Technical Papers

The demand for equipment used to manufacture solar photovoltaic solar cells and modules has grown at an explosive rate over the past five years, and the fastest-growing segment has been for systems used to manufacture thin-film cells and modules. In 2009, demand for this type of equipment reached US$1.9 billion, up from US$0.1 billion in 2004, representing an astonishing 80% compound annual growth rate over the period. However, as with the rest of the industry, 2009 saw sales flattened and the business model change from one of rapid growth to that of sustainability. The result of this transition has been some consolidation, with several major equipment vendors strengthening their position through acquisitions. The outlook for 2010 calls for sales of thin-film production equipment to recover and continue growing at a compound annual growth rate of around 15% over the next five years (see Fig. 1).

The emitter or p-n junction is the core of crystalline silicon solar cells. The vast majority of silicon cells are produced using a simple process of high temperature diffusion of dopants into the crystal lattice. This paper takes a closer look at the characteristics of this diffusion and possible variations in the process, and asks whether this step can lead to optimal emitters or whether emitters should be made with different processes in order to obtain the highest possible efficiency.

Photovoltaic modules are designed to meet the reliability and safety requirements of national and international test standards. Qualification testing is a short-duration (typically, 60-90 days) accelerated testing protocol, and it may be considered as a minimum requirement to undertake reliability testing. The goal of qualification testing is to identify the initial short-term reliability issues in the field, while the qualification testing/certification is primarily driven by marketplace requirements. Safety testing, however, is a regulatory requirement where the modules are assessed for the prevention of electrical shock, fire hazards, and personal injury due to electrical, mechanical, and environmental stresses in the field. This paper examines recent reliability and safety studies conducted at TÜV Rheinland PTL’s solar module testing facility in Arizona.

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.