PVI Issue

Photovoltaics International Volume 6

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The sixth edition of Photovoltaics International was published in November 2009 and includes a special BIPV focus. In addition, the Thin Film section offers a comparison of different ceramic Al-doped ZnO target materials by Fraunhofer IST, and Q-Cells unveils its production technology roadmap for boosting cell efficiences in Cell Processing.

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In this issue...

PVI Paper
Photovoltaics International Papers
After staying relatively quiet for much of the past year, thin-film PV manufacturer Nanosolar came out with a full docket of announcements on 9/9/09: the completion of its major panel-assembly factory near Berlin; the start of serial rollto-roll production of its flexible copperindium-gallium-(di)selenide cells in the company’s San Jose facility; $4.1 billion in panel purchases from customers – including some of the world’s largest utility companies; NREL-verified cell efficiencies up to 16.4%; and new technical details of both its printed CIGS cell technology and utility-scale panels.
PVI Paper
Cell Processing, Photovoltaics International Papers
One-step screen-printing processes are still the most widely-used technique for the front-side metallization of crystalline silicon solar cells in the PV industry. This is because of the knowledge, stability and speed of the process, and despite some big disadvantages exhibited by the resulting contacts. Therefore, the metal contacts of high-efficiency laboratory cells are usually produced via advanced two-step metallization processes, which allow the application of optimized contact structures. In a first step, a narrow metal layer is applied to form the contact to the silicon wafer. Several different techniques have been developed for this first stage. In the second step, the seed layer is reinforced electrochemically with a dense layer of a metal of high conductivity, usually by light-induced plating. The transfer of such techniques into industrial scale has been pursued intensively, and may enter solar cell production lines in the near future. However, the process can still be improved based on a better process understanding, in order to benefit from the full potential of the technology.
PVI Paper
Photovoltaics International Papers, Thin Film
This paper, the third in a series covering cost of ownership (COO) studies for photovoltaics [1], examines the need for metallization of silicon-based solar cells and how it has evolved over the past few years. The technologies and techniques that are being developed for this part of cell manufacturing in the foreseeable future are also discussed. The paper will conclude with a COO case study using the DEK Solar PV3000 as an example.
PVI Paper
Market Watch, Photovoltaics International Papers
An improved understanding of multicrystalline wafer quality can explain variations in cell performance across multicrystalline silicon blocks. Infrared scanning can detect precipitates in a silicon block, while photoluminescence combined with defect etching can reveal needle-like precipitates along the grain boundaries. Such precipitates typically lead to reduced shunt resistance. Crystallographic defects that lower the current collection and the final cell efficiency can also be identified. Understanding the influence of these defects is important for the development of a crystallization technology that results in a substantially better cell efficiency. The use of the improved material quality in an innovative cell and module technology have led to the world record module efficiency of 17%. This paper will illustrate one example of how an improved understanding of multicrystalline wafer quality can explain the variations in cell performance.
PVI Paper
Fab & Facilities, Photovoltaics International Papers
Interconnection of inverters to the electrical grid is a key issue for the widespread integration of distributed energy resources, especially when the scenario surrounding international standards is so unclear. As a pre-normative research step, a round-robin test of two small-scale photovoltaic inverters was performed by nine DERlab laboratories during 2009. The test activity was focused on the verification of individual test procedures, common interpretation of standards and requirements, and determination of problems related to the equipment and facilities involved in conducting roundrobin.
PVI Paper
Photovoltaics International Papers, PV Modules
Upgraded metallurgical-grade (UMG) silicon is a lower cost and lower quality form of solar-grade silicon that is capable of producing solar cells at over 16% efficiency. This paper presents some of the economic advantages and technical concerns and solutions associated with producing silicon based PV from UMG, as well as preliminary solar cell results using this material. Results are based on a comparison of cells made in a turnkey line (Schmid Group) using alloy blends of 10%, 20%, 30% and 100% UMG, mixed with solar-grade Si before ingot growth. Detailed characterization was carried out on these finished cells according to lifetime, LBIC, diffusion length and luminescence imaging to determine correlations of performance with basic parameters. Requirements for material cost and cell performance necessary for UMG solar cells to be cost competitive are also presented.
