Photovoltaic power plant experience at Arizona Public Service: a 5‐year assessment

Arizona Public Service (APS) currently has over 4·9 MW_dc of grid‐connected photovoltaic systems that have been installed in its service territory over the past five years. Most of this installed PV capacity is in support of the Arizona Corporation Commission Environmental Portfolio Standard goal that encourages APS to generate 1·1% of its energy generation through renewable resources by 2007, with 60% of that amount from solar. During this time, much has been learned regarding performance, cost, maintenance, installation and design. This paper presents an assessment of these topics and a perspective associated with this PV experience. Published in 2005 by John Wiley & Sons, Ltd.     

Solar based large scale power plants: what is the best option?

There are very few published data comparing performance and cost of thermal and photovoltaic (PV) based solar power generations. With recent intense technology and business developments there is a need to establish a comparison between these two solar energy options. We have developed a simple model to compare electricity cost using these two options without any additional fuel source of hybridization. Capital along with operation and maintenance (O&M) costs and other parameters from existing large scale solar farms are used to reflect actual project costs. To compete with traditional sources of power generation, solar technologies need to provide dispatchable electric power to respond to demand during peak hours. Different solutions for energy storage are available. In spite of their high capital cost, adding energy storage is considered a better long term solution than hybrid solar systems for large scale power plants. For this reason, a comparison between the two solar options is also provided that include energy storage. Although electricity storage is more expensive than thermal storage, PV power remains a competitive option. Expenses related to O&M in solar thermal plant are about ten times higher than PV, an important factor resulting in higher energy cost. Based on data from proven commercial technologies, this study showed that PV holds a slight advantage even when energy storage is included. Copyright © 2010 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.     

Five years of operating experience at a large,utility‐scale photovoltaic generating plant

Tucson Electric Power Company (TEP), headquartered in Tucson, AZ, currently has nearly 5·0 MWdc of utility‐scale grid‐connected photovoltaic (PV) systems installed in its service territory. These systems have been installed through a multiyear, pay‐as‐you‐go development of renewable energy, with kWhac energy production as a key program measurement. This PV capacity includes a total of 26 crystalline silicon collector systems, each rated at 135 kWdc for a total of 3·51 MWdc, that have been installed at the Springerville, AZ generating plant by TEP making this one of the largest PV plants in the world. This facility started operations in 2001 and recently passed the 5‐year milestone of continuous operations. These systems were installed in a standardized, cookie‐cutter approach whereby each uses the same array field design, mounting hardware, electrical interconnection, and inverter unit. This approach has allowed TEP to achieve a total installed system cost of $5·40/Wdc and a TEP‐calculated levelized energy cost of $0·062/kWhac for PV electrical generation. This paper presents an assessment of operating experience including performance, costs, maintenance, and plant operation over this 5‐year period making this one of the most detailed and complete databases of utility‐scale PV systems available to the US DOE Program. Published in 2007 by John Wiley & Sons, Ltd.     

Dynamic operation and maintenance systems for switching networks

Some important concepts and techniques related to dynamic operation and maintenance (O&M) systems for switching networks are demonstrated. Five types of node that comprise the dynamic network O&M system being developed by the authors are discussed. They are local exchanges, a centralized operation system, a database system, a diagnostics expert system, and maintenance workstations. The nodes are implemented on an efficient distributed system and use a standardized interface. This O&M system, which is geared toward improved maintenance, focuses on the switching network as a whole, rather than on individual exchanges. In the case of alarms and fault messages, O&M takes corrective action automatically     

Is $50/MWh solar for real? Falling project prices and rising capacity factors drive utility‐scale PV toward economic competitiveness

Recently announced low‐priced power purchase agreements (PPAs) for US utility‐scale photovoltaic (PV) projects suggest $50/MWh solar might be viable under certain conditions. To explore this possibility, this paper draws on an increasing wealth of empirical data to analyze trends in three of the most important PPA price drivers: upfront installed project prices, operations, and maintenance (O&M) costs, and capacity factors. Average installed prices among a sample of utility‐scale PV projects declined by more than one third (from $5.8/W_AC to $3.7/W_AC) from the 2007–2009 period through 2013, even as costlier systems with crystalline‐silicon modules, sun tracking, and higher inverter loading ratios (ILRs) have constituted an increasing proportion of total utility‐scale PV capacity (all values shown here are in 2013 dollars). Actual and projected O&M costs from a very small sample of projects appear to range from $20–$40/kW_AC‐year. The average net capacity factor is 30% for projects installed in 2012, up from 24% for projects installed in 2010, owing to better solar resources, higher ILRs, and greater use of tracking among the more recent projects. Based on these trends, a pro‐forma financial model suggests that $50/MWh utility‐scale PV is achievable using a combination of aggressive‐but‐achievable technical and financial input parameters (including receipt of the 30% federal investment tax credit). Although the US utility‐scale PV market is still young, the rapid progress in the key metrics documented in this paper has made PV a viable competitor against other utility‐scale renewable generators, and even conventional peaking generators, in certain regions of the country. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.     

