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.     

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.     

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.     

Life cycle assessment and cost analysis of very large‐scale PV systems and suitable locations in the world

Although the Sahara region has a high potential for solar power plants, the amount of installed photovoltaic (PV) system remains relatively low. This paper aims to evaluate these potentials of PV system installation in terms of environmental and economic viewpoints with indices of cost, energy, and greenhouse gas (GHG) emission. Two 1‐GW very large‐scale PV systems are simulated at Ouarzazate in Morocco and at Carpentras in France. The evaluation was performed using life cycle assessment. The lowest energy consumption and GHG emission are obtained while assuming cadmium telluride module. The result of our simulation shows that energy payback time is 0.9 years and CO₂ emission rate is 27.4 g‐CO_2‐eq/kWh in the Ouarzazate case. In cost estimation, generation costs are 0.06 USD/kWh in Ouarzazate and 0.09 USD/kWh in Carpentras in the case of 3% interest rate and 0.5 USD/W for multicrystalline silicon PV module price. In addition, by adapting 15% internal rate of return for 20% of budget, the generation costs become 0.09 USD/kWh in Ouarzazate and 0.13 USD/kWh in Carpentras under the same condition. Furthermore, the selection for suitable locations to install solar power plants in term of GHG emission is identified using geographical information system. Very high‐potential locations (lower than 38 g‐CO_2‐eq/kWh) could be obtained in North Chili, east and west Sahara, and Mexico. Copyright © 2015 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.     

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.     

Progress in markets for grid‐connected PV systems in the built environment

In the last decade of the 20th century a wide variety of promotion strategies increased the market penetration of small grid‐connected PV systems world‐wide. The objective of this paper is to assess the impact of these promotion strategies on the market for and on the economic performance of small grid‐connected PV systems. The most important conclusions of this analysis are: Pure cost‐effectiveness is not crucial for private customers. Affordability is rather what counts. Non‐monetary issues play an important role for a substantial increase in market deployment. Comprehensive accompanied information and education activities are also important along with financial incentives. There are still considerable barriers in the market: on the one hand transparent and competitive markets exist in only a few countries; on the other hand non‐monetary transaction costs still represent a major barrier. Progress with respect to cost reduction has been achieved, but mainly for non‐module components. Copyright © 2004 John Wiley & Sons, Ltd.     

About the origin of low wafer performance and crystal defect generation on seed‐cast growth of industrial mono‐like silicon ingots

The era of the seed‐cast grown monocrystalline‐based silicon ingots is coming. Mono‐like, pseudomono or quasimono wafers are product labels that can be nowadays found in the market, as a critical innovation for the photovoltaic industry. They integrate some of the most favorable features of the conventional silicon substrates for solar cells, so far, such as the high solar cell efficiency offered by the monocrystalline Czochralski‐Si (Cz‐Si) wafers and the lower cost, high productivity and full square‐shape that characterize the well‐known multicrystalline casting growth method. Nevertheless, this innovative crystal growth approach still faces a number of mass scale problems that need to be resolved, in order to gain a deep, 100% reliable and worldwide market: (i) extended defects formation during the growth process; (ii) optimization of the seed recycling; and (iii) parts of the ingots giving low solar cells performance, which directly affect the production costs and yield of this approach. Therefore, this paper presents a series of casting crystal growth experiments and characterization studies from ingots, wafers and cells manufactured in an industrial approach, showing the main sources of crystal defect formation, impurity enrichment and potential consequences at solar cell level. The previously mentioned technological drawbacks are directly addressed, proposing industrial actions to pave the way of this new wafer technology to high efficiency solar cells. Copyright © 2012 John Wiley & Sons, Ltd.     

