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Renewable Energy 4 > Revision Guidelines > Flashcards

Revision Guidelines Flashcards

1
Q

What are the three main types of greenhouse gases?

A

Carbon dioxide, methane and nitrous oxide

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2
Q

What is the heat trapping factor of methane

A

25-28 CO2e

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3
Q

What is the heat trapping factor of nitrous oxide?

A

256-300 CO2e

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4
Q

What is the efficiency of a solar panel?

A

The comparison of the energy generated to the theoretical maximum with all photos absorbed, full energy is every photon extracted and no thermal dissipation

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5
Q

How does solar panel efficiency affect a solar farm?

A

To account for low efficiency panels, solar farms either need to be larger or include technologies which will increase the amount of light incident on each panel

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6
Q

How is energy extracted from wind?

A

Aerofoil shaped blades are turned by lift force as air passes over. The blades turning turns a turbine to generate electricity

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7
Q

How does the design of wind turbines affect wind farms?

A

Turbines either have to be able to turn into the wind or positioned for the optimal angle of attack in the majority of situations

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8
Q

How does wind speed affect energy production of a wind turbine?

A

Higher speed generates more power up to the point it would cause damage, where output has to be limited to cut maintenance costs

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9
Q

How does the design of a wind turbine affect its efficiency?

A

The swept area of a turbine is directly related to output
Other factors such as number of blades and angle of attack affect the efficiency of energy collection in this area

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10
Q

What are the control strategies used to optimise wind turbine performance?

A

Passive stall control
Active pitch control
Yaw control

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11
Q

What is stall control of a wind turbine?

A

As wind speed increases and rotor speed doesn’t, angle of attack increases, creating a balance of higher torque and stall drag

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12
Q

What is pitch control of a wind turbine?

A

Actively changing the angle of attack of the turbine blades

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13
Q

What is yaw control of a wind turbine?

A

Changing the horizontal axis position of a turbine using a motor or tail plane

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14
Q

How can geothermal energy be used?

A

Direct use
Heat pumps
District heating
Electricity generation
Combined heat and power

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15
Q

What is direct use of geothermal energy?

A

Using surface hot water for heating and bathing

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16
Q

What is a general heat pump?

A

Using stable temperature conditions underground to deliver controlled temperatures above ground

17
Q

What is district heating?

A

Distributing heat from a central source to multiple buildings via underground pipes

18
Q

How is geothermal energy used to generate electricity?

A

Hot and/or pressurised water is brought up from underground and steam is used to turn a turbine

19
Q

What are the four types of geothermal energy sources?

A

Hydrothermal
Geo-pressured
Magma
Hot dry rock

20
Q

What is dry steam?

A

A system which is pressurised to prevent the condensation of steam

21
Q

What is co-produced water?

A

Hot waste water from geothermal electricity production which can then be reused for low temperature heating

22
Q

What factors affect heat extraction for geothermal energy?

A

Extraction method
Source temperature
Source depth

23
Q

Why is hydrothermal production at former fossil fuel wells possible?

A

The production of hydrocarbons also creates water at temperatures of 65-150 degrees C

24
Q

What is the electric power output equation of a geothermal system?

A

Q=Cm(T1-T2)n
C is specific heat capacity
m is mass flow rate
T is temperature
n is efficiency

25
Q

What is the approximate emission of burning coal?

A

1 tonne of CO2 per MWh

26
Q

What is the approximate emission of burning natural gas?

A

0.5 tCO2/MWh

27
Q

What is a Life Cycle Analysis?

A

A standardised process to track the environmental impacts of a product or process through its lifetime

28
Q

What is the purpose of life cycle analysis?

A

To help decision makers understand the environmental performance (cost, emissions etc.) of a given product, process or activity

29
Q

What are the steps of a life cycle analysis?

A

Definition of goals and scope
Inventory analysis
Impact assessment
Application

30
Q

What are potential uses of algae farming?

A

Cleaning water sources
Animal feed
Biofuel
Medicinal uses

31
Q

How can algae be grown for biofuel?

A

Bioreactors
Closed ponds
Raceways

32
Q

How can algae be extracted for conversion to fuel?

A

Vacuum filtration
Flocculation
Centrifuging
Special pumping methods

33
Q

What is the process of producing biofuel from algae?

A

Growth - solid separation - dewatering - extraction - refinement

34
Q

How is algae grown in a raceway?

A

Algal cultures are inoculated in a shallow ring shaped pond which is circulated by a paddle wheel

35
Q

How much CO2 can 1kg of algae sequester?

A

1.8kg

36
Q

What is capacity factor?

A

The actual power generation over the total potential power generation

37
Q

What is the air mass index for solar power?

A

The distance towards the Sun in earths atmosphere/the vertical height of the atmosphere

38
Q

How do you find the maximum power density of a photovoltaic cell?

A

The area of the largest rectangle which fits under the V, J curve

39
Q

How can you improve the efficiency of a solar cell?

A

Anti reflection coating
Textured surfaces
Concentrating light onto cell
Use multiple cell types in series

Renewable Energy 4 (2 decks)

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