PVI Issue

Photovoltaics International Volume 14

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Published in November 2011, the 14th edition of Photovoltaics International provides a variety of technical papers from some of the industry’s stalwarts. Features include: TÜV Rheinland on junction box testing; Laser Zentrum Hannover on laser edge isolation of mc-Si cells; Calisolar on the importance of traceability; Fraunhofer ISE on EWT cells; and EPIA on Europe’s LCOE.

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In this issue...

PVI Paper
Photovoltaics International Papers
The Unite d States and China are embroiled in what the New York Times has dubbed “the most politically charged trade case in many years”. Seven US-based crystalline silicon solar cell manufacturers have formed. The Coalition for American Solar Manufacturing (CASM), led by SolarWorld and First Solar (the identities of the five remaining members are yet to be disclosed). The CASM has accused Chinese manufacturers of violating global trade laws with its “anti-competitive trade aggression”.
PVI Paper
Photovoltaics International Papers, PV Modules
This paper presents a new differential scanning calorimetry (DSC) method that allows the determination of the degree, or level, of crosslinking of ethylene-vinyl acetate (EVA) copolymers, including EVA films used as encapsulants for photovoltaic (PV) applications. This method can also determine additional characteristics of EVA, such as its weight per cent (wt %) vinyl acetate (VA) content and its fluidity. The paper describes the procedure and its application to EVA film samples laminated at 145°C, for different lengths of time in an industrial-type laminator for PV modules, as well as to EVA uncrosslinked samples of different composition and fluidity. The scope of the method compared to other characterization methods for the degree of crosslinking of EVA is discussed. An experimental comparison is also made to rheological and gel content methods.
PVI Paper
Photovoltaics International Papers, PV Modules
This paper describes the technical concepts and current status of back-contact module technology. A back-contact module has the advantage of a higher conversion efficiency because of less shading of the front of the cell, fewer inactive areas in the module and lower series resistance in the interconnection. Aesthetically, back-contact modules are more attractive than standard modules. Furthermore, module manufacturing is gentler due to there being less cell handling during the process. The two main technical concepts related to back-contact modules – interconnector technology and printed circuit backsheet technology – are discussed in this paper. An overview is given of the production status of current back-contact module manufacturers to also show the significant potential of this technology in economic terms.
PVI Paper
Photovoltaics International Papers, PV Modules
Photovoltaic (PV) modules and components are products which have to withstand the diverse effects of extreme conditions during their lifetime. The wide range of climatic conditions and possible mechanical stresses must be taken into account when designing a PV component. To assess whether the quality of a product is sufficient to withstand such influences, some international standards have been developed. TÜV Rheinland operates several ISO 17025-accredited laboratories worldwide for type approval testing of PV components – such as junction boxes, connectors and cables – as well as concentrating PV modules, flat-plate modules and solar thermal systems. Experience of testing PV components has been gained over the last 12 years, and even over the last 20 years in the case of PV modules. New developments in photovoltaics mean that continuous development and review of standards is necessary.
PVI Paper
Photovoltaics International Papers, Thin Film
Sales of critical subsystems used in thin-film PV manufacturing equipment are expected to reach $324M in 2011, and the outlook is for this figure to grow by 3.74% in 2012 to $336M. This expectation is going against the trend for the industry as a whole, which is predicted to decline next year as revenues from cell and module manufacturing weaken. The reason for this countermovement is the opportunities available to manufacturers who are willing to invest in the latest thin-film PV equipment to drive down costs and force unprofitable competitors out of business. While the same opportunities exist for crystalline silicon manufacturing, the number of well-resourced companies signalling their intention to invest in thin-film technologies should ensure a positive year for suppliers of equipment and critical subsystems to this segment of the industry.
PVI Paper
Photovoltaics International Papers, Thin Film
In terms of material properties, plasma-enhanced chemical vapour deposition (PECVD) of ZnO has advantages over sputtering techniques, due to the variety of available precursors, and the different dopants for achieving certain levels of n-type and, controversially discussed, p-type transparent conductive oxides (TCOs) on various substrate materials. This paper considers the deposition of boron-doped zinc oxide for n-type TCO-application on substrates of dimensions up to 50×50cm2 and at a temperature range of 50 to 450°C using a PECVD reactor with a plasma frequency of 13.56MHz. The materials’ characteristics such as transparency, carrier concentration and structural properties are discussed as a function of the deposition parameters. The deposition temperature strongly affects the crystallographic and morphological appearance of the deposited thin films, which was investigated using field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) methods. The electronic band structure-dependent characteristics were studied using ultraviolet-visible (UV-vis) spectroscopy and Hall measurements. Secondary ion mass spectrometry (SIMS) measurements complete the characterization methods for qualitatively verifying the incorporation of dopants and impurities. Results are reported for columnar-grown boron-doped ZnO with optical transparency greater than 80% in the visible range and a maximum carrier concentration of 1020cm-3.
