In the present work the thermal performance of Phase Change Material (PCM) based solar thermal energy storage system under the influence of different heat transfer fluids (HTF) have been investigated. Water, Ethylene Glycol–water and Copper nanofluid are selected as HTF. Paraffin is used as PCM and encapsulated in cylindrical capsules. The thermal energy storage (TES) tank acts as a storage unit consisting PCM capsules packed in three beds surrounded by water, which acts as sensible heat storage (SHS) material. HTF circulated by a pump transfers heat from solar flat plate collector (FPC) to the TES tank. 25% ethylene glycol -75% water HTF is prepared by mixing ethylene glycol (EG) with water. Copper-distilled water nanofluids (0.3% by weight) are prepared using prolonged sonication with sodium dodecyl benzene sulphonate (SDBS) as the surfactant. Various performance parameters such as charging time, instantaneous heat stored, cumulative heat stored and system efficiency are studied for various HTFs. It is found that the charging time is reduced by 33.3% for copper nanofluid and 22.2% for ethylene glycol- water mixture HTFs. It is also observed that there is an increase in system efficiency and cumulative heat stored with reference to charging time for these HTFs when compared with conventional HTF 1 i.e. water.
