Prospecting solar energy in Australia: accounting for temperature losses

In this paper, we prospect the solar potential of 5 varieties of commercially available modules in 15 locations around Australia, accounting for regional temperature and irradiance. We employ irradiance datasets, from the Australian Solar Energy Information System (ASEIS). Through our analysis, we categorise regions around Australia, by their impact on the performance of different solar module technology. From this comparison we find coastal DNI on average is lower in the mornings owing to the high relative humidity and daily temperature variation. These irradiance conditions, slightly alter the optimum installation direction and tilt. The best performing modules are the premium back-contact c-Si modules, and the worst is the standard mc-Si module. Importantly, the impact of a module technology on yield must be determined with site-specific irradiances and ambient temperatures. We find temperature losses correlate most strongly correlated with average mean monthly temperature. An additional interesting finding is that coastal locations have lower direct normal irradiance in the morning, which infers the optimum orientation is slightly West of North

Modelling and analysis of the impact of module design, materials and location on the annual yield of a crystalline solar module

Solar modules are typically sold according to their nominal output power measured under standard test conditions (STC). Furthermore, the design of solar cells and modules is usually optimized separately for these conditions. However, outdoor conditions differ strongly from the standard test conditions, such as angular incoming light of varying intensity and spectrum as well as varying cell temperatures. The assessment of the performance of different module designs under outdoor conditions requires long field exposure of the modules. However, this conflicts with the short development cycles of new module designs and material changes. This thesis presents a methodology to predict the annual yield of crystalline silicon solar modules for varying module configurations and environments. This enables a rapid virtual prototyping of new modules designs under realistic conditions to support the short technology development cycles. Twelve factors that affect annual module performance are quantified, starting with solar cells in air under STC, and finishing with a complete module under realistic conditions. The interaction of optical, thermal and electrical effects in the module are considered and combined with an angular, spectral and time-resolved light source. Consequently, this Cell-to-Module Yield (CTMY) model is validated for crystalline silicon heterojunction solar cell modules and an agreement of the annual yield within 0.7 % is found. Applying the CTMY model, this thesis systematically investigates the impact of specific module design properties on the annual yield. For example, the severe benefits of silver-coated V-grooved backsheet structures can be substantial over- or underestimated under STC compared to the detailed CTMY analysis. The front metallization of a crystalline silicon solar cell is usually optimised for the current generated by a cell surrounded by air. Inside a module compound, the cell current changes due to cell interconnection and the possibility of light recycling on fingers and interconnectors. Therefore, this thesis optimizes the metallization for operation inside a module under STC and then compares the annual yield for six of the best performing module designs. It is found that applying a light redirecting film (LRF) on top of a planar interconnector ribbon achieves the highest yield for full- as well as for half-cut cells. Further, this work investigates the impact of different glass textures, such as planar, V-grooved and pyramid textures as well as anti-reflection coatings. One key finding of that pyramid glass textures outperform planar glass in combination with planar ribbons, however, when LRF ribbons are used, conventional anti-reflective coated planar glass achieves similar performance. A less understood part of the cell-module compound are angular optical effects occurring at the interface between module embedding and cell surface. In this work, special focus is placed on multicrystalline silicon cell texturing, such as plasma texturing, and metal catalysed chemical etching. Most importantly, it is found that the wide spread in angular absorption in air observed for all different cell surface textures is significantly reduced after module embedding. Consequently, the optical advantages of black silicon structures in air are minimized at module level. In summary, optimizing the cell and module design separately for a maximum performance under STC does not result necessarily in an optimum performance under field exposure. Specifically, for module configurations using 'non-symmetrical' elements, such as half-cut cell designs or V-grooves on backsheet materials, the performance can notably vary with installation and environmental conditions. An aligned cell and module design, and an optimization for realistic environments has therefore a strong potential to reduce the levelized cost of electricity

Impact of Damp Heat and Ultraviolet Radiation on Common Solar Module Encapsulant Materials

PV technology is part of a burgeoning industry in renewable energy. Australia is a prime candidate for PV with high insolation levels. An investigation into the degradation of solar modules, of different construction, is important to understanding the prominent degradation pathways and the long term degradation properties of modules as they are exposed to the harsh Australian climate. Also, characterising the reliability of such materials will give an indication of module output in the future, leading to better output prediction. Although any prediction has challenges in being translated to actual field performance. In this paper, the impact of 2 significant degradation mechanisms (damp heat and UV) are detailed and profiled with respect to several common photovoltaic module materials. The degradation conditions were performed in accordance with IEC61215. Several manufacturers were considered and the extent of EVA browning, cell delamination, solar cell cracking and power loss were recorded. Of the materials tested, DH was found to impact the adhesion of the EVA-glass layer more than UV and changed the failure mechanism to the outer layer of backsheet. The optics of the samples were effected by moisture ingress generally lowering transmission