Annual degradation rates of recent crystalline silicon photovoltaic modules

Long‐term reliability and durability of recently installed photovoltaic (PV) systems are currently unclear because they have so far only been operated for short periods. Here, we investigated the quality of six types of recent crystalline silicon PV modules to study the viability of PV systems as dispersed power generation systems under operating conditions connected to an electric power grid. Three indicators were used to estimate the annual degradation rates of the various crystalline silicon PV modules: energy yield, performance ratio, and indoor power. Module performance was assessed both with indoor and outdoor measurements using electric measurements taken over a 3‐year period. The trends in the results of the three indicators were almost consistent with each other. Although the performance of the newly installed PV modules decreased by over 2% owing to initial light‐induced degradation immediately after installation, little to no degradation was observed in all the PV modules composed of p‐type solar cells over a 3‐year operation period. However, the PV modules composed of n‐type solar cells clearly displayed performance degradation originating from the reduction of open‐circuit voltage or potential‐induced degradation. The results indicate that a more continuous and detailed outdoor actual investigation is important to study the quality of new, high‐efficiency solar cells, such as heterojunction, interdigitated back contact solar cells, and passivated emitter rear cells, which are set to dominate the PV markets in the future. © 2017 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.     

Crystalline silicon solar module technology: Towards the 1 € per watt‐peak goal

Crystalline silicon solar module manufacturing cost is analysed, from feedstock to final product, regarding the equipment, labour, materials, yield losses and fixed cost contributions. Data provided by European industrial partners are used to describe a reference technology and to obtain its cost breakdown. The analysis of the main cost drivers allows to define new generation technologies suitable to reduce module cost towards the short‐term goal of 1 € per watt‐peak. This goal roughly corresponds with the cost level needed to enable ‘grid parity’: the situation solar electricity becomes competitive with retail electricity. The new technologies are described and their costs are analysed. Cost reductions due to scale effects in production are also assessed for next generation manufacturing plants with capacities in the range of several hundreds of megawatts to one gigawatt of module power per year, which are to come in the near future. The combined effects of technology development and economies of scale bring the direct manufacturing costs of wafer‐based crystalline silicon solar modules down into the range of 0·9–1·3 € per watt‐peak, according to current insights and information (the range results from differences between technologies as well as from uncertainties per technology). Copyright © 2008 John Wiley & Sons, Ltd.     

Thin Al2O3 passivated boron emitter of n‐type bifacial c‐Si solar cells with industrial process

We have presented thin Al₂O₃ (~4 nm) with SiN_x:H capped (~75 nm) films to effectively passivate the boron‐doped p⁺ emitter surfaces of the n‐type bifacial c‐Si solar cells with BBr₃ diffusion emitter and phosphorus ion‐implanted back surface field. The thin Al₂O₃ capped with SiN_x:H structure not only possesses the excellent field effect and chemical passivation, but also establishes a simple cell structure fully compatible with the existing production lines and processes for the low‐cost n‐type bifacial c‐Si solar cell industrialization. We have successfully achieved the large area (238.95 cm²) high efficiency of 20.89% (front) and 18.45% (rear) n‐type bifacial c‐Si solar cells by optimizing the peak sintering temperature and fine finger double printing technology. We have further shown that the conversion efficiency of the n‐type bifacial c‐Si solar cells can be improved to be over 21.3% by taking a reasonable high emitter sheet resistance. Copyright © 2017 John Wiley & Sons, Ltd.     

Techno‐economic analysis of three different substrate removal and reuse strategies for III‐V solar cells

The high cost of wafers suitable for epitaxial deposition of III‐V solar cells has been a primary barrier to widespread use of these cells in low‐concentration and one‐sun terrestrial solar applications. A possible solution is to reuse the substrate many times, thus spreading its cost across many cells. We performed a bottom‐up techno‐economic analysis of three different strategies for substrate reuse in high‐volume manufacturing: epitaxial lift‐off, spalling, and the use of a porous germanium release layer. The analysis shows that the potential cost reduction resulting from substrate reuse is limited in all three strategies––not by the number of reuse cycles achievable, but by the costs that are incurred in each cycle to prepare the substrate for another epitaxial deposition. The dominant substrate‐preparation cost component is different for each of the three strategies, and the cost‐ranking of these strategies is subject to change if future developments substantially reduce the cost of epitaxial deposition. Copyright © 2016 John Wiley & Sons, Ltd.     

