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Article history:

Available online 1 August 2014

Keywords:Life-cycle assessmentMulti-Si PV systemEnergy payback time

This study performs a life-cycle assessment for a photovoltaic (PV) system with multi-crystalline silicon

the PV system, including the upstream process, ranging from silica extraction to the multi-Si purication,

distributed renewable energy in the world. With advances in

dustry Association (EPIA) estimated that the global crystalline-silicon (c-Si) cell production capacity was approximately27e28 GW in 2010, almost 50% of which was located in China (EPIA,2011). As the largest exporter of solar cells in the world, China hasdeveloped a complete photovoltaic manufacturing industrial chain

sharp decline in demand in the global photovoltaic (PV) market,inese PV industrydepended on in-vercapacity in theantly in 2011. Morewere forced out ofStates and Euro-umping and anti-

subsidy) investigation into Chinese PV products in 2012 (Ling,2012), which made it more difcult to export Chinese PV prod-ucts. In response to both domestic overcapacity and the shrinkingof foreign markets, the Chinese PV industry will inevitably regulatethe market distribution and expand the domestic market.

Regarding the operation process, the PV technology can beconsidered almost completely clean. However, when consideringthe entire life cycle of the PV system, from silica mining to systeminstallation, the energy consumption and emissions to

* Corresponding author. Tel.: 86 25 89680532.

Contents lists availab

Journal of Clean

els

Journal of Cleaner Production 86 (2015) 180e190E-mail address: yuanzw@nju.edu.cn (Z.W. Yuan).technology and reduction in production cost (Li et al., 2009), solarpower has become a renewable energy technology that can bedeveloped and used on a large scale. In the situation where prob-lems of energy security and climate change are becoming increas-ingly serious, solar power has received large amounts of attentionthroughout the world (Bhandari and Stadler, 2011; Hondo andBaba, 2010), especially in Europe. The European Photovoltaic In-

which created a serious situation for the Chbecause more than 90% of Chinese PV productsternational markets. As a result, there was huge oChinese PV industry, and prots dropped signicthan 50% of small and medium-sized companiesproduction. To make matters worse, the Unitedpean Union registered a double reverse (anti-dSolar energy is the most abundant and the most widely nancial crisis and the European sovereign debt crisis, there was aEnvironmental impactsEnvironmental management

1. Introductionhttp://dx.doi.org/10.1016/j.jclepro.2014.07.0570959-6526/ 2014 Elsevier Ltd. All rights reserved.the midstream process, involving crystalline silicon ingot growth and wafering; and the downstreamprocess, consisting of cell and module fabrication. The data were collected with recommendationsprovided by the ISO norms and acquired from typical PV companies in China. The results show that themost critical phase of life cycle of Chinese PV system was the transformation of metallic silicon into solarsilicon, which was characterized by high electricity consumption, representing most of the environ-mental impact. The other electricity generation systems were compared to PV. Considering that Chineseelectricity is mainly produced by coal-red power plants, the installation of multi-Si PV systems isrecommended over exporting them from China. Furthermore, being higher solar radiation areas, areas inwestern China, such as the Tibet Autonomous Region, northeastern Qinghai, and the western borders ofGansu, are best suited for the installation of the PV systems even if the long distance of transportation.Finally, recommendations were provided with respect to the sustainable development of the Chinese PVindustry and environmental protection.

2014 Elsevier Ltd. All rights reserved.

consisting of silicon materials, components, and equipment andapplication systems. However, in the past two years, driven by the18 July 2014Accepted 23 July 2014Received 12 February 2014Received in revised form

(multi-Si) modules in China. It considers the primary energy demand, energy payback time (EPBT), andenvironmental impacts, such as global warming potential and eutrophication, over the entire life cycle ofLife-cycle assessment of multi-crystallinChina

Yinyin Fu, Xin Liu, Zengwei Yuan*

State Key Laboratory of Pollution Control and Resources Reuse, School of the Environm

a r t i c l e i n f o a b s t r a c t

journal homepage: www.hotovoltaic (PV) systems in

Nanjing University, Nanjing 210023, China

le at ScienceDirect

er Production

evier .com/locate/ jc lepro

r Prenvironment cannot be ignored. In today's China, the environ-mental problems behind Green Solar received attention. Becausemost of the PV cells in China are made of polycrystalline silicon (Liand Wang, 2011), whose production process involves the contin-uous purication of industrial silicon, consuming large amounts ofenergy and producing heavy pollution (Ye, 2011). In December2010, the Ministry of Industry and Information Technology of thePeople's Republic of China, the National Development and ReformCommission, and the Ministry of Environmental Protection of thePeople's Republic of China jointly issued Polycrystalline siliconindustry access conditions, which proposed stricter standards forproduction inputs, energy consumption, and pollution emissions ofthe PV industry (Ministry of Industry and Information Technologyof China, 2010). In fact, for the PV industry, apart from the pro-cess of polycrystalline silicon production, other processes, such asquartz mining, metallurgical silicon production, cell and moduleproduction, and the disposal of end-of-life PV systems, alsocontribute substantially to environmental pollution and energyconsumption (Phylipsen and Alsema, 1995). Therefore, it is neces-sary to quantify the resource consumption and environmentalimpacts of PV technology from a life-cycle perspective to determinewhether the production of this PV system is environmentallyfriendly. Life cycle assessment (LCA) is a method of compiling andevaluating the inputs, outputs, and environmental impacts of aproduct or service system throughout its life cycle (ISO14044,2006).