PVI Paper
Materials, Photovoltaics International Papers
As polysilicon producers perform expansions and upgrades to increase production and improve operations, plant safety remains critical. Companies should routinely review their safety policies and effectively plan their projects to ensure uninterrupted product supply and create a safe environment for employees and the communities in which they operate. Both the design and the execution of expansion and upgrades to projects are critical as companies strive for minimal down time so that productivity is not affected. Such hazards and scenarios that may hinder and delay start-up, specifically in relation to polysilicon plants, are highlighted in this paper. Furthermore, the paper outlines how best to avoid these situations, offering methods of execution to achieve the three key measures of success: safety, high purity and minimal downtime.
PVI Paper
Photovoltaics International Papers, Power Generation
Thin-film module production has proven itself as a forerunner in the race to drive down costs for photovoltaics. The type of semiconductor material used is the most differentiating factor for thin-film photovoltaics, playing the decisive role for determining which core processes are employed and what type of equipment is used. This explains why discussions related to thin-film costs and technologies usually focus on the semiconductor type. However, the effects of glass production, processing and handling are often underestimated: factors such as scaling, yield, unit cost and total cost of ownership of the equipment are defined by the glass-production side of the industry. This paper discusses the challenges faced in glass washing and handling in thin-film PV production.
PVI Paper
Fab & Facilities, Photovoltaics International Papers
In most complex manufacturing environments, equipment failures dominate. These failures are commonly referred to as ‘fires’ because of the chaos and damage they inflict on factory operations. For example, a key piece of equipment fails, creating a blockage in the production line. One or more personnel are quickly dispatched to fix the problem. The situation is dire, threatening to slow daily product starts and slip output goals. Those working the problem know this failure is of the utmost importance and know if they can just get the machine at an acceptable level, the stress from management will be lifted. Logic leads these personnel to suspect a specific component, which is then replaced. This paper discusses the best method of ensuring that this ‘patching’ of problems does not become part of the regular maintenance routine.
PVI Paper
Photovoltaics International Papers, Power Generation
Building-integrated photovoltaics or BIPV is one form of solar electricity that looks set to dominate the solar market in the coming years. The increase in BIPV installations is already evident in some European countries as governments begin to tweak their policies in order to provide a platform for this technology. The past few months have seen countries such as France and Italy make efforts to up the installation rate of this integrated form of solar, increasing the feed-in tariff (FiT) rate quite substantially for BIPV and lowering it for the more common installations such as roof and ground-mounted systems in order to increase the uptake. This BIPV-dedicated section will focus on the new policies implemented in France and Italy, concentrating on France’s policies as a blueprint for others. It will provide a focus on why governments are so keen to increase incentives in favour of BIPV and what the future implications of this market shift will be.
PVI Paper
Cell Processing, Photovoltaics International Papers
Despite the fall in silicon prices, wafer thickness continues to be reduced. The handling of thin wafers between 120 and 160µm is under research at the Fraunhofer IPA, where gripper-dependent and independent variables were determined as parameters for the handling process. Diverse grippers are tested on an automated test platform. Among these are grippers that are specifically designed for wafer handling, as well as others that are not but are used for wafer manipulation. The test platform includes several different test and handling equipments and utilizes critical parameters that might be required for achieving a high production rate via shortest cycle times to investigate the impact on thin wafers. The first results of the position accuracy measurement in relation to the physical movement parameters and other industrial key figures in ongoing handling research are presented within this paper.
PVI Paper
Photovoltaics International Papers, Thin Film