Experience with solar home systems in developing countries: a review

Solar energy is widely perceived as a promising technology for electricity generation in remote locations in developing countries. It is estimated that 1.3 million solar home systems had been installed by early 2000. An estimated one‐third of installed systems were backed by foreign donor support in government programmes and two‐thirds supplied by commercial dealers. The estimated growth in the deployment of solar lanterns is less than for SHS. One out of every 100 households that gain access to electricity in developing countries uses solar power. In spite of these successes, doubts have arisen about the effectiveness and suitability of small PV systems for rural development. Many organisational, financial and technical problems appear to present difficulties. A literature survey has been conducted to make an inventory of experience with solar PV applications for households in developing countries. The main finding is that an adequate service infrastructure is required to make projects viable. Household choice in system sizes is often too restricted in donor‐funded projects. Smaller systems sold for cash can be a good alternative to credit systems by offering to increased affordability. Gaps in existing knowledge have been identified, which could be overcome by field monitoring programmes. Copyright © 2001 John Wiley & Sons, Ltd.     

Photovoltaic Cells and Modules towards Terawatt Era

Progresses in photovoltaic technologies over the past years are evident from the lower costs, the rising efficiency, to the great improvements in system reliability and yield. Cumulative installed power yearly growths were on an average more than 40% in the period from 2007 to 2016 and in 2016, the global cumulative photovoltaic power installed has reached 320 GWp. The level 0.5 TWp could be reached before 2020. The production processes in the solar industry still have great potential for optimization both wafer based and thin film technologies. Trends following from the present technology levels are discussed, also taking into account other parts of photovoltaic systems that influence the cost of electrical energy produced. Present developments in the three generations of photovoltaic modules are discussed along with the criteria for the selection of appropriate photovoltaic module manufacturing technologies. The wafer based crystalline silicon (c-silicon) technologies have the role of workhorse of present photovoltaic power generation, representing more than 90% of total module production. Further technology improvements have to be implemented without significantly increasing costs per unit, despite the necessarily more complex manufacturing processes involved. The tandem of c-silicon and thin film cells is very promising. Durability may be a limiting factor of this technology due to the dependence of the produced electricity cost on the module service time.     

Grid‐connected photovoltaic systems: the Brazilian experience and the performance of an installation

Just as in several other countries, the Brazilian experience of installing in place solar photovoltaic technology was first aimed at meeting the needs of rural areas. More recently, the effects of the international trend towards grid‐connected photovoltaic systems are beginning to be felt in Brazil. In less than five years, the first four grid‐connected photovoltaic systems have been installed, and other projects are in progress. This work presents the overall characteristics of the first four systems and the technical performance achieved by one of them, with an annual production in the range of 1500 kW h/kW_p. Copyright © 2001 John Wiley & Sons, Ltd.     

Distributed power generation versus grid extension: an assessment of solar photovoltaics for rural electrification in Northern Ghana

The competitiveness of distributed solar photovoltaic (PV) power generation for rural electrification in northern Ghana is assessed and compared with the conventional option of extending the national grid and increasing the capacity for centralised power generation. A model is constructed to calculate the life‐cycle cost (LCC) of the two options and to test the sensitivity of different parameters. All calculations are based on information from the GEF/UNDP pilot region in the East Mamprusi District. In addition to the economic aspect, issues of quality and environmental effects are discussed. The LCC of distributed PV is lower than that of a grid extension for an electricity demand corresponding to solar home systems of 140 W_p or smaller. Thus, distributed PV is cost competitive for purposes of lighting, entertainment, information and basic public facilities, such as schools and hospitals. The LCC for the option of grid extension with central power generation is dominated by the cost of low‐voltage micro‐grids within the communities. Important factors are the density of households and the penetration (fraction of households electrified), as they affect the line length per connected household. The relatively low cost of regional medium‐voltage grids makes the geographical location of each community less important than expected. Battery replacement every fifth year makes up the major part of the LCC of solar home systems and is also responsible for the large energy input in the production of the systems. This could limit both future cost reductions of distributed PV and its potential to mitigate greenhouse gas emissions. Copyright © 2002 John Wiley & Sons, Ltd.     