The earliest research on PV system from the life-cycleperspective can be traced to the 1970s, in which the energy usein the production of solar cells from materials to the nishedproduct was evaluated. The results showed that the energy paybacktime (EPBT) for terrestrial mono-crystalline silicon (mono-Si)solarcells that time was 12 years (Hunt, 1976), less than its lifetime. Theconcerns about the environmental impacts of PV power systemsare growing with the increasing use of PV technologies. As a result,an increasing number of LCA studies on the EPBT and environ-mental impacts of PV technologies have been conducted (Ashrafand Chandra, 2005; Dones and Frischknecht, 1998; Frankl et al.,1998; Phylipsen and Alsema, 1995), but they have mainly focusedon EPBT and only specic emissions (Baumann et al., 1997;Fthenakis et al., 2008; Lu and Yang, 2010; Zhang et al., 2012),especially greenhouse gases (Alsema, 2000; Kannan et al., 2006;Kato et al., 1998; Krauter and Ruther, 2004; Zhai and Williams,2010). The EBPT and GHG emission rates for multi-Si PV systemsvary by the location and time inwhich theyweremanufactured andinstalled (Fthenakis and Alsema, 2006; Peng et al., 2013; Sherwaniet al., 2010). The results of previous studies had shown that theEBPT of multi-Si was in the range of 1.5e7.5 years, and the GHGemission rate was in the range of 12e170 g CO2-equivalent/kWh(Sumper et al., 2011). More recent study showed that the estimatedenergy payback times of the Amonix 7700 PV system in operationwas only 0.9 year, and its estimated GHG emissions were 27 g CO2-eq./kWh over 30 years, or approximately 16 g CO2-eq./kWh over 50years. The energy payback time at an in-plane irradiation of1700 kWh/(m2 year) could be reduced to below 0.5 years by 2020,less than half of the current (Fthenakis and Kim, 2013).

However, few studies have considered other environmentalimpacts, such as biological toxicity, acidication potential, andeutrophication potential (Jungbluth, 2005; Koroneos et al., 2006;Tsoutsos et al., 2005). Fewer studies have been based on the cur-rent state-of-the-art PV systems produced or installed within China(Ito et al., 2003; Nishimura et al., 2010). Because it is difcult tocompare different studies of PV systems due to the difference intime and location of installation and technological level (Fthenakisand Alsema, 2006), it is important to study the life-cycle environ-

Y. Fu et al. / Journal of Cleanemental impacts of multi-Si PV systems based on current Chinesetechnology, and the data should be collected from Chinese com-panies and the Chinese government.

This paper evaluated the energy payback time and importantenvironmental impacts of multi-Si PV systems produced and usedin China. Based on the results, we examined the instruments tomitigate the environmental impacts of the PV industry in China,explored the pollution transfer and environmental responsibilitydistribution based on the transnational trade of PV products, andnally made suggestions for the sustainable development of theChinese PV industry.

2. Materials and methods

2.1. System boundary and description

The goal of this study was to quantitatively assess the life-cycleenvironmental impacts of PV systems in China and provide a sci-entic basis for policy-making regarding the sustainable develop-ment of Chinese PV industry.

The system boundary of the research was shown in Fig. 1, whichincluded upstream processes, ranging from silica extraction to thecrystalline silicon bar and ingot growth, and midstream processes,which involved cell and module fabrication as well as aluminumframe production. We didn't consider the balance of system (BOS)due to its dependence on the installation and the little inuence onenvironmental impacts. For a rooftop PV application, the BOStypically includes inverters, mounting structures, cable and con-nectors. Large-scale ground-mounted PV installations requireadditional equipment and facilities, such as grid connections, ofcefacilities, and concrete (Fthenakis and Kim, 2011). Previous studiesshow that, BOS accounted for additional ~0.2 years of EPBTof multi-Si PV system, ~5 g CO2-eq/kWh of GHG emissions, ~10 mg/kWh ofNOx emissions and ~18 mg/kWh of SOx emissions (de Wild-Scholten and Alsema, 2005).

The environmental impacts of infrastructure for processing fa-cilities per unit of electricity was not considered, which might leadto underestimation of the environmental impact caused by PVsystems (Cabezaa et al., 2014). However, due to long-term use ofinfrastructure for processing facilities and large production capac-ity during their life cycle, there was little effect on the environ-mental impacts per unit of electricity (Le Tong et al., 2013).

Because multi-Si PV systems accounted for most Chinese PVproducts, we would study multi-Si silicon PV technology as beingrepresentative of the Chinese PV industry. Generally, the life cycleof a product refers the period ranging from its manufacture, use,and maintenance to its nal disposal. However, the use andmaintenance of PV systems was not taken into account becausethe data were unavailable and these stages consumed few re-sources and had a weak environmental impact (Dones andFrischknecht, 1998). Moreover, Chinese PV markets did notdevelop rapidly until 2002 (Sun et al., 2010), and the lifespan of aPV system is generally more than 25 years. Therefore, almost allPV systems in China today have not reached their end-of-life stage,and no mature end-of-life management technology and mecha-nisms currently exist in China. Thus, it is impossible to obtainaccurate data for this stage in China which might slightly under-estimate the primary energy demand and environmental impacts.However, this underestimation can be omitted because the end-of-life disposal accounted for only 1.7% of the total primary en-ergy demand and 1.9% of the total GHG emissions (Kim andFthenakis, 2006).

