Operation and maintenance field experience for off‐grid residential photovoltaic systems

The field performance of photovoltaic systems has been studied extensively for many applications and a number of databases exist in the United States and internationally. However, these databases focus almost exclusively on the system elecrical performance. Published information on the operation and maintenance (O&M) experience and costs for photovoltaic systems is almost nonexistent. At a time when photovoltaics is being considered as a viable option for distributed energy generation, it is critical that maintenance experience be captured to identify lifecycle costs and/or levelized energy costs for these systems, as well as to identify areas for system and component improvements. This paper addresses the data collection, analysis and results of an off‐grid residential customer service program offered by the Arizona Public Service (APS) Company over a six‐year period from 1997 through 2002. Standardized, packaged photovoltaic systems were offered and operated by APS through a lease arrangement with customers throughout the state of Arizona. The operation and maintenance records for these systems were carefully tracked and analyzed. The O&M costs, database development, cost drivers, lifecycle cost implications, and lessons learned are presented and discussed. Copyright © 2004 John Wiley & Sons, Ltd.     

Multilevel Converters: An Enabling Technology for High-Power Applications

Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.      

Measuring the costs of photovoltaics in an electric utility planning framework

Utility planning models evaluate alternative generating options using the revenue requirements method—an engineering-oriented, discounted cash-flow (DCF) methodology that has been widely used for over three decades. Discounted cash-flow techniques were conceived in the context of active expense-intensive technologies, such as conventional, fuel-intensive power generation. Photovoltaic (PV) technology, by contrast, is passive and capital intensive—attributes that are similar to those of other new process technolgies, such as computer-integrated manufacturing. Discounted cash-flow techniques have a dismal record for correctly valuing new technologies with these attributes, in part because their benefits cannot be easily measured using tradiational accounting concepts. This paper examines how these issues affect cost measurement in both conventional and PV-based electricity, and presents kWh-cost estimates for three technologies (coal, gas and PV) using risk-adjusted approaches, which suggest that PV costs are generally equivalent to the gas/combined cycle and about twice the cost of base-load coal (environmental externalities are ignored). Finally, the paper evaluates independent power purchases for a typical US utility and finds that in such a setting the cost of PV-based power is comparable to the firm's published avoided costs.     

Pinpointing users with location estimation techniques and Wi‐Fi hotspot technology

Location awareness is becoming an important capability for mobile computing; however, it has not been possible until now to provide cheap pervasive positioning systems. Wide area coverage is most famously achieved by using global positioning systems (GPS). A constellation of low‐orbit satellites cover the earth's surface. Unfortunately GPS does not work indoors and has limited success in big cities because of the ‘urban canyon’ effect. PlaceLab is a research project that attempts to solve the ubiquity issues surrounding 802.11‐based location estimation. PlaceLab, like RADAR, uses a device's 802.11 interface; however, it does not require the area to be pre‐calibrated. It predicts location via the known positions of the access points detected by the device. Commonly used systems have a number of drawbacks, including cost, accuracy and the ability to work indoors. PlaceLab is a piece of open source software developed by Intel Research that can pinpoint a user within a Wi‐Fi network. We set out here to investigate whether PlaceLab can be used as a means of establishing a user's position. This type of investigation could, if successful, pave the way for the development of other location‐based applications. This report documents the efforts to answer the above question. PlaceLab was found to work, but only in ideal locations where factors such as the number of floors and the lack of available APs did not affect its use. It was concluded that these factors prevent the system from being effective as a means of establishing a user's position in most locations on campus. Copyright © 2008 John Wiley & Sons, Ltd.     

A network processor‐based architecture for multi‐gigabit traffic analysis

The wide availability of cheap and effective commodity PC hardware has driven the development of versatile traffic monitoring software such as protocol analyzers, traffic characterizers and intrusion detection systems. Most of them are designed to run on general purpose architectures and are based on the well‐known libpcap API, which has rapidly become a de facto standard. Although many improvements have been applied to packet capturing software, it still suffers from several performance flaws, mainly due to the underlying hardware bottlenecks. To overcome these issues, this paper proposes a system architecture, which combines the high performance of a Network Processor card with the flexibility of software‐based solutions. It allows for removing most part of the hardware limitations exhibited by a purely PC‐based architecture, while preserving the full compliance to any software applications based on libpcap. In addition, the proposed system enables the use of monitoring applications at the wire speed, with the possibility of on‐the‐fly data processing. The system performance has been thoroughly assessed: the results show that it clearly outperforms the previous PC‐based solutions in terms of packet capturing power, while the timestamping accuracy is as good as that achieved by DAG cards. Copyright © 2009 John Wiley & Sons, Ltd.     