Highly conductive transparent films are of significant interest in the field of thin-film photovoltaics. ZnO-based films in particular have attracted much interest due to the low cost of materials with good film properties for CIGS and a-Si/µc-Si solar modules. Investigations have been ongoing at Fraunhofer IST into ceramic ZnO:Al2O3 targets from different manufacturers. This paper presents a comparison of target material, sputter characteristics and film properties of ZnO:Al. Sputter characteristics are in this case determined by voltage and current data showing arcing rates at different power loads and process pressures. ZnO:Al films are deposited by DC magnetron sputtering with various deposition parameters (e.g oxygen flow, total pressure, sputtering power and substrate temperature) and investigated with respect to optical and electrical properties. A correlation between film properties, sputter characteristics and target material can therefore be determined. As it appears that arcing has the biggest influence on film properties, the ceramic target material can be optimized for minimal arcing.
PVI Paper
Cell Processing, Photovoltaics International Papers
The key to delivering highly efficient solar cells is to absorb as much light as possible from the solar spectrum and convert it effectively into electrical energy. Anti-reflective coatings have served as agents for reducing reflective losses and improving bulk and surface passivation thus enhancing both of the parameters – short circuit current and open circuit voltage of a solar cell. Simulation studies show that an SiN/MgF dual-layer anti-reflective coating is best for a bare cell. This paper takes a closer look at how this coating can reduce the reflectance for a broad range of wavelengths and thus enhance the quantum efficiency of the cell in the blue and red region of the solar spectrum.
PVI Paper
Market Watch, Photovoltaics International Papers
Solar currently represents less than 0.5% of global electricity generation. However, as renewable electricity gains importance in the US$1 trillion global electricity market, we forecast solar photovoltaic shipments to rise at a compound annual growth rate of 50% for the next four years. We expect an increasing number of countries to promote solar energy as the cost gap between solar and fossil fuel-generated electricity closes. This paper provides an overview of what to expect from the PV market in 2010.
PVI Paper
Cell Processing, Photovoltaics International Papers
Photovoltaic modules are designed to meet the reliability and safety requirements of national and international test standards. Qualification testing is a short-duration (typically, 60-90 days) accelerated testing protocol, and it may be considered as a minimum requirement to undertake reliability testing. The goal of qualification testing is to identify the initial short-term reliability issues in the field, while the qualification testing/certification is primarily driven by marketplace requirements. Safety testing, however, is a regulatory requirement where the modules are assessed for the prevention of electrical shock, fire hazards, and personal injury due to electrical, mechanical, and environmental stresses in the field. This paper examines recent reliability and safety studies conducted at TÜV Rheinland PTL’s solar module testing facility in Arizona.
PVI Paper
Photovoltaics International Papers, PV Modules
The emitter or p-n junction is the core of crystalline silicon solar cells. The vast majority of silicon cells are produced using a simple process of high temperature diffusion of dopants into the crystal lattice. This paper takes a closer look at the characteristics of this diffusion and possible variations in the process, and asks whether this step can lead to optimal emitters or whether emitters should be made with different processes in order to obtain the highest possible efficiency.
PVI Paper
Cell Processing, Photovoltaics International Papers
Standard solar cell technology nowadays offers a variety of measures - some linked, some not - to continuously improve conversion efficiency. The starting point for considering the different improvement steps is a kind of standard cell as produced on most current production lines. The main elements of this cell are diffused junction, aluminium back-surface field and screen-print metallization. This type of cell suffers losses from different sources like optics, recombination and resistance that can be considerably lowered to obtain higher cell efficiency. This paper will describe improvement steps on the standard type of multi-crystalline cell before addressing cell concepts that open further potential.
PVI Paper
Photovoltaics International Papers, PV Modules
Although much of the emphasis of Part 1 of this paper (in Photovoltaics International ed. 5) focused on material quality issues and attention to detail on process control, high-volume manufacturing requires a concerted effort to constantly improve productivity of the lamination process and in turn the productivity of the total module manufacturing line. Such is the competitive landscape that greater attention to these factors is becoming a key differentiator for both equipment suppliers and module manufacturers. In this, the second part of the lamination process focus, we will look closely at the dynamics impacting module prices and the developments being undertaken to improve cycle-times of the lamination process, overall productivity and optimization as well as costs to ensure future competitiveness.

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