A Comparative Life Cycle Assessment of PV Solar Systems Kristine Bekkelund Master of Energy and Environmental Engineering Submission date: August 2013 Supervisor: Anders Hammer Strømman, EPT Norwegian University of Science and Technology Department of Energy and Process Engineering Comment to master thesis description In agreement with supervisor and co-supervisor, a slight change in the object of the master thesis has been done. It has been decided to perform a comparative life cycle analysis on different PV technologies rather than conducting a detailed analysis on thin film alone. The scope has been broaden to include multicrystalline silicon PV technology in order to assess the relative competiveness with thin film PV technology in terms of environmental impact. Life cycle inventories should be collected and harmonized. In addition, it has been decided to perform a sensitivity analysis on selected parameters and compare the results with existing renewable energy technology, in this case wind power. The main focus of the sensitivity analysis will be on climate change (GWP). Future implications and possible improvements of the PV value chain should be discussed. i ii Preface This is the preface of the report "A Comparative Life Cycle Assessment of PV Solar Systems" written during the spring of 2013, as part of my master degree in "Science and Technology - Energy and Environment" at the Norwegian University of Science and Technology (NTNU) in Trondheim, Norway. I have learnt a lot from working with this master thesis and have gained interesting insight in the infinite field of photovoltaics. I would like to thank all the people who have shared their valuable knowledge with me: First, I would like to thank my supervisor Anders Hammer Strømman for academic support and guidance during weekly meetings. Thank you for facilitating the working schedule to better suit my needs during this semester. A big thank you goes to my co-supervisor, Thomas Gibon, for having an open door at anytime, useful discussions and help with all of my questions. I would also like to thank Joe Bergesen for quick feedback on all my questions! Thank you to Jon Helge Lande and Marit Torp at Elkem in Kristiansand for clarifying information on the Elkem Solar Silicon production process, Anders Arvesen for help on GWP values from wind power, Turid Worren Reenaas and Marika Edoff for thin film information, Linda Ager-Wick Ellingsen for excel-help! This past year has posed unexpected challenges. I would not have been able to get through it without some very special people around me: I would like to thank my classmates at the program of Energy and Environment; you know who you are! Thank you for all the laughter and jokes during lunches and dinners, keeping the spirit up! Thank you for all the fun times and hard work we have shared together through five amazing years in Trondheim! I would also like to thank all of the wonderful people in NTNUI Swing and folkedans; for giving me something else than school to think about and sharing my love for dance. A special thank you goes to my good friends Eline Rangøy and Astrid Eikill for all the support, love and encouragement during some rough periods, giving me the motivation to keep up my work. Thank you for being so understanding! Finally, I would like to thank my loving family, especially my mother, Anne-Grete Ruud Bekkelund, for continuously supporting me through good and bad times, and for always believing in me. Kristine Bekkelund Trondheim, August 2013 iii iv Abstract In this report, a comparative life cycle assessment (LCA) of a rooftop, grid-connected photovoltaic (PV) system has been conducted. The primary objective has been to assess the environmental impacts resulting from the PV system over its entire lifetime, while the secondary goal has been to perform a sensitivity analysis on selected parameters and compare the results with the impacts from wind power. Four different cases have been assessed: Mc-Si Sim, mc-Si ESS, CdTe and CIGS. The difference between the multicrystalline silicon (mc-Si) cases were the production method for solar grade silicon: One case used the most common, chemical method; the modified Siemens process (mc-Si Sim), while the other case used the metallurgical route developed by Elkem Solar (mc-Si ESS). With a few minor exceptions, mc-Si Sim gave the highest environmental impacts, including the global warming impacts (GWP). The thin film technologies, CdTe and CIGS, had significantly lower impact potentials than the mc-Si cases, while the difference between the two were small. The relative contribution from processes to the impacts scores were different within each case investigated: The energy intensive steps for silicon purification were large contributors in the mc-Si cases, in addition to the PV module manufacturing, which was the dominating contributor in the thin film cases. In all cases, the metal depletion potential was dominated by the inverter and cabling components, due