An energy‐aware approach for resource managing in the fog‐based Internet of Things using a hybrid algorithm

Regarding the recent information technology improvement, the fog computing (FC) emergence increases the ability of computational equipment and supplies modern solutions for traditional industrial applications. In the fog environment, Internet of Things (IoT) applications are completed by computing nodes that are intermediate in the fog, and the physical servers in data centers of the cloud. From the other side, because of resource constraints, dynamic nature, resource heterogeneity, and volatility of fog environment, resource management problems must be considered as one of the challenging issues of fog. The resource managing problem is an NP‐hard issue, so, in the current article, a powerful hybrid algorithm for managing resources in FC‐based IoT is proposed using an ant colony optimization (ACO) and a genetic algorithm (GA). GAs are computationally costly because of some problems such as the lack of guarantee for obtaining optimal solutions. Then, the precision and speed of convergence can be optimized by the ACO algorithm. Therefore, the powerful affirmative feedback pros of ACO on the convergence rate is considered. The algorithm uses GA's universal investigation power, and then it is transformed into ACO primary pheromone. This algorithm outperforms ACO and GA under equal conditions, as the simulation experiments showed.     

美军舰载机着舰数据链的发展与启示

回顾了美国着舰引导系统及着舰数据链发展历程,分析了各着舰引导系统对信息传输需求的差异,总结了各着舰数据链的功能性能特征,描述了美国着舰数据链的发展趋势,探讨了新型着舰数据链的技术体制,最后指出了对我国着舰数据链技术及应用发展的启示。     

Large-vocabulary continuous speech recognition: advances andapplications

The past decade (1990-2000) has witnessed substantial advances in speech recognition technology, which when combined with the increase in computational power and storage capacity has resulted in a variety of commercial products already or soon to be on the market. The authors review the state of the art in core technology, large vocabulary continuous speech recognition, with a view toward highlighting recent advances. We then highlight issues in moving toward applications, discussing system efficiency, portability across languages and tasks, and enhancing the system output by adding tags and nonlinguistic information. Current performance in speech recognition and outstanding challenges for three classes of applications (dictation, audio indexation, and spoken language dialogue systems), are discussed     

Attaining a 30-year photovoltaic system lifetime: The BOS issues

Failures of power conditioning systems and balance of system (BOS) components have been responsible for the majority of system downtime in virtually all of the USA's large grid-tied photovoltaic (PV) power plants. For these and future PV power plants, therefore, improvements in component reliability must be made before the design goal of a 30-year system liftime can be attained. Advances in technology can increase reliability and still reduce costs of PV modules and power conditioning systems. However, since BOS components come generally from mature technologies, increased reliability must be attained through the purchase of higher quality components.     

In‐Vehicle AR‐HUD System to Provide Driving‐Safety Information

Augmented reality (AR) is currently being applied actively to commercial products, and various types of intelligent AR systems combining both the Global Positioning System and computer‐vision technologies are being developed and commercialized. This paper suggests an in‐vehicle head‐up display (HUD) system that is combined with AR technology. The proposed system recognizes driving‐safety information and offers it to the driver. Unlike existing HUD systems, the system displays information registered to the driver's view and is developed for the robust recognition of obstacles under bad weather conditions. The system is composed of four modules: a ground obstacle detection module, an object decision module, an object recognition module, and a display module. The recognition ratio of the driving‐safety information obtained by the proposed AR‐HUD system is about 73%, and the system has a recognition speed of about 15 fps for both vehicles and pedestrians.     

Solar‐powered ZigBee‐based wireless motion surveillance: a prototype development and experimental results

This paper describes the design and implementation of a solar‐powered wireless motion sensor surveillance network. Commercially available systems with similar functionality which exist today have several disadvantages including single points of failure and requires (semi) constant personnel attention as well as an elaborate power system. These systems require a lot of time to set up, they cannot be used in remote areas where a main power supply is unavailable, and are quite costly. Therefore, there is a need to develop a system which is portable, easy to set up, and is energy efficient. The wireless motion surveillance network described in this paper is designed to be portable, economically inexpensive, and energy efficient. The network is created using the IEEE 802.15.4 ZigBee wireless standard by implementing multiple Microchip PICDEM Z nodes. Each node in the network is equipped with a Direction Sensing Infrared Motion Detector (DSIMD) and a solar power unit (SPU). The DSIMD allows for detection of humans and animals alike moving into or out of the network. The system is powered by solar energy that makes it quite adaptable for remote applications. The network is able to cover an area of radius 30 m. By developing a low‐cost system, which is portable, easy to set up, and has an unlimited power supply, this technology is made accessible to a wider range of applications. The implementation of a CMOS camera is discussed at the end which can be used to take a snapshot of the detected object. Copyright © 2007 John Wiley & Sons, Ltd.     

