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.

The current industry situation of more competitive business approaches, increased PV project sizes and investments but declining profit margins renders an accurate knowledge of PV performance a vital factor in remaining competitive. Comprehension of expected lifetime and energy yield of PV generators is essential. Therefore, accurate characterization of PV modules is quickly becoming a more and more significant issue. This article gives an overview of the characterization topics of PV modules in terms of safety, failure susceptibility, overall reliability, system performance and energy rating.

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.

Over the past few decades, the PV equipment manufacturing market has seen a significant change in technologies. Cell sizes are being increased, while cell thickness has decreased at an ever-increasing speed of technological innovation, from 4” 340µm cells in the 1990s to 6”+ 180µm being the current industry standard. Thin-film modules pose completely new challenges to module manufacturing technology with a strong integration of the manufacturing of the active layers into the module production flow. This articles analyses the pros and cons of an increased level of line integration from the viewpoint of an established PV module producer.

Photovoltaic modules and components, due to the nature of their employment, must be designed to withstand the most diverse of environments. The large spectrum of climatic conditions and mechanical stresses that these components must weather merit the application of some standards by which they can be tested for durability, reliability and safety. TÜV Rheinland operates several ISO 17025-accredited laboratories worldwide for type approval testing of flat plate as well as concentrating PV modules, PV components and solar thermal systems. Test data, collected over the past 20 years, shows that there is still a rather high failure rate when it comes to testing of PV modules, and also that there are different failure mechanisms for crystalline and thin-film PV modules. This paper presents data from these tests and draws some conclusions regarding the need for future standards development.

A total of 2MWp of PV modules were sold on pvXchange’s spot market platform in December 2008. This corresponds to a sharp decrease of 60% when compared to the figures seen in the previous month (5.6MWp). Low trade volumes throughout the years are common on pvXchange; this year, bad weather conditions prevented many new installations, as did the current economic climate that saw many buyers waiting for further price decreases. The closing of long-term contracts has been postponed by many PV companies that are concerned that they will not find customers given the current circumstances. Again, First Solar’s CdTe thin-film modules were the most traded technology item on the pvXchange platform for the month of December.

The rapid expansion of high volume manufacturing to meet growing demand in recent years has highlighted the development of increasingly higher throughput machines, especially in the critical bottleneck process of module assembly, specifically characterised by tabbing and stringing steps. Significant productivity improvements have come about with the development of integrated, highly-automated tabber and stringers from a range of equipment vendors. However, module assembly remains the most expensive step in conventional c-Si cell production. Equipment suppliers are also challenged to meet the evolving demands of processing thinner wafers and to address overall production cost reduction strategies while meeting yield/throughput goals that are seen as a significant enabler of reducing the cost per watt.

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.

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.

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.