Study Of Hotspot Of Pv Modules In Flammable Dust Application Environment

Abstract

Background Hotspot over the surface of the Photo Voltaic (PV) Modules due to partial shading through dust deposition can cause a p-n junction breakdown leading to temperature rise over the surface of the modules. When the PV module operating current exceeds the reduced short circuit current(Isc) of the shaded cell, it cannot produce energy, rather starts to consume power from the other PV cells connected in series. Researchers measured hotspot temperature rise in the range of 150~200Deg.C due to partial shading or illumination distribution imbalance. Also the intensity of rise can reach to the tune of +300Deg.C, when hotspot occurs due to a crack / damage on cell. Level of temperature rise depending on numerous factors such as number of PV cells connected in series to shaded cell, Open Circuit Voltage (Voc) of the PV cell, shunt resistance, band gap of the PV cell material and location of shade etc. Installation of grid connected PV solar farms adjacent to flammable dust environment can deposit over the PV modules creating partial shading leading to rise in surface temperature. Auto Ignition Temperature (AIT) of many of the flammable / explosive substances are well classified and above + 85Deg.C can become a source of ignition. By-pass diodes are employed to minimize or prevent the effect of hotspot on PV cell by forward biasing the diode during faulty conditions. Normal design in commercial PV modules consider to add a by-pass diode for a set of 15~18 PV cells. There are characteristics mismatch between the PV cells and by-pass diode hence prevention of hotspot is not ensured in total in the event of diode failure. Encapsulated PV module can withstand localized temperature to the tune of +95~150Deg.C depending on the material, the temperature rise due to hotspot can rise above these limits. Methods: Flammable dust is a mixture of lowest AIT (+102Deg.C) substance Carbon Disulfide(CS2) liquid with ash and saw dust. Partial shading of PV modules by the flammable dust mixture for the test is to select cell current coincides as closely as possible with module Isc. Objectives: The main objective of this research paper is to study and evaluate the effect of hotspot phenomena of the PV Modules in flammable dust environment with a focus on fire safety. Results & Conclusions: Mono crystalline and polycrystalline PV modules with varying voltage levels and power output are setup for the experimental verification. Flammable dust mixture for shading is prepared for the experimentation with CS2, ash and saw dust materials in equal proportion. Lower temperature rise PV module is more suited for a flammable dust environment and this study is aimed to identify the material. Key outcome this research may recommend for an application specific PV module is recommended with following design configurations for use in flammable atmosphere, 1. By-pass diode across 3 ~ 6 PV cells thereby reducing the power to dissipate across the shaded cell. 2. Materials of PV cell with lower Voc or band-gap engineered semiconducting material to reduce the effect of hotspot.