PVI Issue

Photovoltaics International Volume 1

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The first edition of the Photovoltaics International journal, published in August 2008, was created in response to what was deemed to be a growing need for an unbiased technical publication for the solar cell and module manufacturing industry. With this in mind, the first edition of Photovoltaics International saw the commissioning of papers from a wide range of sectors, such as NREL’s overview of the CPV sector, IMEC’s thin-film efficiency gains via plasma texturing, site selection with IBM PLI, Q-Cells on silicon nitride thin films and Navigant Consulting’s market overview.

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In this issue...

PVI Paper
Photovoltaics International Papers, Power Generation
Today’s PV industry is growing at a rapid rate, but the industry would grow even faster if costs could be reduced for both the final products and the capital investment required for scale-up. One strategy for reducing module cost is to reduce the amount of semiconductor material needed (the cost of the silicon solar cells typically comprises more than half of the module cost). Many companies are thinning the silicon wafers to reduce costs incrementally; others use thin-film coatings on low-cost substrates (such as amorphous/microcrystalline silicon, cadmium telluride, or copper indium gallium (di)selenide on glass or other substrates). Concentrating photovoltaics (CPV) follows a complementary approach and uses concentrating optics, which may be designed for low or high concentration, to focus the light onto small cells. Low-concentration concepts use silicon or other low-cost cells; high-concentration optics may use more expensive, higher-efficiency cells. The higher-efficiency cells can reduce the cost-per-watt if the cost of the small cells is minimal.
PVI Paper
Photovoltaics International Papers, Thin Film
Thin-film silicon solar cells are a potentially low-cost alternative to solar cells based on bulk silicon that are commonly used in the industry at the present time. However, a major drawback of the current epitaxial semi-industrial screen-printed cells is that they only achieve an efficiency of about 11-12%. By upgrading their efficiency, this kind of solar cell would become more attractive to the photovoltaic industry. The optimization of the front surface texture by dry texturing based on a fluorine plasma and the introduction of an intermediate porous silicon reflector at the epi/substrate interface (multiple Bragg reflector) has proven to result in an efficiency boost up to about 14%.
PVI Paper
Materials, Photovoltaics International Papers
Thin-film solar cell manufacturing is poised to make a giant leap in scale with the birth of the gigawatt fab. Commercial thin-film plants are typically sized based on the capacity of the production line from the chosen equipment supplier. In most cases, initial investments have been for a single line, typically with an output capacity of no more than 60MWp. This period of initial development has allowed the industry to prove the robustness of the technology and capabilities of the equipment, as well as to understand the significance for the cost-per-watt of key cost drivers such as materials reduction, cell efficiency increases, and productivity. While large-scale manufacturing will positively impact costs, it presents a unique set of challenges for equipment and material suppliers, as well as the engineering and contracting companies tasked with designing, building, equipping and running a facility on this scale. In this paper, we present the insights of two specialty companies in the solar industry. Turner and Townsend, a design and project management consultancy, and Linde, glass manufacturer and gas and chemical company - share their views of the challenges of the gigawatt fab in three dedicated sections.
PVI Paper
Fab & Facilities, Photovoltaics International Papers
Each year, the photovoltaic market grows at a two-digit growth rate. However, the resulting economy-of-scale effects are not enough to achieve grid parity on their own. In order to reduce the production costs to grid parity level, new concepts and ideas must be realised as the basis for a photovoltaic factory. There are four main requirements that must be fulfilled in order to adhere to this cost reduction strategy: a highly integrated factory; automated and stable processes; a production control system (PCS) that provides the statistic data in order to continually optimise the processes; and an optimally-sized aligned production capacity.
PVI Paper
Photovoltaics International Papers, PV Modules
Design and performance qualification testing of PV modules consists of a set of well-defined accelerated stress tests with strict pass/fail criteria. ASU-PTL is an ISO 17025-accredited testing laboratory and has been providing photovoltaic testing services since 1992. This paper presents a failure analysis on the design qualification testing of both crystalline silicon (c-Si) and thin-film technologies for two consecutive periods: 1997-2005 and 2005-2007. In the first period, the industry was growing at a slower rate with traditional manufacturers, with qualification testing of c-Si technologies being primarily conducted per Edition 1 of the IEC 61215 standard. In the second period, the industry was growing at an explosive rate with new manufacturers joining the traditional manufacturers, while qualification testing of c-Si was primarily conducted per Edition 2 of IEC 61215. Similar failure analysis according to IEC 61646 has also been carried out for thin-film technologies. The failure analysis of the test results presented in this paper indicates a large increase in the failure rates for both c-Si and thin-film technologies during the period of 2005-2007.
