generators come in the form of AC (alternating current) or DC (direct current). Most generators have a wired loop or coil that is rotated in a magnetic field to produce a current, this is called electromagnetic induction. The wired loop or coil is attached to a turbine that will turn when it is impacted by steam, wind or water, thus creating a current.
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Renewable Resources
| Non-renewable Resources
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The questions you need to ask yourself are:
- Does this fuel release greenhouse gases and contribute to global warming?
- Does this fuel pose a risk to human health or other living organisms?
- Does this fuel pollute or pose a threat to the environment?
- Is fuel source renewable or non-renewable?
- Is this fuel expensive?
- Does this fuel have a high or low energy density?
- Is the fuel continuously available or is it dependent on factors such as weather or time of the day/night?
The demand of a power station is the amount of joules needed in a certain period of time to comply with the required energy at that moment. In simpler terms, it is the amount of energy that needs to be generated in order to satisfy the demand of a group of people. Fossil fuels have a high energy density so they are able to meet the current demand, however, as the demand increases, more fossil fuels need to be burned.
Energy density can be used to calculate power through the following formula:
- Power output = efficiency x mass of fuel burned every second x energy density
The mass of fuel burned every second can also be defined as the rate of consumption.
Advantages
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Natural gas power stations are the most efficient types of power stations. They are able to convert nearly half of the chemical energy in gas to electricity (45% efficient). Efficiency can be raised if the excess thermal energy is used to heat houses, or if surplus heat from a gas turbine is used to heat water and produce steam.
The factors that affect the efficiency of power plants include:
- The type of fuel used
- The load factor (ratio of average energy demand to maximum demand during a period)
- Technology used
Problems with fossil fuels in power stations
| Problems with retrieval of fossil fuels
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Nuclear Power
In order to gather enough Uranium-235, samples of ordinary Uranium must be enriched. Not all Uranium is fissile (able to sustain a chain reaction), therefore the fissile isotopes of Uranium must occupy a certain percentage of the overall sample in order to drive nuclear fission; a high percentage of non-fissile Uranium would cause the reaction to stop. A sample of Uranium typically contains 99.2% Uranium-238 and 0.72% Uranium-235. Enriched Uranium contains at least 2-5% Uranium-235, although higher percentages are possible. Nuclear weapons require a sample that contains 99% Uranium-235. Uranium is enriched through the formation of hexafluoride followed by the separation of Uranium-238 and Uranium-235 in a gas centrifuge. In more detailed terms, a type of Uranium gas is put into a centrifuge — a series of cylinders with a rotor inside of them. The mixture of isotopes is spun around at high rates (up to 70,000 rev/min). The heavier Uranium-238 requires a larger centripetal force to stay in the circular path and thus moves to the outside of the centrifuge, while the Uranium-235 requires a smaller force and collects together in the enter. The Uranium-238 (now called “depleted Uranium”) can then be scraped off the edges while the remaining Uranium is spun a few more times. This process is repeated until the Uranium has the desired percentage of 3% Uranium-235. It requires very technical and challenging engineering, partly because of the tremendous forces involved.
The critical mass is the minimum amount of Uranium needed to sustain a controlled reaction. As the surface area to volume ratio of an object increases, the higher the probability of a neutron colliding with it, thus a greater percentage will cause fission. Uranium that contains 20% Uranium-235 has a critical mass of 400 kg.
The thermal fission nuclear reactor or Magnox reactor utilizes nuclear fission to create energy.
- The control rods, held by electromagnets, take in neutrons in order to control the reaction and ensure that for every fission, one more fission is triggered at a constant, manageable rate. Control rods can be made of boron or cadmium steel, since these materials absorb neutrons without fissioning. When the reaction goes out of control, the control rods are released from their magnets in order to stop the fission reaction completely.
- Fast neutrons (neutrons at around 1-2meV) will end up bursting through the nucleus, so they need to be slowed down by the moderator. Moderators can come in the form of graphite, water, deuterium monoxide, beryllium and liquid sodium. These materials have small atoms with masses that correspond with the neutrons. The neutrons are slowed down from a speed of 10^6 ms-1 (“fast neutrons”) to 10^4 ms-1. At this speed, they are known as thermal neutrons. Thermal neutrons have an energy of around 0.2MeV.
Since Plutonium-239 has a half-life that is significantly higher than that of Uranium and Neptunium, it is easily stored. The short amount of time required to produce Plutonium also makes it an attractive source of fuel. Plutonium-239 can also be used in a nuclear weapon if it is pure enough.
Uranium enriched with 20% Plutonium-239 can be used in a fast breeder reactor. In this reactor, the fast neutrons released from the fission of Plutonium-239 are capable of triggering more fissions, therefore a moderator is not required. This saves spacing and costs. The overall process operates at a very high temperature that requires liquid sodium to cool it down. The liquid sodium can be contained with electromagnetic pumps.
Some problems associated with using nuclear power include:
- A thermal meltdown can occur when a component fails and the reactor core overheats. This usually occurs due to a lack of coolant or a power surge that overrides the coolant’s abilities. It can also be caused by failed control rods. A prime example would be the disaster at Chernobyl.
