Muhammad Tayyib

Initial light-induced degradation study of multicrystalline modules made from silicon material processed through different manufacturing routes

The paper presents results of initial light-induced degradation (LID) of multicrystalline silicon photovoltaic (PV) modules made of crystalline silicon from different manufacturing processes. The modules were installed within the Sunbelt, in Hyderabad, India. Current-voltage (I-V) characteristics are measured and infra-red (IR) images of the modules are taken at regular intervals. A relationship of the IV degradation with the IR images is discussed. Results from laboratory LID tests at room temperature are performed parallel to the outdoor degradation of PV modules. It was found that the total LID, measured on the module level, after the initial 40 hours is similar for both materials resulting in approximately 1.0% degradation of the maximum module power output. This is slightly higher than what was found in laboratory accelerated light induced degradation (ALID) tests at 120°C on the cell level [1].

Two years performance comparison of Elkem Solar multicrystalline silicon with polysilicon in a PV grid-connected system

Summarizes two years performance of an Elkem Solar and polysilicon photovoltaic (PV) system installed in the Sunbelt Region, which has been fully operational since 2011. The PV system consists of 28 multicrystalline silicon PV modules made from the standard Siemens process and from material produced by a metallurgical route - the Elkem Solar Silicon (ESS®) process. The present study suggests that after two years of field operation, both types of modules show similar degradation of power at STC. The ESS® PV modules have better performance than standard polysilicon modules as a function of solar irradiation, and thereby the total kWh generated has been slightly higher for the ESS® modules.

Performance assessment of a grid-connected mc-Si PV system made up of silicon material from different manufacturing routes

Summarises the performance of an Elkem Solar photovoltaic (PV) system installed in the Sunbelt Region (between 35 North and 35 South) in Hyderabad, India, which has been fully operational since August 2012. The PV system consists of 28 multicrystalline silicon PV modules made from the standard Siemens process and from material produced by a metallurgical route - the Elkem Solar Silicon (ESS™) process. A comparative performance study of the ESS™ modules with respect to standard polysilicon has been carried out under the various climatic and solar radiation conditions at the location. The present study suggests that the ESS™ PV modules have a slightly better performance than standard polysilicon modules as a function of solar irradiation, and thereby the total kWh generated has also been higher for the ESS™ modules.

Test of the European Joint Research Centre performance model for c-Si PV modules

The performance of ten c-Si PV modules is studied at different levels of illumination and module temperatures and is modeled in terms of relative efficiency with respect to Standard Testing Conditions (STC). A recently proposed model is tested in Nordic conditions for generic mono- and mc-Si devices with screen-printed cells as well as for some high-efficiency cell designs. Two of the modules are field aged. Averaged model coefficients are derived and compared to values found in the literature. Irradiance and module temperatures measured in 2011 are then used to estimate the expected annual energy yields. The measured yields equal the predicted ones within 1.6% (mean bias error -1.0%) which suggests good modeling accuracy. The annual average relative efficiency of new c-Si modules for the test site in Southern Norway is 0.95, among the highest values in Europe. It is attributed to cool ambient air and frequent windy conditions. A theoretical relationship is derived between the first coefficient of the performance model and I-V curve model parameters. Fitted and predicted values agree well for most of the tested devices. The equation may be used by module manufacturers as a quantitative guideline for designing products with superior energy yields.

Influence of spectral composition on the temperature coefficients of solar cells from Elkem Solar

The temperature coefficients of solar cells from two different feedstocks - a compensated silicon, the Elkem Solar Silicon (ESS®), and polysilicon - under full and selective parts of the light spectrum are presented based on results obtained using a AAA sun simulator. These results are of particular interest in understanding the possible causes behind the better temperature coefficients usually observed for ESS® compared to polysilicon solar cells when measured with a full AM1.5 spectrum. The optical filtered lights from four different regions of the spectrum have been used to examine the influence of temperature coefficients on the spectral composition. ESS® solar cells showed considerable advantage over polysilicon solar cells in all spectral regions.

Impurity analyses of silicon wafers from different manufacturing routes and their impact on LID of finished solar cells

Summarizes the measurements of impurity concentrations in directionally solidified silicon ingots from different feedstocks. The substitutional Carbon and interstitial Oxygen are measured on as-sawn wafers using FTIR. Active iron concentration is mapped on a-Si:H passivated wafers. It is observed that these impurities present in Elkem Solar Grade Silicon (ESS™) concentrations are comparable to the standard polysilicon which are in the acceptable ranges for silicon for solar industry. The measured LID of the finished solar cells is also comparable.

Microscopic defects and impurity analyses of multicrystalline silicon solar cells from different manufacturing routes

It is important to fully understand the physical behavior of solar cells made by materials from alternative process routes. Solar cells from Elkem Solar Grade Silicon and standard polysilicon have been investigated with light beam induced current and electroluminescence imaging. The low efficiency regions have been further analyzed by Scanning Electron Microscopy under different imaging modes. It was found that cell regions of low performance had undergone plastic deformations resulting in the creation of crystalline defects appearing as subgrain patterns. Similar patterns were observed in both ESS™ and standard polysilicon. Energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) were used to study crystallographic orientations and impurities.

Outdoor Performance of 10 year Old a-Si and Poly-Si Modules in southern Norway conditions

The outdoor performance of 10 years modules has been measured in southern Norway conditions. For this study, Poly-Si and a-Si modules are selected and the measurements are carried out using a portable electronic load. The I-V characteristics and maximum power have been recorded for several modules of each technology. It is found that Poly-Si modules perform very well even after 10 years of span whereas some of a-Si modules have visual degradation which causes significant power losses. The experimentally outdoor monitored values of Pmp, Vmp, short circuit current (Isc), Open circuit voltage (Voc) and efficiency for different modules are compared with manufacturers values.