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Climate Change - Renewables > Energy Storage - Introduction > Flashcards

Energy Storage - Introduction Flashcards

1
Q

Where is energy storage useful?

A

Grid-scale storage
Transport
Load balancing

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2
Q

Forms of energy…

A

Kinetic, potential, mechanical, thermal, electromagnetic, chemical nuclear.

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3
Q

Examples of energy storage based on type of energy…

A

Kinetic in fly wheels, mechanical energy in pumped hydro, electric storage in capacitors and supercapacitors

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4
Q

Parameters when considering storage efficiency…

A

Energy Density
Efficiency
Instantaneous Power
Degradation Rate
Longevity

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5
Q

Energy Density

A

The power of energy that can be compacted, especially in mobile energy storage

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6
Q

How are electricity demand flucutations regulated?

A

Peaking generators, especially for solar and wind energy.

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7
Q

Example of batteries in off-peak times…

A

Lithium-ion batteries hundreds per adult for solar power.

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8
Q

Types of low-density energy storage…

A

Pumped water, compressed air or thermal storage.

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9
Q

Pumped Hydro Stroage

A

Electricity generated by water falling through a turbine generator.

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10
Q

Current mechanism for grid energy storage…

A

Pumped Hydro Storage

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11
Q

How pumped hydro storage works?

A

Water pumped uphill using energy where water can then be released and used to run a turbine when needed

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12
Q

Efficiency of Pumped Hydro Storage

A

80%

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13
Q

Limits to pumped hydro storage…

A

It must be undergroun, more expensive.

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14
Q

Compare pumped hydro storage to batteries…

A

More economically viable but less energy density.

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15
Q

Adiabatic

A

A process without heat/mass transfer between the system and its surroundings

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16
Q

Impracticality of thermal storage in wind/solar…

A

Second law of conversion of electrical to tehrmal then reconversion has efficiency penalties.

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17
Q

Method of thermal storage…

A

Molten salt containing binary mixture of NaNO3 and KNO3

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18
Q

Important factor for transport storage…

A

Energy density

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19
Q

Carnot Limit

A

Sets a limit on the efficiency with which heat energy can be turned into useful work.

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20
Q

Dielectric

A

These are insulating materials or very poor conductors of electrical current

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21
Q

When is an electrical field generated in a capactior?

A

Voltage application across the plates with accumlation of electrons on one plate and equal number drawn from other plate.

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22
Q

Capacitance

A

This is a measure of the ability to store electrons, being dependent on geometry, closeness and size of dielectric constant of the material.

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23
Q

What is energy stored in capacitor proportional to?

A

Capacitance and square of the voltage across the plates.

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24
Q

What is the equation for capacitance?

A

E = 1/2 X C X V^2 where E is energy stored, C is capacitance and V is voltage across plates.

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25
Q

Why doe electrons accumulate on one plate in a capactiro?

A

Electric field generated by voltage, plate expelling electrons connected to negative terminal, attracted to postive charge of other plate with postive terminal of voltage source.

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26
Q

Virtual Photons

A

These are electromagnetic exchanging particles

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27
Q

Magnetic Fields

A

These are the forces exeperience by the charged particles in the presence of other charged particles, being a vector field descriing direction and strength of the force a positive charged woudl experience.

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28
Q

What is magnetic field described by?

A

Electrons wavefunction

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29
Q

What causes zeeman effect?

A

Interaction with electron motion and external magnetic fields.

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30
Q

Zeeman Effect

A

This is the atomic energy level splitting as well as splitting of spectral lines of a sample when an external magnetic field is imposed on a sample.

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31
Q

What does zeeman effect arise from?

A

Magnetic field interaction with magnetic moment of the electron.

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32
Q

Magnetic Moment

A

This is the magnetiusm resulting from an electron due to its spin and electric charge.

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33
Q

What is magnetic moment proportional to?

A

Angular momentum

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34
Q

What does magnetic field interaction with magnetic moment cause?

A

Energy levels to split into sub-levels.

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35
Q

What are the conductive plates in Capacitors made of?

