Photovoltaics International Volume 2

In PV power systems the choice of an appropriate location for the installation of the PV array box (or DC combiner box) is an important undertaking. It is essential that the box be placed so that the amount of DC cabling is minimized in order to not only save cable costs but also reduce voltage losses. This paper presents a fast solution to this problem, based on a mathematical model for the minisum location of the combiner according to the Manhattan metric between the PV array and the DC combiner box. The target function and its optimal solution (i.e. the most economical amount of cabling) for this particular model were obtained, and the optimality of the solution proved by contradiction. The application of this model is illustrated by means of two typical examples, involving an odd and an even number of strings in a PV array. The proposed model is efficient and easy to apply, and as such should be of interest to PV engineers and designers.

This paper presents a detailed assessment of the value of photovoltaic energy within the German energy supply structure, taking into account the correlation between actual consumption and local power generation. Contrary to previous statistical approaches, this paper takes a new dynamic approach, modelling the dynamic behaviour of the PV power generation as a one-year time series. A comparison with the time series of the power demand allows assessment of the value of PV energy. The value of PV energy mainly results from its ability to substitute conventional power generation and the benefit of this kind of decentralized power generation for network stability and quality. An evaluation of these aspects is carried out for the year 2005 and a likely scenario in 2015.

The costs of a photovoltaic installation are driving the market and the need for subsidized schemes, such as feed-in tariffs. Concentrated photovoltaics (CPV) is leading the development of future lowcost renewable energy sources in two ways: on one hand offering high efficiency systems, and on the other, being most capable of reducing manufacturing costs. The idea to decrease the cost of the photovoltaic system using optical elements to focus the radiation into the cell to reduce the size of the cells has been in the mind of the scientists since the 1970s [1]. But, apart from a reduced market, there were several issues that did not allow CPV success at that time. This paper puts forth the proposition that the key is to replace the area of active material, which is the most expensive, with optic elements, which are well known and cheaper.

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 offset surplus, while buyers are able to access attractive offers on surplus stocks and supplement existing supply arrangements as a last resort.

The reliability of United Solar Ovonic (Uni-Solar) triple-junction amorphous-silicon thin-film photovoltaic modules is critical to their success in an increasingly competitive PV market. Modules must show useful operating lifetimes of 20 to 30 years, and although module efficiency is very important, the total energy that a module will produce largely depends on its operating lifetime. Thus, module reliability must be evaluated to estimate lifetime and establish customer warranty periods. While real-world outdoor exposure testing is necessary and important, accelerated environmental test methods must also be utilized to provide more rapid feedback regarding failure modes, design flaws and degradation mechanisms. The following paper gives an overview of the methodology used to ensure long-term reliability of Uni-Solar flexible thin-film modules.

Back-sheet materials for photovoltaic modules serve several purposes such as providing electrical insulation, environmental protection and structural support. These functions are essential for modules to be safe for people working near them and for the structures to which they are attached. To ensure that all modules meet a minimum set of requirement, they must pass qualifications tests such as IEC 61646, 61215, 61730, and 62108. This paper puts forward the design and composition requirements of back- and front-sheet materials for achieving the highest possible quality performance from PV modules.

In the perpetual struggle to reduce the costs associated with PV energy generation, one aspect of the manufacturing process has potential to shine. To date, the PV sector is dominated by crystalline silicon wafers (90%), which largely use silver as the conducting medium for the front side grid, and to a lesser extent the backside contact. The conducting media are crucial to the overall efficiency of the cell by providing the means for current to flow when sunlight strikes the doped silicon wafer. This paper presents silver as a vital factor in the PV process, and discusses the future industry requirements as well as a projection for the overall silver market for the next eight years.

The continued tight supply and high cost of polysilicon, coinciding with the growth in demand for solar energy, has been a key catalyst for the rapid adoption of thin-film technologies in just the last two years. Although the technology has in development for over 15 years, it is only now that thin film has emerged as a viable low cost-per-watt alternative to conventional crystalline silicon cells. Taiwan, a powerhouse in the electronics and microelectronics industries, is also turning its attention to photovoltaics. Playing catch-up is something at which the Taiwanese have proven to be very effective, with a growing emphasis on thin film as a means to become another major centre and net exporter.

