Electrochemical aging effects in photovoltaic modules

Leakage currents were experimentally measured in PV modules undergoing natural aging outdoors, and in PV modules undergoing accelerated aging in laboratory environmental chambers. The significant contributors to module leakage current were identified with a long range goal to develop techniques to reduce or stop module leakage currents. For outdoor aging in general, module leakage current is relatively insensitive to temperature fluctuations, but is very sensitive to moisture effects such as dew, precipitation, and fluctuations in relative humidity. Comparing ethylene vinyl acetate (EVA) and polyvinyl butyral (PVB), module leakage currents are much higher in PVB as compared to EVA for all environmental conditions investigated. Leakage currents proceed in series along two paths, bulk conduction followed by interfacial (surfaces) conduction

A Framework for Secure and Survivable Wireless Sensor Networks

Wireless sensor networks increasingly become viable solutions to many challenging problems and will successively be deployed in many areas in the future. A wireless sensor network (WSN) is vulnerable to security attacks due to the insecure communication channels, limited computational and communication capabilities and unattended nature of sensor node devices, limited energy resources and memory. Security and survivability of these systems are receiving increasing attention, particularly critical infrastructure protection. So we need to design a framework that provide both security and survivability for WSNs. To meet this goals, we propose a framework for secure and survivable WSNs and we present a key management scheme as a case study to prevent the sensor networks being compromised by an adversary. This paper also considers survivability strategies for the sensor network against a variety of threats that can lead to the failure of the base station, which represents a central point of failure.key management scheme, security, survivability, WSN

Universality and the five-dimensional Ising model

We solve the long-standing discrepancy between Monte Carlo results and the renormalization prediction for the Binder cumulant of the five-dimensional Ising model. Our conclusions are based on accurate Monte Carlo data for systems with linear sizes up to L=22. A detailed analysis of the corrections to scaling allows the extrapolation of these results to L=\infinity. Our determination of the critical point, K_c=0.1139150 (4), is more than an order of magnitude more accurate than previous estimates.Comment: 6 pages LaTeX, 1 PostScript figure. Uses cite.sty (included) and epsf.sty. Also available as PostScript and PDF file at http://www.tn.tudelft.nl/tn/erikpubs.htm

Moisture-temperature degradation in module encapsulants: The general problem of moisture in photovoltaic encapsulants

A general research approach was outlined toward understanding water-module interactions and the influence of temperature involving the need to: quantify module performance loss versus level of accumulated degradation, establish the dependence of the degradation reaction rate on module moisture and temperature levels, and determine module moisture and temperature levels in field environments. These elements were illustrated with examples drawn from studies of the now relatively well understood module electrochemical degradation process. Research data presented include temperature and humidity-dependent equilibrium leakage current values for multiparameter module material and design configurations. The contributions of surface, volume, and interfacial conductivities was demonstrated. Research directions were suggested to more fully understand the contributions to overall module conductivity of surface, volume, and interfacial conductivities over ranges of temperature and relative humidity characteristic of field environments

Observations of solar-cell metallization corrosion

The Engineering Sciences Area of the Jet Propulsion Laboratory (JPL) Flat-Plate Solar Array Project is performing long term environmental tests on photovoltaic modules at Wyle Laboratories in Huntsville, Alabama. Some modules have been exposed to 85 C/85% RH and 40 C/93% RH for up to 280 days. Other modules undergoing temperature-only exposures ( 3% RH) at 85 C and 100 C have been tested for more than 180 days. At least two modules of each design type are exposed to each environment - one with, and the other without a 100-mA forward bias. Degradation is both visually observed and electrically monitored. Visual observations of changes in appearance are recorded at each inspection time. Significant visual observations relating to metallization corrosion (and/or metallization-induced corrosion) include discoloration (yellowing and browning) of grid lines, migration of grid line material into the encapsulation (blossoming), the appearance of rainbow-like diffraction patterns on the grid lines, and brown spots on collectors and grid lines. All of these observations were recorded for electrically biased modules in the 280-day tests with humidity