In addition, the transport modes and distances of different PVprojects varied strongly, making them difcult to evaluate. As aresult, this study mainly considered the manufacturing stage of the

oduction 86 (2015) 180e190 181multi-Si PV system, especially that of the PVmodule, which was the

China. The characteristics of the modules were shown in Table 1.

Fig. 1. Life cycle of a m

Y. Fu et al. / Journal of Cleaner Pr1822.2. Data sources and LCA inventory

The inventory data, including the material consumption andenvironmental emissions involved in the production of solar-gradesilicon, wafers, ingots, cells, and modules, were mainly collectedfrom companies that represent the current domain multi-Si PVtechnologies in China. The energy consumption data referred to thereport Clean Production of Solar PV in China (Li and Chang, 2012).The data of MG-Si production was from literature about MG-Simost important and distinctive part of a PV system. And thetransportation of PV modules would be discussed later.

The functional unit of the LCA study was 1 kWh based on amulti-Si PV module with a capacity of 200Wp. It was assumed thatthe average number of peak sunshine hours in China was 1300 andthe lifespan of a PV system was 25 years. In fact, the lifespan of PVsystems was usually lower than that due to the poor maintenance,which might lead to an underestimate of primary energy demandand environmental impacts per kWh generated by PV systems inTable 1Characteristics of the module in this study.

Item Description

Module size 1482 992 35 mmMass 16.8 kgFrame Aluminum alloyFront glass Tempering glass 3.2 mmEVA sheet thickness 0.5 mmWafer thickness 200 mm 20 mmNumber of cells per module 54 (6 9)Cell area 156 156 mm2Efciency of cells 16%Operation life 25yearsAnnual solar radiation 4680 MJ m2 a1

Open circuit voltage (Voc) 33.4 VOptimum operating voltage (Vmp) 26.2 VShort-circuit current (Isc) 8.12 AOptimum operating current (Imp) 7.63 AMaximum power at STCa (Pmax) 200 WpOperating temperature 40 C to 85 CMaximum system voltage 1000 V DCMaximum series fuse rating 20 APower tolerance 3%

STC: irradiance 1000/m2; module temperature 25 C; AM 1.5.produced in China (Ye, 2008). Some important parameters anddata resources of the life cycle of multi-Si PV power productionwere shown in Table 2. For the calculation, these data wereimplemented into the model built with software GaBi4, which wasable to perform life-cycle calculations and includes access to a richdatabase, and could be compatible with the Ecoinvent database.The upstream data for energy and other auxiliary materials werefrom this database.

Some simplications and assumptions had been made for pro-cesses that were not in the database, which were substituted byother similar processes included in the GaBi4 or Ecoinvent data-base. For example, in the pickling stage of cells, the production of32% hydrochloric acid was used instead of that of 37% hydrochloricacid. The anhydrous alcohol was replaced by 96% ethanol in themodel since there was no process of anhydrous alcohol in thedatabase. The 70% nitric acid was substituted by 60% nitric acidsince their processes were similar and there was no process of 70%nitric acid in the database. The 21% KOH solution was modeled byprocess of potassium hydroxide and water due to lacking process of21% KOH in the database.

ulti-Si PV system.

oduction 86 (2015) 180e190The production processes of PV modules included solar-grademulti-Si (SoG-Si) production, ingot casting, wafer slicing, and cellprocessing andmodule assembly (see Supporting information). Theeffect of product transportation was not considered here and willbe discussed later.

2.3. Life-cycle impact assessment (LCIA)

Life-cycle impact assessment (LCIA) aimed to understand andevaluate the magnitude and signicance of the potential environ-mental impacts for a product system throughout its life cycle. LCIAconsists of both mandatory and optional elements. The formerinclude selection of impact categories, category indicators andcharacterization models, assignment of the inventory data to theselected impact categories (classication) and calculation of impactcategory indicators using characterization factors (characteriza-tion). The later include calculation of the magnitude of categoryindicator results relative to reference values (normalization),grouping and weighting the results, and data quality analysis.Impact categories include climate change, stratospheric ozonedepletion, photo oxidant formation (smog), eutrophication, acidi-cation, water use, noise, etc. Here, we considered the potentialenvironmental impacts of acidication, eutrophication, climate

Table 2Key parameters of the life cycle inventory for multi-Si PV power production.

Flows Data sources

Metallurgical silicon smeltingInputsQuartz sand 20.48 kgStandard coal 45.40 kg

OutputsSilicon (99%) 6.08 kg LCA Study of Metallurgical Silicon Process (Ye, 2008)Carbon dioxide emissions to air 132.91 kgCarbon monoxide emissions to air 1.70 kgSlag from MG silicon production for disposal 4.38 kgNitrogen oxides emissions to air 279.55 gSilicon dioxide emissions to air 1.70 kgSulfur dioxide emissions to air 0.79 kg

Solar grade multi-Si puricationInputsMetallurgical silicon (>99%) 6.08 kg Companies that represent the current domain PV technologies in ChinaCalcium oxide 6.52 kgHydrochloric acid (30%) 2.93 kgHydrouoric acid (20%) 0.06 kgHydrogen (>99.8%) 0.50 kgNitric acid (35%) 0.22 kgNitrogen gaseous 71.16 kgSilicon tetrachloride (>99%) 8.29 kgSodium hydroxide (20%) 4.81 kgWater 10,396.87 kgElectricity 2287.25 MJ Clean Production of Solar PV in China (Li and Chang, 2012)Steam 385.02 kg