A

Metal like Al or Tantalum, whilst dielectric made of ceramic, paper or plastic.

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36
Q

Why are metals used in electrodes?

A

Good electrical conductors.

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37
Q

Supercapacitors

A

These are high-capacity capactiros with a much higher capacitance value.

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38
Q

How do supercapacitors differ to capacitors?

A

Dielectric much thinner, with higher capacitance and higher energy density and faster charge.

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39
Q

Mechanism of supercapacitor…

A

Voltage application results in postively charged plate and negatively charged plate, both attracting opposite charges from the electrolyte, forming an EDL at electrode-electrolyte interaface, acting as a deielectric,

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40
Q

Electrolyte

A

THis is a medium for ion movement, either being anionic and cationic.

41
Q

What does voltage application to a supercapacitor do?

A

Makes the - charge become anionic and the _ charge cationic , allowing electrolyte ionic movement to charged electrodes forming EDL.

42
Q

Electric Double Layer

A

This is a structure appearing on surface of an object when exposed to a fluid being two parallel layers of charge.

43
Q

What is the strutcuted of the EDL?

A

Layer of anions near cathode and layer of cations near anode

44
Q

What is ionic movmeent in an electrolyte governed by?

A

Electrochemistry laws: Ohms law and nernst equation, as well as viscosity, conductivtiy and ionic strenght.

45
Q

Electrochemistry

A

This is the study of electron movement in an oxidation or reduction reaction at a polarized electode surafce

46
Q

Ohms Law

A

This says electrical resistance is the ratio of applied voltage to the current between two electrode in contact with a materla.

47
Q

Nernst Equation

A

Calculates extent of reaction between two redox systems.

48
Q

How is Ohms law expressed?

A

I = V/R where I is current, V voltage and R electrolyte resistance.

49
Q

What does ohms law calculate?

A

It relates current flowing through electrolyte to voltage applied across it.

50
Q

What does nernst equation calculate?

A

Ion concentration in electrolyte to voltage required to drive their movement, thus voltage required to drive ion movement.

51
Q

What are the useful properties of supercapacitors?

A

High power density, long life cycle, low maintenace…

52
Q

What is superconducting magnetic electrical storage?

A

This stores energy in the form of a superconducting magnetic could.

53
Q

Superconduction

A

This is a property of zero electrical resistance at very low absolute temperatures.

54
Q

Mechanism of SMES?

A

Currents passed through the coil, magnetic field is generated and stores energy density proprtional to square of the magnetic ield strength.

55
Q

What is energy stored in SMES proportional to?

A

Square of current passing through the coil and coil volume.

56
Q

Why is a cryogenic chamber required in SMES?

A

Maintenance of superconducting state, below boiling point of liquid nitrogen(-129C

57
Q

How is superconduction conditions maintained in SMES?

A

Liquid helium, cooling the coil enclosed in a vaccum-sealed chamber.

58
Q

Electrical Resistance

A

This refers to the measure of an objects opposition to flow of electric current.

59
Q

Peaking Gnerators

A

These store energy for use in high demand, being gas-fired combustion turbines started quickly to power output

60
Q

What are peaking generators based on?

A

Brayton Cycle

61
Q

Brayton Cycle

A

This is a thermodynamic cycle describing operation of certain heat engines that have air or some other gas as their working fluid.

62
Q

Process of peaking generators..

A

Fuel-air mixture compressured, mixed with fuel, ignite for combustion(rapid gas expansion) pushing a turbine, converting gas expansion energy to rotational energy then electrica.

63
Q

What are peaking generator process described by?

A

Isentropic(constant entropy) and Isobaric(Constant pressure)

64
Q

What is the structure of a generator?

A

A coil of wire, a magnet and a mechanical source of motion.

65
Q

Simple mechanism of a generator…

A

A voltage/electrical current is generated where the coil of wire is rotated inside a magnetic field.

66
Q

Faradays Law of Electromganetic Induction

A

This predicts how magnetic field interacts with an electric circuit to produce an electromotive force)

67
Q

Electromotive force

A

This is difference in potential tending to give rise to an electrical current.