Organic Apple Production in Washington State: An Input-Output Analysis

This paper provides an Input-Output (I/O) based economic impact analysis for organic apple production in Washington State. The intent is to compare the economic “ripple” effect of organic production with conventional production. The analysis is presented in two scenarios: first we compare the economic impact of organic versus conventional apple production for a l demand increase of one million US$ as measured in sales. The second analysis looks at the economic impact of organic and conventional apple production in terms of given unit of land (405 hectares of production). Both state-wide output (sales) and employment (jobs) impacts are estimated under each scenario. Results are presented in terms of direct, indirect, and induced economic impact. Organic apple production was more labor intensive than conventional production. While, the organic apple sector used less intermediate inputs per unit of output than conventional production it also produced higher returns to labor and capital. As a result, the indirect economic effect was lower for the organic sector than the conventional sector, but the induced economic effect was higher for organic. Given the organic price premium, the economic impact (direct, indirect and induced) was larger for organic apple production than conventional apple production.conventional and organic apple production, multiplier effects, output, and employment effects, IMPLAN

National hazard exposure worker surveillance: exposure to biomechanical demands, pain and fatigue symptoms and the provision of controls in Australian workplaces

Biomechanical demands such as repetitive hand or arm movements, lifting heavy loads or working in awkward postures contribute to the development or worsening of inflammatory or degenerative musculoskeletal disorders. However, little is known about patterns of exposure to different biomechanical demands and how they relate to the demographic and employment characteristics of Australian workers. To address this, in 2008 the National Hazard Exposure Worker Surveillance [NHEWS] survey collected information on 4500 Australian workers’ exposure to nine biomechanical demands, pain and fatigue symptoms and the provision of various risk controls. Almost all workers reported some level of exposure to the biomechanical demands surveyed and 22 per cent were deemed to have high overall (composite) biomechanical demand exposure. In particular, young workers, male workers, night workers and lower skilled workers were most likely to report exposure and had the highest overall biomechanical demand exposure. The reporting of pain and fatigue symptoms was highly related to the level of biomechanical demand exposure. Workplace size (number of workers at a site) and the overall level of biomechanical demand exposure were the best predictors of control provision: workers from large workplaces and those with high exposure were most likely to be provided with biomechanical demand controls. This report presents detailed findings of the NHEWS survey and discusses the implications of these findings for work health and safety policy

Methodological issues in measures of imitative reaction times

Ideomotor (IM) theory suggests that observing someone else perform an action activates an internal motor representation of that behaviour within the observer. Evidence supporting the case for an ideomotor theory of imitation has come from studies that show imitative responses to be faster than the same behavioural measures performed in response to spatial cues. In an attempt to replicate these findings, we manipulated the salience of the visual cue and found that we could reverse the advantage of the imitative cue over the spatial cue. We suggest that participants utilised a simple visuomotor mechanism to perform all aspects of this task, with performance being driven by the relative visual salience of the stimuli. Imitation is a more complex motor skill that would constitute an inefficient strategy for rapid performance

Interconnect fatigue design for terrestrial photovoltaic modules

The results of comprehensive investigation of interconnect fatigue that has led to the definition of useful reliability-design and life-prediction algorithms are presented. Experimental data indicate that the classical strain-cycle (fatigue) curve for the interconnect material is a good model of mean interconnect fatigue performance, but it fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming the classical fatigue curve is combined with experimental cumulative interconnect failure rate data to yield statistical fatigue curves (having failure probability as a parameter) which enable (1) the prediction of cumulative interconnect failures during the design life of an array field, and (2) the unambiguous--ie., quantitative--interpretation of data from field-service qualification (accelerated thermal cycling) tests. Optimal interconnect cost-reliability design algorithms are derived based on minimizing the cost of energy over the design life of the array field

New frontiers in Iranian Archaeology: digital technology and cultural heritage

Inspired by my recent work in Iran - were I was able to compile a digital corpus of material culture related to the ancient Iranian civilization of Elam - I stipulate and encourage archeological and museological objectives cognizant of twenty-first-century challenges. At its core, this vision is compelled by a philosophical understanding of the museum as a research and didactical institution, while critically considering the complex relationships between museums and politics, and the imperative need to merge computer literacy with a sound understanding of the material at hand. At the end it is the archaeologist, I argue, that through our privileged role as interpreters of the material past, together with a full awareness of present cultural and political realities, is uniquely positioned to advocate for fully-implemented digital museum systems which would make archaeological collections truly accessible to a global audienc