Three buzzwords dominate the discussion about the future of the photovoltaic market in the U.S. right now: ITC (investment tax credit), credit crunch, and Obama. All three have the potential to shape how the solar industry will look in the next decades. Primary data results from EuPD Research show that after a year that featured much wailing and gnashing of teeth, market participants are now “realistically optimistic” on the prospects for the industry, despite the influence of the international credit crisis.

Crystalline wafer and thin-film photovoltaics manufacturing have experienced dramatic expansion in recent years, but future growth requires increasingly effective strategies to reduce costs and increase the competitiveness of PV power. Reducing PV manufacturing costs has been a prime focus of the industry. In the current climate, cost reduction is especially critical given the industry shakeout that many analysts are forecasting. Now more than ever, it is important to bring manufacturing capacity online quickly and cost effectively. The vast majority of commercial-scale PV manufacturing capacity is new construction (greenfield), meaning it is purpose-built on an unused piece of land; however, there are alternatives. This paper will outline opportunities for re-use of existing obsolete semiconductor fabs, and the steps required to convert from one manufacturing strand to another.

A vast majority of silicon solar cells are manufactured using silver paste that is screen printed onto the front side of the wafer and fired to form the front-side contact. Though this method is well established within the industry, it continues to present several areas for potential efficiency improvements. The Fraunhofer Institute [1] has, among others, studied the potential of using electrodeposition of silver on top of the front side silver paste as a way to improve the front-side contact and increase cell efficiency. These results have shown cell efficiency increases of up to 0.4% absolute. This type of improvement has captured the interest of many manufacturers, but there has been a hesitancy to adopt electrodeposition as there is uncertainty as to what they can expect on their cells. Since efficiency gains are dependent upon many factors that can be unique to an individual cell, this paper provides a much-needed exploration of the potential effects of electrodeposition of silver in a way that isolates its effects from that of other factors.

A new wafer technology, named CDS (Crystallization on Dipped Substrate), is under development and has been found to be effective in the reduction of wafer cost and silicon feedstock. CDS technology was applied to 156mm x 156mm-sized wafers, obtained via the throughput of 1825cm2/min, and the resulting cell efficiency of 14.8% was confirmed. This paper outlines the principle behind the technology and outlines the procedure.

Investments in large photovoltaic factories can lead to high capital expenditure. To achieve a fast return on investment, it is essential to ensure a high utilization of process equipment. Optimization of photovoltaic factory performance requires a fundamental understanding of the processes as well as of the material flow and manufacturing equipment. Fraunhofer IPA has developed an approach to gather and analyze the factory data in order to detect and understand the logistic influencing factors. With this factory data, the performance of material flow systems and production equipments can be evaluated, leading to detection and elimination of inefficiencies in the manufacturing lines. The methods of acquiring and analyzing factory performance data as outlined in this article mainly focus on thin-film manufacturing lines, but are also applicable to crystalline technologies.

Inline processing, one of the fastest-growing production processes for crystalline silicon solar cells, uses continuously operated belt furnaces to achieve higher overall throughput compared with traditional batch processing. A second, major advantage of inline processing is improved manufacturing yields through reduced breakage of today’s thinner, increasingly delicate wafers. This is accomplished by eliminating several handling steps unique to batch processing techniques. This paper describes the influence of ECN-Clean, as developed by Mallinckrodt Baker and ECN in 2006, whose application increases the efficiency of solar cells produced using inline processing by approximately 0.3 percent absolute, compared with standard inline processing.

The Semiconductor Equipment and Materials International (SEMI) International Standards Program has a proven track record of more than 35 years of facilitating standards for high-tech industries, and aims to apply its experience to the emerging PV industry. Unlike other pre-established industries, where standard activities are mainly initiated by mature companies with clear requirements to standards, the PV industry, with its huge number of newly founded companies, is currently focused on ramping up their production lines and stabilizing their production processes. By structuring and utilizing standards requirements, it is possible to focus recourses to the most valuable standards in this critical phase of the fast-growing PV industry. SEMI intends to achieve these goals by proving recommendations for new standards activities, linking experts together to accomplish the deliverables, and speed up the process of standards deployment.