OutputsSolar grade multi-Si 5.52 kg Companies that represent the current domain PV technologies in ChinaCOD emissions to water 82.21 gChlorosilane emissions to air 28.56 gHydrogen chloride emissions to air 36.24 gHydrogen uoride emissions to air 0.22 gNitrogen dioxide emissions to air 3.15 gSilicon dust to air 8.29 gSilicon dust (99%) for recovery 0.83 kgSilicon tetrachloride emissions to air 9.23 gSuspended solids to fresh water 54.81 gTrichlorosilane emissions to air 31.33 gWater (evapotranspiration) emissions to air 5991.76 kg

Ingot castingInputsSolar grade multi-Si 5.52 kg Companies that represent the current domain PV technologies in ChinaSilicon carbide 61.92 gQuartz crucible 15.37 kgArgon 10.5 kgHydrouoric acid (49%) 254.03 gCompressed air 18.76 m3

Sodium hydroxide 46.88 gWater 492.47 kgElectricity 157.54 MJ Clean Production of Solar PV in China (Li and Chang, 2012)Steam 7.60 kg

OutputsMulti-Si ingot 5.47 kg Companies that represent the current domain PV technologies in ChinaHydrogen uoride emissions to air 0.60 gSilicon carbide 61.43 gWaste acid 348.72 gWaste quartz crucible for recovery 15.37 kgWater (evapotranspiration) to air 375.08 kg

Wafer slicingInputsMulti-Si ingot 5.47 kg Companies that represent the current domain PV technologies in ChinaGlass 2.47 kgSilicon carbide 175.78 gSteel wire 17.11 kgAcetic acid 0.60 kgDetergent 2.23 kgCompressed air 29.05 m3

Water 528.63 kgElectricity 24.01 MJ Clean Production of Solar PV in China (Li and Chang, 2012)

OutputsMulti-Si Wafer 3.34 kg Companies that represent the current domain PV technologies in ChinaAcetic acid 0.60 kgGlass 2.47 kg

(continued on next page)

Y. Fu et al. / Journal of Cleaner Production 86 (2015) 180e190 183

Data sources

Companies that represent the current domain PV technologies in China

Clean Production of Solar PV in China (Li and Chang, 2012)

r Production 86 (2015) 180e190Table 2 (continued )

Flows

Glue residues for disposal 243.28 gSilicon scrap for recovery 2.07 kgWaste water 336.94 kg

Cell processingInputsMulti-Si Wafer 3.34 kgAmmonia 88.10 gEthanol (99.7%) 0.23 kgHydrochloric acid (37%) 2.57 kgHydrouoric acid 0.78 kgNitric acid (70%) 1.43 kgNitrogen 7.62 kgPhosphoric acid (85%) 9.31 gKOH (21%) 2.76 kgSilver 67.90 gAluminum 0.38 kgWater 866.04 kgNatural gas 0.59 kgElectricity 686.69 MJSteam 26.15 kg

OutputsMulti-Si Solar cell 1.09 kWAmmonia emissions to air 7.86 g

Y. Fu et al. / Journal of Cleane184change, human toxicity, ozone depletion, and photochemical ozonecreation. The characterization involves the conversion of LCI resultsto common units and the aggregation of the converted resultswithin the same impact category. The conversion uses character-ization factors, which are typically the output of characterizationmodels. The outcome of the calculation is a numerical indicatorresult. The aim of the normalization is to understand better therelative magnitude for each indicator result of the product system.Grouping is the assignment of impact categories into one or moresets, and it may involve sorting and ranking. Weighting is theprocess of converting and possibly aggregating indicator resultsacross impact categories using numerical factors based on value-choices.

Various LCIA methods have been developed and are currentlyavailable in the database of LCA dedicated software on the market.The methods include life cycle environmental impact assessment,environmental design of industrial products (EDIP), tool for thereduction and assessment of chemical and other environmentalimpacts (TRACI), and ecological scarcity (Cavalett et al., 2013). TheCML is a problem-oriented LCA method developed by the Instituteof Environmental Sciences of the University of Leiden (CML), whichaims to offer best practice for midpoint indicators and operation-alizes the ISO 14040 series of standards. CML includes

Hydrogen chloride emissions to air 4.92 gHydrogen uoride emissions to air 3.93 gNitrogen oxides emissions to air 61.00 gNMVOC to air 34.64 gWater 888.13 kg

Modules assemblyInputsMulti-Si solar cell 1.09 kWGlass 63.26 kgAluminum 11.77 kgPolyethylene terephthalate part (PET) 3.27 kgPolyvinyl uoride lm (PVF) 3.27 kgEthanol 56.97 gEthylene vinyl acetate copolymer (EVA) 7.52 kgIsopropanol 17.67 gWater 118.04 kgSteam 16.22 kgElectricity 72.00 MJ

OutputsSolar panels 1.00 kWActivated carbon (charged) for recovery 61.11 gWater (evapotranspiration) emissions to air 94.26 kgWater emissions to fresh water 23.78 kgCompanies that represent the current domain PV technologies in Chinarecommended methods for normalization but weighting is notincluded (Guinee, 2001). CML2001-Dec.07.Worldwas chosen in ourresearch to assess the environmental impacts of the PV system perkWh, and acidication potential (AP), eutrophication potential (EP),

Companies that represent the current domain PV technologies in China

Clean Production of Solar PV in China (Li and Chang, 2012)

Companies that represent the current domain PV technologies in China

Fig. 2. Primary energy demands from renewable and nonrenewable resources [MJ/kWh].

global warming potential (GWP 100 years), human toxicity poten-tial (HTP), ozone layer depletion potential (ODP), and photochem-ical ozone creation potential (POCP) were taken into account. TheLCA software GaBi (version 4.3) developed by PE-International wasapplied to help establish the LCA model and to perform thecalculations.

