Scientific Comment of Fraunhofer to Life Cycle Assessement of CdTe Photovoltaics

Fraunhofer-Center für Silizium-Photovoltaik CSP

Several studies have been carried out over the last years to investigate the environmental profile of CdTe photovoltaics and energy pay-back time. The most recent studies are based on the module production data of First Solar from 2004-2011 [1]-[3], [5], [7], [15], [16] and Abound Solar [10].

(28.02.12)

The last two years have seen some development in the field of production of cadmium telluride PV modules. Whereas First Solar remains the biggest producer of this PV technology, a couple of other manufacturers emerged, among them Abound Solar, Calyxo and GE Energy. The most representative life cycle analysis results on CdTe PV modules are based on First Solar data and have been updated in 2011. In addition LCA data based on the production process of Abound Solar confirms the overall LCA profile of CdTe PV. Recent LCA studies were mainly carried out from de Wild-Scholten [11] and Held and Ilg [12], which all use comprehensive inventory data of First Solar, the leading CdTe PV module producer.

All current studies account for caused life cycle emissions throughout the whole life cycle of CdTe photovoltaic modules. In 2009 the potential life cycle emissions of CdTe PV module recycling processing have been added to the evaluation [14], [15]. All studies come to similar conclusions and show that CdTe PV Modules exhibit environmental advantages in comparison with conventional power generation technologies using fossil fuels (e.g. oil, coal, gas) regarding environmental impacts on global warming, acidification, eutrophication, summer smog, primary energy demand. In addition, CdTe PV has been found to produce environmental Cd emissions to air that are no higher than those from conventional silicon PV technologies on a life cycle basis [3].

Recent more application-specific life cycle analysis of CdTe PV modules has been performed for roof-mount [11] and ground-mount [12] systems.  The evaluations consider the influence of differences in production and installation locations, respectively, on life cycle product impacts.  Because of the relatively low energy requirements for CdTe PV production, life cycle impacts of CdTe PV are less sensitive to differences in manufacturing location than other PV technologies, and CdTe PV has the lowest carbon footprint and energy payback time in the industry [11]. While prior life cycle analysis of CdTe PV has been largely based on data provided by First Solar, recent life cycle analysis performed by Boustead Consulting on Abound Solar CdTe PV modules has found comparable results with regards to carbon footprint and energy payback time [10].

Toxity Assessment

Most of the currently available studies investigate the caused life cycle emissions on a quantitative level [1] but do not evaluate the emissions in terms of toxicity indicators. Held [15] stated that impact categories addressing toxicity aspects were not applied on impact category level since characterization methods are unstable and still under development. Therefore, no definite conclusion can be drawn since a commonly agreed characterization method referring to the recommendation of Apledoorn declaration from April 15th 2004 development [39]-[41] is missing. Moreover, the decision of SEES, D7 report categories are still under scientific discussion and development. As a result different models produce very different results for the same toxicity impact categories [42].

With regards to Classification & Labeling of the compound CdTe, toxicity testing has recently been evaluated related to acute inhalation and oral toxicity, reproductive/developmental toxicity, mutagenicity, bioavailability, solubility, and acute aquatic toxicity [32]-[38] . CdTe exhibits aqueous solubility and bioavailability properties that are approximately two orders of magnitude lower than the 100% solubility and bioavailability of ionized cadmium chloride (CdCl2), which means that CdTe does not readily release the reactive ionic form of Cd (Cd2+) upon contact with water or biological fluids. CdTe has low acute inhalation, oral, and aquatic toxicity, and is negative in the Ames mutagenicity test.  Based on notification of these results to the European Chemicals Agency (ECHA), CdTe is no longer classified as harmful if ingested nor harmful in contact with skin, and the toxicity classification to aquatic life has been reduced. Therefore, compound CdTe clearly cannot be classified by regulations of metallic Cadmium or other Cadmium compounds but has to be classified individually.

Risk Assessment

The currently available life cycle analysis studies of CdTe PV modules assume that there are no unexpected incidents in the modules life cycle and that spent modules are disposed correctly or recycled in the end of life. Because life cycle analysis is used to model routine impacts of a product during its intended use, evaluating impacts of non-routine events (e.g., fire, leaching) has been addressed in several risk assessment studies. Main concerns of CdTe technologies are unexpected incidents, like released emissions in case of fire or uncontrolled disposal and leaching to ground water.