PVI Paper
Cell Processing, Photovoltaics International Papers
Increasing the efficiency and yield of production line processes forms an integral part of PV manufacturers’ technology roadmaps. For their next generation production lines, non-contact processing equipment is considered essential. This prioritizes laser-based processing, already established at several steps in c-Si and Thin-Film cell manufacturing. This paper summarizes the key issues when using lasers within PV production lines.
PVI Paper
Photovoltaics International Papers, PV Modules
The importance of rapid and accurate measurement of the electrical power output and related characteristics of photovoltaic (PV) modules or panels concluding the manufacturing process cannot be overemphasized. Even though these modules will likely be deployed under a variety of outdoor solar illumination conditions, they must be tested under a set of standard conditions to assure consistency of results demanded by both the manufacturer and the customer. The ability to provide a measurement tool for this critical manufacturing step that possesses the proper specifications and qualities, ranging from spectral accuracy to ease-of-use, is imperative.
PVI Paper
Cell Processing, Photovoltaics International Papers
Standardized requirements for the quality of PV modules, solar cells and wafers are given in the according IEC norms (e.g., IEC 61215, 61646, and IEC 61730 for modules). However, the manufacturers of cells purchasing wafers and the module manufacturers purchasing cells want information beyond the final check of the product and to monitor each step during the production process to identify harsh handling and/or machine faults at the earliest stage possible. With consequential improvements of the process enabled, continuous improvements in throughput and yield improvement of the factory are likely, also allowing an early feedback on quality issues to the raw material supplier. Furthermore, by knowing all characteristics and factors of the cell and the module, prediction of electrical energy yield during the life cycle of a PV power plant is becoming more accurate and more reliable.
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 these stock levels at short notice, thus creating a spot market. Spot markets serve the short-term trade of different products, where the seller is able to permanently or temporarily off-set surplus, while buyers are able to access attractive offers on surplus stocks and supplement existing supply arrangements as a last resort.
PVI Paper
Photovoltaics International Papers, Thin Film
The rapidly-growing photovoltaic market has placed a strong demand on manufacturers to decrease solar cell production costs. For thin-film solar cells, this can be achieved by increasing substrate sizes to achieve a better productivity and by adding more advanced layer stack systems to enhance the solar cell’s efficiency. Nearly all required layers of the prominent thin-film-based solar cell types (a-Si/µc-Si, CdTe and CI(G)S) can be deposited by using plasma processes. On the one hand, plasma-enhanced chemical vapor deposition (PECVD) is used for the deposition of a-Si and µc-Si layers. On the other hand, magnetron sputtering is used for coating with transparent conductive oxides as ITO (indium tin oxide) and ZAO (aluminium-doped zinc oxide), metallic back contact layers such as Ti, Al and Mo, or components of the compound semiconductor layers such as Cu and In. Magnetron sputter processes use direct current (DC) or pulsed DC, whereas radio frequency (RF) power is used for PECVD processes. Of utmost importance to get a reliable, high-efficiency solar cell is a good uniformity of the deposited layers and the need for the layer to be defect-free. Defects such as particles and splashes are created inside the plasma when an unwanted local discharge - a so-called arc - occurs. This arc can be eliminated by switching off the power supply. The faster this is done, and the less energy that is delivered into the arc, the smaller and more insignificant the defect creation will be. For this reason, as well as for precise control of electrical power, advanced, fast-reacting arc management is very important to attain high-quality solar cell coatings.
PVI Paper
Photovoltaics International Papers, Thin Film
The next two years will be crucial in determining the market viability and future of what many see as the most promising thin-film photovoltaics technology: copper indium gallium (di)selenide (CIGS) and its gallium-free cousin, CIS. With potential conversion efficiencies just below that of crystalline silicon PV, low-cost manufacturing strategies offering a chance to reach sub-dollar-per-watt manufacturing costs on both glass and flexible modules, and applications ranging from utility- and industrial-scale farms to building-integrated commercial and residential uses, the quaternary compound has a large grid-parity upside - if the very real challenges of scaling production to commercial volume can be met.
PVI Paper
Photovoltaics International Papers, Power Generation
