PVI Issue

Photovoltaics International Volume 16

Share on facebook
Facebook
Share on twitter
Twitter
Share on linkedin
LinkedIn
Share on reddit
Reddit
Share on email
Email

This sixteenth edition of Photovoltaics International marks four years of production of the quarterly journal. As always, our focus is on efficiency and quality improvement and cost reduction in manufacturing.

L3dwLWNvbnRlbnQvdXBsb2Fkcy9sZWdhY3ktcHVibGljYXRpb24tcGRmcy82ZjhiNzY3ZmQxLXBob3Rvdm9sdGFpY3MtaW50ZXJuYXRpb25hbC12b2x1bWUtMTYucGRm

In this issue...

PVI Paper
Photovoltaics International Papers, Thin Film
Lifetime guarantees of more than 20 years are a target for the long-term stability of solar modules. An important point for the future of CIGS solar cells is to understand the impact of metastable behaviour on long-term stability. Accelerated ageing under open-circuit conditions leads to a drop in open-circuit voltage (Voc). A decrease in the net doping density is responsible for the drop in Voc and consequently the drop in the photoluminescence (PL). In the initial state the electroluminescence (EL) ideality factor exhibits a value close to unity, as expected from theory. After the dark anneal an increase in the EL ideality factor is observed, and an EL measurement at constant voltage shows a decrease in EL: both these behaviours are due to a pile-up of negative charges at the heterointerface. The application of a positive bias or an illumination during the endurance test leads to an optimization of stability. This paper shows that PL and EL can distinguish between bulk and interface properties and are well suited for the detection of degradation mechanisms.
PVI Paper
Materials, Photovoltaics International Papers
Unidirectional solidification of large Si ingots from the melt phase is currently one of the most important technologies for producing mc-Si for PV cells. Si ingot furnaces began from casting equipment, and have been improved by DSS (directional solidification system) or DSS-like methods. To improve PV cell efficiency and reduce costs, intensive development has focused on increasing a single ingot’s volume, reducing impurities and controlling the growth speed and temperature gradient. One of the latest developments of Si ingot furnaces is mono-like crystalline silicon growth using a seed preservation method and more accurate control. The Si ingot furnaces are optimized with precise control of temperature gradients and growth speed for the formation of a large unit of quasi-monocrystalline Si. This optimization can further improve a PV cell’s efficiency by at least 1%. In order to obtain fundamental knowledge about the key process steps that determine the growth and electrical quality of mc-Si via directional solidification in an ingot furnace, a combined modelling-measuring approach is essential. Moreover, a mathematical model of the Si ingot casting process can be used for model-based process control.
PVI Paper
Photovoltaics International Papers, Thin Film
This paper presents Calyxo’s recent advances in product design that have resulted in independently confirmed peak aperture-area efficiencies of 13.4% for modules and 16.2% for cells. Some insight is given into a suitable product design for achieving the highest reliability possible, even in hot climates such as Australia, with no signs of degradation during the first three years of deployment in the field. These technical advances and the midterm production-cost target of US$0.50/Wp allow a forecast levelized cost of electricity (LCOE) of under US$0.10/KWh, especially in sunny regions of the world.
PVI Paper
Cell Processing, Photovoltaics International Papers
Wet chemical process equipment is widely used in industrial solar cell production, and inline etching systems in particular have attracted more and more attention since their introduction 10 years ago. The horizontal wafer transport within these systems has made it possible to think about single-side wafer treatments even for wet chemical process applications. Since its market introduction in 2004, the chemical edge isolation process based on the single-side removal of the parasitic emitter at the rear side of the solar cells has gained an increasing share of the market in comparison to competing technologies that use laser techniques. However, stabilization and control of such a process under mass production conditions remains challenging. The introduction of new high-efficiency cell concepts involving passivated rear sides will increase the importance of single-side wafer treatments, as the final solar cell performance is significantly affected not only by the complete removal of the parasitic emitter but also by an ideally polished surface on the rear side of the wafer.
PVI Paper
Photovoltaics International Papers, PV Modules
With current state-of-the-art PV module tests stipulating only a static mechanical load test in accordance with IEC 61215 and IEC 61646 standards, hardly any fatigue stressing is carried out on cells, cell connectors or rigid component parts such as the glass or framing. This paper presents research on dynamic load testing of PV modules and discusses reliability aspects of these essential requirements that must be considered in future standardization work.
PVI Paper
Photovoltaics International Papers, PV Modules
Flexible copper-indium-gallium-(di)selenide (CIGS) absorbers offer a wide range of possible applications in rigid as well as flexible and lightweight solar module designs. The main advantage of CIGS in comparison to the well-known flexible module technology based on amorphous silicon is its currently higher efficiency and the promising optimization potential of its efficiency in the future. Because of low cell thicknesses of less than 40µm and the general sensitivity of CIGS to moisture, it is a challenge to develop suitable interconnection and encapsulation technologies that promote long-term reliability of solar modules. Selected aspects of our work in this area will be discussed in this paper.