For example, recent risk assessment of rainwater leaching of broken modules and emissions from fire has modeled media-specific exposure point concentrations of Cd in soil, air, and groundwater, concluding that they are highly unlikely to pose potential health risks to residents, workers, consumers, or emergency responders [28].  Potential health risks from ground-mount CdTe PV installations on agricultural lands were also recently evaluated by the Bavarian Agricultural Agency [29]. Risks from potential leaching were found to be minimal.

The first fire simulation emissions testing  for BP Solar Apollo CdTe PV modules was carried out by the Fire Research Station in the UK  in the name of BP Solar [30]. Ten minute average concentrations of Cd in an 800-900 ˚C fire were measured with continuous sampling methodology, yielding air concentrations of 1.33 and 500 µg/m3 in gas and particle phase, respectively.  These concentrations are below the acute exposure guideline (AEGL) for 10 min exposure to Cd in air (1400 µg/m3; AEGL-2 guideline for disabling, irreversible or long-term adverse effects).

In 2005 Fthenakis [23] performed fire simulations between 760-1100°C according to standard fire test procedures to investigate the potential emissions of Cd and CdTe. Based on the results Fthenakis concludes that released Cd emissions of typical residential fires (760°C-900°C) are negligible. This study has been criticized by stating that the tests did not reflect the conditions of real fire cases, in particular in terms of changing temperature distributions during fires, different orientations of modules and temperatures higher than 1100°C. However, the test have been carried out according to ASTM and UL standards and evaluated as correct by the EU [25].

More recently, an independent experimental study on fire, worst-case fire dispersion modeling (assuming total release of Cd from CdTe PV modules), has been conducted by the Bavarian Environmental Agency [31]. Ground-level Cd concentrations in air under stable atmospheric conditions (inversion layer at 20 m) at 100 m downwind of a roof-top CdTe PV fire were estimated to range from 30-600 µg/m3, which is also substantially below AEGL-2 guidelines.

Concerning leaching, there are several independent studies of CdTe Modules concerning mass concentration test and standard leaching tests commonly used in the European Union to assess whether or not a waste is hazardous and what type of landfill may accept the waste [26], [27]. These tests confirmed the European Waste classification of CdTe PV modules as non-hazardous waste and that they could be disposed of in ordinary landfills in accordance with European waste laws. This is also confirmed by independent waste characterization certificates of the module producers First Solar and Calyxo currently available on the market.

In conclusion, currently standard test procedures have been carried out for unexpected incidences in case of fire and disposal.

Requirement for further research and standardization

Since a number of new CdTe producers have entered in the last years the CdTe module market,there are more very detailed life cycle emission studies available for different kinds of inventory data including recycling issues. The initial data base of First Solar seems to be representative also for other CdTe companies. We still recommend for the future individual  LCA and waste characterization certificates for all new CdTe Companies entering the market since the database is still too low with three companies.

Concerning the risk and toxicity assessment of CdTe photovoltaic modules, the number of studies world wide indicate that CdTe cannot be classified by Cd in this particular application case and regulation authorities have to define application specific regulation of CdTe.

Selected Literature and further reading

Life cycle analysis studies  

[1]       Fthenakis V.M. Sustainability of photovoltaics: The case for thin-film solar cells. Renewable and Sustainable Energy Reviews 2009; 13: 2746–2750

[2]       Fthenakis V.M., Raugei M., Held M. Update of environmental impacts and energy payback times of photovoltaics. 24th European Photovoltaic Solar Energy Conference (EU PVSEC), 2009; 6DO.10.5

[3]       Fthenakis V.M., Kim H.C., Alsema E. Emissions from photovoltaic life cycles.  Environmental Science & Technology. 2008; 42 (6), 2168-2174

[4]       Raugei, M., Bargigli, S., Ulgiati. S. Life cycle assessment and energy pay-back time of advanced photovoltaic modules: CdTe and CIS compared to poly-Si. Energy, 2007; 32: 1310–1318

[5]       Fthenakis V.M., Kim H.C. CdTe Photovoltaics: Life-cycle environmental profile and comparisons, Thin Solid Films, 2007; 515: 5961-5963

[6]       SENSE. Sustainability Evaluation of Solar Energy Systems. Summary Report on LCA Analysis. 2006; www.sense-eu.net

[7]       Fthenakis V.M., Alsema E. Photovoltaics Energy Payback Times, Greenhouse Gas Emissions and External Costs: 2004 – early 2005 Status. Progress in Photovoltaics Research and Applications, 2006; 14: 275-280