- Radioactive waste can be produced from nuclear power; it is generally costly to maintain. This waste can be either high-level or low-level, depending on its radiation per mass or volume. High-level waste is converted to a rock-like form and placed underground, while low-level waste is buried (20 ft) in shallow depths in soil. Incidents can occur with material that is not disposed of appropriately, leakages during transport, abandoned waste or stolen waste. Inappropriately handled waste can harm humans and other living organisms
- Mining uranium can cause toxic radon gas emissions, which decay to Radon-222, a carcinogen. Mining Uranium can also contaminate air, water and soil.
- Nuclear weaponry is possible. The Plutonium-239 generated in breeder reactors is very pure and Uranium enrichment is another process that can produce fuel for nuclear weapons.
Although nuclear fusion theoretically seems to be the cleanest and most efficient energy source, it is very difficult to manage with current-day science.
Overall, the difficulty of confining high density plasma is what makes nuclear fusion unsustainable. Below — the Russian Tokamak thermonuclear reactor core.
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Solar Power
Photovoltaic Cell
Photovoltaic cells or solar cells create a direct conversion from light energy to electrical energy. Silicon, gallium and other semi-conducting materials are able to emit electrons when excited by photons. These electrons can only move in one direction, creating a potential difference. | Solar Heating Panel
A solar panel uses solar heat to heat up water or air. Solar panels are usually connected to heat exchangers; the heated water or air can be provided to homes or used to produce steam and turn turbines. Most solar cells operate at less than 20% efficiency, with future hopes aiming at 40%. |
- Weather and climate will affect the intensity of the sun. Some areas are more cloudy than others.
- Due to the earth’s spherical shape, the sunlight is more spread out near the poles because it is hitting the earth at an angle, as opposed to hitting the earth straight-on at the equator. There is also less atmosphere at the equator, allowing more sunlight to reach the earth. Hence, the intensity varies depending on the geographical latitude of the location.
- Due to the earth’s rotation, all areas are not consistently exposed to sunlight. Areas that are experiencing ‘nighttime’ are not receiving a lot of the sun’s power, therefore the time of the day or night will affect the solar constant.
- The angle of the surface to the horizontal at that location
Hydroelectric Power
When water is able to freely flow downwards, the gravitational potential is converted to kinetic energy, which can be used to drive a turbine. In order for this process to work, it must be cyclical.
There are three different types of hydroelectric power:
- Water storage in lakes
- Tidal water storage
- Pump storage
Water storage in lakes
Water storage in lakes is when water flowing down from mountains or from the sky (as rain) is stored in artificial lakes and run through dams, turning turbines and generating electricity. These lakes are called reservoirs. The processed water usually continues to flow into a river. Some of the water in the river evaporates due to convection currents and forms clouds, which then release either rain or snow, allowing more water to be stored in the reservoir. The largest dam in the world is the three gorges dam on the Yangtze river. | Tidal water storage
Tidal water storage is when dams take advantage of the gravitational attraction between the earth and the moon. As the earth spins on its axis, this gravitational attraction causes some parts of the ocean to rise and others to fall. Oceans rise and fall approximately twice every day. Water is stored behind a dam through sluices at a high tide and then released at a low tide to generate electricity. The gravitational potential energy of the high tide is used to produce electrical energy by spinning turbines. |
Pump storage When the demand for power is low, electricity can be expended to pump water back to a higher location. At night, power stations operate at a lower efficiency and use some of the energy to pump water back up then release it during the day for extra power. |
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Wind Power
The wind turbine is composed of a tower, rotating blades, a generator and a storage or grid system. When the blades of the wind turbine move, the axle rotates. This axle is connected to coil of wire in a generator — this is called the armature. The armature is then rotated in a magnetic field and creates a current.
The mass can be defined as the volume of air hitting the blades at each given second. This is written as the volume of the air multiplied by its density. The volume can be redefined as the area multiplied by the velocity, since the amount of wind passing each second is equal to the length of the wind ‘cylinder’ hitting the blades:
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Wave Power
Solar Radiation
| The intensity of the sun’s power can be calculated at various points through the following formula:
If we imagine that the sun produces a sphere of radiation, the radius of this sphere would be the distance from the sun to the target object. The P in this case would be the luminosity of the sun (power emitted by the sun due to fusion reactions), which is defined by 3.84 × 10^26W. The radiation incident on the target object is hence represented by the intensity I. |
The solar constant represents the average amount of incoming solar electromagnetic radiation per unit area on the earth’s surface. This constant constitutes all types of solar radiation, including UV and infrared. It is thought to be approximately 1.361kW/m^2. The accuracy of the solar constant is questionable due to the following generalizations:
- This radiation is assumed to be incident on a plane perpendicular to the earth’s surface.
- It is assumed that the earth is at its mean distance from the sun.
- Seasons have different cloud formations and latitude. In thin clouds, albedo varies from 30-40% whereas in thicker clouds it can be up to 90%.