Relative performance of tracking versus fixed tilt photovoltaic systems in the USA

Tracking systems can increase the amount of electricity generated by photovoltaic (PV) modules, by actively orienting each module to intercept more solar energy. We find that horizontal one‐axis tracking systems can increase PV generation by 12–25% relative to south‐facing fixed mount PV systems with 25° tilts in the contiguous USA, and two‐axis tracking systems can increase PV generation by 30–45% relative to fixed mount systems. Tracking systems increase PV generation more significantly in arid regions such as the southwest USA than in humid regions with persistent cloud cover such as the Pacific Northwest and coastal Atlantic states. We find that fixed and tracking PV systems have similar interannual variability in their generation profiles, and this variability is primarily driven by project location. Tracking PV projects cost more than fixed tilt systems, per unit capacity, and we explore how much more tracking projects could cost while generating similar levelized costs of energy as fixed tilt systems. We define this as the breakeven additional cost of tracking and find that it is primarily driven by three factors: (i) regional tracking performance, (ii) fixed tilt system costs that tracking projects compete against, and (iii) additional tracking operation and maintenance costs. Using this framework, we explore the relative competitiveness of tracking systems for a range of fixed and tracking PV prices and evaluate how tracking competitiveness varies by region. Copyright © 2013 John Wiley & Sons, Ltd.     

Analyzing historical cost trends in California's market for customer‐sited photovoltaics

This paper reports highlights from a detailed statistical analysis of the cost of customer‐sited, grid‐connected photovoltaic installations in the largest solar market in the United States: California. It is based on an analysis of 18 942 PV systems, totaling 254 MW_AC, either funded or approved for funding under two separate rebate programs overseen by the California Energy Commission and the California Public Utilities Commission. We find that: (1) solar costs have declined substantially over time; (2) policy incentives have impacted pre‐rebate installed costs, and some cost inflation is apparent; (3) economies of scale have driven down costs for larger systems; (4) systems installed in new home developments and in affordable housing projects have experienced much lower costs than the general retrofit market; and (5) installer experience and type have affected costs, but the effects differ by program. Results hold important implications for solar suppliers and customers, and for policymakers designing incentive programs. Copyright © 2006 John Wiley & Sons, Ltd.     

现代电信网运行维护的技术支持系统

在电信网达到一定规模，网路建设速度放慢之时，在设备 应商的名费技术支持到期后，数千万端口多种型号的交换设备和大量传输设备的技术支持由谁来承担？中国电信将采用什么策略 技术手段来保障维护部门能及时得到优质高效的技术支持？本文作者长期从事本地网网管和集中监控系统的开发和工程实施，深深感到与网管配套的运行维护技术支持系统在电信支撑网的建设中的重要性。     

Photovoltaic systems: an end‐of‐millennium review

The production of electricity from photovoltaics continues to attract worldwide interest, most recently as a power source for distributed energy generation. Today's photovoltaic systems are already being used effectively for smaller power needs in remote applications. For both of these applications, the issues of reliability, efficiency, safety, and low cost are the principal drivers of system technology. This review uses these design issues to provide a system perspective on the current status of the technology, the changes it has already experienced and the necessity for improvements, especially in tomorrow's systems. The discussion of remaining issues focuses on the reduction of area‐related and collector costs, the accurate prediction of performance and lifetime, and the need for developing much better information on recurring costs for maintenance and component replacement. Copyright © 1999 John Wiley & Sons, Ltd. This paper was produced under the auspices of the US Government and it is therefore not subject to copyright in the US.     

