SIMULATION RESULTS OF LIFE-CYCLE ASSESSMENT OF 30 KWP PV SYSTEM INSTALLED AT UNIVERSITY POLITEHNICA OF BUCHAREST ROMANIA

Transcription

1 ISSN Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 3 (17) SIMULATION RESULTS OF LIFE-CYCLE ASSESSMENT OF 30 KWP PV SYSTEM INSTALLED AT UNIVERSITY POLITEHNICA OF BUCHAREST ROMANIA Paul Cristian ANDREI ICPE SA, NES Laboratory, 313 Splaiul Independentei, Bucharest sus_ace@yahoo.com Abstract The concerns about environmental impacts of Photovoltaic (PV) systems are growing with the increasing expectation of PV technologies. Since PV systems feed on a clean energy source, they do not produce polluting emissions during their operation. However, they carry the environmental weight of other phases in their life cycle. In order to analyze the environmental impact of these systems, it is necessary to take into account also the hidden impacts related to production, transportation and system disposal at the end of its technical life. The life cycle assessment (LCA) methodology is applied to offer a complete and extended environmental impact of PV systems. In this paper the LCA is applied to study the 30 kwp PV grid-connected power system installed at University Politehnica Bucharest. A commercial software product SIMAPRO is used for LCA analysis and the simulation results are presented. Keywords: PV system, PV technologies, LCA, environmental impact, SIMAPRO, simulation results. 1. INTRODUCTION In this study, the LCA analysis is applied to derive a complete and extended energy and environmental profile of photovoltaic systems. Life Cycle Assessment is a framework for describing the possible lifespan environmental impacts of material/energy inputs and outputs of a product or process. LCA is used in evaluating the environmental impacts of energy technologies, and its results are increasingly used in decisions about R&D funding and energy policies [1]- [4]. As reference case a conventional multi-crystalline building integrated system is selected, retrofitted on a tilted roof, located at Politehnica University of Bucharest, Romania. Environmental pay back times of the assessed systems are then calculated for CO2 equivalent emissions and embodied energy. All the analyzed configurations are characterized by environmental pay back times one order of magnitude lower than their expected life time (3 4 years vs years). Thanks to a wider exploitation of PV potential during its zero emission operation, these results are further lowered by photovoltaic hybrid. 2. LCA OF PV SYSTEMS: STATE OF ART AND METHODOLOGY Life cycle assessment (LCA) aims at comparing and analyzing the environmental impacts of products and services. LCA studies for photovoltaic power plants have a long tradition of more than 15 years. In the technical literature the results obtained by Hagedorn [5], a pioneer in the field of LCA, had a noticeable theoretical and practical importance. He analyzed the material-and energy-flows in silicon solar-cell production facilities in Germany around 1990, covering prototypes of crystalline-and amorphous-silicon module technologies. His work formed the basis for many later studies and, in fact, it was the underlying dataset for the ExternE analysis of PV systems. Others valuable contributions appeared in the literature, such as Jester and Knapp [6] which used actual records of energy in a production plant to assess energy payback times for monocrystalline silicon and CIS modules, but their estimates can not be scaled-up. Generic, scalable estimates were included in the Ecoinvent 2000 [7], [8], and ECLIPSE databases [9]. The published studies show a high variation in results and conclusions. The cumulative energy demand, for example, has been investigated by different authors, ranging from 3410 to MJ-eq per square meter of a polycrystalline panel. The main reasons for the different LCA results were evaluated in the late 1990s. The production technology for photovoltaic power plants has constantly been improved over the last few decades, e.g., for the efficiency of cells, the amount of silicon required, and the actual capacity of production processes. The data availability is a major problem for establishing a high-quality inventory, because only a few producers provide reliable and verifiable data. In an attempt to formalize a very open and general framework, several organizations have developed standards for LCA, including the Society for Environmental Toxicology and Chemistry (SETAC), the Environmental Protection Agency and the International Standards Organization, as part of the ISO Environmental Management Systems standards. The LCA methodology allows assessing the potential environmental impacts of a product or service during its whole life cycle (from the cradle to the grave). 45

