Technical Papers

This paper, the third in a series covering cost of ownership (COO) studies for photovoltaics [1], examines the need for metallization of silicon-based solar cells and how it has evolved over the past few years. The technologies and techniques that are being developed for this part of cell manufacturing in the foreseeable future are also discussed. The paper will conclude with a COO case study using the DEK Solar PV3000 as an example.

Upgraded metallurgical-grade (UMG) silicon is a lower cost and lower quality form of solar-grade silicon that is capable of producing solar cells at over 16% efficiency. This paper presents some of the economic advantages and technical concerns and solutions associated with producing silicon based PV from UMG, as well as preliminary solar cell results using this material. Results are based on a comparison of cells made in a turnkey line (Schmid Group) using alloy blends of 10%, 20%, 30% and 100% UMG, mixed with solar-grade Si before ingot growth. Detailed characterization was carried out on these finished cells according to lifetime, LBIC, diffusion length and luminescence imaging to determine correlations of performance with basic parameters. Requirements for material cost and cell performance necessary for UMG solar cells to be cost competitive are also presented.

Building Information Modelling (BIM) is an approach that is fast gaining traction in the architect, engineer and construction (AEC) industries. BIM combines the construction of a virtual model with all aspects of a facility, from design (space planning) to construction (cost and scheduling), and from operations to maintenance (planning and asset management). BIM is also a process as well as a project. Even though the technology for implementation of BIM will change, and probably change rapidly, the process and underlying concepts will likely change very little. This paper outlines the guiding principles of BIM and its ability to enhance the project delivery process of the AEC industries.

Among all of the tests performed in the production chain of solar cells, each with the scope of production control and the aim of driving engineering improvements, the electrical final test is certainly the most important. The final test defines the gate to module manufacturing and has a direct impact on finances and customer satisfaction. The test procedure itself is well known and continues to undergo constant further development, but that shall not be the scope of this article. This paper will elucidate on the issues faced by bringing these tests into high volume production, highlighting some issues on measurement accuracy and degradation of the internal calibration standards. In addition to pure electrical testing, the paper will discuss the Q-Cells approach to identifying hot spots and subsequent binning of the affected cells without adding process time to the test procedure, and will show their straightforward correlation to heat generation of these hot spots in real-life condition-encapsulated module tests.

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.

As polysilicon producers perform expansions and upgrades to increase production and improve operations, plant safety remains critical. Companies should routinely review their safety policies and effectively plan their projects to ensure uninterrupted product supply and create a safe environment for employees and the communities in which they operate. Both the design and the execution of expansion and upgrades to projects are critical as companies strive for minimal down time so that productivity is not affected. Such hazards and scenarios that may hinder and delay start-up, specifically in relation to polysilicon plants, are highlighted in this paper. Furthermore, the paper outlines how best to avoid these situations, offering methods of execution to achieve the three key measures of success: safety, high purity and minimal down time.

Interconnection of inverters to the electrical grid is a key issue for the widespread integration of distributed energy resources, especially when the scenario surrounding international standards is so unclear. As a pre-normative research step, a round-robin test of two small-scale photovoltaic inverters was performed by nine DERlab laboratories during 2009. The test activity was focused on the verification of individual test procedures, common interpretation of standards and requirements, and determination of problems related to the equipment and facilities involved in conducting round-robin tests. Compilation of test results and first conclusions of this activity will be presented in this paper.

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.