Solar power

Environmental impact of semiconductor material and solar cell production

The research project examined strategies for reduction of greenhouse gases emitted by semiconductor and solar cell production. The project delivers material flow models, environmental impact estimates and an evaluation of exhaust gas treatment technologies in the field of semiconductor production.

Summary

Industrial manufacture of semiconductor materials and solar cells produces substantial amounts of climate-relevant gases such as carbon dioxide CO2, sulphur hexafluoride SF6, nitrogen trifluoride NF3 and perfluorocarbons (PFC). The project therefore examined a range of reduction strategy approaches and analysed optimisation potential. The consortium, consisting of plant manufacturers, factory planners and scientific institutes, divided the project into two work packages: i) development and optimisation of exhaust gas treatment methods and ii) examination of material flows and overall ecological optimisation and strategy formulation. However, substantial changes to the semiconductor market during and prior to the project period, these work packages were modified. Thus, no new technologies for exhaust gas treatment were developed. Instead, existing treatment methods for volatile organic compounds (VOC) were evaluated.

Results:

  • Per m² of semiconductor produced, a total of approx. 3.2 (DRAM wafer) to 9.3 t (logic wafer) of CO2 equivalents are released. This includes all pre-production sequences.
  • Calculations of the CO2 footprint of solar cells supply approx. 31 g of CO2/kWh for the predominant silicon technology, 25 to 35 g CO2/kWh for thin-film silicon technologies and 15 g CO2/kWh for cadmium-telluride technologies.
  • All common production methods for solar cells can be regarded as positive in terms of their energy balance. The determined energy payback periods for cost-effective plants in Southern Europe range from 1 to 1.5 years.
  • Despite local oxidation at 400°C or at 800°C without heat recuperation is the ecologically least favourable variant for treatment of VOC, it has become established in the market.
  • The results of the VOC treatment’s evaluation show that the overall environmental strain is increased rather than reduced through thermal exhaust gas treatment if the exhaust concentrations are low. At higher concentrations, the treatments achieve a reduction of impact on human health but, due to the use of fossil fuels, result in a (long-term) shift of environmental effects.
  • Incorporation of complete environmental data and the corresponding conclusions is so far insufficient within the industries and can be improved through, among other things, suitable communication structures.

More Project Information

Project title: Technologien und Konzepte zur Minderung von Treibhausgasemissionen bei der Herstellung von Halbleiter-Bauelementen und Solarzellen

Project number: 01LS05090

Project period: 2006 - 2009

Project region: Germany (Baden-Württemberg)

Project contact:

Herr Dr. Schottler

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Source: German National Library of Science and Technology Hannover (TIB)