Impact of PV module configuration on energy yield under realistic conditions

Photovoltaic cell and module manufactures optimise their products according to power measurements performed at a set of standard-test conditions. A key parameter for the financing of a solar project is yield under field or realistic conditions. Field testing modules is time consuming and costly. Hence, we develop a methodology for simulating PV module yield based on the optical, thermal and electrical properties of the components, and the module configuration regarding the cell spacing, interconnection and module layers. With our procedure, we model the performance of standard, half cell and encapsulant free modules in different locations. We present results using our cell to module yield framework for 16 different locations in Australia based on one-minute ground measured solar irradiance and ambient temperature values. We find low-light irradiance losses are directly correlated to the number of cloudy days at a given site. The majority of fielded losses are due to temperature effects, which can be predicted by the average temperature at 3 p.m. We note that wind speed is not accounted for and it will be incorporated in future studies.The authors acknowledge the Australian Renewable Energy Agency funding of this work through Grant Nos. 3-F006, and 2014/RND008

How cell textures impact angular cell-to-module ratios and the annual yield of crystalline solar modules

Two emerging trends in multicrystalline silicon cell texturing are plasma texturing, and metal catalyzed chemical etching. Both processes roughen silicon surfaces in order to increase light absorption. These processes are attractive as they are applicable to diamond-wire sawn wafers. This work investigates the optical properties of these surfaces, and other conventionally textured surfaces like isotropic acidic and random pyramid textures, are investigated for cells in air and after encapsulation for a large range of angles of incidence. We find that the angular optical performance in air varies strongly with cell texture, but when embedded in a module structure these variations are significantly mitigated: the advantages of a high angular absorption of solar cells are not fully transferred to the module level. This is especially notable for plasma etched, black silicon cell structures which suffer comparatively from poorer index matching and light recycling inside a module structure. The losses caused explicitly by the module embedding (described in the cell to module ratio) are in the range of 1–5% for perpendicular incoming light, and increase to 6–15% at an angle of incidence of 70°. Based on these angular performances, we calculate the annual yield of the modules and find that it varies by less than 2% for the cell textures. Nevertheless, the annual optical yield for the black silicon cell structures are the highest, whereas the metal catalyzed chemical etching cell structures show the lowest performance. Further, we find that different annual distributions of the incoming light at the two investigated locations (Melbourne and Alice Springs) only impact the relative performance of the cell textures at high module tilt angles

Optical Simulation and Analysis of Iso-textured Silicon Solar Cells and Modules Including Light Trapping

AbstractSolar cells made from multicrystalline silicon (mc-Si) wafers play an important role in photovoltaics. Nevertheless, tools for the optical simulation of these devices are scarce. In the present work, the reflectance and charge carrier generation of mc-Si cells and modules are for the first time simulated successfully in the complete spectral range including light trapping and escape light, as the comparison with measured reflectance of the finished cells and mini-modules shows. The “spherical caps” geometry is used to model the front surface reflection of iso-textured silicon solar cells. The characteristic angles of the spherical caps are determined from the reflectance of iso-textured wafers for three different texture strengths. Based on this calibration, the reflectance and charge carrier generation rates of cells encapsulated with EVA and glass are simulated and analysed. Iso-textured cells with full-area aluminium back surface field (Al-BSF) and with passivated emitter and rear (PERC) are quantitatively compared regarding the photo-generated current density jPh. The simulations demonstrate that the direct cell-to-module loss of iso-textured mc-Si cells with Al-BSF (0.7 mA/cm2) is smaller than for PERC cells (1.2 mA/cm2)

CALUX measurements: statistical inferences for the dose response curve

Chemical Activated LUciferase gene eXpression [CALUX] is a reporter gene mammalian cell bioassay used for detection and semi-quantitative analyses of dioxin-like compounds. CALUX dose–response curves for 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD] are typically smooth and sigmoidal when the dose is portrayed on a logarithmic scale. Non-linear regression models are used to calibrate the CALUX response versus TCDD standards and to convert the sample response into Bioanalytical EQuivalents (BEQs). Several complications may arise in terms of statistical inference, specifically and most important is the uncertainty assessment of the predicted BEQ. This paper presents the use of linear calibration functions based on Box–Cox transformations to overcome the issue of uncertainty assessment. Main issues being addressed are (i) confidence and prediction intervals for the CALUX response, (ii) confidence and prediction intervals for the predicted BEQ-value, and (iii) detection/estimation capabilities for the sigmoid and linearized models. Statistical comparisons between different calculation methods involving inverse prediction, effective concentration ratios (ECR20–50–80) and slope ratio were achieved with example datasets in order to provide guidance for optimizing BEQ determinations and expand assay performance with the recombinant mouse hepatoma CALUX cell line H1L6.1c3.status: publishe