International Journal of Engineering and Advanced Technology (IJEAT) ISSN: 2249 – 8958, Volume-2, Issue-2, December 2012 110 Abstract— The effect of operational environment on the reliability performance of solar photovoltaic module can be analysed . The first step is to identify which factors have the most significant influence on the reliability performance of photovoltaic modules and systems and how large is the effect. The available information about the operating conditions of the PV modules can be uniformly formulated based on two alternatives , good/desired (+1) and bad/undesired (-1) conditions. With respect to reliability, the available method PHM (Proportional Hazards Model) can be used for predicting the effect of environment on the system reliability. The reliability characteristics of PV modules can be influenced by environmental conditions such as temperature , snow, wind etc and these influences therefore need to be seriously considered in the prediction of reliability in the design phase. The conventional reliability equation deals with over a time interval and is a measure of the probability for failure-free operation during the given interval, i.e., it is a measure of success for a failure free operation. It is often expressed as R(t) = exp(-t/MTBF) = exp(-λt), where MTBF is the Mean Time Between Failure and λ is the failure rate, which is the reciprocal of MTBF. In this paper an attempt is made to modify the time equation of reliability with incorporating environmental impacts like temperature, wind and snow. Index Terms—Mean Time Between Failures, Failure rate, Weibull distribution, Proportional Hazards Model, Time to failure (TTF) Ttime between failures (TBF). I. INTRODUCTION There are a number of factors affecting PV module performance, viz, the nonlinear dependence of conversion efficiency on module temperature (which in turn depends on air temperature, the type of mounting and wind) and irradiance levels, typically declining for low irradiances and for high temperatures, Changes of reflectivity when irradiance hits the module at an angle that differs from perpendicular usually termed angle-of-incidence effect (AOI) considering different type of modules surfaces, angle and type of dirtiness, Changes of efficiency of PV modules due to the variable spectrum of the sunlight, which in turn depends on sun height and meteorological conditions, usually termed spectral effects, For thin film modules, changes in conversion efficiency due to its previous state, the history of the module (usually termed light-soaking and thermal annealing effects), Changes of modules performance with long-term exposure to outdoor conditions (normally degrades), which in turn affects the overall lifetime energy output (ageing effects), Intermittent occasional variables such as shading, pollution, snow, mismatch, etc. The above list is not exhaustive. The Manuscript received on December, 2012. E. Suresh Kumar, Production Engineering Department, Jadavpur University, Kolkata- 700 032, India. Dr. Bijan Sarkar, Production Engineering Department, Jadavpur University, Kolkata- 700 032, India. strength of these effects varies between PV technologies and even between modules using the same class of PV material. At the PV system level there are other factors determining PV power production: (1). Losses in cables and interconnections. (2). Efficiency of inverters, transformers and other power electronics. (3). PV system downtime due to component failures or maintenance. But several other issues should be considered for failure free operation of the system in the site even though the modules and the balance of system components have high reliability and life time. The following are the factors which should be considered for long term reliability of the overall system in the field. 1. Sun shine hours at the site. 2. Lightning and thunder at the site. 3. Earthquake at the site. 4. Wind and wind direction at the site. 5. Corrosion at the site. 6. Strategic importance of the site. 7.Power availability and demand mismatch. 8. Shades at the site.9. Alternate power availability at the site. 10. Transportation access to the site. 11. Albedo effect at the site. 12. Icing and snow at the site. 13. Dust at the site. 14. Land availability. 15. Staebler- Wronski effect. 16.Heat island effect at the site. A PV module will be typically rated at 25 o C under 1 KW/m 2 . However , when operating in the field, they typically works under a lot of environmental stresses like varying module temperature, ambient temperature, long term degradation, spectral issues, irradiance , wind speed, wind direction, air gap between modules, dust, rainfall, corrosion, water vapour intrusion, delamination of encapsulant materials, Thermal expansion, ultraviolet radiation, humidity, mechanical load, salt mist, partial shading, heat island impact, global climate change, summer-winter climate change, Staebler- Wronski effect, Clearness of sky, urban heat island (UHI) effect, ageing and component derating. Further, the PV performance depends on material technology, production and manufacturing process. Literature survey shows that experimental, analytical and simulation studies of PV system is the measurement of performance of the system with varying irradiance for different technologies. Also the study reveals the variation in performance of the system under STC and real field. Real field implies that the location chosen by the analyst. But the same performance may not be available from the system when the geographical area is changing. In India itself, the climate and the weather is totally different for different parts, like Leh( The temperature can range from −28°C in winter to 33 °C ) in summer, Bikaner ( In summer, temperatures exceed 50 °C and during the winter it dips to freezing point ), Chennai ( 18°C to 45°C ), Mumbai ( The temperatures in average about 30 °C in summer and 18 °C in winter ). This will be totally different even for other cities in the Asian countries. The performance entirely varies for Europe, American and African Countries. Proportional Hazards Modeling of Environmental Impacts on Reliability of Photovoltaic Modules E. Suresh Kumar, Bijan Sarkar