Cloudbusting

Forecasting | Short-term PV forecasting offers a multitude of benefits, from trading on wholesale power markets to improved plant operation. Sara Verbruggen reports on some of new the technologies driving forward improvements in the accuracy of forecasting techniques.

Potential induced degradation (PID): a test campaign at module level

By J. Carolus, Hasselt University and imec vzw; M. Daenen, Hasselt University and imec vzw

Potential induced degradation (PID) of photovoltaic (PV) modules gets a lot of attention since 2010 when Solon published their findings about a degradation mechanism in their PV modules caused by high potential differences. When multiple PV modules are connected in series, a potential difference up to 1000 V or at some places even 1500 V is created between the cell and the grounded frame. This electrical field causes a leakage current and ion diffusion. PID is a multi-level degradation with causes and solutions at cell, module and system level. A test campaign was conducted within the frame of a feasibility study for pidbull, a curing technology for PID developed by pidbull nv. 80 PV modules were characterized whereof 49 PV modules were stressed and cured for PID. The selected set of PV modules was composed of 49 different module types of 33 brands. The test was done according to the foil-method, as described by the standard in progress IEC 62804. However, to apply higher stressing and curing rates, the modules were tested with an aluminium foil inside a climate chamber for 96 hours. After the stress test, only 22% of the tested modules passed the 5% loss criteria as described by IEC 62804. In other words, 78% out of a set of today's most installed PV modules in Flanders are PID sensitive. Remarkable is that only 16 out of the 49 PV modules have less than 20% PID after the stress test. Additionally, a linear trend for PID reversibility was shown for modules with a stress level of less than 85%. The modules which lost more than 85% due to PID showed a lower recovery rate or in worst case didn’t recover at all.

Innovation for optical, electrical and economic improvement of thin-film PV technology

By Joop van Deelen & Marco Barink, TNO

Innovation in the field of thin-film cells, in addition to economy of scale and the manufacturing learning curve, is an important element in keeping the price of this technology competitive. Most papers on these cells focus on their technology; however, the economic potential of the technology is also important. Of even greater significance, a realistic estimation of the potential, along with the associated costs, of advanced technology, is part of the equation for profitability. Two examples of technology – metallic grids and texturing – are given in this paper; the designs are discussed, and a brief economic analysis is presented for various scenarios of the technologies. Although the profitability of these technologies can be considerable, it is shown that one should be wary of basing decisions purely on potential and on ideal scenarios, and how the cost of a technology can turn a great prospect into a trade-off.

Technical progress in high-efficiency solar cells and modules

By Rulong Chen, Xi Xi, Jie Zhou, TingTing Yan & Qi Qiao, Wuxi Suntech Power Co., Ltd

This paper focuses on the technical progress of high-efficiency crystalline silicon solar cells and modules, specifically with regard to passivated emitter and rear cell (PERC) processes, module description and light induced degradation (LID) data. Through appropriate optimizations of the solar cell and module processes, the cell efficiency achieved in mass production is 21.3%, with module power exceeding 300W. To solve the LID problem, hydrogenation technology developed by UNSW is used, bringing the cell LID rate down to below 1%.

PV manufacturing capacity expansion plans in 2016 exceeded 55GW

By Mark Osborne, Senior News Editor, Photovoltaics International

In this quarterly report on global PV manufacturing capacity expansion announcements we will provide a detailed analysis of 2016. Despite a significant slowdown in new announcements in the second half of the year, 2016 surpassed 2015 by around 16% to exceed a total of 55GW of thin-film, dedicated solar cell and module assembly and integrated PV expansion plans.

Quo vadis bifacial PV?

By Radovan Kopecek & Joris Libal, ISC Konstanz

This paper presents a summary of the status of bifacial PV in respect of the technology in mass production, the installed PV systems, and the costs relating both to module production (cost of ownership – COO) and to electricity (levelized cost of energy – LCOE). Since the first bifacial workshop, organized by ISC Konstanz and the University of Konstanz, in 2012, many things have changed. Bifacial cells and modules have become cost effective, with installed systems now adding up to more than 120MWp and the technology becoming bankable. Large electricity providers have recognized the beauty of bifacial installations, as the lowest costs per kWh are attainable with these systems. The authors are sure that by the end of 2017, bifacial PV systems amounting to around 500MWp will have been installed, and that by 2025 this type of system will become the major technology in large ground-mounted installations.

Progress in co-plating contacts for bifacial cells designed for multi-wire interconnection

By Richard Russell, Loic Tous, Emanuele Cornagliotti, Angel Uruena de Castro, Filip Duerinckx & Jozef Szlufcik, Imec, Kaneka Belgium N.V.

For many applications, bifacial modules offer a cost-effective way of increasing energy yields, which explains why the interest in bifacial cells in the PV industry is steadily growing and is expected to continue. However, the metallization of bifacial cells creates new challenges, as the same materials and techniques developed for n surfaces are generally not directly, or simultaneously, applicable to p surfaces; this necessitates sequential metallization of each side, resulting in added cost and/or complexity. This paper introduces a simple co-plating approach with the objective of simplifying the metallization of bifacial cells in a cost-effective way, and which is designed for multi-wire module integration. The metallization route is described, and high cell efficiencies of up to 22.4% are demonstrated using this co-plating approach with bifacial nPERT+ cells (where ‘+’ signifies the bifacial nature of these cells). Initial thermal-cycling reliability data of test structures and 1-cell laminates is presented. Finally, cost-of-ownership (COO) estimates are given, which predict the co-plating approach to be ~40% cheaper than bifacial screen-printed metallization. It is shown that the combination of the high efficiency potential of nPERT+ cells and the reduced costs of co-plating has the potential to deliver module-level costs of ~$0.25/Wpe (glass–glass configuration).