[8]       Fthenakis V. Life Cycle Impact Analysis of Cadmium in CdTe Photovoltaic Production. Renewable and Sustainable Energy Reviews. 2004; 8: 303-334

[9]       Fthenakis V. Life cycle impact analysis of cadmium in CdTe PV production, Renewable and Sustainable Energy Reviews 2004; 8: 303-334

[10]    Boustead Consulting & Associates, Ltd., Analysis of Environmental and Energy benfits of “AVA Solar manufacturing Facilities” project, 2009

[11]    de Wild-Scholten, M. Environmental Profile of PV Mass Production: Globalization, 26th European Photovoltaic Solar Energy Conference, Hamburg, Germany, 2011

[12]    Held, M., Ilg, R. Update of environmental indicators and energy payback time of CdTe PV systems in Europe. Progress in Photovoltaics Research and Applications, 19:614-626, 2011

Recycling

[13]    Reckziegel, C. Recycling in der Photovoltaikindustrie – Stand und Perspektiven; Recycling und Rohstoffe, Band 3, 2010; ISBN 978-3-935317-50-4, P677-689

[14]    Held, M., Ilg, R., Ökobilanz des Recyclings von CdTe Dünnschichtsolarmodulen, Recycling und Rohstoffe, Band 3, 2010; ISBN 978-3-935317-50-4; P691-706

[15]    Held, M.; Life Cycle Assessment of CdTe module recycling, 24th European Photovoltaic Solar Energy Conference (EU PVSEC). 2009; 3CO.7.4

[16]    Sander K., Schilling S., Reinschmidt J., Wambach K., Schlenker S., Müller A., Springer J., Fouquet D., Jelitte A., Stryi-Hipp G., Chrometzka T. , 2007. Study on the development of a take back and recovery system for photovoltaic products. PVCYCLE association

Balance of Systems

[17]    Mason T., Fthenakis V.M., Kim H.C. Energy Payback and Life Cycle CO2 Emissions of the BOS in optimized 3.5 MW PV installation. Progress in Photovoltaics Research and Applications, 14:179-190, 2006 (Comment: electronic components are only represented by material production)

Cadmium Flows and Emissions

[18]    Raugei, M., Fthenakis, V. Cadmium flows and emissions from CdTe PV: future expectations. Energy Policy (2010), doi:10.1016/j.enpol.2010.05.007

[19]    Held, M., Ilg, R. Life Cycle Assessment (LCA) of CdTe thin film modules and Material Flow Analysis of cadmium within EU27. 23rd European Photovoltaic Solar Energy Conference (EU PVSEC), 2008, 3BV.4.25

[20]    Fthenakis, V. et al., Environmental Impacts of PV electricity generation – A comparison of energy supply options, European Photovoltaic Solar Energy Conference (EU PVSEC), 2006, 8CO.1.3

[21]    Oosterhuis, F.H., Brouwer, F.M. and Wijnants, H.J. A possible EU wide charge on cadmium in phosphate fertilizers: Economic and environmental implications. 2000; Institute for Environmental Studies, Amsterdam, The Netherlands.

Risk Assessment

[22]    ECB, 2007. European Union Risk Assessment Report: Cadmium metal and Cadmium oxide, final report. European Chemicals Bureau. ecb.jrc.ec.europa.eu/existingsubstances

[23]    Fthenakis, V.M., Fuhrmann, M. Heiser, J., Lanzirotti A., Fitts J. and Wang, W., 2005. Emissions and Encapsulation of Cadmium in CdTe PV Modules During Fires, Progress in Photovoltaics: Research and Applications 13, 717-723.

[24]    UNEP, 2006. Interim review of scientific information on cadmium. United Nations Environmental Programme. Link

[25]    Jaeger-Waldau et al. "Peer Review on major published studies on CdTe (Full Report)" European Commission DG JRC 2005

[26]    Environmental risks regarding the use and end-of-life disposal of CdTe PV modules, NGI Report no. 20092155-00-1-R, February 17th, 2010.

[27]    Steinberger, H.: Health, Safety and Environmental Risks from the Operation of CdTe and CIS Thin-film Modules, Progress in Photovoltaics: Research and Applications, 1998; 6, 99-103.

