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

Question 1 (17 marks)

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

energy system

Type of system Input energy

form

Output energy

form

Hydroelectric dam generating

plant

Potential energy Electrical energy

(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)

TMA 01

  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.

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Question 2 (12 marks)

Question 3 (16 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 × 10 ) 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)

9

  1. Calculate the total stored potential energy in GWh assuming a sea

water density of 1.025 kg l , taking g as 9.81 m s and 1

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

(3 marks)

1

2

iii. 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)

  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:

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)

  1. their energy histories between 1950 and 2009

and

  1. their energy situations in 2009.
  2. 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

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Question 4 (12 marks)

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 CO released

per GJ of heat produced.

(2 marks)

2

  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/m , calculate the heat

energy produced by burning 1.0 cubic metre of wood.

(2 marks)

3

  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/m , how much space would be

required to store this amount of coal?

(2 marks)

3

  1. Figure 1 shows UK primary energy and delivered energy consumption for the

year 2009 (Figure 3.10 in Energy Book 1).

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Question 5 (15 marks)

Figure 1 2009 primary energy and delivered energy View larger image

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)

  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)

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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)).

Question 7 (15 marks)

  1. For each of the three pollutants, briefly describe a cleanup

technology as

used in coalfired

power stations.

(6 marks)

  1. Define each of the three terms reserves, conditional resources and

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)

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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.

  1. A heat engine is working between an input temperature T and an outlet

temperature T . 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

2

  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)

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Copyright © 2016 The Open University

Clearly articulate ideas, proposals and arguments relating to energy, in a

variety of ways for differing contexts and audiences.

TMA 01