Every day, mankind consumes as much energy as it took the earth 1,370 years to store. The International Energy Agency estimates that by the year 2030, worldwide electricity consumption will have increased annually by approximately 2.4%. City Solar AG is seeking to increase renewable energy stocks through grid-connected solar power utilities. As one of the leading producers of large-scale photovoltaic plants, City Solar is uniquely placed to give us a better understanding of how these plants are put together.
PVI Paper
Fab & Facilities, Photovoltaics International Papers
Many readers will equate SEMI with the SEMICON trade shows around the world, business and technical conferences, EHS and advocacy initiatives and, most of all, industry standards. Currently, SEMI has close to 2,000 member companies, about 20% of which are active in the photovoltaic sector. These companies form a community called PVGroup – a community that addresses opportunities and obstacles collectively, bringing low-cost PV technology and sustainable clean energy to the world. SEMI is supporting this segment by expanding our key competencies – shows, standards, advocacy, and market research – into this new space.
PVI Paper
Cell Processing, Photovoltaics International Papers
Si etch processes are vital steps in Si solar cell manufacturing. They are used for saw damage removal, surface texturing and parasitic junction removal. The next generation of Si solar cells, featuring thinner wafers and passivated rear surface, will pose more stringent demands on those steps. Surface decoupling (achieving different surface treatments on the front and the rear) has to be achieved while minimizing Si consumption. Plasma texturing is an emerging technique that appears very promising in that respect, as efficiencies as high as 17.4 % have been achieved on screenprinted multicrystalline Si solar cells incorporating this process.
PVI Paper
Market Watch, Photovoltaics International Papers
The photovoltaic industry was once, and for quite some time, the unappreciated renewable technology. Perceived as too expensive without subsidies to reduce the price of ownership, and sometimes as an energy choice primarily for environmental zealots, the industry has continued, nonetheless, to grow at a compound annual rate of 34% over the past 30 years. Growth at this rate would be envied by any industry, and certainly deserves recognition, particularly as it has come with significant problems and has been extremely difficult to achieve. Now, with worldwide consensus on global warming along with sufficient evidence that fossil fuels are rapidly depleting, solar electricity is finally earning some respect - but the industry still has perception problems to solve.
PVI Paper
Materials, Photovoltaics International Papers
The rapid growth of the solar energy industry owes its success to the development and production of mono- and multi-crystalline solar cells. This growth has been limited in recent years due to the lack of available supply of polysilicon, the key raw material for making the wafers that serve as the basis of the solar cell. As a result of this limitation, the price of polysilicon has increased dramatically and this has led to significant new and planned capacity expansions. These new capacity expansion announcements have been highly publicized, with little additional outside focus on other chemicals and materials.
PVI Paper
Fab & Facilities, Photovoltaics International Papers
Climate change, oil shortage, green energy, energy security – these are some of the global `mega´-topics currently dominating the agenda in the news, in politics and in private lives. One of the industries that has most profited from the ever-growing consciousness about the need to de-carbonize current energy use is the photovoltaic industry. With this economic background, the photovoltaic industry has experienced impressive growth rates in the last decade and is expected to grow at 30% per year over at least the next couple of years. Since its upswing, it has become a multi-billion dollar industry and subject to speculation on stock exchanges worldwide.
PVI Paper
Cell Processing, Photovoltaics International Papers
The deposition of thin films is a key technology for a large variety of technical and scientific applications. Among them is the deposition of silicon nitride (SiNx) to passivate the surface of silicon solar cells. The SiN film serves several purposes. It is a broadband anti-reflection layer, it serves to saturate dangling bonds and/or other surface states of the silicon, and last but not least, it is a protection layer to prevent alkali ions and other impurities from diffusing into the silicon causing perturbations of the performance of the solar cell. This multitude of properties to be fulfilled at the same time often causes difficulties in assessing the effect of a single process parameter, let alone the task of optimizing the SiN film in all required aspects at the same time. The aforementioned technical features of the SiN film provide the very property that largely determines the aesthetically pleasing appearance of a cell, and hence a PV module, as the colour of the module is determined by the cell composition. In order to complicate things further, there are numerous deposition techniques being applied both on a scientific level as well as in production environments.

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