Photovoltaic (PV ) technology has seen exciting growth in the field of energy for the past few decades. With strong government programs in China, Japan, Germany, and Netherlands, PV systems have grown to become a dominant source of renewable energy. Thin film silicon based a-Si:H solar cells are 2ndgeneration solar cells. They have the ability to be applied on glass or polymer, free of toxic materials in the manufacturing process, and are extremely flexible. Even though they exhibit a lower efficiency with respect to other proven technologies, a lower temperature coefficient and the unique ability to self-anneal in warmer months make it an attractive option. HyET Solar Netherlands B.V. manufactures thin-film solar cells based on a-Si:H technology. These modules are extremely flexible and relatively cheaper to manufacture, hence are suited for Building Integrated Photovoltaics (BIPV ) setups in the form of soundwalls, curved roofs, and solar blinds among many others. The primary aim of this research is to understand the performance variation of the solar modules when they are not under Standard Test Conditions (STC) but are aged outdoor. To understand this, data was collected from solar modules installed outdoor. The installed PV system consists of 16 arrays, each array comprising of two modules connected in series and each module consisting of 28 cells in series. However, during installation, some of the modules were damaged, and analysis was solely done on the best-performing array. To analyse the system, irradiance, temperature, and operating maximum powerpoints(mpp) were recorded every minute while the JV-curves were measured every fifteen minutes. The modules were analysed on two levels: on the system level and the cell level. Analysing the modules on system level was done by calculating the performance ratio and daily energy yield. It was found that the modules performed significantly better in warmer months than in cooler months. This could be explained by a combination of the annealing effect and relatively lower losses due to higher irradiance in warmer months. Upon analysing the daily energy yields of the modules, it was found that the system suffered degradation of 10.3% in the second year of operation. To analyse the modules on the cell level, JV-curve data were used. To extract the intrinsic parameters of the modules from a JV-curve, an in-house software "DoktorDEP" was utilised. In order to validate the output from the software, two experiments were performed, where JV-curve were measured at different temperature points and irradiance. While the experiments were successful in estimating the intrinsic parameters, certain requirements were not met at the outdoor data, hence the focus was now shifted to explicit JV-curve parameters such as short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), open-circuit resistance (Roc) and shot-circuit resistance (Rsc). Upon analysis, it was found that there was a Jsc loss of 0.63mA/cm2 and Voc loss of 0.02V/c in the second year of operation. Moreover, the ontained trends of FF and Roc exhibited a definite degradation while the Rsc did not exhibit a degrading trend. Even though data analysis was performed on damaged modules, the obtained trends in this study can be of vital importance in developing strategies for reliability of the modules. The same techniques can be applied to a set of undamaged modules to estimate the performance. Because the JV-parameter Roc was affected drastically as the modules aged, future experiments can be designed to observe and tweak Roc to improve both efficiency and reliability. Lastly, based on the insights about DoktorDEP, future versions can be rolled out with the ability to analyse outdoor JV-curve data to discern the intrinsic parameters and their variation when aged outdoor. This could help in targeting and prioritising the factors affecting module performance and hence resulting in a robust product.