PVI Paper
Market Watch, Photovoltaics International Papers
Recently, PV demand forecasting has seen greater contributions from countries that had previously been lumped together in the rest-of-world (RoW) bucket – a category previously reserved for the collective PV demand from countries or regions outside of major (FiT-stimulated) European PV markets. Research has shown that PV adoption outside Europe will not simply increase overall PV demand levels, but will assist in smoothing out erratic demand cyclicality. At first glance, the increased gigawattage of demand being added from the RoW grouping provides an essential component in driving long-term industry growth scenarios. Non-European PV demand is forecast to increase from approximately 30% to 60% of global PV demand between 2011 and 2016. However, more tangible benefits of having an increased number of countries feeding into the global demand mix extend beyond just the significant ‘growth’ potential this situation offers to the PV supply chain. Of these various benefits, perhaps the one that will provide the greatest level of comfort to the PV supply chain will be a collective ‘smoothing’ effect in quarterly demand swings. This should have a positive effect on factory shipment schedules and hopefully provide an end to some of the boom-and-bust cycles that have negatively impacted the fortunes of the PV supply chain during 2010 and 2011.
PVI Paper
Fab & Facilities, Photovoltaics International Papers
Although the different roadmaps for PV vary somewhat from each other, the bottom line always remains the same: exponential growth is predicted over the next 5 –10 years. The latest cell technologies meet the demand for grid parity even in central Europe and PV will therefore continue to be the most popular source of renewable energy. In consequence, the whole PV industry has developed from a niche product towards mass production. Every player along the entire value chain is now faced with the need to stay profitable while meeting the ever-increasing demands of the market. Implementing suitable automation can improve competitiveness and thus pave the way to becoming or remaining successful in this turbulent market.
PVI Paper
Fab & Facilities, Photovoltaics International Papers
What does an industry need for sustainable, long-term success? A market, customers and suppliers, and – most certainly – excellent products that can be sold. When looking at various different mature industries there is one thing they all have in common – they have industry-initiated roadmaps! With SEMI’s experience in the semiconductor industry over the last 40 years, the example of the International Technology Roadmap for Semiconductors (ITRS) has proved that pre-competitive industry collaboration among the supply chain and among competitors leads to a reduction in costs, a better time to market and an increased efficiency. Moreover, it helps all players to benefit from jointly solved manufacturing challenges.
PVI Paper
Photovoltaics International Papers, Power Generation
A typical financial structure for a utility-scale (i.e. larger than a few MW) PV project is the so-called ‘non-recourse project financing’. Experience shows that lenders may occasionally refuse financing because they dislike a technology or even a certain supplier. This past behaviour has created the ‘myth of bankability’ and the perceived necessity of manufacturers to get onto the banks’ ‘bankability lists’. But there is no strictly defined process for doing this, and many of the experienced banks do not even work with such lists for good reason. Moreover, ‘bankability’ is not a feature that a manufacturer or a product can achieve or maintain forever.
PVI Paper
Photovoltaics International Papers, Power Generation
India is a unique market. As part of an India-specific strategy on the part of the players, solar capital costs in India have significantly fallen in relation to the global average. This paper describes the trend for lower cost modules and services to be offered by module suppliers and EPC companies in order to capture the greatest share of the Indian market. In this context, more importance is being given to gaining a greater market share than earning a higher return.
PVI Paper
Materials, Photovoltaics International Papers
China has become the largest manufacturing base for crystalline silicon modules in the world, and is becoming increasingly reliant on a domestic supply base. This article discusses the emergence of local supply chains and the strategic responses of global suppliers to this domestic competition. It proceeds to review a set of conclusions from four case studies of formulated material supply within China that can apply to supply chain participants in the PV industry, concluding with some strategic considerations for suppliers on the cusp of entering the Chinese market.
PVI Paper
Photovoltaics International Papers, PV Modules
