Evaluation and improvement of the single diode model's parameters used for solar PV modelling

Thesis (MEng)--Stellenbosch University, 2017.ENGLISH ABSTRACT: Solar photovoltaics are one of the leading renewable energy generators that are being installed in South Africa. The understanding of how this technology works and how it responds to radiation, is important. This thesis evaluates the different parameters that influence the performance of a solar cell. The parameter extraction method is of interest as it tells the story of what is happening internally in a solar cell when subjected to environmental conditions. The response of the cell to certain light is part of this study to evaluate the influence of different light and how it relates to the testing condition on the data sheet of the solar module. The solar cell parameters of the single diode equivalent circuit model are studied. The data originate from a testing facility in the Northern Cape. The data were examined to extract the five parameters from the current voltage curve, measured in 10 minute intervals on the site. The parameter extraction method of De Soto is presented and implemented to compare the induced errors made with this method. The error was an overestimation of 13.71% in the maximum power point. The evaluation of the error resulted in an observation of a linear error with regards to temperature and irradiance. The output of the method was adjusted with a function to result in an improvement of a percentage error of -2,99%. The adjustment function was optimised and the error in extracting the maximum power point was reduced to only -0.062%. The individual parameters are examined and adjusted, to present five new equations for the parameter extraction that are developed from De Soto’s method. The new equations have shown an increase in parameter accuracy. When the new parameter extraction equations are used together, the maximum power point error is -1.73%. An automated spectrum and solar module performance monitoring system was developed. The system measures the current voltage curve from the solar module with the solar spectrum at an interval of 10 minutes. The data are stored on a local and web-based database for analysis. The data were firstly analysed in the different bands of wavelength that each colour in the spectrum occupies. This has shown that red light is the dominant colour in the spectrum that was measured. The relationship between the average photon energy and the current and voltage of the module are examined and have shown that the voltage is high regardless of the amount of energy, as long as there is direct sunlight on the module. The current increases as the average photon energy quantification parameter increases. From this study it is evident that the spectrum also plays a role in the modelling of photovoltaics, especially when the conditions are not standard test conditions. The solar spectrum can change considerably and it is important to take it into consideration when accurate modelling of photovoltaics is conducted.AFRIKAANSE OPSOMMING: Son fotovoltaïese tegnologie is een van die gewildste hernubare energie opwekkers wat tans in Suid-Afrika geïnstalleer word. Dit is belangrik om te verstaan hoe hierdie tegnologie werk en hoe dit op bestraling reageer. Hierdie tesis ondersoek die verskillende parameters wat die prestasie van ’n sonsel beïnvloed. Die parameter ekstraksie metode is van belang, aangesien dit verduidelik wat binne-in ’n sonsel aangaan wanneer dit blootgestel word aan verskeie omgewingstoestande. Deel van die studie is om die invloed van verskillende lig en die verband daarvan met betrekking tot standaard toets toestande, op die sonpaneel se data blad, te evalueer. Die enkeldiode ekwivalente stroombaanmodel se parameters word bestudeer. Die data is afkomstig van ’n toetsfasiliteit in die Noord-Kaap. Die data is ondersoek om vyf parameters van die stroom-spanningskurwe, wat in 10 minute intervalle op die perseel gemeet word, te onttrek. De Soto se parameter ekstraksie metode word voorgelê en toegepas om die foute wat hierdie metode maak, te ondersoek. Die metode bied ’n oorskatting van 13.71% van die maksimum drywingspunt. Toe die fout ondersoek is, is ’n lineêre fout ten opsigte van die temperatuur en bestraling gevind. Die metode se uittree is met ’n funksie aangepas, wat tot ’n verbetering van ’n -2, 99% fout gelei het. Die aanpassingsfunksie is geoptimeer en die fout van die maksimum drywingspunt is verminder na slegs -0.062%. Die individuele parameters is ondersoek en aangepas om vyf nuwe vergelykings vir die parameter ekstraksie te bied wat van De Soto se metode ontwikkel word. Die nuwe vergelykings toon ’n toename in akkuraatheid. As die nuwe parameter ekstraksie vergelykings saam gebruik word, is die fout van die maksimum drywingspunt -1.73%. ’n Geoutomatiseerde spektrum en sonpaneel prestasie moniteringstelsel is ontwikkel. Die stelsel meet die stroom-spanningskurwe van die sonpaneel in 10 minute intervalle. Die data word op ’n plaaslike en web-gebaseerde databasis gestoor vir analise. Die data is eerstens in verskillende bande golflengtes van elke kleur in die spektrum ontleed. Dit het getoon dat rooi lig die dominante kleur in die gemeetde spektrum is. Die verhouding tussen die gemiddelde fotonenergie en die stroom en spanning van die sonpaneel is ondersoek en het aangetoon dat die spanning hoog is, ongeag die hoeveelheid energie, mits daar direkte sonlig op die sonpaneel skyn. Die stroom neem toe soos die gemiddelde fotonenergie kwantifisering parameter toeneem. Dit is duidelik dat die spektrum ook ’n rol speel in fotovoltaïese modellering, veral as die toestande nie standaard toets toestande is nie. Die sonspektrum kan aansienlik verander en daarom is dit belangrik om dit in ag te neem as akkurate fotovoltaïese modellering gedoen word