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.     

The present status and future direction of technology development for photovoltaic power generation in Japan

In 2004 NEDO established the PV Roadmap Toward 2030 PV2030 as a long‐term strategy for PV R&D. In this Roadmap, PV is expected by 2030 to supply approximately 50% of residential electricity consumption (cumulative installed capacity in the range of 100 GW). In terms of economic efficiency, electricity costs are targeted to equal commercial use, approximately 14 Yen/kW h, by 2020 and industrial use, approximately 7 Yen/kW h, by 2030. For future PV systems, it is essential to improve the stand‐alone capabilities of PV system with electricity storage and to develop community‐based PV systems using multi‐function inverters. Advanced technological innovations beyond the existing levels are also essential. Therefore, NEDO is undertaking 2‐year projects for preliminary research to make clear the next R&D of solar cells and PV system technology. Copyright © 2005 John Wiley & Sons, Ltd.     

Life cycle assessment of crystalline photovoltaics in the Swiss ecoinvent database

This paper describes the life cycle assessment (LCA) for photovoltaic (PV) power plants in the new ecoinvent database. Twelve different, grid‐connected photovoltaic systems were studied for the situation in Switzerland in the year 2000. They are manufactured as panels or laminates, from monocrystalline or polycrystalline silicon, installed on facades, slanted or flat roofs, and have 3 kW_p capacity. The process data include quartz reduction, silicon purification, wafer, panel and laminate production, mounting structure, 30 years operation and dismantling. In contrast to existing LCA studies, country‐specific electricity mixes have been considered in the life cycle inventory (LCI) in order to reflect the present market situation. The new approach for the allocation procedure in the inventory of silicon purification, as a critical issue of former studies, is discussed in detail. The LCI for photovoltaic electricity shows that each production stage is important for certain elementary flows. A life cycle impact assessment (LCIA) shows that there are important environmental impacts not directly related to the energy use (e.g., process emissions of NO_x from wafer etching). The assumption for the used supply energy mixes is important for the overall LCIA results of different production stages. The presented life cycle inventories for photovoltaic power plants are representative for newly constructed plants and for the average photovoltaic mix in Switzerland in the year 2000. A scenario for a future technology (until 2010) helps to assess the relative influence of technology improvements for some processes. The very detailed ecoinvent database forms a good basis for similar studies in other European countries or for other types of solar cells. Copyright © 2005 John Wiley & Sons, Ltd.     

Theory and experiments on the back side reflectance of silicon wafer solar cells

New passivation layers for the back side of silicon solar cells have to show high performance in terms of electrical passivation as well as high internal reflectivity. This optical performance is often shown as values for the back side reflectance R_b which describes the rear internal reflection. In this paper, we investigate in detail the meaning of this single‐value parameter, its correct determination and the use in one‐dimensional simulations with PC1D. The free‐carrier‐absorption (FCA) as non‐carrier‐generating absorption channel is analyzed for solar cells with varying thickness. We apply the optical analysis to samples with different thickness, silicon oxide layer thickness, rear side topography as well as passivation layers (SiO₂, SiN_x, SiC and stack systems). Additionally, the optical influence of the laser‐fired contacts (LFC) process is experimentally investigated. Finally, we show that with correct parameters, the one‐dimensional simulation of very thin silicon solar cells can successfully be performed. Copyright © 2007 John Wiley & Sons, Ltd.