In-line quality control in highefficiency silicon solar cell production

By Johannes M. Greulich, Jonas Haunschild, Stefan Rein, Lorenz Friedrich, Matthias Demant, Alexander Krieg & Martin Zimmer, Fraunhofer Institute for Solar Energy Systems ISE

There are numerous tools and methods available on the market for the optical and electrical quality control of high-efficiency silicon solar cells during their industrial production, and even more are discussed in the literature. This paper presents a critical review of the possibilities and limitations of these tools along the value chain, from wafer to cell, in the case of passivated emitter and rear cells, as well as a discussion of some showcases. Economic and technological challenges and future trends are addressed.

HPM silicon: The next generation of multicrystalline silicon for PV

By Matthias Trempa, Iven Kupka, Christian Kranert, Christian Reimann & Jochen Friedrich, Fraunhofer IISB, Fraunhofer THM

High-performance multicrystalline (HPM) silicon, achieved by nucleation on special seed layers at the crucible bottom, is now increasingly replacing conventional multicrystalline (mc) silicon, which is solidified on the standard silicon nitride coating. The HPM material is characterized by a very fine initial grain structure consisting of small, regularly shaped grains surrounded by a large number of random-angle grain boundaries. These grain structure properties, which differ significantly from those of conventional multicrystalline silicon, lead to a much lower dislocation content in the material, and therefore result in higher efficiencies of the silicon solar cells produced. This paper gives a rough overview of the worldwide R&D activities on HPM silicon in recent years, supplemented by several research results obtained at Fraunhofer IISB/THM. The focus is on the different seeding methods, the grain structure properties and the development of the grain and defect structure over the ingot height, as well as on the main challenges for further improvements in material quality and production costs.

Solar PV manufacturing in 2017: factors driving technology change

By Finlay Colville, Head of Market Research, Solar Media Ltd

Having installed more than 75 gigawatts in 2016, the solar industry continues to create opportunities for cell and module manufacturers to expand capacities, while upgrading technologies and improving process flows. Supply remains dominated by p-type crystalline silicon modules, despite ongoing research into n-type variants and the addition of PERC on p-type mono cells. The efficiency increases from p-type mono are now driving p-type multi cell producers to accelerate changes to production lines from both black silicon and PERC. This is now setting new benchmarks for the supply of solar modules in 2017 to utility-scale solar installations.

19.31%-efficient multicrystalline silicon solar cells using MCCE black silicon technology

By Xusheng Wang, Shuai Zou & Guoqiang Xing, Canadian Solar Inc. (CSI)

A novel nanoscale pseudo-pit texture has been formed on the surface of a multicrystalline silicon (mc-Si) wafer by using a metal-catalysed chemical etching (MCCE) technique and an additional chemical treatment. A desirable nanoscale inverted-pyramid texture was created by optimizing the recipe of the MCCE solution and using a proprietary in-house chemical post-treatment; the depth and width of the inverted pyramid was adjustable within a 100–900nm range. MCCE black mc-Si solar cells with an average efficiency of 18.90% have been fabricated on CSI’s industrial production line, equating to an efficiency gain of ~0.4%abs. at the cell level. A maximum cell efficiency of 19.31% was achieved.

The Global Energy Storage Opportunity

This special supplement on energy storage looks at a global market which has already come a long way and shows no sign of looking back. From residential to grid-scale, to microgrids and vehicle-to-grid, from safety to finance, we’ve condensed some of the biggest topics and themes into a handy collection which we hope will help illuminate and inform you all. Energy storage is growing into a cornerstone of the grid (and is arguably even more important off-grid); a vital component of decentralised, decarbonised and even digitalised future energy systems. Yet so many misconceptions and concerns remain and there is still so much work to be done in helping stakeholders gain a better understanding of what batteries – and other forms of energy storage – can do.

The risks and returns of African PV

By Danielle Ola , Solar Media - Reporter

Finance | Danielle Ola looks at some of considerations of investors looking to capitalise on the opportunities for solar in Sub-Saharan Africa.

Preventive O&M - Maximising PV plant availability

By Arnoud Klaren, Arnoud Klaren is Foresight’s senior portfolio manager and technical director for UK and Spain. He joined Foresight in 2011 from SolFocus, where he spent four years managing solar projects in Spain, Saudi Arabia and Greece based on concentrated PV technology. Prior to SolFocus he founded and managed ThinkSpectrally, a spin-off company of the University of Valencia in Spain, dedicated to quality assurance in PV manufacturing.

Asset management | As one of the biggest utility PV owners in the UK, Foresight has extensive experience of getting the most out of operational solar plants. Its technical director Arnoud Klaren draws on some of the lessons the company has learned from minimising the risks that affect solar projects over their lifetime.