[28]    Sinha, P., R. Balas, and L. Krueger, Fate and Transport Evaluation of Potential Leaching and Fire Risks from CdTe PV. 37th IEEE Photovoltaic Specialist Conference, Seattle, WA, 2011

[29]    Ebert, T., Muller, C., Schadstoffe in Photovoltaik – Freiflächenanlagen – Eine Gefahr für den Boden? Bodenschutz, 16(3): 69-74, 2011

[30]    Patterson, M. H., Turner, A. K., Sadeghi, M., Marshall, R.J., Health, Safety, and Environmental Aspects of the Production and Use of CdTe Thin Film Photovoltaics Modules. 12th European Photovoltaic Solar Energy Conference, Amsterdam, Netherlands, 1994

[31]    Beckmann, J., Mennenga, A., Berechnung von Immissionen beim Brand einer Photovoltaik-Anlage aus Cadmiumtellurid-Modulen.  Bayerisches Landesamt für Umwelt, Augsberg, Germany. Available at: www.lfu.bayern.de/luft/doc/pvbraende.pdf., 2011

Toxicity Assessment

[32]    Zayed, J and Philippe, S. Acute Oral and Inhalation Toxicities in Rats with CdTe, Int. J. Toxicology 28, 259-265, 2010

[33]    Kaczmar, S., Evaluating the read-across approach on CdTe toxicity for CdTe photovoltaics, Society of Environmental Toxicology and Chemistry North America 32nd Annual Meeting,  Boston, MA, 2011

[34]    Chapin, R. E., M.W. Harris, J. D. Allen, E. A. Haskins, S. M. Ward, R. E. Wilson, B. J. Davis, B. J. Collins and A. C. Lockhart, The systemic and  reproductive toxicities of copper indium diselenide, copper gallium diselenide and cadmium telluride in rats’, Understanding and Managing Health and Environmental Risks of CIS, CGS, and CT Photovoltaic Module Production and Use: A Workshop (BNL-61480), eds. P. D. Moskowitz, K. Zweibel and M. P. DePhillips, Brookhaven National Laboratory, Upton, NY,1994 (Chapter 2)

[35]    Agh, The testing of cadmium telluride with bacterial reverse mutation assay. Lab Research Ltd, Veszprém, Hungary, 2010

[36]    Brouwers, T. Bio-elution test on cadmium telluride. ECTX Consult, Liège, Belgium, 2010

[37]    Brouwers, T. Long term transformation/dissolution test of cadmium telluride. ECTX Consult, Liège, Belgium, 2010

[38]    Agh, Acute toxicity test with cadmium telluride on zebrafish. Lab Research Ltd, Veszprém, Hungary, 2011

Apledoorn declaration and related publications

[39]    Declaration of Apeldoorn on LCIA of Non-Ferrous Metals, Apeldoorn, April 15th, 2004, www.chem.unep.ch

[40]    SEES, Sustainable Electrical & Electronic System for the Automotive Sector (TST3-CT-2003-506075), D7: Economical and Environmental Assessment, 2005; www.seesproject.net/contents/File/D7_Report.pdf

[41]    TNO Environment, Energy and Process Innovation, Report R2004/347, “Improvement of LCA Characterization factors and LCA practice for metals”, www.leidenuniv.nl/cml/ssp/projects/finalreportmetals.pdf

[42]    Development of LCA toxicity impact characterization factors is complicated by multiple LCA impact methods (e.g., CML, Eco-indicator, IMPACT 2002+, ReCiPe, USEtox) that are not comparable due to different endpoints and units, and the complexity of fate and transport analysis in modeling the migration of chemicals from the emission point to the point of exposure.  Improving the understanding of toxicity impact characterization factors is a complex and long-term research area that will benefit from improved understanding of CdTe toxicity, fate and transport analysis, and harmonization of existing impact methods. Currently, LCA toxicity impact characterizations are not recommended as a basis for business or policy decision making, consistent with working procedure #1 from the Apeldoorn declaration.

 

Fraunhofer Institute for Building Physics
Contact:
Dipl.-Ing. Michael Held
E-Mail Michael.Held@ipb.fraunhofer.de

Fraunhofer Center for Silicon Photovoltaics
Contact:
Dr. Christian Hagendorf
E-Mail Christian.Hagendorf@csp.fraunhofer.de
Prof. Dr. Jörg Bagdahn
E-Mail Joerg.Bagdahn@csp.fraunhofer.de

Fraunhofer Institute for Mechanics of Materials
Contact:
Prof. Dr. Ralf B. Wehrspohn
E-Mail Ralf.Wehrspohn@iwmh.fraunhofer.de