Internet of Things Applications: Opportunities and Threats

In the century of automation, which is digitized, and more and more technology is used, automatic systems' replacement of old manual systems makes people's lives easier. Nowadays, people have made the Internet an integral part of humans' daily lives unless they are insecure. The Internet of Things (IoT) secures a platform that authorizes devices and sensors to be remotely detected, connected, and controlled over the Internet. Due to the developments in sensor technologies, the production of tiny and low-cost sensors has increased. Many sensors, such as temperature, pressure, vibration, sound, light, can be used in the IoT. As a result of the development of these sensors with new generations, the power of the IoT technology increases, and accordingly, the revolution of IoT applications are developing rapidly. Therefore, their security issues and threats are challenging topics. In this paper, the benefits and open issues, threats, limitations of IoT applications are presented. The assessment shows that the most influential factor for evaluating IoT applications is the cost that is used in 79% of all articles, then the real-time-ness that is used in 64%, and security and error are used in 57% of all reviewed articles.

     

On the problems of symbol‐spaced tapped‐delay‐line models for WSSUS channels

This paper analyzes the validity and statistical behavior of symbol‐spaced tapped‐delay‐line (SSTDL) models for wide‐sense stationary uncorrelated scattering (WSSUS) mobile radio channels. SSTDL models are obtained by sampling the channel impulse response (CIR) in delay domain at a rate equal to the reciprocal of the symbol duration. They were proposed more than four decades ago as canonical channel models for band‐limited time‐variant linear (TVL) systems, and are nowadays widely in use for assessing the performance of several wireless communication systems. The applicability of these tapped‐delay‐line (TDL) models seems to be unquestionable, as they were developed in the framework of the sampling theorem. Nonetheless, we show here that SSTDL models should be used with care to model WSSUS channels, because the channel's uncorrelated scattering (US) condition might easily be violated. Furthermore, we show that SSTDL models suffer from strong limitations in emulating the channel frequency correlation function (FCF). This drawback leads to an inaccurate performance evaluation of wireless communication systems sensitive to the FCF. To cope with this problem, we present a simple solution by doubling the channel's sampling rate. The benefits of this solution are demonstrated with some exemplary simulation results. Copyright © 2008 John Wiley & Sons, Ltd.     

A Low‐Voltage High‐Performance CMOS Feedforward AGC Circuit for Wideband Wireless Receivers

Wireless communication systems, such as WLAN or Bluetooth receivers, employ preamble data to estimate the channel characteristics, introducing stringent settling‐time constraints. This makes the use of traditional closed‐loop feedback automatic gain control (AGC) circuits impractical for these applications. In this paper, a compact feedforward AGC circuit is proposed to obtain a fast‐settling response. The AGC has been implemented in a 0.35 μm standard CMOS technology. Supplied at 1.8 V, it operates with a power consumption of 1.6 mW at frequencies as high as 100 MHz, while its gain ranges from 0 dB to 21 dB in 3 dB steps through a digital word. The settling time of the circuit is below 0.25 μs.     

On the performance of UNB for machine‐to‐machine low earth orbit (LEO) satellite communications

Ultra narrow band (UNB) is a widely used technology for machine‐to‐machine and low‐power wide‐area communications. Its properties, long range with small RF power, make it naturally attractive for satellite communications but also draw new challenges compared with terrestrial systems where this technology is already deployed. Indeed, the main advantage of UNB signals, their small bandwidth, makes them more sensitive to frequency drifts that are particularly present in the case of LEO satellite systems. It also implies the use of a random access method in which the carrier frequency is a parameter unknown by the receiver. In this paper, we propose a general semianalytical model to evaluate the performance of a terrestrial or satellite system using UNB technology, taking into account the multiuser interference and the frequency drift. This model is then used to assess the performance (packet loss ratio and throughput) on the return link medium access control (MAC) of a representative LEO satellite system. With our model, we analyze the effect of frequency drift on the system performance. This paper also proposes to investigate more deeply the multiuser interference modeling in order to estimate accurately the performances of a UNB system in terms of bit error rate (BER). We propose a semianalytical approach to study the interference in presence of arbitrary power imbalance that includes the effect of frequency offset and frequency drift and applicable for any linear modulation and any pulse‐shaping filter. The expression of the multiuser interference is established in the general case. We then propose a methodology to compare this exact model to the Gaussian interference approximation (mainly used through the central limit theorem) in order to assess its accuracy.     

