TES Exam 1 Review
Effective TES requirements
Be stratified-volumes of water at different temps which should not mix Minimize amount of dead water volume Minimal heat loss/gain
Charging of pumped hydro
CHARGING: at night(low energy demand) pump moves water upward from a body or water to a higher elevation resevoir pond.
Magnetic and electromagnetic energy storage
Capacitors Supercapacitors Superconducting Magnetic Es
TES Storage process
Charging Storing Discharging
Hot storage
Charging: a hot working fluid transfer thermal energy from a source to storage medium via heat transfer. (Fluid may/may not be in direct contact with storage medium) (working fluid may be the storage medium) Discharging: a cold working fluid gains thermal energy from hot storage medium via heat transfer and is sent to the load.
Chemical criteria for PCM
Chemically stable Noncorrosive to construction materials non-toxic nonflammable nonexplosive Not susceptible to chemical decomposition LOW cost and COMMERCIALLY available
In-organic PCM disadvantages
Corrosive to metals Super-cooling phase Phase segregation Congruent melting High volume change
Economics of TES
Cost effectiveness- high upfront cos requires low operational costs for effective payback.
Thermal energy storage(TES)
Deals with the storage of energy by cooling, heating, melting, solidifying, or vaporizing a material Sensible and latent TES may occur in the same storage material
Charging of compressed air storage
During off-peak hours a compressor is used to compress air into large underground storage tank
Discharging of compressed air
During peak hours, air is released to drive a gas turbine generator.
DIscharging of pumped hydro
During the day(high energy demand) reservoir releases water allowing it to flow downhill, turn a turbine and generate electricity.
Cost
Economic factor, sometimes expressed in terms of cost per unit energy ($/kWhour)
Thermochemical Energy Storage
Energy is stored in a Charging: thermal energy is applied to drive the endothermic reaction Discharging: condidtions are changed so that the reverse, exothermic reaction occurs.
Electrochemical storage
Energy is stored in an electrochemical
Compressed air storage
Energy is stored in the high pressure of AIR
Pumped hydro operation
Energy is stored in the potential energy of the flud. CHARGING: water up from pump DISCHARGING: water down through turbine Can reach 30 seconds to reach 100% power
Thermal energy storage
Energy is stored thermal energy of substance. Can be sensible, latent, or a combo.
Energy effiency
Energy recovered from TES/Energy input to TES
Biological energy storage
Fats Chemiosis(ATP) Biofuels
Organic PCM disadvantages
Flammable Low thermal conductivity Low volumetric latent heat storage capacity
Advantages of Latent to sensible
High gravimetric and volumetric energy density Most energy stored at a specific temp
In-organic PCM advantages
Higher thermal conductivity than organics Low cost Not flammable Sharp phase change High volumetric latent heat storage capacity Low volume change
Benefits of TES
Increase generation capacity(production side) Enable better operation of cogeneration plants Shift energy purchases to low-cost periods Increase system reliability and reliance Integration with other functions
Electrolyte
Ionic conductor, provides the medium for transfer of charged species(ions) inside the cell between the electrodes.
Eutectic PCM Disadvantages
Limited data on thermophysical properties for many combinations High cost
Sensible TES material
Liquid solids
Sensible storage Pro vs Cons
Liquids can be pumped but thermal stratification more difficult Solids generally easier to achieve and maintain thermal stratification
Kinetic criteria for PCM
Little to no supercooling (i.e stays a liquid at temperatures below melting point)
Sensible storage (Water)
Low cost, high specific heat, limited temp range and needs good containment
Sensible storage (Rocks)
Low cost, temp range, lower specific heat than water
Rock TES storage
Low cost, use for storage over 100 C
Concrete TES Storage
Low cost, widely available, can be poured into different geometries, use for storage over 100 C
Criteria for new PCM
Melting point in desired operating temp High latent head of fusion per unit mass (less amount of material to store given amt of energy) High density High specific heat High thermal conductivity Small volume change during phase transition
Primary battery
NON-rechargable. Discharging: electrochem reaction releases electrons.