2 Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 3 (17) ISSN A LCA study is divided into the following steps [10], [11]: 1. Goal and scope definition. 2. Life cycle inventory. 3. Life cycle impact assessment. 4. Interpretation of results. These steps are shown in Fig. 1. In step 1 the key parameter to be fixed is the functional unit, i.e. the reference unit for which environmental impacts are calculated. The functional unit is related to the service offered by the product. The geographical and time boundaries of the analysis are defined as well, Step 1 Goal and scope definition effect as 21 kg of CO2, the reference substance for this indicator. LCA has been embraced by the environmental community, but it is not limited to that type of analysis. Similar assessments could be done to calculate the number of deaths caused by a product over its lifetime, or the number of sheets of paper consumed by an industrial sector. We are primarily concerned with LCAs done for environmental analysis here. In the last step of LCA, the results of the study are analyzed in detail and compared with the initial goals. The limits of the performed analysis, and consequently its applicability, are underlined. Some changes to the initial hypotheses may be needed after the result of calculation, in order to obtain more useful, reliable and meaningful outputs. Step 2 Life cycle inventory Step 3 Life cycle impact assessment Step 4 Interpretation of results Figure 1. Phases of a LCA underlining the phases excluded from the analysis (cutoff criteria). Step 2, named life-cycle inventory, or LCI, encompasses the entire data gathering steps associated with LCA, but stops short of doing analysis of what that data means, either to the environment or the economy. Critical issues during modeling of a life cycle inventory (LCI) for photovoltaic are: modeling of silicon inputs and use of off-grade or solar-grade silicon, allocation between different silicon qualities in the silicon purification process, power mixes assumed for the production processes, and process-specific emissions. When performing step 3 - life cycle impact assessment, the data collected in the previous step are grouped into aggregate indicators, such as greenhouse effect, primary energy consumption or solid waste production. To calculate these indicators, a relative weight factor is associated to every substance emitted or resource consumed. In the greenhouse effect indicator, for example, the weight factor for methane (CH4) is 21; therefore, 1 kg of methane has the same 3. DESCRIPTION OF PV SYSTEM AND LCA ANALYSIS 3.1 Description of PV system installed at Polytechnic University of Bucharest, Romania The installation of the 30 kwp PV plant, shown in Fig. 3, at the Polytechnic University of Bucharest, on the roof of the Electrical Engineering Faculty, coordinates Latitude 44 25, Longitude 26 07, and its commissioning to demonstrate the viability of the technology represents a reference moment in the propagation of this clean technology for electrical energy generation from renewable energy sources [13, [14]. The installed PV system is complementary to an ample project, PV Enlargement, financed by the European Union, in whose frame will be installed PV systems with an overall power of over 1000 kwp, in 26 PV plants, locate all over Europe. Critical issues during modeling of a life cycle inventory (LCI) for photovoltaic are: modeling of silicon inputs and use of off-grade or solar-grade silicon, allocation between different silicon qualities in the silicon purification process, power mixes assumed for the production processes, and process-specific emissions. The project brings together European technical universities, academies and producers of photovoltaic modules of 17 member states. The monitoring of all these systems in a common context using the Internet platform, will provide the scientific community and policy makers from EU countries the concrete operating parameters and evaluating the effectiveness of this technology for producing electricity in different climatic conditions in Europe (Portugal, Greece, Italy and to Germany, United Kingdom), including Romania. 46

