Power Prediction of PV Modules Contaminated by Bird Droppings via an Image Thresholding Process

Environmental factors that influence marine photovoltaic (PV) systems differ considerably from those affecting overland PV systems. The bird dropping, which is one of them, is a main cause of marine PV power reduction. The power prediction of a PV module contaminated by bird droppings is hard because light could pass through the bird dropping depending on the thickness of it unlike hard shading condition. This article shows differences between a bird-dropping shading and hard shading of the contaminated modules, and suggests a prediction model considering a transmittance of a bird dropping using image processing (IP). First, the shading rate (SR), which is the PV module surface ratio covered by bird droppings, is calculated using IP technologies. The accuracy of the SR is verified through an experiment creating artificial hard shading on the module using black masking tape. It has an error rate of 3% compared to our targeted benchmark SRs. Subsequently, an equivalent step methodology, which combines IV curves from individual cells to yield an IV curve for the entire PV module, was adopted to predict the power. The accuracy of this methodology is confirmed, and it showed a 5% error. However, in the case of real bird-dropping shades, discrepancies up to 15% are observed. In this article, the light penetration through bird droppings by a transmittance function was considered to predict the output of modules contaminated by the bird droppings. Errors fluctuate between 1%–20% based on the quantification of light interferences.