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Stellenbosch University (2017)

The Influence of Dust Soiling on the Performance of Photovoltaic Modules in the Semi-Arid Areas of South Africa

Du Plessis, Armand

Titre : The Influence of Dust Soiling on the Performance of Photovoltaic Modules in the Semi-Arid Areas of South Africa

Auteur : Du Plessis, Armand

Université de soutenance : Stellenbosch University

Grade : MEng, Electrical and Electronic Engineering, 2017

Résumé
With various commercial photovoltaic (PV) power plants in South Africa located in the semiarid areas of the Northern Cape, this thesis provides field generated data for PV modules subjected to this environment. The effects of dust soiling, concerning the performance of PV modules, are analysed and the results obtained serve as a quantitative and mechanistic understanding for PV system engineers and investors. In attempt to determine whether cleaning PV modules is a relevant option, experimental dust mitigation methods are investigated. These methods include the application of a hydrophobic anti-soiling coating, as well as the execution of biweekly and long term (six months) cleaning routines, consisting of water based (wet) and dry cleaning methods. Results of these mitigation methods are compared to that of modules exposed indefinitely. The research objectives are successfully investigated by means of the design and commissioning of a PV research facility. The facility consists of 16 stationary mounted polycrystalline (pc-Si ) modules, analysed for the six month period of May to October 2016. A single axis tracker (SAT) system, is also designed and implemented. This provides the required experimental platform for the investigation of dust soiling on four tracking pc-Si modules, during a three month period of mid-August to November 2016. Raw data validation is established with comprehensive weather monitoring (ambient temperature, wind speed, wind direction, rainfall, pressure, and humidity), plane of array irradiance (GPOA) and PV module back sheet temperatures recorded, in accordance with the IEC 61724 standard. A MasterController, an intelligent data logging and communications device, is also designed and implemented, which is responsible for the gathering of the meteorological on-site data, measured at one minute log intervals. Also, as specified by the IEC 61724 standard, an intelligent device capable of extracting I-V curves, from individual PV modules at a 10 minute interval is utilised. PV module power output is derived from the measured I-V curves, validated with a singlediode curve fitting routine. A comparative study between various modules is analysed with a performance ratio (PR), defined as the temperature and irradiance corrected performance factor of a PV module. A clearness ratio (CR) is also used to further quantify dust soiling for the stationary modules, which compares the PR of modules to that of two reference modules, cleaned biweekly. For the six month stationary module analysis, results conclude a maximum recorded reduction in CR of 2.7 %. A maximum ideal PR difference of 1:9 % is recorded for both the coated and uncoated sets of long term exposed modules, compared to the short term cleaned modules. This maximum deviation in performance is recorded after a 75 day absence of rainfall. The analysis does suggest that a rainfall of about 6 mm, every four to six weeks, is substantial to maintain the CR of unclean stationary modules, within 1 % of the cleaned reference modules. Results further indicate little to no deviation in performance between dry cleaned stationary modules and a set of water (distilled) cleaned modules. Regarding the SAT modules, a maximum ideal PR difference of 5.5 % is recorded for a coated, as compared to an uncoated module. The applied self-cleaning capability of the SAT system did not yield any conclusive remarks regarding this dust mitigation method. It is concluded that the hydrophobic coating for both topologies, stationary and tracking, promoted dust soiling. Finally, the research also suggests that SAT modules, which adopt a horisontal resting position during night time, are more vulnerable to dust soiling than stationary modules.

Mots Clés : Photovoltaic power systems – Semi-Arid regions ; UCTD ; Photovoltaic power systems ; Dust control ; Hydrophobic surfaces

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Page publiée le 3 septembre 2017