3 ISSN Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 3 (17) Figure 2. PV system Figure 3. Technical Characteristics of PV system 3.2 LCA analysis of PV system using SimaPro The data needed to assess materials and energy factors from PV manufacturing process are specific to and change with the process. For mono and multi crystalline Silicon, more old process data are available, and one might be tempted to use them after upgrading of silicon wafer thickness and utilization rates [15]-[17]. However, in the last decade there have been changes in the parameters of the silicon production, silicon recycling and cells processing. Validated data from real production lines are required for these processes, as well as newer processes (shown in Table 1). For processing thin films, limited studies have been made on Si, CIS and CdTe, and they must be updated and completed. Future scenarios should consider a better utilization rate of materials and thin films [18]-[20]. Based on a study made by LCA practitioners in 2006, most of the life cycle assessments are performed with dedicated software packages. 58% of respondents used Gabi software developed by PE International, 31% used SimaPro developed by PRE-Consultants, and 11% a number of other instruments. According to the same survey, LCA is used primarily to support business strategy (18%) and research and development (18%), as inputs to product or process design (15%), education (13%) and for labeling or product declarations (11%). The importance of LCA study is growing and can be evaluated by the companies implementing these studies. System for Integrated Environmental Assessment of Products - SimaPro is a software for professional LCA studies. The analysis of environmental impact of products or systems is done through a set of impact assessment methods. These methods provide information about the elements that go into the product or system being analyzed. In this paper, one used this software for the LCA study of the photovoltaic system installed at the Faculty of Electrical Engineering, of the Polytechnic University of Bucharest (Fig. 2). The purpose of this study was to determine the amount of carbon dioxide (CO 2 ) and other greenhouse gas emissions resulted from the production of aluminum and silicon quantities that go into the system, as well as the system life cycle. The system consists of 96 polycrystalline silicon modules, arranged in 24 strings, with 4 modules per string (Fig. 3). After all dimensions of the system were measured, the following quantities were evaluated, which represent the input data to the program: the total mass of 895 kg of aluminum, of which 254 kg is the mass of the module frames and 641 kg the mass of the module stands; the total mass of silicon of which the modules are made of 3682 kg. Figure 4 shows the structure of the photovoltaic system and the materials incorporated in it. Each material is assigned a percentage contribution. Figure 5 displays various types of emissions based on environmental impact. It is noted that the production of aluminum has a 95% contribution to the emission of carcinogenic substances, unlike silicon by 5%. At the greenhouse gas emission, however, silicon has a contribution of 94% and aluminum 6%. Of the input data entered for the considered example, the program calculated the carbon dioxide emissions resulted from the production of the total quantity of aluminum and silicon: 9.9 tons of CO 2 for Al, respectively 157 tons CO 2 for Si, which is presented in absolute units in Figure 6 and graphically in Figure 7. Figure 8 shows other greenhouse gas emissions (tetrafluor-methane, methane fossil dinitrogen), which are much smaller than CO 2. Figure 9 illustrates the CO 2 emissions and other greenhouse gases corresponding to a kwh in the PV system life cycle. It is noted that CO 2 has the largest emissions, of 30 g/kwh. It should be noted that during operation, the PV system does not emit any pollutants or greenhouse gases. The figured values are due to the manufacturing of the modules, module transport and system building. 47

4 Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 3 (17) ISSN Silicon yield air emissions energy consumption solid waste Remarks - EG-Si feedstock (Siemens process) - cryst. (CZ and casting) - wafering (incl. cleaning) - ribbon techn. (EFG, SR) Crystalline silicon current prod. technology LD/NU LD/NU ND A LD/NU ND Table 1 energy data are crucial; SiHCl3 recycling data needed CZ energy uncertain; effect of internal Si recycling unknown A A A slurry recycling LD NN ND ND - cell +module prod. A A A Uncertainty, overhead energy use - system use NN NN NN NN - EOL disposal / module recycling LD* LD* A* lead-free soldering needed; little recycling experience Crystalline silicon new prod. technology - SoG processes ND ND LD ND - new ribbon techn. LD* NN LD* NN (RGS) - dry etching processes NN LD LD - new contacts NN ND ND emissions/abatemen t cost FCs replacement for silver needed Thin film c-si - substrate material NN ND ND ND - dep. + processing LD ND ND ND Legend for Table 1: A Available LD Limited data, * only data for a pilot process NU Need to be updated (outdated numbers in databases) NA Not Available ND No Data NN Not needed (not applicable or emissions are neither toxic nor greenhouse-gases) dbg = double-glass modules VTD Vapor Transport Deposition. 48

5 ISSN Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 3 (17) Fig. 4. Photovoltaic system structure and its components Fig. 7. The amount of carbon dioxide from the production of aluminum and silicon Fig. 5. Different types of emissions according to the environmental impact Fig. 8. Greenhouse gases from the production of aluminum and silicon Fig. 6. Material contribution to the production of carbon dioxide Fig. 9. CO 2 and other greenhouse gas emissions per kwh in the life cycle of PV plant 49

