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]