The etching technology currently used in the solar industry is mostly based on wet chemical processing. Plasmaenhanced dry chemical etching at atmospheric pressure is an alternative to the existing technology, especially when combined with similar process technologies, for example plasma-enhanced deposition techniques at atmospheric pressure, to provide a continuous in-line processing of crystalline silicon solar cells. This paper presents the use of plasma chemical etching using Fourier Transform infrared (FT-IR) spectroscopy to monitor different silicon wafer processing steps as an alternative to the widely used wet chemical processing approach.

With the thin-film silicon industry facing the problems of high-quality material deposition at high rates and narrowing deposition process windows, the “no-drift regime” is an important part of this development. In the case of the plasma-enhanced chemical vapor deposition (PECVD) of thin silicon films, the inconstancy of the concentration of silicon-containing particles (SCP) in the plasma leads to changes in deposition conditions, causing a deterioration of film properties, and, therefore, decreasing the performance of the solar cells. During the last few decades, evidence about the process instabilities has been accumulated in different laboratories. In this study, Fourier transform infrared absorption spectroscopy (FTIR), optical emission spectroscopy (OES), self-bias voltage and plasma impedance controls were applied as in-situ process diagnostics during the deposition of amorphous and microcrystalline silicon thin-films. Results of the study were then discussed.

Although the entire solar manufacturing industry, from raw materials to finished modules, has enjoyed strong double-digit growth rates over the past several years, few sectors have soared like the amorphous-silicon thin-film photovoltaic equipment space. Much of this prodigious multibillion-dollar booking activity can be attributed to the acceptance of the turnkey production packages offered by the likes of Applied Materials, Oerlikon and Ulvac. These suppliers’ plug-and-play, standard toolset solutions are attractive to companies seeking to get into the TFPV module business on a fast track and then scale up their capacities in multimegawatt chunks to achieve grid-competitive cost-per-manufactured-watt metrics.

The use of perfluorinated gases such as NF3, CF4 or SF6 for PECVD (plasma enhanced chemical vapor deposition) chamber cleaning has a much higher impact on global warming than does the use of onsite-generated F2. This holds true even when supposing that in the future much more effort is paid for the correct abatement and a leak-free supply and take-back chain. This paper will discuss the steps available to the PV industry for control and reduction of carbon emissions in the chamber cleaning process.

Anyone familiar with the PV industry can attest to the remarkably accelerated pace of innovation aimed towards generating solar power more cost effectively relative to conventional means of producing electricity. Many of high-technology’s best minds are bringing expertise in materials, manufacturing process, and electronics to tackle the challenge. The resultant gains in cost effective manufacturing, silicon availability and greater irradiance conversion efficiency will make continuous and sustainable impact to cost per kW generated akin to the predicable improvements in transistors per mm2 which has fuelled the semiconductor industry for the past 25 years (although we are not yet so bold as to devise the PV version on Moore’s Law). As less than 0.01% of electricity generated comes from PV installations [1], demand will materialize and the need for public subsidies will decline as the economics improve. This paper will investigate the steps required to make every solar project a “perfect” project by putting forth parameters for evaluating solutions for the problem areas.

Apart from some obstacles and bureaucratic hindrances, the Italian PV market has recently joined the upper echelons of the solar industry. Along with small and medium-sized systems, the commercial and large-scale segment in particular has a great deal of promise. Even though the local industry is still trying to block the domestic market from international competitors, increasing numbers of foreign investors are entering the market. In this close-up of the Italian PV market, the country’s participation in the solar energy industry is reviewed and a projection to 2010 is given, with particular emphasis on the country’s potential to be a major player in the large-scale installation sector.

Until recently, Solyndra had been one of the stealthiest thin-film photovoltaics operators, its glistening, prominently logoed headquarters building reminding tech-savvy commuters plowing up and down the I.880 corridor near Fremont, CA, of how little they knew about the company. But Solyndra has finally let the sunshine in and come out of the closet — even if it hasn't quite changed some of its stealthy ways. After a well-planned media and analyst rollout, the public knows that for this copper-indium-gallium-(di)selenide (CIGS) thin-film PV manufacturer, the world — or at least its solar-module form factor — is not flat. Like many TFPV purveyors, Solyndra loves glass as a substrate, but the company's meter-long CIGS-coated cylindrical modules look like a fluorescent light-bulb tube, not just another rectangular slab of the smooth stuff.