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In this study, the outputs from a simple PV performance model were compared to measurements of AC power for three PV systems located across Sydney, Australia. The study aimed to investigate the level of uncertainty and bias of the model when onsite measurements of plane of array (POA) irradiance and module temperature were not available. The results demonstrated that the simple PV performance model estimated the AC performance with a low level of model bias (NBME = ±3.2%) and uncertainty (NRMSE < 6%) when onsite measurements of POA irradiance and module temperatures were available. For POA irradiance, the results indicated that modelling uncertainty increased significantly (NRMSE < 13%) when alternative methods to estimate POA irradiance were utilised. For module temperature, the results indicated that the choice of model coefficients had a significant impact on the performance of the module temperature models. In particular, for the three parallel roof mounted PV systems studied, the results suggested that the open rack/free standing or well ventilated module temperature coefficients should be used within the module temperature models investigated. This selection of coefficients was not directly evident given the PV systems investigated were parallel roof mounted PV systems, not free standing rack mounted arrays. [ABSTRACT FROM AUTHOR]

Abstract: The focus of this paper is to investigate the impact of using estimated solar irradiance data in building energy simulations. A series of annual weather files were developed with the estimates from two global and three diffuse/direct irradiance models for three locations in Australia. A weather file was also developed using the modelled values of global, diffuse and direct irradiance as estimated by EnergyPlus'' (Version 7.0.0) auxiliary weather generator program. In addition weather files were generated with measured irradiance data and satellite derived irradiance data from the Australian Bureau of Meteorology. The influence of irradiance data was tested via the simulation of a simple 15 × 15 × 3.5 m building under two construction scenarios with varying window to wall ratios (WWR). This study indicates that the level of bias and uncertainty in the simulation results was low when global irradiance was measured and only diffuse and direct irradiance were estimated. However, when global irradiance was unknown the level of bias and uncertainty increased significantly and was shown to be highly dependent on the WWR, whilst only the level of bias was shown to be dependent on the building envelope construction. The results also indicated that the Skartveit diffuse/direct irradiance model used in combination with the BOM''s satellite derived global irradiance data set achieved better results than the complete (global and direct) satellite derived irradiance data set from the BOM. The worst correlation in the simulation results occurred for the case where the irradiance data was estimated by EnergyPlus'' auxiliary weather generator program. [Copyright &y& Elsevier]

Abstract: Hourly diffuse and direct solar irradiance data are required for weather files used in building energy simulation as well as Photovoltaic and solar thermal calculations. Access to up to date hourly observation data or satellite derived data for these parameters is currently only available for a selection of the Australian Bureau of Meteorology measurement locations. This study aims to investigate the accuracy of the methods used to estimate solar irradiance data from meteorological observations either in the absence of observed irradiance data or when irradiance observations are limited to global irradiance. In particular the focus of this paper is to investigate the accuracy of the process of coupling together global and direct/diffuse models. Five global and four diffuse/direct irradiance models are presented and compared to experimental data for four locations in Australia. In the case where experimental global irradiance data is available, values are used as input into various models to obtain diffuse and direct irradiance. In the absence of experimental irradiance data, the approach taken is to estimate global irradiance with a separate model and then feed these values into the diffuse/direct models. The errors associated with both of these approaches are investigated by comparing the modelled diffuse and direct irradiance values with known experimental data for four Australian locations over a period of a number of years. This study indicates that no single diffuse/direct irradiance model consistently outperformed the other models at estimating diffuse and direct irradiance whilst the Zhang and Huang global irradiance model with coefficients from Seo and Huang achieved the best estimates of global irradiance for the locations investigated. For the approach where global irradiance is estimated from a model, the resulting direct and diffuse data was found to differ significantly from the experimental data. The results indicate that the individual models that achieved the best estimates of global irradiance did not achieve the best estimates of diffuse and direct irradiance when coupled with a diffuse/direct model. [Copyright &y& Elsevier]