PVI Paper
Photovoltaics International Papers, Thin Film
Because of its attractive electronic and optical properties, zinc oxide (ZnO) has found widespread use as a front and back electrode in commercial solar cells. ZnO can be deposited on glass using a variety of different methods, of which vacuum-based techniques are the most commonly used in industrial applications. Aluminium-doped sputtered ZnO:Al (AZO) has been studied intensively for use as a front contact in a-Si/μc-Si tandem cells. The implementation of AZO in series production has been hindered by reproducibility issues stemming from the combination of deposition and subsequent etching steps that are necessary to tune the ‘haze’ of the layers for optimal light scattering. Boron-doped ZnO:B (BZO), deposited by low-pressure chemical vapour deposition (LPCVD), has become a cost-effective option for module manufacturers, since the desired layer morphology can be produced as grown without the need of post-growth chemical etching. This paper addresses the different aspects of using AZO and BZO layers as front contacts for a-Si/μc-Si tandem modules fabricated in series production. The properties of the underlying ZnO layers put restrictions on the layer properties and process parameters that are used in the deposition of a-Si and μc-Si.
PVI Paper
Cell Processing, Photovoltaics International Papers
Crystalline silicon wafer technology currently dominates industrial solar cell production. Common devices feature opposing electrodes situated at the front and the rear surface of the wafer, and subsequent front-to-rear interconnection is used for module assembly. This paper describes the status and perspectives of the emitter wrapthrough (EWT) cell concept, which is a fully back-contacted solar cell. The functions which have to be fulfilled for this concept, as well as the corresponding challenges and advances, are discussed.
PVI Paper
Materials, Photovoltaics International Papers
Silver paste is a key component of the design of nearly all silicon wafer solar cells manufactured in 2011. The high cost of the precious metal in the paste formulation means that silver paste is also the second-highest component of the total cost of materials. This article reviews the silver paste supply chain and the challenges in silver paste formulation and manufacture, and discusses some of the approaches for reducing or removing entirely the use of silver in crystalline silicon cell manufacture.
PVI Paper
Materials, Photovoltaics International Papers
The reliable analysis of trace elements in silicon is of fundamental importance for the understanding of material properties and quality control of solar cells. This paper presents a demonstration of the power of two analytical techniques for the determination of trace elements in solar silicon: inductively coupled plasma mass spectrometry (ICP-MS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). These techniques are among the few that achieve sufficiently low detection limits and they may complement each other because of their specific performance. Examples are given of the quantitative chemical analysis of boron, phosphorus and iron in different types of solar silicon, as well as of the enrichment of metals and alkali metals in Si3N4 precipitates.
PVI Paper
Fab & Facilities, Photovoltaics International Papers
For a vertically integrated solar cell production starting with purification of silicon feedstock and ending with the production of solar cells, it is necessary to have control over all possible parameters that may affect yield, efficiency and product quality. This paper presents an approach for tracking products with minimal effort using a contactless technique. The method allows wafers to be virtually reconstructed into bricks and ingots, as well as recognizing the precursor wafer for each solar cell.
PVI Paper
Cell Processing, Photovoltaics International Papers
In the photovoltaic industry, laser edge isolation (LEI) is a well-established process at the end of the process chain. However, because the cell properties vary from one cell producer to the next, no systematic approach is defined in industry for establishing an efficient isolation groove. Nevertheless, a general approach has to be defined for analyzing the LEI process for silicon solar cells. Besides the material aspects and laser parameters, atmospheric boundary conditions must be considered. This paper presents investigations into the ablation of a specific type of mc-silicon solar cell, and the most suitable laser, as well as the ambient parameters, is determined based on the results of the experiments.
PVI Paper
Fab & Facilities, Photovoltaics International Papers
How much carbon is emitted in producing a solar PV module and launching it on the market? This could be an important question which project developers, installers, investors, government agencies and end customers might ask solar PV manufacturers in the future. To answer it, producers need to know the direct emissions from the manufacturing process, as well as those generated from the activities of manufacturers in the upstream supply chain (including raw material acquisition, upstream energy use, packaging, transportation and procurement), and also those arising from module usage and eventual recycling. This paper, written in a cooperation between EuPD Research and Deutsches CleanTech Institut (DCTI), presents an overview of PV’s carbon footprint.
PVI Paper
Market Watch, Photovoltaics International Papers
