Phase Changing Phase Changing Material in Solar Material in Solar Thermal Energy Thermal Energy

StorageStorage

Tiffany WuTiffany WuEnergy Technology and PolicyEnergy Technology and PolicyUniversity of Texas at AustinUniversity of Texas at Austin

((www.powerfromthesun.net/chapter1/Chapter1.htmwww.powerfromthesun.net/chapter1/Chapter1.htm ) )

ContentsContents

IntroductionIntroduction Benefits and Drawbacks of PCMBenefits and Drawbacks of PCM PCM Options PCM Options EncapsulationEncapsulation Increasing Thermal ConductivityIncreasing Thermal Conductivity ConclusionConclusion

IntroductionIntroduction Most systems have a disconnectMost systems have a disconnect

between supply and demandbetween supply and demand

Intermittent solar energy supply Intermittent solar energy supply can be maximized with a heat can be maximized with a heat storage systemstorage system

Thermal energy can be Thermal energy can be stored both as sensible stored both as sensible and latent heatand latent heat

Continued efforts to find a phase changing material is Continued efforts to find a phase changing material is currently underwaycurrently underway

(Fath, 1998; Kousksou, 2007; Pasupathy, 2008)

Benefits and Drawbacks Benefits and Drawbacks of PCMof PCM

Benefits:Benefits: Higher storage density than sensible heatHigher storage density than sensible heat Smaller volumeSmaller volume Smaller temperature change between storing and Smaller temperature change between storing and

releasing energy releasing energy

Drawbacks:Drawbacks: High costHigh cost CorrosivenessCorrosiveness Density changeDensity change Low thermal conductivityLow thermal conductivity Phase separationPhase separation Incongruent meltingIncongruent melting SupercoolingSupercooling

(Pasupathy, 2008)

PCM OptionsPCM Options

(Pasupathy, 2008)

PCM OptionsPCM OptionsInorganicInorganic

Glauber’s salt, calcium chloride hexahydrate, sodium thiosulfate penthydrate, sodium carbonate decahydrate

Benefits:Benefits: Low cost and readily availableLow cost and readily available High volumetric storage densityHigh volumetric storage density Relatively high thermal conductivityRelatively high thermal conductivity

Drawbacks:Drawbacks: CorrosiveCorrosive DecompositionDecomposition Incongruent meltingIncongruent melting SupercoolingSupercooling

(Pasupathy, 2008; Farid, 2004)

PCM OptionsPCM OptionsOrganicOrganic

Paraffin waxes and fatty acidsParaffin waxes and fatty acids

Benefits:Benefits: Melts congruentlyMelts congruently Chemically and physically stableChemically and physically stable High heat of fusionHigh heat of fusion

Drawbacks:Drawbacks: More expensive and flammableMore expensive and flammable Low thermal conductivity in solid stateLow thermal conductivity in solid state Lower heat storage capacity per volumeLower heat storage capacity per volume

(Pasupathy, 2008; Farid, 2004)

PCM OptionsPCM Options

EncapsulationEncapsulation Prevents reactivity towards Prevents reactivity towards

environment environment Compatible with stainless steel, Compatible with stainless steel,

polypropylene, and polyolefinpolypropylene, and polyolefin Controls volume as phases changeControls volume as phases change Prevents large drops in heat transfer Prevents large drops in heat transfer

ratesrates

(Farid, 2004)

(Kenisarin, 2007)

Increasing Thermal Increasing Thermal ConductivityConductivity

Metallic fillers Metallic fillers Metal matrix structuresMetal matrix structures Finned tubesFinned tubes

Aluminum filling with VSP 25 and VSP 50

PCM-Graphite Matrix(Farid, 2004; Kenisarin, 2007)

Finned Tubes

(Kenisarin, 2007)

The VSP25 filling provided the highest thermal conductivity of 1W/(mK), which is about six times that of pure paraffin

Total solidification time of PCM is shorter with fins and lessing rings, but the total quantity of stored heat is slightly smaller

ConclusionConclusion

Thermal energy storage is imperative to Thermal energy storage is imperative to make solar energy more reliable and make solar energy more reliable and competitivecompetitive

Further research in phase changing Further research in phase changing material can improve the efficiency of material can improve the efficiency of energy storageenergy storage

Design of the system is also important in Design of the system is also important in optimizing energy storageoptimizing energy storage

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Other ApplicationsOther Applications Cooling of heat and electrical engines Cooling: use of off-peak rates Cooling: food, wine, milk products (absorbing peaks in demand),

greenhouses Heating and hot water: using off-peak rates Medical applications: transportation of blood, operating tables, hot–

cold therapies Passive storage in bio-climatic building/architecture (HDPE, paraffin) Safety: temperature level maintenance in rooms with computers or

electrical/electronic appliances Smoothing exothermic temperature peaks in chemical reactions Solar power plants Spacecraft thermal systems Thermal comfort in vehicles Thermal protection of electronic devices (integrated in the appliance) Thermal protection of food: transport, hotel trade, ice-cream, etc. Thermal storage of solar energy

(Kenisarin, 2007)