Why is energy storage needed?
Needed whenever there is a disconnect between when energy is produced, and when NEEDED. Helps to even-out production.
Anode
Negative electrode: reducing or fuel electrode. Gives up electrons to external circuit(oxidized during reaction)
Organic PCM advantages
No super cooling No phase segregation Low vapor pressure Large temp range Self-nucleating Recyclable High heat of fusion
Technical considerations of TES
Operating temp, Expecteded charging and discharging periods, individual vs aggregate system, storage period
Cathode
Positive electrode, oxidizing electrode. Accepts electrons from external circuit(reduced during reaction)
Electrochemical Storage
Rechargable Flow batteries
Secondary battery
Rechargeable Charging: electricity is applied to force the reaction in the direction to drive electrons to anode. Discharging: Battery is connected to a load which always for the reverse the chem reaction and releases electrons.
Thermal Energy Storage
Sensible Latenent TES
Eutectic PCM Advantages
Sharp melting point Properties can be tailored to match specific requirements High volumetric thermal storage density
Examples of when energy storage is needed in everyday life.
Solar energy at times when it is not sunny. Wind when not windy. To help meet on-peak energy demand with off-peak energy To allow for a portable device that can be used when desired.
Latent TES material
Solid liquid(Organic, inorganics, eutectics) Liquid-gaseous Solid-Solid
Applications of TES Storage
Space/water heating Cooling AC Temp modulation Proposed use with nuclear reactiors Solar thermal
Sensible heat storage
Storage by causing a material to rise or lower in temp. Delta(E) = mcDelta(T)
Latent heat storage
Storage by phase change. Delta(E) = mh(1-2)
Technical Criteria for TES
Storage capacitity, lifetime, size, efficiency, safety, cost, installation, environmental standards
TES System components
Storage medium Container Input/output devices for HTF
Flywheel energy
Store energy in rotational kinetic energy. Used for short term emergency power, and can be used for regenerative breaking.
Process for Thermodynamic analysis
Subdivide process into as many sections as deisered. Perform mass and energy balances on the process to determine all basic quantities Select a reference-environment model Evaluate enery and exergy values relative to ref-environment Perform exergy balances, including exergy destruction Select efficiency definitions depending on the measure of merit desired and evaluate values for efficiencies Interpret results and draw conclusions.
Specific power or power density(W/kg)
The rate at which it can deliver energy per unit mass
Latent storage
Thermal energy is stored by chanign the phase(solid-liquid) of a substance
Sensible storage
Thermal energy is stored by elevating or lowering the temp of a substance
Chemical Energy storage
Thermochemical Hydrogen Ammonia (SNG LNG)
Design considerations for solid storage
Uniform particle size Design for thermal stratification Pressure drop through bed Containment: volume-to-outer surface area
Hydrogen in TES(long term)
Use energy source to produce hydrogen Store hydrogen until energy is needed Consume hydrogen for end use
Liquid tank for TES
Used for heating and air conditioning applications Water most common medium
Low thermal conductivity
easeier to achieve thermal stratification but can make it more difficult to add/remove energy from material.
High specific heat
high specific energy
Harry Thomason's method rock storage
hot water from collector enters at top of water tank Sinks as it cools Cold water leave the bottom to recirculate to collector Tank surrounded by rock Air passed through rock to heat it and used for space heating
Disadvantages of latent compared to sensible
material costs Higher system complexity and control
Cycle life
number of times the energy storage medium can be charged and discharged during it's lifetime
Mechanical energy storage
pumped ES Compressed air Flywheel
Discharging of flywheel
when power needed, the flywheeel rotational energy is used to turn a shaft in a generator and generate electricity.
1 Watt-Hour to kJ
3.6 kJ
Charging of Flywheels
A motor is used to spin a relatively large mass
Specific Energy (Wh/kg)
Amount of energy stored per unit mass(or weight) [Gravimetric energy density]
Energy density(Wh/L or Wh/m^3)
Amount of energy stored per unit volume [volumetric energy density]
