oa Fire safety evaluation of photovoltaic modules in an explosive atmosphere

Background: Application of photovoltaic (PV) modules as a source of electrical power in an explosive atmosphere needs thorough evaluation in fire hazard perspectives. Surface temperature above 85°C can become a source of ignition in an explosive atmosphere in a hydrocarbon industry. PV modules fire safety aspects are well defined with classifications based on voltage levels and access by human etc., through the IEC 61730, ANSI/UL 790 standards. However, evaluation of safety based on application specifics is not covered in design standards. Hot spot heating phenomena occurring in PV modules, caused by faulty conditions such as partial shading, material imperfection, fabrication flaws, damages etc., are the result of reverse biasing of cells which can lead to a localized p-n junction breakdown. Hot spots due to partial shading or illumination distribution imbalances causes localized heating wherein the temperature can rise in the range of ~150-200°C. Also, the intensity of the temperature rise can reach up to 300°C when hot spots occur due to a crack or damage of a cell. Autoignition temperatures (AIT) of many of the flammable, explosive substances fall within this temperature range. Objectives: The main objective of this research is to study and evaluate the suitability of PV module applications in an explosive atmosphere with fire safety perspectives through empirical research design. Methods: It is not practically possible to predict the actual fault conditions occurring in PV modules and therefore the worst case conditions are the testing criteria. Shaded and flawed cells are developed to test the worst case conditions. Results & Conclusions: Reverse bias characteristics of PV cells vary based on their shunt resistance. Cells can have either high shunt resistance where the reverse performance is voltage-limited or low shunt resistance where the reverse performance is current-limited. Current research test results published indicate that the PV modules applied in explosive atmospheres can lead to fire hazards even protected through bypass diodes and encapsulation due to unpredictable failure of PV cells.