Direction for element managers and network managers

In the past, each new network element of a wireless network had a corresponding management system to provide management capabilities. Each of these management systems had a different user interface, employed a different computing platform, and typically managed one type of network element. The total O&M system was the sum of these independent resources, consuming partial solutions that made network management tasks inefficient, complex, time consuming, and expensive to administer. Large operations costs borne from these inefficiencies were once buffered by large cellular operator profits. With the introduction of PCS, operators became extremely cost conscious and sought to eradicate these large costs. Additionally, wireless service providers moved into a mixed vendor environment, where network elements manufactured by several vendors are used, so they could no longer afford different management systems for each network element. In today's environment, a wireless service provider who can provide better service quality at the lowest price will be the ultimate winner. The key to providing better service quality at the lowest price is to have efficient network management. As the wireless industry strives to push wireless prices on a par with wireline, the necessity for reduced network operation and management costs takes on increasing importance     

Solar photovoltaics in Sri Lanka: A short history

With a significant unelectrified rural population, Sri Lanka has followed the evolution of solar photovoltaic (PV) technology in the West very closely since the 1970s as terrestrial applications for photovoltaics were developed. It was not until 1980 that the Sri Lankan government embarked on the promotion of solar photovoltaics for rural domestic use when the Ceylon Electricity Board formed the Energy Unit. Since then, solar photovoltaics has attracted the private sector, where several companies have been operating at different levels with varying degrees of success-Vidya Silpa, agents for Arco and now Showa, selling solar photovoltaic systems on a small scale; Power & Sun (now S.P.&L. Co. Ltd) with its solar photovoltaic module assembling facility and a marketing operation; Sunpower Systems, agents for BP Solar Australia, focusing on institutional systems; and BP Solar Australia working on government-funded projects-so that private solar photovoltaic promoters have now gained valuable experience in a variety of dissemination methodologies. In addition, Australian and Sri Lankan government-funded pilot projects such as the Pansiyagama 1000 home programme and the Uva Infrastructure Project with 74 large-scale solar photovoltaic systems for rural hospitals and water pumping schemes- both administered by the National Housing Development Authority (NHDA) -have given all the local promoters further valuable insight into how and how not to promote solar photovoltaics. The establishment of community-based solar photovoltaic programmes by non-governmental organizations, such as the Sarvodaya Shramadana Society and the newly formed Solanka Associates, has developed a novel approach to bridge the gap between this state-of-the-art technology and the remotely located end-users. The developments in the Sri Lankan solar photovoltaic scene have attracted the attention of the World Bank. to quote from a paper presented by Loretta Schaeffer, Program Manager of the Bank's Asia Alternative Energy Unit in Washington at the Solar Energy Forum-SOLTECH'93-held on 28th April 1993 in Washington, DC: ‘The Bank may get involved in providing PV-powered household systems throughout the country as there is a strong private sector involvement and use of proven local experience in systems design, development, installation, operation and maintenance’. Even though 70% of the 3.3 million homes are unelectrified, acceptance of solar photovoltaics as a viable alternative by policy makers is yet to be fully realized in Sri Lanka. the main obstacle has been the relatively high cost of photovoltaics. In spite of this, the private sector companies, certain government agencies (such as the NHDA) and the non-government organizations view photovoltaics as a technology that could meet the basic needs for electricity of the rural people who, otherwise, would be left in the dark.     

Energy,cost and LCA results of PV and hybrid PV/T solar systems

Hybrid photovoltaic/thermal (PV/T) solar systems provide a simultaneous conversion of solar radiation into electricity and heat. In these devices, the PV modules are mounted together with heat recovery units, by which a circulating fluid allows one to cool them down during their operation. An extensive study on water‐cooled PV/T solar systems has been conducted at the University of Patras, where hybrid prototypes have been experimentally studied. In this paper the electrical and thermal efficiencies are given and the annual energy output under the weather conditions of Patras is calculated for horizontal and tilted building roof installation. In addition, the costs of all system parts are included and the cost payback time is estimated. Finally, the methodology of life cycle assessment (LCA) has been applied to perform an energy and environmental assessment of the analysed system. The goal of this study, carried out at the University of Rome ‘La Sapienza’ by means of SimaPro 5·1 software, was to verify the benefits of heat recovery. The concepts and results of this work on energy performance, economic aspects and LCA results of modified PV and water‐cooled PV/T solar systems, give a clear idea of their application advantages. From the results, the most important conclusion is that PV/T systems are cost effective and of better environmental impact compared with standard PV modules. Copyright © 2005 John Wiley & Sons, Ltd.     

Solar home system electrification in dispersed rural areas: a 10‐year experience in Jujuy,Argentina

This paper presents a technical approach to the electrification of dispersed rural areas with the so‐called Solar Home Systems. Lessons learned from the past show not only problems and mistakes but also interesting positive points. The electrification of remote areas, with low‐density population and low energy consumption is still a problem to solve. Sustainability is a main issue addressed in all rural electrification assessment actions, together with financing of programs and systems. This work tries to advance in the knowledge on reliability and maintenance, planning and execution, in a dispersed rural electrification market. It is based on the 10‐year field experience in the province of Jujuy, Argentina. In the most dispersed areas of the province, there are about 3000 households plus a minor number of schools, churches, health posts, and community premises electrified with small individual photovoltaic systems from a decade ago. Most remarkable outcomes from a long‐term operation and monitoring action are summarized and analyzed in the following pages. Copyright © 2011 John Wiley & Sons, Ltd.     

