PV by-pass diode performance in landscape and portrait modalities

By-pass diodes are frequently used to minimize the effects of shading on PV module power generation. However, the functionality and effectiveness of these diodes depends on proper installation of a module with respect to potential shade sources. The lack of general manufacturer guidelines for proper module installation paired with the current level of technical knowledge held by many general contracting firms, may often lead to compromises in the electrical output of a photovoltaic system. The current produced by a single PV cell is directly proportional to the amount of solar irradiation that it is exposed to. However, in power modules many cells are wired in series allowing current flows to be limited by the most shaded cell. Testing of various module types with and without bypass diodes were performed in accordance with the experimental protocols developed at Rowan University´s Center for Sustainable Design (CSD). I-V curves were obtained for a wide range of load impedances using a digital electronic load for both portrait and landscape modalities. Multiple test runs were performed at each shading increment for a single row of cells and the average I-V curve was calculated. Cell row shading was varied from 0-100% in 20 percent increments of cell row height. The study was conducted on multiple modules, covering the primary manufacturing types including: mono-crystalline, poly-crystalline and amorphous silicon. The results of this experimentation showed that the performance efficiency and functionality of by-pass diodes is highly dependent on the orientation of the PV modules. The circuital configuration of PV modules must be taken into consideration when designing a PV array. Depending on the orientation, bypass diodes can be rendered completely ineffective to the point that single cell row shading can reduce power output of the module by as much as 92% and also result in permanent damage to the PV modules.