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a. Explain the difference between electrical energy and electrical power, and state the units used for each.

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  • Post Date 2018-11-08T12:40:34+00:00
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a. Explain the difference between electrical energy and electrical power, and state the units used for each.

 

TMA 01

 

This tutor­marked assignment (T213 TMA 01) must be submitted by 12 noon (UK local time) on 1 December 2016.

 

This module requires all assignments to be submitted electronically. To submit an assignment, please follow the link(s) from your StudentHome page to the online TMA/EMA service.

 

If you foresee any difficulty with submitting your assignment on time then you should contact your tutor well in advance of the cut­off date.

 

For further information about policy, procedure and general submission of assignments please refer to the  Assessment Handbook, which can also be accessed via your StudentHome page.

 

Numerical answers

 

Where a question asks for a calculated numerical answer, this should be given to an appropriate number of significant places. Inappropriate answers will be penalised.

 

Question 1 (17 marks)

 

  1. Explain the difference between electrical energy and electrical power, and state the units used for each.

 

(3 marks)

 

  1. Table 1 below shows the input and output forms of energy for some different types of energy system. Copy the table and complete it by filling in the six blanks (i) to (vi) with the input energy form, or the output energy form, as appropriate. The entry in the first row has been completed for you as an example.

 

Table 1 Input and output forms of energy for some different types of energy system

 

 

Type of system

Input energy

Output energy

 

 

form

form

 

Hydroelectric dam generating

Potential energy

Electrical energy

 

plant

 

 

(i)

Gas boiler

?

Heat

(ii)

Torch battery

Chemical energy

?

(iii)

PV (solar) cell

?

Electricity

(iv)

Wind turbine

Kinetic energy

?

(v)

Electric table fan

?

Kinetic energy

(vi)

Radio transmitter

Electrical energy

?

 

(6 marks)

 

 

  1. A new pumped storage plant is proposed at Espejo de Tarapaca in Chile. It will use sea water flowing to and from a new high level lake situated on top of a cliff 600 m above sea level.

 

  1. The high level lake is described as having an area of 375 hectares and being capable of holding 14 billion (14 × 109) US gallons of water. What will be the average depth of water in the lake in metres? (Conversion factors between different units of area and volume are given in Appendix A3 of Energy Book 1.) Give your answer to 3 significant figures.

 

(3 marks)

 

  1. Calculate the total stored potential energy in GWh assuming a sea water density of 1.025 kg l­1, taking g as 9.81 m s­2 and 1

kWh = 3.6 MJ. Give your answer to 3 significant figures.

 

(3 marks)

 

  1. Assuming a turbine efficiency of 85%, calculate the maximum number of hours that the plant will be able to supply its rated output of 300 MW. Give your answer to 3 significant figures.

 

(2 marks)

 

Question 2 (12 marks)

 

  1. Explain in your own words what is meant by the reserves/production (R/P) ratio for a fossil fuel resource.

 

(2 marks)

 

  1. Chapter 2 of Energy Book 1 describes the energy situation in six different countries, including the USA and the UK.

 

List the key ways in which the USA and the UK differ in:

 

  1. their energy histories between 1950 and 2009 and

 

  1. their energy situations in 2009.

 

Make sure your list includes the following, along with any other points of interest:

 

the role played by coal and oil in the two countries

 

the energy self­sufficiency of the two countries in 2009, with comments on their natural resources, imports and exports

 

differences in per capita energy consumption

 

the relative contributions of oil and natural gas to energy consumption.

 

Your answer should be no longer than 300 words.

 

(10 marks)

 

Question 3 (16 marks)

 

  1. Write the chemical equation for the combustion of carbon.

 

(2 marks)

 

  1. Explaining your reasoning, use this equation to show that the combustion of 5 kg of carbon should release just over 18 kg of carbon dioxide. (The relative

 

atomic masses of carbon and oxygen are 12 and 16 respectively.)

 

(2 marks)

 

  1. A high quality anthracite coal can be considered to be almost pure carbon. The combustion of 1.0 kg of this coal produces 34 MJ of heat energy. Use this fact, and the result of part (b) above, to find the mass of CO2 released per GJ of heat produced.

 

(2 marks)

 

  1. The combustion of 1.0 kg of wood, on the other hand, produces 15 MJ of heat energy. If the density of the wood is 480 kg/m3, calculate the heat energy produced by burning 1.0 cubic metre of wood.

 

(2 marks)

 

  1. A small all­year holiday cabin in the United States has a rudimentary wood stove for heating. In the USA, wood is commonly sold by the unit of the ‘cord’, equivalent to 128 cubic feet of wood. Express 1.0 cord in cubic metres. (Conversion factors for different units of volume are given in Appendix A3 of Energy Book 1.)

 

(2 marks)

  1. Typically the owners of the holiday cabin use 1.0 cord of wood every three months during the colder months. How much energy in gigajoules will they use over six winter months?

(2 marks)

  1. In the USA, coal is usually sold by the ‘short ton’ of 2000 lb. Show that the holiday cabin would require approximately 1.7 short tons of anthracite to provide the same amount of heat as the wood in part (f). (Conversion factors between different units of mass are given in Appendix A3 of Energy Book 1.)