40% efficient sunlight to electricity conversion

Increasing sunlight conversion efficiency is a key driver for on‐going solar electricity cost reduction. For photovoltaic conversion, the approach most successful in increasing conversion efficiency is to split sunlight into spectral bands and direct each band to a dedicated solar cell of an appropriate energy bandgap to convert this band efficiently. In this work, we demonstrate conversion of sunlight to electricity in a solar collector with an efficiency value above 40% for the first time, using a small 287‐cm² aperture area test stand, notably equipped with commercial concentrator solar cells. We use optical band‐pass filtering to capture energy that is normally wasted by commercial GaInP/GaInAs/Ge triple junction cells and convert this normally wasted energy using a separate Si cell with higher efficiency than physically possible in the original device. The 287‐cm² aperture area sunlight‐concentrating converter demonstrating this independently confirmed efficiency is a prototype for a large photovoltaic power tower system, where sunlight is reflected from a field of sun‐tracking heliostats to a dense photovoltaic array mounted on a central tower. In such systems, improved efficiency not only reduces costs by increasing energy output for a given investment in heliostats and towers but also reduces unwanted heat generation at the central tower. Copyright © 2015 John Wiley & Sons, Ltd.     

III‐V concentrator solar cell reliability prediction based on quantitative LED reliability data

III‐V Multi Junction (MJ) solar cells based on Light Emitting Diode (LED) technology have been proposed and developed in recent years as a way of producing cost‐competitive photovoltaic electricity. As LEDs are similar to solar cells in terms of material, size and power, it is possible to take advantage of the huge technological experience accumulated in the former and apply it to the latter. This paper analyses the most important parameters that affect the operational lifetime of the device (crystalline quality, temperature, current density, humidity and photodegradation), taking into account experience on the reliability of LEDs. Most of these parameters are less stressed for a III‐V MJ solar cell working at 1000 suns than for a high‐power LED. From this analysis, some recommendations are extracted for improving the long‐term reliability of the solar cells. Compared to high‐power LEDs based on compound semiconductors, it is possible to achieve operational lifetimes higher than 10⁵ hours (34 years of real‐time operation) for III‐V high‐concentration solar cells. Copyright © 2007 John Wiley & Sons, Ltd.     

An efficient location cache scheme for three‐level database architecture in PCS networks

Recently, hierarchical architecture for location databases has been proposed in order to accommodate the growing number of personal communication systems users. With the three‐level hierarchical database architecture, which is compatible with the current cellular mobile systems, newly developed additional databases, including the regional location database (RLR), are positioned between the HLR and the VLRs. We propose an efficient cache scheme, the double T‐thresholds location cache scheme, which could reduce the network and database costs to lookup a portable using the three‐level architecture. This scheme extends the existing T‐threshold location cache scheme, which is effective only under the two‐level architecture of location databases currently adopted by IS‐41 and GSM. The idea behind our proposed scheme is to use two pieces of cache information, VLR and RLR, which serve the called portables. These two pieces are required in order to exploit not only the locality of a registration area (RA), but also the locality of a regional registration area (RRA), a wide area covered by the RLR. We also use two threshold values in order to determine whether the two pieces are obsolete. In order to model the RRA residence time, the branching Erlang‐∞ distribution is introduced. The cost analysis presented in this paper shows that the double T‐thresholds location cache scheme significantly reduces the network and database costs for most patterns of portables. Copyright © 2001 John Wiley & Sons, Ltd.     

NixSy Nanowalls/Nitrogen‐Doped Graphene Foam Is an Efficient Trifunctional Catalyst for Unassisted Artificial Photosynthesis

