Energy Storage - Introduction Flashcards
Where is energy storage useful?
Grid-scale storage
Transport
Load balancing
Forms of energy…
Kinetic, potential, mechanical, thermal, electromagnetic, chemical nuclear.
Examples of energy storage based on type of energy…
Kinetic in fly wheels, mechanical energy in pumped hydro, electric storage in capacitors and supercapacitors
Parameters when considering storage efficiency…
Energy Density
Efficiency
Instantaneous Power
Degradation Rate
Longevity
Energy Density
The power of energy that can be compacted, especially in mobile energy storage
How are electricity demand flucutations regulated?
Peaking generators, especially for solar and wind energy.
Example of batteries in off-peak times…
Lithium-ion batteries hundreds per adult for solar power.
Types of low-density energy storage…
Pumped water, compressed air or thermal storage.
Pumped Hydro Stroage
Electricity generated by water falling through a turbine generator.
Current mechanism for grid energy storage…
Pumped Hydro Storage
How pumped hydro storage works?
Water pumped uphill using energy where water can then be released and used to run a turbine when needed
Efficiency of Pumped Hydro Storage
80%
Limits to pumped hydro storage…
It must be undergroun, more expensive.
Compare pumped hydro storage to batteries…
More economically viable but less energy density.
Adiabatic
A process without heat/mass transfer between the system and its surroundings
Impracticality of thermal storage in wind/solar…
Second law of conversion of electrical to tehrmal then reconversion has efficiency penalties.
Method of thermal storage…
Molten salt containing binary mixture of NaNO3 and KNO3
Important factor for transport storage…
Energy density
Carnot Limit
Sets a limit on the efficiency with which heat energy can be turned into useful work.
Dielectric
These are insulating materials or very poor conductors of electrical current
When is an electrical field generated in a capactior?
Voltage application across the plates with accumlation of electrons on one plate and equal number drawn from other plate.
Capacitance
This is a measure of the ability to store electrons, being dependent on geometry, closeness and size of dielectric constant of the material.
What is energy stored in capacitor proportional to?
Capacitance and square of the voltage across the plates.
What is the equation for capacitance?
E = 1/2 X C X V^2 where E is energy stored, C is capacitance and V is voltage across plates.
Why doe electrons accumulate on one plate in a capactiro?
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.
Virtual Photons
These are electromagnetic exchanging particles
Magnetic Fields
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.
What is magnetic field described by?
Electrons wavefunction
What causes zeeman effect?
Interaction with electron motion and external magnetic fields.
Zeeman Effect
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.
What does zeeman effect arise from?
Magnetic field interaction with magnetic moment of the electron.
Magnetic Moment
This is the magnetiusm resulting from an electron due to its spin and electric charge.
What is magnetic moment proportional to?
Angular momentum
What does magnetic field interaction with magnetic moment cause?
Energy levels to split into sub-levels.
What are the conductive plates in Capacitors made of?
Metal like Al or Tantalum, whilst dielectric made of ceramic, paper or plastic.
Why are metals used in electrodes?
Good electrical conductors.
Supercapacitors
These are high-capacity capactiros with a much higher capacitance value.
How do supercapacitors differ to capacitors?
Dielectric much thinner, with higher capacitance and higher energy density and faster charge.
Mechanism of supercapacitor…
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,
Electrolyte
THis is a medium for ion movement, either being anionic and cationic.
What does voltage application to a supercapacitor do?
Makes the - charge become anionic and the _ charge cationic , allowing electrolyte ionic movement to charged electrodes forming EDL.
Electric Double Layer
This is a structure appearing on surface of an object when exposed to a fluid being two parallel layers of charge.
What is the strutcuted of the EDL?
Layer of anions near cathode and layer of cations near anode
What is ionic movmeent in an electrolyte governed by?
Electrochemistry laws: Ohms law and nernst equation, as well as viscosity, conductivtiy and ionic strenght.
Electrochemistry
This is the study of electron movement in an oxidation or reduction reaction at a polarized electode surafce
Ohms Law
This says electrical resistance is the ratio of applied voltage to the current between two electrode in contact with a materla.
Nernst Equation
Calculates extent of reaction between two redox systems.
How is Ohms law expressed?
I = V/R where I is current, V voltage and R electrolyte resistance.
What does ohms law calculate?
It relates current flowing through electrolyte to voltage applied across it.
What does nernst equation calculate?
Ion concentration in electrolyte to voltage required to drive their movement, thus voltage required to drive ion movement.
What are the useful properties of supercapacitors?