The PV industry stands on the verge of an enormous achievement – an installed base of PV plants with 100GW of energy generation capability. This milestone has come about because of the contributions of a fully global industry that has blossomed in the past decade. Yet even though the PV industry traces its heritage to before the space programme, as with any dynamically growing industry most industry members have joined in the past five years. And each generation often makes the same mistakes that a previous generation made. Sometimes the same people move from one industry to another and repeat the same mistakes there. The PV industry is rediscovering ultra-competitive market dynamics that have previously been seen in other high-technology commodity markets. This paper begins with a discussion of one such market – the dynamic random access memory (DRAM) industry – and then looks at the current PV market and the industry outlook.
PVI Paper
Market Watch, Photovoltaics International Papers
The benefits of solar photovoltaic (PV) power are well known, and, as this awareness rises and the cost of generating PV electricity declines, the technology is becoming more competitive with conventional electricity sources in market segments all across Europe. But bureaucratic hurdles remain a persistent threat to the widespread installation and integration of PV, often making it difficult to take advantage of the technology. In many countries, administrative processes and permitting procedures still require significant improvement. As a result, planning and connecting a solar photovoltaic system to the grid can still take several years in Europe.
PVI Paper
Photovoltaics International Papers, Power Generation
It is essential to understand the investment and operating costs of photovoltaic power plants in terms of economic parameter calculations such as levelized cost of electricity (LCoE). The dynamic behaviour of national and international markets requires a precise and detailed estimation of costs, and this knowledge is especially important to investors and policymakers. Only if the investment and operating costs of PV power plants are known can the price of electricity and the more detailed levelized cost of electricity be precisely calculated. High investment costs also require reliable investment policies and close cooperation between financial institutions (such as banks and investment funds) and power plant owners. Investment in large-scale PV power plants requires a detailed evaluation of solar radiation potential and grid availability, as well as a load analysis and a precise economic evaluation. When the investment cost based on the above-mentioned parameters is known, an estimation of the operating costs should be the next step. When all the costs of a PV power plant have been estimated, the price of electricity, or even a more detailed LCoE, can be calculated. This paper presents the trend of investment costs and some typical maintenance costs, and calculations of electricity price based on recent real data for large-scale PV power plants.
PVI Paper
Photovoltaics International Papers, Power Generation
The solar industry suddenly finds itself in an altered business climate in which construction markets seem permanently damaged and government subsidies are under challenge. This paper outlines how BIPV provides a strategy for expanding the market for PV and creating value-added products in a radically changed political, economic and financial environment.
PVI Paper
Photovoltaics International Papers, Power Generation
In recent years solar photovoltaic electricity has shown a steady decrease in cost, thanks to technological improvements and economies of scale. Over the last 20 years the price of PV modules has dropped by more than 20% each time the cumulative volume of PV modules sold has doubled. System prices have fallen accordingly: during the last 5 years a price decrease of 50% has been seen in Europe. This trend will continue in the foreseeable future. System prices are expected to fall in the next 10 years by 36–51%, depending on the segment. Importantly, there is a huge potential for further reductions in generation costs: around 50% by 2020. The cost of PV electricity generation in Europe could decrease from 0.16–0.35€/kWh in 2010 to 0.08–0.18€/kWh in 2020, depending on system size and irradiance level. That decline in cost will continue in the coming years as the PV industry progresses towards becoming competitive with conventional energy sources. Under the right policy and market conditions, PV competitiveness can be achieved in some markets as early as 2013, and then spread across the Continent in the different market segments by 2020. This paper summarizes the first part of a newly published EPIA report about PV competing in the energy sector. The report illustrates why PV can become a mainstream player in the energy field before 2020. The study, carried out with the support of the strategic consulting firm A.T. Kearney, shines new light on the evolution of Europe’s future energy mix and PV’s role in it.
PVI Paper
Cell Processing, Photovoltaics International Papers
A new production process for crystalline silicon (c-Si) solar cells, specifically p-type back-contact solar cells, is proposed. In contrast to the conventional c-Si solar cell manufacturing method, this new technology eliminates the etching process and reduces the industrial three-step electrode printing to only one step, greatly improving the technological process. Furthermore, the proposed process is also largely compatible with a traditional c-Si solar cell production line. Oxidation technology for producing the SiO2 film on a c-Si wafer, together with corrosive window technology, such as through HF corrosive paste screen printing, for creating the patterning on the wafer covered with SiO2 film, are used in the fabrication of the p-type back-contact solar cells.
PVI Paper
Photovoltaics International Papers, PV Modules
Solar enterprises will each be faced with the occasional surplus or lack of solar modules in their lifetimes. In these instances, it is useful to adjust stock levels for modules at short notice, thus creating a spot market. Spot markets serve the short-term trade in different products, by enabling the seller to permanently or temporarily offload surplus, while buyers are able to access attractive offers on surplus stocks and supplement existing supply arrangements as a last resort.

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