Solar‐to‐hydrogen (STH) conversion through unassisted artificial photosynthesis (APS) devices is one of the promising and environmentally friendly strategies for sustainable development. However, the practical large‐scale application of the unassisted APS devices is impeded by the need for expensive noble metal‐based catalysts in photovoltaics and/or electrolyzers. Herein, well‐aligned 2D Ni_xS_y nanowalls (2D Ni_xS_y NWs) on a 3D nitrogen‐doped graphene foam (3D NGF) are synthesized and further employed it in unassisted APS. Due to the positive synergistic effect between the highly electrocatalytic activity of Ni_xS_y NW and excellent conductivity of NGF, this low cost material of (2D/3D) Ni_xS_y NW/NGF is highly efficient as a multifunctional catalyst in various applications: a counterelectrode for dye‐sensitized solar cell (DSSC) and a “bifunctional” electrocatalyst for oxygen and hydrogen evolution for electrocatalytic overall water splitting. Furthermore, three Ni_xS_y NW/NGF‐based DSSCs as a tandem cell for unassisted solar‐driven overall water splitting is connected, using Ni_xS_y NW/NGF itself on nickel foams as the anode and cathode. Impressively, such integrated photovoltaic‐electrolyzer APS device can achieve an STH efficiency of 3.2% with an excellent stability and low cost. This work opens an avenue to advanced multifunctional materials for the low‐cost and unassisted solar‐driven overall water splitting.     

Role of radiation-hard solar cells in minimizing the costs of global satellite communication systems

An analysis embodied in a personal computer program is presented, which quantitatively demonstrates how the availability of radiation hard-solar cells can help to minimize the cost of a global satellite communication system. An important distinction between the currently proposed systems, such as Iridium, Odyssey and Ellipsat, is the number of satellites employed and their operating altitudes. Analysis of the major costs associated with implementing these systems shows that operation at orbital altitudes within the Earth's radiation belts (10³–10⁴ km) can reduce the total cost of a system by several hundred per cent,^1,2 so long as radiation-hard components, including solar cells, can be used. A detailed evaluation of the predicted performance of photovoltaic arrays using several different planar solar cell technologies is given, including commercially available Si and GaAs/Ge, and InP/Si which is currently under development. Several examples of applying the program are given, which show that the end-of-life (EOL) power density of different technologies can vary by a factor of ten for certain missions. Therefore, although a relatively radiation-soft technology can usually provide the required EOL power by simply increasing the size of the array, the impact upon the total system budget could be unacceptable, due to increased launch and hardware costs. In aggregate, these factors can account for more than a 10% increase in the total system cost. Because the estimated total costs of proposed global-coverage systems range from $1 billion to $9 billion, the availability of radiaton-hard solar cells could make a decisive difference in the selection of a particular constellation architecture.     

Performance stability of photovoltaic modules in different climates

The current–voltage ( I‐V) characteristics of 15 different photovoltaic modules are monitored during more than 2 years of operation at four locations (Germany, Italy, India and Arizona) corresponding to four different climate zones. The electrical stability of the photovoltaic modules during the time of outdoor exposure is investigated in terms of measured I‐V curve translated to standard test conditions. This translation compensates the influence of module temperature, irradiance, spectral effects and soiling on the I‐V curves. The changes of output power after these corrections are attributed to initial consolidation phases, to long‐term degradation of the electrical properties and to seasonal cycles associated with metastabilities. Modules made from crystalline Si turn out to show no or only minor effects. Thin‐Film modules (CdTe, Cu(In,Ga)Se₂ and thin‐film Si) exhibit a wide spread of metastable behaviour with consistent patterns for identical modules in different climates but with significant differences amongst different manufacturers of the same thin‐film technology. We show further that this metastable behaviour influences the energy yield of the modules. Copyright © 2017 John Wiley & Sons, Ltd.     

Tracking US photovoltaic system prices 1998–2012: a rapidly changing market

The number of US photovoltaic (PV) systems has grown rapidly in recent years, driven by a wide array of government incentives and other supportive policies aimed, in part, at reducing PV system prices. This article draws from a sample of more than 200,000 US residential, commercial, and utility‐scale PV projects to summarize price trends for PV systems installed from 1998 through 2012. These data show that the average installed price of US residential and commercial PV systems declined 6–7% annually during 1998–2012, although the pace and source of price reductions varied. In 2012, the median reported installed price of residential and commercial PV systems was $5.3/W for systems of 10 kW or smaller, $4.9/W for systems of 10–100 kW, and $4.6/W for systems larger than 100 kW. The capacity‐weighted average installed price of crystalline, fixed‐tilt, utility‐scale PV systems (ground‐mounted systems at least 2 MW in size) declined from $6.2/W during 2007–2009 to $3.3/W in 2012. Recent price reductions are associated primarily with a precipitous drop in PV module prices, while non‐module costs have remained relatively stagnant since 2005. Further system price reductions will be needed to expand US PV deployment as incentive programs reduce their financial support. Because further module price reductions are limited, additional deep reductions in installed prices will require significant reductions in non‐module costs, particularly non‐hardware (“soft”) costs. Lower installed prices in international markets suggest that deep near‐term soft cost reductions in the USA are possible with the help of targeted policies. Copyright © 2014 John Wiley & Sons, Ltd.