- Light surfaces such as deserts will tend to have a higher albedo while dark surfaces, such as seawater, will absorb more radiation.
- Areas of ice and snow have a high albedo compared to the rest of the planet and will reflect most of the radiation.
The Greenhouse Effect
Carbon dioxide Source: Consumption of fossil fuels ie. petroleum, cellular respiration, decaying matter/fossilization Effect: The most abundant manmade greenhouse gas, contributes significantly to the greenhouse effect | Methane Source: Agricultural land (soil fermentation, animals), burning of biomass, coal mining, gas drilling Effect: 5x more effective in causing the greenhouse effect than carbon dioxide, the oxidation of methane gives off carbon dioxide and water vapour |
CFC’s Source: Aerosols, solvents, air conditioners, refrigerants Effect: Responsible for 15-20% of global warming. When CFC’s are released into the atmosphere, UV radiation breaks them down into chloride ions. The chloride ions then react with ozone and break it down to oxygen; one chloride ion is capable of destroying 100,000 ozone molecules. The thinning of the ozone layer allows more UV radiation to enter the atmosphere, which results in more InfraRed being reflected back and heating up the atmosphere. |
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A black-body is an object that is capable of absorbing all electromagnetic radiation within its surrounding area. The black-body is at thermodynamic equilibrium; its temperature is constant. The radiation emitted by a black body has a special spectrum and intensity that depends on the temperature of the body.
A black body in thermal equilibrium has two notable properties:
- It is an ideal emitter: it emits energy that is more or equal to any other body at the same temperature, at every frequency
- It is a diffuse emitter: the energy is radiated isotropically, independent of direction
In this example, a reduction of outgoing intensity by 2W per meter squared (the current average intensity is 342) would result in an increase of 0.16K. This equation inaccurately suggests that reduced activity would continue to increase global temperature. By using this equation to model climate change, we would be making the following mistakes:
- Any increase in surface temperature would also increase the outgoing radiation, according to the Stefan-Boltzmann law.
- The calculation ignores possible changes to the Earth’s climate due to increasing temperatures (ie. increased cloud cover, melting ice etc.)
- The model does not consider changes in human activity
- It does not take other natural processes that periodically affect the earth’s temperature into account
The accuracy of climate projection could potentially be increased by redoing the calculation every week, day, minute or even second. The problems involved in predicting future temperature and climate result from the numerous interlinked unknowns. For example, scientists are still unsure about the role of clouds in climate change. The surface temperature of the earth is also difficult to determine with a high degree of accuracy and there is some uncertainty regarding the current value of average outgoing radiation intensity.
Milankovitch cycles
| Volcanic activity
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Solar flare activity
| Carbon dioxide emissions
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The enhanced greenhouse effect has mostly been attributed to:
- The burning of fossil fuels, which release greenhouse gases into the atmosphere.
- The reduction of ice/snow cover due to global warming, which reduces albedo and increases the rate of heat absorption.
- Reductions in the solubility of carbon dioxide in the sea due to increases in temperature, which increase atmospheric carbon dioxide concentrations.
- Deforestation reduces carbon fixation by plans, which in turn increases carbon dioxide concentrations.
A rise in mean sea level can occur due to:
- Atmospheric pressure
- Plate tectonic movements
- Wind
- Tide
- Flow of rivers into the sea
- Changes in water salinity
A change in sea level is normal and occurs naturally, however, the enhanced greenhouse effect is a newly developed cause. The change in sea level has, as a result, reached an unnatural rate. Some reasons why this prediction is difficult to make include:
- The anomalous expansion of water (water will expand above 4 degrees Celsius and contract below 4 degrees Celsius, hence, rises in sea level only occur at a certain temperatures)
- Differences between ice melting on water as opposed to land (when ice on the sea (ie. icebergs) melts, the water replaces the area where the ice used to be, therefore there is no change in sea level)
Political steps have also been taken to aid in the reduction of global climate change. These include the intergovernmental panel on climate change (IPCC), kyoto protocol and asia-pacific partnership on clean development and climate (APPCDC).
- The IPCC is the leading international body for assessment of climate change. It was established by the united nations environment program (UNEP) and world meteorological organization (WMO) to provide the world with scientific reasoning on climate change and its potential impacts. It reviews and assess the most recent scientific data produced worldwide to further understand climate change. It is open to all members of the UN and currently 195 countries are signed.
- The Kyoto Protocol is an international agreement linked to the united nations framework convention on climate change. This agreement sets binding targets for the 37 industrialized countries and the european community regarding greenhouse gas emissions. Kyoto mechanisms include emissions trading (“carbon market”), clean development (CDM) and joint implementation (JI).
- The APPCDC was an international, voluntary public-private partnership between Australia, Canada, India, Japan, the People’s Republic of China, South Korea and USA in 2005. These members account for over 50% of the world’s greenhouse gas emissions, energy consumption, GDP and population. Unlike the Kyoto protocol, which imposes mandatory limits on greenhouse gas emissions, this partnership engages member countries to accelerate the development and deployment of clean energy technologies, with no mandatory enforcement mechanism.