PV 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.

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.

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.

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 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.

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.

Among the different packaging materials used in photovoltaic solar modules, ethylene vinyl acetate-based (EVA) encapsulants play an important role during the lifespan of the module assembly. Prior to lamination, EVA is a thermoplastics polymer containing a number of additives. During the lamination process, EVA cross-links into a three-dimensional network structure, i.e., a thermoset, which provides protection for solar cells against detrimental environmental conditions. Since EVA has a very low glass transition temperature and melting points, proper cross-link density has to be achieved through the lamination process to prevent the EVA from cold flowing in the field. As a result, module manufacturers constantly monitor the cross-link density or gel content of EVA after lamination. This paper proposes a new method of measuring this density value while avoiding many of the current pitfalls.

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 encapsulation of solar cells is one of the most enduring ‘traditional’ process steps in the fabrication of a photovoltaic module. The need to protect the delicate semiconductor active solar cell with protective material to ensure long-term operation remains a critical step in the module assembly process. However, continued development of the lamination process and materials used for encapsulation are required to meet increased demands of 25-year guaranteed module operation in the field, shorter cycle-times and lower production costs. In this two-part article, we look at the challenges these and other factors are having on the lamination process, the equipment required and the developments taking place to meet module manufacturers’ requirements now and in the future.