6 Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 3 (17) ISSN CONCLUSIONS During operation, no PV system affects the environment by the emission of pollutants or greenhouse gases. According to studies, conducted by various researchers and organizations concerned with environmental protection, PV systems have an average emission of greenhouse gases in the range of g/kwh throughout their life cycle, which takes into account manufacturing technologies, transport, deployment and disposal/recycling of all component materials of the system. By comparison, a thermoelectric natural gas plant emits g/kwh, a thermoelectric oil plant 893 g/kwh, and a thermoelectric coal plant g/kwh. LCA analysis with SimaPro for PV systems demonstrates the existence of pollutants and greenhouse gases in manufacturing technology, transport and implementation of system components. Emissions of these harmful substances can be reduced by improving existing technologies for aluminum and silicon production, reducing transport distances, but also by finding clean modern techniques for recycling these materials. In this first phase of the LCA analysis it was not presented the environmental impact assessments related to disposal or recycling of components of a PV system. When implementing a PV system appears as obviously the need to analyze the environmental impact factor, combined with ISO requirements imposed to the system location, along with other specific types of technical and economic analysis. 5. REFERENCES [1] Battisti R, and Corrado A, Evaluation of technical improvements of photovoltaic systems through life cycle assessment methodology. In: Energy 30 (2005) [2] Australian Coal Industry Association, ACARP, Coal in a Sustainable Society, [3] Marriott J, An Electricity-focused Economic Input-output Model: Life-cycle Assessment and Policy Implications of Future Electricity Generation Scenarios. In : Report of Carnegie Mellon University, Pittsburgh, PA, January, [4] Nijs J, Mertens R. et al., in Advances in Solar Energy, K.W. Boer, (ed.), American Solar Energy Society, Boulder, CO, vol. 11, , [5] Hagedorn G and E. Hellriegel, Umweltrelevante Masseneinträge bei der Herstellung verschiedener Solarzellentypen - Endbericht - Teil I: Konventionelle Verfahren. 1992, München, Germany: Forschungstelle für Energiewirtschaft.. [6] Knapp K and Jester T, Solar 200: ASES Annual Conference, June 16-21, 2000, Madison, Wisconsin. [7] Jungbluth N, Photovoltaik. In: Sachbilanzen von Energiesystemen: Grundlagen für den ökologischen Vergleich von Energiesystemen und den Einbezug von Energiesystemen in Ökobilanzen für die Schweiz (ed. Dones R.). Final report Ecoinvent 2000 No. 6, Swiss Centre for Life Cycle Inventories, Duebendorf, CH. [8] Frischknecht et al., Ecoinvent LCA database, [9] [10] Frankl P, Corrado A and Lombardelli S, Environmental and Ecological Life Cycle Inventories of Present and Future PV Systems in Europe for Sustainable Policies. In : Proc. of the 19-th European PVSEC, Paris, France, June 7-11, 2004, pp [11] Fthenakis VM and Alsema EA, Photovoltaics Energy Payback Times, Greenhouse Gas Emissions and External Costs: 2004 early 2005 Status. Progress in Photovoltaics: Research and Applications, 2006; 14: , Published online in Wiley InterScience ( DOI: /pip.706 [12] Alsema EA and Nieuwlaar E, Energy Policy, 28, , [13] Craciunescu A, Predescu M, Grottke M, Popescu MO, Popescu CL, Ciumbulea G, Nedelcu A, Mirtroi O, and Bejinariu A, Monitoring resultas of the 30 kwp PV-grid connected power system installed at University Politehnica of Bucharest, in Proc. of ICREPQ 09, Valencia 2009, April. [14] Grottke M, PV Enlargement developing a nucleus for PV expertise in accession countries and focusing on PV new technologies in EU15, in Proc. of European Photovoltaic Solar Energy conference and exhibition Paris 2004, 7-11 June, pp [15] Alsema EA and Wild-Scholten MJ de, Environmental Life Cycle Assessment of Advanced Silicon Solar Cell Technologies, 19th European Photovoltaic Solar Energy Conference, Paris, 7-11 June [16] European Commission, Directorate-General for Research (2003): External costs. Research results on socioenvironmental damages due to electricity and transport; Office for Official Publications of the European Communities, Luxembourg, , EUR [17] Wild-Scholten MJ de, and Alsema EA, External costs of photovoltaics. In : Proc. of Workshop on Life Cycle Analysis and Recycling of Solar Modules - The Waste Challenge, Brussels, Belgium, March [18] Jungbluth N, Life Cycle Assessment of Crystalline Photovoltaics in the Swiss ecoinvent Database. Progress in Photovoltaics: Research and Applications, Published online in Wiley InterScience ( DOI: /pip.614 [19] Fthenakis VM, Alsema EA and Wild-Scholten MJ de, Life Cycle Assessment of Photovoltaics: Perceptions, Needs, and Challenges. in 31 st IEEE Photovoltaic Specialistis Conference Proc., Jan. 3-7, 2005, Orlando, FL. [20] Fthenakis VM and Kim HC, Life cycle energy use and greenhouse gas emissions embedded in electricity generated by thin film CdTe photovoltaics. Material Research Society Fall Meeting, Symposium G: Life Cycle Analysis Tools for Green Materials and Process Selection, Paper G3.5, Nov. 2005, Boston, MS. 50