3. Results

3.1. Primary energy demand and energy payback time (EPBT)

primary energy demand of cells production accounted for 19% ofthe total, and that of ingots accounted for 5%. The direct energydemand of the entire PV system accounted for more than 50% of thetotal primary energy demand, which was mainly due to electricityconsumption.

The EPBT was a frequently used parameter because of itsinputeoutput format and its easy interpretation. The simpliedcalculation method was as follows.

EPBT Total primary energy demandMJ

Table 3Annual power generation and the EPBT of the PV system (200 Wp) in China.

First-class areas Second-class areas Third-class areas Fourth-class areas Fifth-class areas

Peak sunshine hoursa (h) 1855.6e2100 1625e1855.6 1388.9e1625 1166.7e1388.9 772.2e1166.7Annual power generation (MJ) 1001.3e1134.4 877.5e1001.3 750e877.5 630e750 416.3e630EPBT (years) 2.22e2.52 2.52e2.87 2.87e3.3.36 3.36e4 4e6.05

a The peak sunshine hours refers to the equivalent number of hours per year when solar irradiance averages 1 kW/m2 and is calculated using annual solar radiation.

Y. Fu et al. / Journal of Cleaner Production 86 (2015) 180e190 185Based on the data collected in China and with the help of GaBi,the total primary energy demand from renewable and nonrenew-able resources (net calorie value) of the PV systemwas calculated as0.517 MJ/kWh, as shown in Fig. 2. That is to say, the primary energydemand of a multi-Si PV system of 200 Wp in China was 2522 MJ.Flows accounting for less than 0.1% were ignored in thecalculations.

The primary energy demands were mainly nonrenewable en-ergy resources, including hard coal, crude oil, and natural gas,because the production stages, especially the production of solar-grade multi-Si and cells, consumed a lot of electricity generatedin China, which was mainly produced by coal-red power plants(National Energy Administration of China, 2012). Crude oil andnatural gas were mainly consumed in the module assembly stage,wherein the manufacture of ethylene vinyl acetate (EVA) copol-ymer, polyethylene terephthalate (PET) lm, and polyvinyl uoride(PVF) lm consumed most of the crude oil and natural gas. And theprimary energy demand of module assembly accounted for 25% ofthe total. Moreover, the stage of solar-grade multi-Si productioncontributed most (approximately 48.5%) to the total primary en-ergy demand, which was mainly due to the large amounts ofelectricity required in the process. The stages of cell processing andingot casting were similar, whose primary energy demand was alsomainly due to the use of electricity generated by hard coal. TheFig. 3. Acidication potential [kg SO2-equivalent/kWh].=Annual power generationMJ=year 1

Annual power generation PowerW *Peak sunshine hoursh*Performance ratio

(2)

Because China receives a wide range of solar radiation(2780e7560MJ m2 a1) due to its large land area, the annual solarradiation differs by location within China (Lu et al., 2010). As aresult, the annual power generation and the EPBTof a PV system arenot the same due to the different location. Considering the losses ofthe PV module-wiring-inverter-transformer system and the othereffect, the performance ratio of multi-Si PV system in China wasusually 0.75 (Kawajiri et al., 2011). The annual power generationand the EPBT of the PV system with capacity of 200 W which waslocated in different areas of China were evaluated (shown inTable 3). Chinese ve-class areas with different solar radiation areshown in S3 of Supporting information.

The results show that, wherever in China the multi-Si PV systeminstalled, the EPBTwas far less than its lifespan. It was best to installthese systems in the rst-class areas, where it took only approxi-mately 2 years to pay back the energy consumed during its life-cycle stages. Even for installation in the worst (fth-class) areas,the EPBT was only 6 years. Thus, the development of PV systems inFig. 4. Eutrophication potential [kg PO43-equivalent/kWh].

mainly stemming from the production of Chinese electricity used in

Fig. 7. Ozone layer depletion potential [kg R11-equivalent/kWh].

Y. Fu et al. / Journal of Cleaner Production 86 (2015) 180e190186almost all the life-cycle stages of the PV system, because Chineseelectricity is mainly generated by coal-red power plants, and thestages of coal mining and power generation emit phosphate toChina was practical from the aspect of energy. What about othertypes of environmental impact?

3.2. Environmental impacts

The AP for the PV system was 4.27E-4 kg SO2-equivalent/kWh,which was almost completely dominated by emissions to air, asshown in Fig. 3.

Sulfur dioxide contributed the most (approximately 73.4%),which was mainly due to the electricity consumed in each stage,especially the production stage of solar-grade poly-Si, becauseChinese electricity is mainly generated by coal-red power plants,which emit large amounts of sulfur dioxide and nitrogen oxides.

The EP of the PV system was 4.23E-5 kg PO43-equivalent/kWh,whichwas dominated by emissions to air and freshwater, includingnitrogen oxides, phosphate, and nitrate, as shown in Fig. 4.