to their use of metals like copper and tin. Metallizarion pastes used in the mc-Si solar cell production contributed to toxicity potentials. Contributions from other processes in the PV value chains were less 2 significant. The GWP-scores in kg CO2-eq./m of PV system were found to be 260 for mc-Si Sim, 155 for mc-Si ESS, 75 for CdTe and 86 for CIGS. Main contributors were the energy feed stock used in the solar grade silicon production (mc-Si cases), and the primary aluminium and glass used in manufacturing of the PV module (all cases). A base case was used for comparison with existing LCA studies, giving corresponding GWP-scores of 42,5, 30,8, 16,8 and 20,6 g CO2-eq./kWh, which are within the range of published values. The current thin film technologies are already competitive with wind power in terms of GWP. By performing different combinations of improvement measures, all cases, except mc- Si Sim, could achieve GWPs as low as 5,1-5,8 g CO2-eq./kWh (below the minimum value of wind power). Switching the electricity supply towards a higher share of renewable energy and improving in the conversion efficiencies will have a significant effect in reducing the GWP. To improve the material efficiency, manufacturing waste should be reduced and recycled, and the solar cells should be made thinner. The silicon purification methods need to be made more energy efficient by e.g. implementing energy recovery, using biogenic carbon sources as reduction agents or switch from using the modified Siemens method to using more energy efficient methods like the Elkem Solar Silicon production process or the Fluidized Bed Reactor process. Recycled aluminium or steel should be used for the frame of the PV module and the mounting structure. End-of-life PV modules should be recycled to reduce the demand for primary material, e.g. aluminium, glass and rare metals. v vi Sammendrag I denne rapporten har det blitt gjennomført en sammenlignende livssyklusanalyse (LCA) av et solcellepanel, som er montert på tak og koblet til strømnettet. Hovedmålet har vært å vurdere miljøpåvirkningene fra solcellepanelet over hele livsløpet, mens det sekundære målet har vært å gjennomføre en sensitivitetsanalyse på utvalgte parametere og sammenligne resultatene med miljøpåvirkningene fra vindkraft. Fire ulike alternativer ble undersøkt: Mc-Si Sim, mc-Si ESS, CdTe og CIGS. Forskjellen mellom de multikrystallinske silisium (mc-Si) alternativene var metoden som ble bruk til å produsere superrent silisium: Et alternativ brukte den mest vanlige, kjemiske metoden; den modifiserte Siemens- prosessen (mc-Si Sim), mens det andre alternativet brukte en metallurgisk metode utviklet av Elkem Solar (mc-Si ESS). Potensialet for miljøpåvirkninger var med få unntak høyest for mc-Si Sim, inkludert global oppvarming (GWP). Tynnfilmteknologiene, CdTe og CIGS, hadde signifikant lavere potensialer for miljøpåvirkning enn mc-Si tilfellene, mens forskjellen mellom de to var små. Det relative bidraget fra ulike prosesser til potensialene for miljøpåvirkning var ulikt innenfor hvert enkelt alternativ: Den energikrevende stegene for rensing av silisium var de største bidragsyterne i mc-Si-tilfellene, i tillegg til modulproduksjonen, som var den dominerende bidragssyteren i tynnfilm-tilfellene. I alle tilfellene dominerte komponenter til inverter og kabler potensialet for mineraluttømming pga. bruken av metaller som kopper og tinn. Bruk av metalliseringspasta i producksjonen av mc-Si solceller bidro til toksisitetspotensialene. Bidraget fra andre prosesser i verdikjeden var av mindre betydning. GWP verdiene i kg CO2- ekv./m2 solcellepanel ble beregnet til å være 260 for mc-Si Sim, 155 for mc-Si ESS, 75 for CdTe og 86 for CIGS. De største bidragsyterne var knyttet til energikildene som brukes i produksjonen av superrent silisium, og aluminium og glass som brukes i solcellemodulen. Det ble brukt et referansescenario for sammenlikning med eksisterene LCA studier, noe som ga tilhørende GWP-verdier lik 42,5, 30,8, 16,8 og 20,6 g CO2-ekv./kWh. Dette er innenfor verdiområdet som er publisert i andre studier. De eksisterende tynnfilmteknologiene er allerede konkurransedyktige med vindkraft når det gjelder GWP. Ved å utføre ulike kombinasjoner av forbedringstiltak kunne alle alternativer, untatt mc-Si Sim, oppnå så lav GWP som 5,1-5,8 g CO2-ekv./kWh (under minimum verdien for vindkraft). Å vri energiforsyningen mot en høyere andel av fornybar energi og å forbedre virkningsgraden til solcellemodulen vil ha en betydelig effekt for å redusere GWP. For å forbedre materialeffektiviteten, bør produksjonsavfall reduseres og resirkuleres, og solcellene bør gjøres tynnere. Rensemetodene for silisium bør bli mer energieffektive ved å f.eks. implementere energigjenvinning, bruke biogene karbonkilder som reduksjonsmiddel eller bytte fra å bruke den modifiserte Siemens prosessen til å bruke mer energieffektive metoder som den metallurgiske prosessen utviklet av Elkem Solar eller "Fluidized Bed Reactor" prosessen.