Photovoltaics International Papers

In today’s market, crystalline silicon wafer technology dominates industrial solar cell production. Common devices feature opposing electrodes that are situated at the front and rear surface of the wafer and subsequent front-to-rear interconnection is used for module assembly. This paper reflects the functions which have to be fulfilled for the back-side contact of the solar cell as well as challenges and advances for the two basic classes: full-area and local rear contact formation. While full-area contacting has proven to be a reliable technology for industrial production, local contacting through dielectric layers has yet to be put through its paces in industrial implementation.

To date, the United States’ photovoltaic markets have largely been driven by net-metered residential and commercial customer projects, in large part due to federal, state, and utility incentives (see Fig. 1). The rapid growth of the commercial market in particular can almost entirely be attributed to the development of the well-known ‘solar-services’ business model, also known as the solar performance or the third-party solar model, which began in the early 2000s. In short, the commercial solar market surpassed the residential sector, and in 2008 represented only 10% of the number of installations but well over two-thirds of the annual grid-connected megawatts in the U.S. PV market [1]. This article will provide background information on the U.S. solar markets, and define what a utility solar business model is and the drivers of different model types.

The recent photovoltaic industry shakeout which started around Q3 2008 has faced the overcapacity, credit crunch, and economic crisis that significantly declined the average selling price by 50 - 65%, including the price of thin-film photovoltaic modules. The changing business environment has put significant pressure on all PV manufacturing technologies but more candidly on amorphous silicon thin-film single-junction module manufacturers to advance and scale up the device efficiency and aggressively drive cost reduction. This paper outlines the approach taken at Moser Baer Photovoltaic Technologies India Limited (PVTIL), including process optimization and device management strategies, to enhance the module efficiency (total area) of the single-junction amorphous silicon quarter size, 1.43m2, substrate as manufactured using Applied Materials’ SunFab line.

The main goal of the solar industry is to reach grid parity as soon as possible. This can be achieved by reducing the manufacturing costs, by increasing conversion efficiencies and/or by improving the lifetime of solar modules. Driving down the cost of modules is not straightforward. Commercially available PV modules are typically sold with 20-year warranties, and changing these materials for economic reasons requires extensive material testing and recertification of the new module design. In the following sections, we will focus on the cost drivers of module manufacturing processes and how that could evolve into new module designs.

In today’s PV modules, the solar cells are commonly encapsulated in EVA. During lamination EVA undergoes a crosslinking reaction. From a practical point of view, two major interests arise. For quality control purposes, one needs to know the degree of curing of the EVA encapsulant after lamination. The focus in process optimization is on understanding the kinetics of the crosslinking as a chemical reaction. If this is known (and proven), one can predict appropriate crosslinking conditions (i.e. lamination temperature and time) that have to be matched to reach a certain degree of crosslinking. This contribution mostly deals with this latter aspect. DSC as well as DMA data and model-free kinetics were used in this study to establish the kinetics of the EVA crosslinking process. It was found that both techniques adequately predict the degree of crosslinking for any temperature as a function of the curing time.

Building integrated PV | Despite plenty of hype, BIPV has remained a niche segment in the solar business, held back by a combination of high costs and low efficiencies. But as Ben Willis hears, the high-profile entry of Tesla on to the BIPV scene could herald the start of a new era for the sector. In late October, with all the usual fanfare that accompanies an Elon Musk announcement, the CEO of EV and battery storage manufacturer, Tesla, took to the stage to lift the lid on a heavily trailed new product. Most of Musk’s recent utterances on energy have been about storage, particularly Tesla’s high-profile foray into the world of stationary storage through its Powerwall battery system. But this was something a bit different – a buildingintegrated PV (BIPV) product designed to emulate various kinds of roofing tile and eliminate the need for clunky conventional roof-mounted modules once and for all.

Heat transfer and control of the temperature field are important in the production of silicon solar cell wafers. Present work focuses on the first steps of the production chain, i.e. crystallization and wafering. For the crystallization process, control of heat transfer is crucial for the ingot quality in terms of grain structure, impurity distribution, particle formation, and ingot stresses. Heat transfer is also important during subsequent processes, in particular the wire sawing of the silicon blocks into wafers. The paper emphasises the role of heat transfer and explains the consequences for these processes. Examples from experimental trials and measurements are combined with models and simulation methods.

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.

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.

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.