The phosphate emissions to the freshwater accounted for 45.6%,

Fig. 5. Global warming potential (GWP100years) [kgCO2-equivalent/kWh].water. The emission of nitrogen oxides to air accounted for 44.4%,mainly due to the use of electricity and steam. The reason was also

Fig. 6. Human toxicity potential [kg DCB-equivalent/kWh].that Chinese electricity and steam were mainly generated by coal,which emitted large amounts of nitrogen oxides. However, in themodule production stage, the PVF lm, aluminum frame, and EVAwere the main contributors to the EP because they emitted phos-phate and nitrogen oxides during their life cycles. Moreover, ac-counting for only 5%, the others category, which includedammonia, nitrogen dioxide, nitrous oxide emissions to air, biolog-ical oxygen demand (BOD), total organic bounded carbon, ammo-nium emissions to fresh water, and the slight emissions to seawaterand industrial soil, was negligible.

The calculated GWP of a PV system was 5.09E-2 kgCO2-equiv-alent/kWh, which was dominated by carbon dioxide (83.6%) andmethane (11.2%), as shown in Fig. 5.

The most critical phases were the production of solar-gradepoly-Si, accounting for approximately 50% of the GWP, due to itshigh electricity and steam consumption. The cell production alsorepresented an important contribution (20.5%) to GWP because ofits electricity consumption. The reason was also that Chineseelectricity was mainly generated by coal-red power plants, whichemit plenty of greenhouse gases. However, for the module pro-duction, the second highest contributor (22.8%) to GWP, materialsconsumption had a greater impact than electricity consumption. Infact, aluminum framing contributed 46.1% and PVF lm 26.4%,while the electricity use contribution was only 8.2%, because theFig. 8. Photochemical ozone creation potential [kg ethene-equivalent/kWh].

r Prproduction process of aluminum and PVF produced plenty of CO2.Note that there was a small negative emission of GWP, whichcaused by the use of little CO2 during generation of Chineseelectricity.

The HTP of the PV system was 1.76E-2 kg DCB-equivalent/kWh,which was dominated by the emissions to air and fresh water.

The emissions to air contributed 74.4%, including heavy metal,inorganic, and organic emissions, as shown in Fig. 6. The heavymetals included arsenic, chromium, nickel, and selenium, mainlyfrom the electricity and steam consumption of all the stages and theuse of materials in the module production stage. Because Chineseelectricity and steamwere generated by coal, which including thoseheavy metals and they were emitted when coal was burned. Inor-ganic emissions to air weremainly hydrogen uoride, also resultingfrom the energy consumption. Organic emissions to air weremainly polychlorinated dibenzo-p-dioxins generated by thedisposal process of waste glass during wafer production. Theemissions to fresh water contribute 25.5% to the impact and weremainly heavy metals, including selenium, vanadium (III), andthallium, caused by electricity generation.

The ODP was 3.02E-9 kgR11-equivalent/kWh, dominated byHalon (1301), carbon tetrachloride, and Halon (1211), as shown inFig. 7.

Halon (1301) contributed 67.8% to the impact, generated by theproduction stages of modules and solar-grade poly-Si, duringwhich the aluminum frame and electricity were consumed.Because Hanlon (1301) was emitted during the life cycle of the

Fig. 9. Normalization results of environmental impacts per Wp of different processes.

Y. Fu et al. / Journal of Cleanealuminum and electricity in China. The Halon (1211) also came fromthe module production process, during which the PVF lmcontributed the most. The carbon tetrachloride accounted for 15.6%of the ODP due to emissions during the solar-grade poly-Si pro-duction phase, which also emitted most of the R12 and R22.

The evaluated POCP was 2.69E-5 kg ethane-equivalent/kWh,dominated by inorganic and organic emissions to air, as shown inFig. 8.

Sulfur dioxide was the largest contributor to the impact, ac-counting for 56.1%, mostly due to the electricity and steam con-sumption of the production stages of solar-grade poly-Si, cells,ingots andwafers, as well as the aluminum frame and PVF lm usedin the module production stage. The reason was that Chineseelectricity was mainly generated by coal-red power plants and thecoal in China included sulfur. The sulfur dioxide would be gener-ated and emit when the coal was red. Nitrogen dioxide accountedfor 15%, and it had the same characteristics as sulfur dioxide. Non-methane volatile organic compounds (NMVOC) were the secondcontributor as a result of the consumption of the aluminum frame,EVA, and PVF in module production; NMVOC emissions to airduring cell production; and electricity and steam used in everystage.

3.3. Normalization

The normalization results were shown in Fig. 9, which inte-grated different types of environmental impacts according todifferent processes of PV system.

Acidication Potential was the biggest environmental impact ofthe PV system, accounting for 40.6%, which mainly came from theproduction stages of solar grade poly-Si, cells and modules. Thesecond contributor to the whole environment was Global WarmingPotential, accounting for 27.5%, which mainly produced in thestages of solar grade poly-Si, cells and modules. The next werePOCP and HTP, accounting for 15.4% and 10.4%, respectively.Comparing the environmental impacts of each processes, we foundthat the production of solar grade poly-Si contributed the most tothe environment, which accounted for about 52.4% of the totalenvironmental effect. The next were processes of cells and mod-ules, accounting for 20.1% and 18.6% respectively.

3.4. Sensitivity analyses

In this section, a sensitivity analysis of the primary energy de-mand and environmental impacts was conducted considering thatthe processing technology was unchanged. The analysis was basedonly on the characteristics of modules and solar radiation in Table 1.

The sensitivity analysis was conducted to nd out the effect ofthe following factors on the energy demand and environmentalimpacts: electricity and steam consumption during production ofsolar grade poly-Si, glass consumption and disposal during processof wafer slicing, electricity consumption during process of cells,aluminum and glass consumption during modules assembly. Theresults of the sensitivity analysis were presented in Table 4.

