A Spectral Guide: the analysis of solar irradiance and soiling through spectroradiometry

Lewis, Carmen (2017-12)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The influence of soiling on photovoltaic (PV) modules has been investigated in many research projects before, but this project extended the methods of soiling analyses on photovoltaic (PV) modules through the implementation of spectroradiometry. The objective with the implementation of a spectrometer was to remove the associative characteristics of PV modules within the measurements. Since spectroradiometric measurements are not often used for this application, several measuring and analysis methods are discussed in terms of PV applications. Previous research either failed to consider the module characteristics (such as temperature and manufacturing variances) or spectrometers have not been implemented in the measurement of irradiance and soiling under natural conditions. An automated measuring system was designed and built to ensure repeatable and accurate measurements of clear-sky irradiance and comparative measurements through glass samples. The combination of these two types of measurements allowed for the determination of relative transmission losses , as a result of the refraction and absorbance by dust particles and glass particles. Furthermore, lab measurements were acquired to indicate that the method used to determine relative transmission losses, was accurate. This project was used to generate a spectral measurement and analysis guide, specifically for the measurement of irradiance and determining the influence of soiling on the transmission of irradiance. Through relative transmission loss measurements, it was found that clean low-iron float glass (a good approximation for solar glass) induced a transmission loss of 8.6 - 9.2%. Furthermore, with automated measurements at a fixed angle, the transmission loss was calculated as 9:32% to 12:53% from clean to minor soiling solar glass samples. Also, an analysis on the shift in transmission within a measurement in the wavelength bands of UV, visible and NIR light was discussed - it was found that the soil and inherent glass particles supressed some photons within the UV and NIR ranges, causing a slight increase in content within the visible range. Several recommendations regarding the automated system design are supplied. A recommendation in regards to the measurement equipment was that a measuring range greater than 300 - 1000nm with good resolution is required for these measurements. This might mean the implementation of a second spectrometer specifically for measuring the NIR range. It was also found that measurements acquired in the direction of the sun location, rather than at a fixed measuring angle, increased the stability and accuracy of measurement, allowing for better approximations of transmission loss as a result of soiling.

AFRIKAANSE OPSOMMING: Die invloed van stofbesoedeling op fotovoltaïese (FV) panele is al ondersoek deur talle navorsingsprojekte, maar hierdie projek brei uit op die metodes van analise van stofbesoedeling op FV deur die gebruik van radiometriese spektrometrie. Die hoof doel van die gebruik van 'n spektrometer is om die assosiatiewe eienskappe van die FV panele te vermy in die metings. Aangesien spektrometriese metings nie gereeld in die FV veld gebruik word nie, is vele meet en analise metodes bespreek in terme van hierdie FV toepassing. Vorige navorsing het of nie die paneeleienskappe (soos temperature en vervaardigingsverskille) in ag geneem nie, of nie die spektrometermetings voltooi in natuurlik sonstraling en stof omstandigehede nie. 'n Geoutomatiseerde meetopstelling is ontwerp en is gebou om herhaalbare en akkurate metings van sonstraling deur 'n glaspaneel te verseker. Die kombinasie van bloulug en glasmetings laat toe vir die bepaling van relatiewe transmissieverlies, as gevolg van die refraksie en absorbies deur die stof patikels, sowel as die glas partikels. Verder is labratorium-metings bekom om hierdie metode van relatiewe transmissie as akkuraat te bevestig. Hierdie projek was dus gebruik om 'n gids op te stel oor die meet en analise van die sonspektrum, spesifiek vir die bepaling van die sonstraling en om te bepaal wat die invloed van stof is op die transmissie van sonstrale. Deur hierdie relatiewe transmissie toetse is dit bevind dat skoon "float" glas, met 'n lae yster inhoud (wat 'n goeie benadering vir FV paneel glas is), 'n verlies in transmissie tussen 8.6% en 9.2% veroorsaak het. Verder, met geoutomatiseerde toetse, teen 'n vaste meethoek, is dit bepaal dat daar 'n transmissieverlies was van 9:32% tot 12:53% vanaf skoon tot lig stowwerige FV glaspanele. 'n Analisie op die skuif in transmissie binne die UV, sigbare en NIR lig golflengte bande onderskeidelik, is ook bespreek, en so is gevind dat stof en selfs partikels inherent in die glas sekere fotone in die UV en NIR bande onderdruk wat dus 'n verhoging in die sigbare ligband veroorsaak. Verskeie aanbevelings vir die geoutomatiseerde stelsel is bespreek. 'n Aanbeveling in term van die meet gereedskap is dat 'n groter meet band as 300-1000nm benodig word met goeie resolusie. Dit kan selfs beteken dat 'n twee spektrometer benodig sal word om spesi ek die NIR band te meet. Dit is ook gevind dat die metings wat in lyn met die son geneem was en nie by 'n vaste meethoek nie, die stabiliteit en akkuraatheid van metings verbeter het wat weer toegelaat het vir 'n beter benadering van transmissieverliese, as gevolg van stofneerslag.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102793
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