The Influence of albedo and cooling on the yield of floating PV systems

Patel, Shahina Salim (2021-03)

Thesis (MEng)--Stellenbosch University, 2021.

Thesis

ENGLISH ABSTRACT: Floating PV (FPV) technology is an innovative technique of deploying PV modules on water bodies. Floating solar PV plants conserve the land areas and operate under lower temperatures, which lead to higher power outputs due to the cooling effect from the water. Due to the reflective and evaporative properties of the water surface, the performance of FPV systems is affected by the water surface reflectance and the heat transfer between the PV modules and the atmospheric environment. In the absence of measured reflected radiation from water, a default albedo value of 0.2 is commonly used to simulate PV systems as varying water surface albedo is currently not integrated into the PV simulation software. Therefore, the research work provides the modelling of the time-varying water surface albedo with the change in solar elevation; as changes in weather patterns strongly affect the radiation received on the FPV modules and the reflection off the water surface. Results show that the water surface albedo is affected by the spectral and angular dependencies of the irradiance; and that the albedo is lower at higher solar elevations and higher at lower solar elevations. Furthermore, this research studies Ocean Sun’s FPV technology that uses the concept of using floating PV modules on a flexible polymer floating structure on the water surface. Performance analysis shows that the water-cooled string, which is in thermal contact with the floating canvas, performs between 3.17 % to 7.32 % better than the air-cooled string, which is lifted 32 mm above the floating canvas using 32 mm polypropylene pipes. A thermal model is also being investigated to estimate the cooling effect of an air-cooled and a water-cooled FPV string in comparison to a ground-mounted PV string. Average U-values of 30 W/m2.K and 89 W/m2.K for the air-cooled and water-cooled string is observed, respectively. Higher U-values corresponds to a better cooling effect due to the direct thermal contact of the PV mod- ules with the floating canvas on the water surface. An average U-value of 27 W/m2.K is observed from the ground-mounted PV system. The research also tests the ability of solar PV simulation software, PVsyst, to successfully simulate FPV systems and to compare the energy yield of an FPV system with hypothetical tilted strings and increasing U-values in the same location. The influence of the tilted panels at different tilt angles on the energy yield of the FPV system using the default albedo versus the modelled albedo is analysed. PVsyst simulation shows that the energy production increases with an increase in U-values and the energy difference increases with an increase in the tilt angles due to the lower irradiance experienced at higher tilt angles.

AFRIKAANSE OPSOMMING: Drywende PV (DPV) tegnologie is ’n innoverende tegniek om PV-modules op water in te span. Drywende sonkrag-PV-aanlegte bewaar die landgebiede en werk onder laer temperature, wat lei tot hoër kraglewering as gevolg van die verkoeling van die water. As gevolg van die reflekterende en verdampingseien- skappe van die wateroppervlak, word die opbrengs van DPV-stelsels beïnvloed deur die wateroppervlakrefleksie en die hitte-oordrag tussen die PV-modules en die atmosferiese omgewing. In die afwesigheid van gemete waardes vir die gereflekteerde straling van water word ’n standaard albedo-waarde van 0.2 gebruik om PV-stelsels te simuleer, aangesien wisselende wateroppervlak albedo tans nie in die PV- simulasiesagteware geïntegreer is nie. Die navorsing bied die modellering van die tydswisselende wateroppervlak albedo met die verandering in sonhoogte aan; aangesien veranderinge in weerpatrone die bestraling wat die DPV-modules ontvang grootliks beïnvloed, asook die weerkaatsing van die wateroppervlak af. Resultate toon dat die wateroppervlak albedo beïnvloed word deur die spektrale inhoud en hoek afhanklikheid van die bestraling; en dat die albedo laer is by hoër sonhoogtes, en hoër by laer sonhoogtes. Verder bestudeer hierdie navorsing Ocean Sun se DPV-tegnologie wat die kon- sep gebruik om drywende PV-modules op ’n drywende buigsame polimeer struktuur te plaas om sodoende op die wateroppervlak te dryf. Opbrengs- analise toon dat die waterverkoelde string, wat termiese in kontak is met UITTREKSEL v die drywende doek, tussen 3.17% en 7.32% beter presteer as die lugverkoelde string, wat 32 mm bo die drywende doek gelig is met behulp van 32 mm po- lipropileenpype. ’n Termiese model word ook ondersoek om die verkoelingseffek van ’n lugver- koelde en ’n waterverkoelde DPV-string te skat in vergelyking met ’n grond ge- monteerde PV string. Gemiddelde U-waardes van 30 W/m2.K en 89 W/m2.K vir die lugverkoelde en waterverkoelde stringe word onderskeidelik waarge- neem. Hoër U-waardes stem ooreen met ’n beter verkoelingseffek as gevolg van die direkte termiese kontak van die PV-modules met die drywende doek op die wateroppervlak. ’n Gemiddelde U-waarde van 27 W/m2.K word waar- geneem vir die grond gemonteerde PV-stelsel. Die navorsing toets ook die vermoë van sonkrag-PV-simulasiesagteware, PVsyst, om DPV-stelsels suksesvol te simuleer en om die energie-opbrengs van ’n DPV- stelsel met hipotetiese gekantelde stringe en toenemende U-waardes op die- selfde plek te vergelyk. Die invloed van die gekantelde panele by verskillende kantelhoeke op die energie-opbrengs van die DPV-stelsel met die gebruik van die standaard albedo teenoor die gemodelleerde albedo word geanaliseer. Die PVsyst simulasie toon dat die energieopbrengs toeneem met ’n toename in U-waardes en dat die verskil in energie toeneem met ’n toename in die kantel- hoeke as gevolg van die laer bestraling wat by hoër kantelhoeke ervaar word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/110547
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