Fig. 1. The City of Wilmington in Delaware, USA, is installing two solar photovoltaic arrays.
Research in Europe and Japan has shown that the efficiency of solar cells can be substantially improved. At the same time, solar power is being increasingly adopted as part of mixed renewable energy projects around the world. Sean Ottewell reports.
Forschungen in Europa und Japan haben gezeigt, dass sich die Effizienz von Solarzellen erheblich steigern lässt. Gleichzeitig wird Solarstrom überall auf der Welt immer häufiger in gemischte erneuerbare Energieprojekte aufgenommen. Ein Bericht von Sean Ottewell.
Des recherches menées en Europe et au Japon ont démontré que l’efficacité des cellules solaires pouvait être sensiblement améliorée. Parallèlement, l’énergie solaire est de plus en plus souvent adoptée dans le cadre de projets d’énergie renouvelable mixtes dans le monde. Dossier de Sean Ottewell.
New solar-grade silicon feedstock ups efficiency
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ased in Norway, the SINTEF Group is the largest independent research organisation in Scandinavia. It has just finished co-ordinating the EU’s three-year FoXy programme
which drew together participants from 10 other organisations to focus on the development of solar- grade silicon feedstock for crystalline wafers and cells by purification and crystallisation. And there has been no lack of results: a series of
joint sub-projects and work-packages has enabled the scientists to develop a new, less expensive grade of raw material for solar cells. And the best news is that the new modules are just as efficient as current solar cells. The ambition of the programme has always been to develop a new material that would make future solar cells both at least as efficient as those of today and cheaper than them. “We are very proud of what we have done,”
says Marisa Di Sabatino of SINTEF Materials and Chemistry. “Many people before us have been working on solar energy, but our results are actually quite important. We started out with metallic silicon that contains around one per cent impurities - which is not good enough for use in solar cells. We attempted both to reduce the impurities in the metallic silicon and to cut down the amount of
impurities that are already in the raw material by means of heat treatment, for example,” she explains. The research group managed to shorten the long
production process currently employed by most solar cell manufacturers by adopting a simpler, more direct route. They managed this by using a special smelter and a kiln that removes trace of carbon. The scientists used pure carbon that contaminates
the silicon far less than coke or coal, as well as ultrapure quartz from the Norwegian County of Nordland. This process is much less costly and energy-
intensive than the conventional chemical process. “With today’s solar cells, the energy used to produce them is paid off in the course of two years: with the new materials, the payback time could be as little as six months,” added Di Sabatino. Impurities in silicon cause problems. For example,
silicon recycled from industry contains boron and/or phosphorus that can alter the electrical characteristics of the material. Other contaminants can, for example, lead to the formation of poor-quality particles that in turn mean less efficient solar panels. However, the project group concluded that even if
contaminants are present, we can still produce good- quality material with the aid of special procedures that reduce or eliminate them. It is just a matter of
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