(2 marks)

  1. If the density of anthracite is 1100 kg/m3 , how much space would be required to store this amount of coal?

(2 marks)

 

Question 4 (12 marks)

  1. Figure 1 shows UK primary energy and delivered energy consumption for the year 2009 (Figure 3.10 in Energy Book 1).

Figure 1 2009 primary energy and delivered energy                     

Using your own words, define the terms primary energy and delivered energy.

(2 marks)

  1. In 2009 over 30% of UK primary energy consumption was ‘lost in conversion and delivery’. Give two main areas within the UK energy system where these losses occurred.

(4 marks)

  1. The top bar of Figure 1 shows a large amount of primary energy is supplied from coal. Explain why only a small amount of ‘solid fuel’ appears in the second (delivered energy) bar.

(2 marks)

  1. Assuming that transport uses only liquid fuel, roughly how much of the energy delivered as liquid fuel was used for purposes other than transport? You may also wish to look at Table 3.4 in Energy Book 1, page 93. Give your answer to the nearest 100 PJ.

(2 marks)

  1. Assuming all the delivered energy used for machinery is used by industry, how much energy was used by industry for purposes other than machinery? Give your answer to the nearest 100 PJ.

(2 marks)

Question 5 (15 marks)

  1. Chapter 1 of Energy Book 1 describes three outlooks for future world energy use: ‘growthist’, ‘peakist’ and ‘environmentalist’. Peakists and environmentalists both believe that fossil fuel use will decline significantly by 2050 but for different reasons. Briefly explain in your own words the key differences between these two outlooks.

(6 marks)

  1. List three atmospheric pollutants in the flue gases of a coal­fired power station, other than carbon dioxide.

(3 marks)

  1. For each of the three pollutants, briefly describe a clean­up technology as used in coal­fired power stations.

(6 marks)

Question 6 (13 marks)

Figure 1 below is a McKelvey diagram showing the relationship between reserves, conditional resources and hypothetical resources.

Figure 2 McKelvey diagram (repeat of Energy Book 1

Figure 5.17 (a)).

  1. Define each of the three terms reserves, conditional  resourcesand hypothetical resources in your own words.

(3 marks)

  1. A coalfield was suspected to exist on the edge of a currently exploited mine but had not been confirmed. Exploration confirmed both that it existed and that it would be economic and feasible to extract the coal. To which of the three categories in the diagram would the coal have initially been assigned, and to which would have it been moved after the exploration?

(4 marks)

  1. In April 2016, the US coal mining company, Peabody Energy, filed for bankruptcy saying that low world coal prices made much of its quoted coal reserves uneconomic to mine. To which of the three categories above should their coal reserves now be assigned?

(2 marks)

  1. UK coal reserves are now only a small fraction of what they were in 1900. Most of the remaining coal has not been extracted and there has been over a century of development of new mining technology. Why have the UK coal reserves fallen so dramatically, and what category in the diagram is the remaining coal now in?

 

(4 marks)

Question 7 (15 marks)

  1. A heat engine is working between an input temperature T1 and an outlet temperature T2. State Carnot’s formula for its maximum possible efficiency. What temperature scale must be used and how does this relate to the Celsius scale?

(4 marks)

  1. A new concentrating solar power (CSP) plant was completed in 2013 at Ivanpah in Arizona. It has three power towers and is similar in design to the Spanish plants shown in Figure 14.20 of Energy Book 1. It can produce steam at a temperature of 550 °C. It uses air cooling and a final condenser outlet temperature of 60 °C can be assumed. It has a design efficiency of 28.7%. Show that this is about a half of the theoretical Carnot efficiency for these temperatures.

(4 marks)

  1. The full Ivanpah site covers 16 square kilometres of land. On average, over a year, the solar radiation falling on the site is 2000 kWh per square metre. In 2015 the solar power plant produced 650 GWh of electricity. Express this as a percentage of the total incident solar radiation falling on the site.

(3 marks)

  1. In 2009, what was the average per capita electricity consumption for the USA? How does this compare to the equivalent figure for the UK? Calculate the number of ‘average’ residents in each country whose electricity consumption equals the output of the Ivanpah plant.

(4 marks)

Learning outcomes

This TMA assesses the following learning outcomes.

Knowledge and understanding

 

The forms of energy and the various definitions of ‘sustainable’ energy, and the relevance of sustainability to the design and implementation of energy systems.

The principal sources of primary energy in use today, their development over the past century, and the general patterns of world, regional and national energy consumption.

The basic principles underlying the design and use of energy supply systems, and the basic principles underlying the efficient use of energy.

The pollutants produced through the combustion of fossil fuels, their environmental impacts and the amelioration of these (for coal).

Cognitive skills

Critically evaluate differing explanations and arguments for the relative resource depletion impacts of different energy technologies (for coal).

Key skills

Use appropriate scientific and mathematical techniques applied to energy related issues or contexts.

Analyse information about energy and its use, from a variety of sources and using ICT tools.

Clearly articulate ideas, proposals and arguments relating to energy, in a variety of ways for differing contexts and audiences.


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