Frequently, PV systems are affected by dirt, dust or shadowing from surrounding elements, such as trees and buildings. The shadows can cause partial shading conditions, when the irradiance is not uniform on PV installation, which lead to losses of power. Thus, the shadow prediction is primordial for a better output power estimation and to minimize its losses. The aim of this article is to propose a methodology using intuitive and available tools for shading prediction and losses assessment on PV installations. A study about the shadow pattern and module orientation (portrait and landscape) influence and an analysis of the shading losses on a PV plant were performed in order to demonstrate the applicability of the methodology. The shading effect is drastic when the shading is parallel to the short edge, whereas the effect is lower when it is parallel to the long edge. On the other hand, the losses due to shading and the difference in the position of the modules (landscape or portrait) have a lower impact on the photovoltaic plant case. It was concluded that the methodology is feasible and applicable for shading impact evaluation, despite limitations for large systems due to the simulation time.
Software for simulation of photovoltaic (PV) systems is widely used for dimensioning and forecasting electrical production. A factor of losses in PV installations is the partial shading caused by surrounding elements, and these software allow the user to estimate this effect. However, the accuracy of these simulated results for shaded PV systems is not widely studied. The purpose of this article is to investigate the accuracy and quantify the differences between simulated and measured data of partially shaded PV systems, obtained with the widely used tools SAM and PVSyst. Measured data from a PV installation were compared to results from simulations performed using the different shading calculation options available in both tools. The simulated outputs were both underestimated and overestimated in the shading situations. This variation was related to the use of an hourly fraction of shading and, in the case of SAM, due to the limitations of the 3D tools available for representation. Another source of differences between simulated and measured values was the use of uniform shading factors for diffuse and albedo. In addition, the simplification of the 3D model had a significant impact on the predicted energy, mainly on cloudy days. Both software overestimated the electricity production for the entire measurement period, reaching differences between the predicted and the measured energy varying from 9% to 24%. Shaded PV systems must be carefully analyzed, and the simulated results may differ from the measured values, which may even influence the decision on the feasibility of an installation.
O uso eficiente e racional de energia pode ser promovido através de melhorias construtivas na envoltória de edificações e utilização de equipamentos mais eficientes. Com base nessa diretriz, o objetivo deste trabalho foi avaliar o impacto no consumo energético de medidas de melhoria no desempenho térmico da envoltória de uma edificação localizada em Porto Alegre (RS, Brasil). Foi realizada uma simulação anual de desempenho energético utilizando os programas computacionais SketchUp e EnergyPlus. A edificação projetada seguindo as práticas comuns serviu de base comparativa para a análise da adição de medidas de eficiência na envoltória. Verificou-se que paredes duplas, telhado branco e vidros duplos foram as medidas que tiveram menor impacto na redução do consumo. A aplicação de isolante térmico no forro e nas paredes contribuiu para uma redução de 33,1% e 22,2%, respectivamente, no consumo de climatização. A simulação de um caso ótimo resultou em uma redução de 60,7% no consumo anual de climatização. Portanto, a adição de medidas de isolamento na envoltória de uma edificação tem resultados significativos na redução do consumo energético, o que deveria pautar o desenvolvimento de políticas públicas que incentivem e promovam a aplicação dessas medidas.
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