68
Q

What does coil rotation in a generator do?

A

Cuts magnetic field lines, generating electrical currents for power

69
Q

What does cutting magnetic field lines mean?

A

Changing amount of electromagnetic lines passing through an area, this creating the electromotive force when the wire/coil moves through the magnetic field.

70
Q

What thermodynamic properties are importatn in molten salt?

A

Heat Capacity
Melting Point
Specific Heat
Conductivity

71
Q

What compounds are used in molten salt storage?

A

NaNO3 and KNO3

72
Q

Capacitor

A

An electrical component with the property of storing electrical charge, that being electrical energy in an electrical field.

73
Q

What is chemical density determined by?

A

Energy stored within the chemical bonds and size and weight(higher molecular weights have higher energy density.

74
Q

Why is lithium good in batteries?

A

Third smallest atom and cationic thus driven from cathode to anode when battery charged

75
Q

Why is strong electrochemical potential important in lithium?

A

Loss of electron results in it becoming cationic which the 1+ cation seeks to gain lost electron through chemical bond formation with material with high eleectron affinity

76
Q

What happens when lithium loses valence electron?

A

Becomes reducing, with tendency to donate electrons to cathodes, increasing ionization energy.

77
Q

Ionization Energy

A

This is the energy change when an electron is removed from a neutral atom or molecule in its ground state.

78
Q

What are anodes typically made of in Li batteries?

A

Transition metal oxide LI combines with forming stable componds

79
Q

How does lithoium interact with cathode?

A

Electrostatic interactions and ionic.

80
Q

Why is Li easier to use than H?

A

Li being a reducing agent makes it able to be used as an anode, donating electrons to cathode and storing electrical chemical energy, whilst H exists in H2 form.

81
Q

Where is H used in cathodes?

A

Hydrogen fuel cells

82
Q

What is the mechanism of H fuel cells?

A

Hydrogen oxidized at anode with O reduced at cathode, H2 spplit into H+ and electrons through electrolyis, protons moving to cathode and electrons externally.

83
Q

Why do H fuel cells require platinum catalysts?

A

Acceleration of reaction due to high activation eenrgy between H and O

84
Q

Why is H better used as an anode?

A

Low ionization potential meaning it readily loses electrons to become cationic.

85
Q

How do supercapacitors store energy?

A

Electrostatic energy through passivation in electrical field between two electrodes.

86
Q

What happens when voltage applied to supercapactiro?

A

Double layer forms on either electrode creating electrical field.

87
Q

What is the best material for supercapacitor electrodes?

A

A porous material for more surface area for charge binding like activated carbon.

88
Q

Helmholtz Layer

A

This is a phase boundary between an electronic conductor(electrode) and a liquid ionic conductor(electrolyte) behaving like a plate capacity with a nanometre thin dielectric)

89
Q

What two layers is the DL made of?

A

Helmholtz
Gouy Chapman

90
Q

Gouy-Chapman

A

This is the less tightly bound layer extending beyond where majority of charge stored

91
Q

Why is electrolyte important in supercapacitor?

A

Formation of EDL, anions/cations moving to opposite electrode with voltage application.

92
Q

Where can supercapacitors be used?

A

Electrical vehicles rapid charge/discharge
Renewable energy off-peak storage
Grid-scale storage

93
Q

Why do supercapacitors rapidly discharge?

A

Charge storage purely electrostatic whilst batteris rely on slow chemical reactions

94
Q

Why cant supercapacitors store as much energy per unit mass?

A

Pure electrostatic charge ant the couloumb law

95
Q

Coulomb Law

A

This states that electrical field strength is proportional to the inverse square of the distance between charged particles.

96
Q

What are the common electrolytes used in supercapactiros?

A

KOH, NaS

97
Q

What are the common electrode materials?

A

Activated carbon(cathode, - charge) and metal oxide(anode, + charge)

98
Q

How is carbon made to charge?

A

It has high surface area and modified with heteroatoms like N or S to introduce negative charges.

Climate Change - Renewables (12 decks)

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