A 10% decrease in electricity consumption during solar gradepoly-Si production would lead to a 3.37% drop in the primary en-ergy demand, whereas a 10% increase would lead to a 3.37% in-crease, correspondingly. Electricity consumption during solar gradepoly-Si production was the factor that had the most inuence onthe primary energy demand, Acidication Potential and Eutrophi-cation Potential, followed by electricity consumption during cellsprocessing, steam consumption during solar grade poly-Si pro-duction, aluminum and glass consumption during modules as-sembly. Electricity consumption during solar grade poly-Siproduction was also the factor that had the most inuence on theGlobal Warming Potential and Photochemical Ozone Creation Po-tential, followed by electricity consumption during cells processing,aluminum consumption during modules assembly, steam con-sumption during solar grade poly-Si production, and glass con-sumption during modules assembly. On Human Toxicity Potential,electricity consumption during solar grade poly-Si production hadthe most inuence, about 2.98%, followed by glass consumptionand disposal during wafer slicing (2.11%). Aluminum consumptionduring modules assembly was the factor that had the most inu-ence on Ozone layer Depletion Potential, while 10% decrease onaluminum consumption during modules assembly would lead to a7.01% drop in the Ozone layer Depletion Potential.

4. Discussion

4.1. Comparison with other power generation systems in China

The Chinese power generation capacity came from coal-redpower (72.31%), hydropower (21.93%), wind power (4.35%), nu-

oduction 86 (2015) 180e190 187clear power (1.18%), solar-photovoltaic (0.21%), and others (0.02%)

Table 4Sensitivity analysis for important parameters.

Process Parameter Variation Primaryenergydemand

Acidicationpotential

Eutrophicationpotential

Globalwarmingpotential

Humantoxicitypotential

Ozone layerdepletionpotential

Photochemicalozone creationpotential

Solar gradepoly-Si

Electricity consumption 10% 3.37% 3.97% 3.81% 3.56% 2.98% 0.43% 3.21%10% 3.37% 3.97% 3.81% 3.56% 2.98% 0.43% 3.21%

Steam consumption 10% 0.69% 1.06% 0.46% 0.69% 1.02% 0.00% 0.90%10% 0.69% 1.06% 0.46% 0.69% 1.02% 0.00% 0.90%

Wafer slicing Glass consumption anddisposal

10% 0.00% 0.00% 0.00% 0.00% 2.11% 0.01% 0.00%10% 0.00% 0.00% 0.00% 0.00% 2.11% 0.01% 0.00%

Y. Fu et al. / Journal of Cleaner Production 86 (2015) 180e190188Cells Electricity consumption 10% 1.61% 1.90%10% 1.61% 1.90%

Modulesassembly

Aluminum consumption 10% 0.49% 0.72%10% 0.49% 0.72%

Glass consumption 10% 0.17% 0.07%10% 0.17% 0.07%(National Energy Administration of China, 2012). With the help ofGaBi4 software, we compared the energy demand and environ-mental impacts of PV systems with that of the other types of powergeneration systems. The data from the other power systems wascollected from the GaBi4 database and the ecoinvent database,supplemented by literature data. It was assumed that the averagenumber of peak sunshine hours in China was 1300 and the lifespanof a PV systemwas 25 years, yielding 24 kWh perWp during the PVlife cycle when located in China. The primary energy demand andenvironmental impacts per kWh of electricity generated by PV andother power generation systems in China were shown in Fig. 10.

The primary energy demand and environmental impacts perkWh of a PV power through its life cycle were far less than those forcoal-red power in China. Of these types of electricity generation,coal-red power demands almost themost primary energy and hadthe largest environmental impact. Therefore, improving the pro-portion of PV and reducing that of coal-red power in the electricitymix would reduce the primary energy demand and environmentalimpacts of China's electricity mix. Taking the year of 2011 as anexample, electricity consumption of China was approximately

Fig. 10. Primary energy and environmental impacts

Table 5Environmental impacts of a PV system located in Tibet and Beijing.

Environmental impacts

Acidication potential (kg SO2-e/kWh)Eutrophication potential (kg PO43-e/kWh)Global warming potential (kg CO2-e/kWh)Human toxicity potential (kg DCB-e/kWh)Ozone layer depletion potential (kg R11-e/kWh)Photochemical ozone creation potential (kg ethane-e/kWh)

a The numbers in brackets are the environmental impacts per kWh of module transpo1.83% 1.70% 1.43% 0.21% 1.54%1.83% 1.70% 1.43% 0.21% 1.54%0.29% 1.00% 0.23% 7.01% 1.48%0.29% 1.00% 0.23% 7.01% 1.48%0.13% 0.12% 0.06% 0.25% 0.09%0.13% 0.12% 0.06% 0.25% 0.09%4693 billion kWh. If multi-Si PV systems completely replaced thecoal-red power plants, the primary energy demand woulddecrease by 3.98E 13 MJ, and the mitigation of AP, EP, GWP, HTP,and ODP would be 4.57E 10 kg SO2-equivalent,3.96E 09 kg PO43-equivalent, 4.75E 12 kg CO2-equivalent,1.29E 12 kg DCB-equivalent, 7.06E 03 kgR11-equivalent, and2.32E 09 kg ethane-equivalent, respectively. However, it's notrealistic to replace coal by PV in total China now due to the highereconomic cost of PV compared to coal-red generation, and somearea with very low solar radiation is not suitable for installation PV.However, it is possible to replace coal-red generation graduallywith PV power generation considering cost decreasing and the helpof subsidies and incentives by government. In the near future China,both the large-scale grid-connected PV system and small distrib-uted PV system are foreseen to large scale of the application.