High power density, long life cycle, low maintenace…
What is superconducting magnetic electrical storage?
This stores energy in the form of a superconducting magnetic could.
Superconduction
This is a property of zero electrical resistance at very low absolute temperatures.
Mechanism of SMES?
Currents passed through the coil, magnetic field is generated and stores energy density proprtional to square of the magnetic ield strength.
What is energy stored in SMES proportional to?
Square of current passing through the coil and coil volume.
Why is a cryogenic chamber required in SMES?
Maintenance of superconducting state, below boiling point of liquid nitrogen(-129C
How is superconduction conditions maintained in SMES?
Liquid helium, cooling the coil enclosed in a vaccum-sealed chamber.
Electrical Resistance
This refers to the measure of an objects opposition to flow of electric current.
Peaking Gnerators
These store energy for use in high demand, being gas-fired combustion turbines started quickly to power output
What are peaking generators based on?
Brayton Cycle
Brayton Cycle
This is a thermodynamic cycle describing operation of certain heat engines that have air or some other gas as their working fluid.
Process of peaking generators..
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.
What are peaking generator process described by?
Isentropic(constant entropy) and Isobaric(Constant pressure)
What is the structure of a generator?
A coil of wire, a magnet and a mechanical source of motion.
Simple mechanism of a generator…
A voltage/electrical current is generated where the coil of wire is rotated inside a magnetic field.
Faradays Law of Electromganetic Induction
This predicts how magnetic field interacts with an electric circuit to produce an electromotive force)
Electromotive force
This is difference in potential tending to give rise to an electrical current.
What does coil rotation in a generator do?
Cuts magnetic field lines, generating electrical currents for power
What does cutting magnetic field lines mean?
Changing amount of electromagnetic lines passing through an area, this creating the electromotive force when the wire/coil moves through the magnetic field.
What thermodynamic properties are importatn in molten salt?
Heat Capacity
Melting Point
Specific Heat
Conductivity
What compounds are used in molten salt storage?
NaNO3 and KNO3
Capacitor
An electrical component with the property of storing electrical charge, that being electrical energy in an electrical field.
What is chemical density determined by?
Energy stored within the chemical bonds and size and weight(higher molecular weights have higher energy density.
Why is lithium good in batteries?
Third smallest atom and cationic thus driven from cathode to anode when battery charged
Why is strong electrochemical potential important in lithium?
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
What happens when lithium loses valence electron?
Becomes reducing, with tendency to donate electrons to cathodes, increasing ionization energy.
Ionization Energy
This is the energy change when an electron is removed from a neutral atom or molecule in its ground state.
What are anodes typically made of in Li batteries?
Transition metal oxide LI combines with forming stable componds
How does lithoium interact with cathode?
Electrostatic interactions and ionic.
Why is Li easier to use than H?
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.
Where is H used in cathodes?
Hydrogen fuel cells
What is the mechanism of H fuel cells?
Hydrogen oxidized at anode with O reduced at cathode, H2 spplit into H+ and electrons through electrolyis, protons moving to cathode and electrons externally.
Why do H fuel cells require platinum catalysts?
Acceleration of reaction due to high activation eenrgy between H and O
Why is H better used as an anode?
Low ionization potential meaning it readily loses electrons to become cationic.
How do supercapacitors store energy?
Electrostatic energy through passivation in electrical field between two electrodes.
What happens when voltage applied to supercapactiro?
Double layer forms on either electrode creating electrical field.
What is the best material for supercapacitor electrodes?
A porous material for more surface area for charge binding like activated carbon.
Helmholtz Layer
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)
What two layers is the DL made of?
Helmholtz
Gouy Chapman
Gouy-Chapman
This is the less tightly bound layer extending beyond where majority of charge stored
Why is electrolyte important in supercapacitor?
Formation of EDL, anions/cations moving to opposite electrode with voltage application.
Where can supercapacitors be used?
Electrical vehicles rapid charge/discharge
Renewable energy off-peak storage
Grid-scale storage
Why do supercapacitors rapidly discharge?
Charge storage purely electrostatic whilst batteris rely on slow chemical reactions
Why cant supercapacitors store as much energy per unit mass?
Pure electrostatic charge ant the couloumb law
Coulomb Law
This states that electrical field strength is proportional to the inverse square of the distance between charged particles.
What are the common electrolytes used in supercapactiros?
KOH, NaS
What are the common electrode materials?
Activated carbon(cathode, - charge) and metal oxide(anode, + charge)
How is carbon made to charge?
It has high surface area and modified with heteroatoms like N or S to introduce negative charges.