Forward‐link analysis of a two‐tier CDMA system with imperfect power control

Power control is an effective technique to reduce cochannel interference and increase capacity for cellular radio systems. The purpose of forward‐link power control in a CDMA system is to reduce the amount of interference in neighbouring cells by reducing the total amount of power transmitted. In an underlaying two‐tier system, microcell's capacity is limited by the forward link due to the interference from macrocell's basestation. Therefore, forward‐link power control is required to enhance system capacity and reduce outage probability. In this paper, we study the effect of imperfect forward‐link power control due to the limitation of power transmitted by basestation. Performance measures including capacity, outage probability and service hole area are analysed. Copyright © 2002 John Wiley & Sons, Ltd.     

Future development promise for plastic‐based solar electricity

Plastic‐based photovoltaic (PV) technology, also known as organic photovoltaic (OPV), has the development promise to be one of the third PV generation technologies, practically where sunlight reaches a surface area both indoors and outdoors. This paper presents the economic forecast for solar electricity using OPV technology based on a 1 kWp domestic system. With reference to OPV roll‐to‐roll manufacturing, the paper discusses lifetime, efficiency, and costs factors of this emerging PV technology. Taking an outlook of historic PV technology developments and reflect future anticipated technology developments, the future levelised electricity cost is calculated using system life cycle costing techniques. Grid parity at levelised electricity cost below 25 c/kWh may already be reached within 10 years' time, and the technology would have been widespread, assuming a typical southern Europe average solar irradiance of 1700 kWh/m²/year. The influence of solar irradiance and the way the module performs over long periods of time expecting various degradation levels is studied using sensitivity analysis. Eventually, the financial attractiveness to mature silicon‐based PV technology may decline suddenly as financial support schemes such as the popular Feed‐in‐Tariffs dry out. This would give rise to other promising solutions that have already been proven to be less energy intensive and cheaper to produce but may require a different integration model than present technologies. This paper demonstrates that under no financial support schemes emerging PV technologies such as OPV will manage to attract business and further developments. Copyright © 2015 John Wiley & Sons, Ltd.     

WiSE – a satellite‐based system for remote monitoring

Recent technological advancements in sensors, processors and communications technology make it viable to perform digital acquisition of environmental data from remote locations. Declining costs and miniaturisation of electronics and sensors have enabled design of systems for intelligent remote monitoring. These advances pave the way for new tools to support field work by virtually extending researchers' reach to the field study area from the comfort of their offices. The Wireless Internet Sensing Environment project developed an architecture providing control and retrieval of data from networked sensors and cameras at a remote location using Internet backhaul. Satellite connectivity enabled this equipment to be deployed to remote locations to support an ecological application. This paper describes architecture and innovative design features for this challenging problem space, including motion event detection, power management and a method to upload collected data. © 2016 The Authors. International Journal of Satellite Communications and Networking published by John Wiley & Sons Ltd.     

Low‐Power‐Photon Up‐Conversion in Dual‐Dye‐Loaded Polymer Nanoparticles

Sensitized triplet–triplet annihilation in multicomponent organic systems is already demonstrated to be suitable for obtaining efficient up‐conversion in solution with excitation power densities comparable to solar irradiance, but loses efficiency in the solid state. Here, it is demonstrated that it is possible to reduce this limitation by incorporating a standard bicomponent system in polymer nanoparticles. The confinement of all of the involved photophysical processes in a nanometer‐scale volume makes each nanoparticle a single and isolated high‐efficiency up‐converting unit. As a consequence, these dual‐dye‐loaded nanoparticles can be used to produce drop‐cast films, as well as dopants for polymeric matrices, preserving the performances of the starting moieties in solution.     

几种光传送网技术的比较

随着业务需求特别是宽带业务的增长,人们对高容量系统,特别是光传送网技术进行了大量的研究。目前研究的内容主要涉及到波分复用光网络,光时分复用技术和光码分复用技术。波分复用技术已经在网络中广泛采用,是目前唯一成熟且付诸实用的超大容量光传输系统;光时分复用的研究近几年取得了较大的进展,是未来极具潜力的技术,但远不如波分复用成熟;光码分复用可大大提高光纤的利用率,降低网络成本,简化网络管理,具有较高的网络