IB Physics/Energy Power and Climate Change

8.1: Energy degradation and power generation

8.1.1: Parameter of power generation

In any system, thermal (heat) energy can be converted into work in a single process (i.e. heating a piston on a stove to make it expand and do work), but to continuously gain work for said energy, a cyclical process needs to take place, with a transfer of energy from the system to bring it back to the beginning again (i.e. cooling the piston once it's reached maximum volume to return it to normal and continue gaining work from the heat energy of the stove).

You need to be able to State this.

8.1.2: Degraded energy

Degraded energy is thermal energy that is released into the surrounding environment after any process. Once released into the surroundings, this heat energy is completely useless for energy production and is considered 'dead' or 'degraded' energy.

You need to be able to Explain this concept.

8.1.3: Sankey diagrams

A Sankey diagram is something that is designed to show energy losses in various stages in a power generation process. On the left hand side of the diagram, all energy to be converted is drawn as a the stem of an arrow. As you move to the right, the arrow will branch off to either side (depends on the individual diagram) so as to represent energy losses as percentages of what you started with (in Joules or equivalent), until you get to the end, which represents the useable energy produced in the process.

An important thing to note is that the thickness of the stem is, and must be, proportional to the percentage of usable energy remaining. For example, if you drew a Sankey diagram on a graph pad, you could make the stem 10 squares wide. Then say that the first energy loss is 10 percent. So, the arrow that branches off of the main stem would be 1 square wide, with the rest of the stem being left at 9 squares (or 90 percent).

You need to be able to Draw and Interpret these diagrams for various systems, including those detailed in sections 8.3 and 8.4.

8.1.4: General generator mechanism

To produce electrical energy from a power plant, coils of wire are rotated in a magnetic field. This is called a dynamo. Note that saying a turbine generates the energy will not earn you any marks. A turbine simply turns the linear kinetic energy (from steam in a steam turbine, for example) into rotational kinetic energy to be used in the dynamo.

You need to be able to Outline this concept. This process is detailed further in Topic 12: Electromagnetic induction but details are NOT expected in this section of the course.

8.2: World energy sources

8.2.1: Different energy sources

You should know of the existance of the following energy sources: coal, natural gas, oil, biofuel, nuclear fuel, wind, tidal, solar and wave.

Coal is plant matter that, over many thousands of years, has turned into a sedimentary rock. It has had nearly all of its moisture taken out in its formation. Oil and natural gas are the products of decaying plant matter in a lack of oxygen - they are found in pockets underground, with the gas found just above the oil. Biofuel is a fuel made from sugar canes and the like. Solar, wind, tidal and wave are pretty self-explanitory. Nuclear fuel is usually made up of Uranium-235, mined from under the ground.

For the most part, the Sun is the main precursor in all of our energy sources - fossil fuels are made from long dead plant matter (which was around because of the sun), and wave, solar and wind are all to do with weather (which the sun plays an inportant role in).

You need to be able to Identify these sources.

8.2.2: Non-Renewable versus Renewable

The main difference between the renewable and non-renewable sources is that non-renewable sources (fossil-fuels) release CO₂ when used to make energy. Alternaitvely, you can just say that non-renewable sources are burnt.

On that note however, biofuel, which can almost be classified as renewable as it doesn't use the long-decayed matter, does in fact release CO₂ when used. BUT, unlike fossil fuels, it can be renewed by planting more of its source product.

You need to be able to Distinguish between the two.

8.2.3: Energy density versus Specific energy

Specific energy is the amount of energy per unit mass of a fuel, given by Jkg^-1.

Energy density is the amount of energy per unit volume of a fuel, given by Jm^-3.

You need to be able to Define this.

8.2.4: Choice of fuel

As a general rule of thumb, fuels with higher energy density will be chosen over one with a lower energy density. Uranium-235 has the highest energy density, but it is expensive to start and run a nuclear power generator. Among fossil fuels, which are used often, natural gas has the highest density, followed by oil and then coal.

You need to be able to Discuss these concepts.

8.2.5: Relative proportions

The list of energy source by proportional useage goes like this: Oil ≈ 35%, Coal ≈ 25%, Natural Gas ≈ 20%, Renewable sources (all of them) ≈ 15%, Nuclear ≈ 5%.

Note that you only need approximate values for these. The proportions are what really matters.

You need to be able to State this.

8.2.6: Advantages and Disadvantages

You need to be able to discuss the pros and cons of each energy source listed previously.

Advantages

Fossil fuels

• Found on every continent, so relativly easy to find and use.
• Easy to gain energy from - no large technological demand relative to other sources.
• Easy to construct power station in basically any area.

Nuclear Energy

• Extremely high energy density.
• Doesn't contribute to the enhanced global warming effect.

Hydropower

• Very efficient compared to other sources.
• Low running costs.
• Renewable.
• Doesn't contribute to the enhanced global warming effect.

Wave Power

• Doesn't contribute to the enhanced global warming effect.
• Very high potential power output.

Tidal power

• Renewable.
• Doesn't contribute to the enhanced global warming effect.

Solar energy

• Widespread source.
• Doesn't contribute to the enhanced global warming effect.
• Can work in more remote areas.

Wind Power

• Doesn't contribute to the enhanced global warming effect.
• Many possible sites for construction.
• Can work in more remote areas.

Disadvantages

Fossil fuels

• Contributes heavily to the enhanced greenhouse effect.
• Non-renewable - supplies will run out quite fast at current rate of consumption
• Low energy density

Nuclear Energy

• High set up and maintanance costs
• Creates highly radioactive and hard-to-dispose-of waste.
• Possibility of a reactor meltdown.

Hydropower

• Requires large dams to be built - high cost.
• Causes up river flooding and down river drought.
• Dam can break and release of water can cause significant damage.

Wave Power

• Hard to build.
• High maintanance cost due to power of waves.

Tidal power

• Low energy output.
• Long construction times - high cost.

Solar energy

• Very low energy output.
• Intermittent energy output.
• Can't work at night.

Wind Power

• High setup and maintanance costs.
• Creates noise pollution.

You need to be able to Discuss these points.

8.3: Fossil Fuel Power Production

8.3.1: Historical and geographical reasons for use

Fossil fuel consumption increased massively during the Industrial Revolution. Previously, coal, oil and gas were being used, so people knew where to go to get them. Power plants were created to mass produce energy from these sources.

Geographically speaking, fossil fuels, especially coal, is found in at least small amounts all over the world. These are some of the easiest sources of fuel to find.

You need to be able to Outline these concepts.

8.3.2: Energy density.

Basically, the questions will most likely ask you to calculate the energy density (measured in J/kg) given efficiency, mass of fuel consumed (M, measured in kg) and power output (P, measured in J). As can be seen, the formula Energy density = P×ε/M will be used.

You need to be able to Discuss this.

8.3.3

The following problems can be caused by digital equipment :

Quantization : This is caused by converting continuous analogue data into individual digital numbers.

Sampling frequency : The digital systems can only 'grab' a piece of data every x sec (let's say 0.01). If the data is changing significantly within this amount of time, then the sampled results will be almost random compared to the actual signal.