Low-temperature thermal stresses in a manufactured photovoltaic module (PVM) based on crystalline silicon (Si), before the PVM is fastened into a metal frame, are assessed on the basis of a simple, analytical (mathematical), easy-to-use and physically meaningful predictive stress model. The PVM considered comprises the front glass, ethylene vinyl acetate (EVA) encapsulant (with silicon cells embedded into it) and a laminate backsheet. The stresses addressed include normal stresses that act in the cross sections of the constituent materials and determine their short- and long-term reliability, as well as the interfacial (shearing and peeling) stresses that affect the assembly’s ability to withstand delaminations. The interfacial stresses also determine the cohesive strength of the encapsulant material. The calculated data, based on the developed model, indicate that the induced stresses can be rather high, especially the peeling stress at the encapsulant-glass interface, so that the structural integrity of the module might be compromised, unless the appropriate design-for-reliability (DfR) measures, including stress prediction and accelerated stress testing, are taken. The authors are convinced that reliability assurance of a photovoltaic (PV) product cannot be delayed until it is manufactured – such an assurance should be considered and secured, first of all, at the design stage.
PVI Paper
Cell Processing, Photovoltaics International Papers
The selective emitter (SE) concept features two different doping levels at the front surface of the cell. Both doping profiles are tailored individually to best suit their specific purposes, thus achieving both low contact resistance of the emitter electrode and low recombination in the emitter and at the Si/SiNx:H interface. This paper details the experience gained since the first tools for generating an SE structure were installed two years ago. The approach taken is discussed and a presentation given of the physical concept and properties of SE technology, along with the different aspects that have to be considered when integrating SE into an otherwise unchanged production facility.
PVI Paper
Materials, Photovoltaics International Papers
Solar-grade silicon (SoG-Si) based on metallurgical refining processes, often called upgraded metallurgical-grade silicon (UMG-Si), is expected to play an important role in achieving the solar industry’s necessary cost targets per Wp in order to compete with other energy sources. The broad term ‘UMG-Si’ currently embraces types of silicon feedstock that differ quite substantially in product quality and performance. This paper presents a summary of the work carried out by Elkem on low-cost production of silicon feedstock via a flexible, recycling metallurgical processing route with the lowest carbon footprint on the market. Results are given that qualify Elkem Solar Silicon® (ESS™) as a SoG-Si, with comparable efficiencies to polysilicon (poly-Si) from the traditional Siemens process. The latest results on the performance of modules based on ESS are reported. An indication of the stability of older modules based on SoG-Si feedstock from Elkem is also considered. On the basis of the results, there is no reason to expect modules based on ESS to differ from other commercial modules based on poly-Si. ESS is therefore shown to be a viable alternative to conventional poly-Si, but with the additional benefit of lowering specific energy use and cost per Wp.
PVI Paper
Cell Processing, Photovoltaics International Papers
Texturization of (100) monocrystalline silicon (mono-Si) for solar cells is still an issue in the industrial production of standard screen-printed mono-Si solar cells. This fact is due to the properties of isopropyl alcohol (IPA), which is used together with potassium hydroxide (KOH) in the standard etching solution KOH-IPA (or used with sodium hydroxide NaOH in NaOH-IPA). The low boiling point of IPA (82.4°C) limits the etching temperature and thus the processing speed. Furthermore, KOH-IPA etching solution is very sensitive to the wafer pre-treatment characteristics of as-cut mono-Si wafers. Two ways to overcome these disadvantages are presented in this paper. The first approach involves the use of a high boiling alcohol (HBA) instead of IPA in the standard KOH-IPA etching solution. This allows higher etching temperatures to be used, without evaporation losses of the alcohol, but with reduced etching times. The second approach consists of using a closed etching bath in which vacuum (low-pressure) steps (i.e. pressure oscillations between atmospheric and below-atmospheric pressure) are achievable; in addition, a cooling system located on top of the etching bath allows the liquefaction of the evaporated IPA. The second texturing approach considerably decreases the etching time of mono-Si wafers. Examples of mono-Si wafers were textured using the new KOH-HBA etching solution and then processed into solar cells; the current-voltage results of the processed solar cells are presented.
PVI Paper
Market Watch, Photovoltaics International Papers
Solar photovoltaic (PV) electricity continued its remarkable growth trend in 2011, even in the midst of a financial and economic crisis and despite the PV industry going through a difficult period. Once again PV markets grew faster than anyone had expected, just as they have done for the past decade, especially in Europe but also around the world. While such a rapid growth rate cannot be expected to last forever in Europe, prospects for growth around the world remain high. The results of 2011 – and indeed the outlook for the next several years – show that under the right policy conditions, PV can continue its progress towards competitiveness in key electricity markets and be a mainstream energy source. The major system-price decrease that was experienced in 2011, combined with measures taken in Germany and Italy after the Fukushima nuclear disaster, allowed the market to further develop in 2011, particularly in these two countries. However, the price decrease also helped weaken the policy support in many countries, with policymakers facing growing discontent with regard to the perceived cost of PV and the ailing PV industry in Europe.

Subscribe to Newsletter

Upcoming Events

Upcoming Webinars
August 19, 2021
At 9am (PT) | 6pm (CEST)
Solar Media Events
August 25, 2021
Solar Media Events
October 6, 2021
Solar Media Events
October 19, 2021
BRISTOL, UK