In fact, more than 90% of the PV products produced in Chinawere exported to foreign countries, such as the USA and Europe,which implied that the production stages that consumed energyand discharged pollutants were located in China, but the use phase,which was almost completely clean, was located in foreign

of different power generation systems in China.

Jiangsu to Tibet Jiangsu to Beijing

2.69E-04 (3.82E-06)a 3.43E-04 (1.21E-06)2.67E-05 (6.68E-07) 3.39E-05 (2.11E-07)3.20E-02 (6.36E-04) 4.07E-02 (2.01E-04)1.10E-02 (2.05E-05) 1.42E-02 (6.47E-06)1.87E-09 (1.19E-12) 2.41E-09 (3.77E-13)1.69E-05 (3.28E-07) 2.16E-05 (1.04E-07)

rtation.

r Prcountries. That was, the export of PV products was a transfer ofpollution, and the importing country should take responsibility forthe pollution. On the other hand, from the perspective of globalenvironmental protection, compared to Europe and the USA, it wasmore appropriate to install PV systems in China because it had bothlarge electricity demand and large CO2 and primary energy con-sumption reduction potentials (Kawajiri and Genchi, 2012).Therefore, the impact of replacing Chinese power plants with PVcould be much better.

4.2. Location and transportation effect

In the study of the environmental impacts, the location of thePV systems and transportation effects were not taken into accountin the above analysis. However, they did affect the results. Forconvenience of calculation, we simplied the problem, consideringonly the installation location of PV systems rst. According to theregional distribution characteristics of solar radiation, the Chinesearea was divided into ve regions (Kawajiri et al., 2011). Theenvironmental impacts per kWh electricity generated by PV sys-tems located in these regions differed because their life-cyclegeneration capacities vary due to the different solar radiationthey receive. Taking the AP for example, the AP of PV systemslocated in rst-class areas was 2.65E-04e3.0E-04 kg SO2-e/kWh,that of PV systems located in second-class areas was 3.0E-04e3.43E-04 kg SO2-e/kWh, and that in fth-class areas was4.77E-04e7.2E-04 kg SO2-e/kWh. The life-cycle generation ca-pacity of PV systems located in rst-class areas was twice that infth-class areas, and the environmental impacts per kWh wereless than half of that in fth-class areas. Thus, for the same PVsystem, the installation location in China strongly affected itsenvironmental impacts. It was appropriate to install PV system inareas with high solar radiation, such as the Tibet AutonomousRegion, northeastern Qinghai and western borders of Gansu, aswell as southern Inner Mongolia, northern Shanxi and Ningxia,central and northwest Gansu, eastern Qinghai, southeast Tibet,and southern Xinjiang. However, research show that current PVsystems in China were mainly located in Beijing and Hebei, wherethe cumulative capacity accounted for 73.1% and 8.3% of the totalcapacity in China (Chen and Wang, 2012). In addition, the PVproduction companies were clustered in the Yangtze Delta area,Pearl River Delta area, and Bohai Rim, including Guangdong,Zhejiang, Shanghai, Beijing, and Jiangsu (Chen and Shen, 2012).Accounting for the transportation of PV modules from the pro-ducing area to operating area would change the calculated envi-ronmental impacts of PV systems.

To determine how the transportation affected the energy de-mand and environmental impacts, we discussed the following twosituations: modules transported by container truck from Jiangsu tothe Tibet Autonomous Region and to Beijing. The distance fromJiangsu to Tibet was approximately 4500 km, and that to Beijingwas approximately 1100 km.

From the previous study, we knew that Tibet was a rst-classarea with an annual solar radiation of 7560 MJ m2 a1, and thegenerating capacity of a poly-Si PV system located there was39.4 kWh throughout its life cycle. Beijing was a third-class areawith an annual solar radiation of 5850 MJ m2 a1, and thegenerating capacity of a poly-Si PV system located there was30.5 kWh through its life cycle.

The total primary energy demand of the transport of PV mod-ules from Jiangsu to Tibet was 0.36 MJ/Wp, which was, 9.14E-3 MJ/kWh, 2.7% of the primary energy demand of the whole PV system,and that of PV modules from Jiangsu to Beijing was 0.087 MJ/Wp,which was, 2.85E-3 MJ/kWh, 0.69% of the whole PV system. Taking

Y. Fu et al. / Journal of Cleanethe transportation of modules into account, the AP of the PV system5. Conclusions

Briey, the most important results of the analysis were thecalculation of a primary energy demand of 12.61 MJ/Wp, that was,0.041e0.87 MJ/kWh, and an energy payback time of 2.2e6.1 yearsof multi-Si PV systems produced and installed in China areas. Giventhat the lifespan of PV system was approximately 25 years, it ispractical and economic to install the PV systems in China.

Concerning the primary energy demand and environmentalimpacts, such as AP, EP, GWP, HTP, and POCP, the stage of multi-Siproduction contributed the most due to its large consumption ofelectricity, which was mainly produced by coal-red power plantsin China (National Energy Administration of China, 2012), leadingto high energy consumption and pollution.

Compared with the other power generation systems, we foundthe multi-Si PV systems to be cleaner. If multi-Si PV systemscompletely replaced the coal-red power plants of China in 2011,the primary energy demand would decrease by 3.98E 13 MJ andthe other environmental impacts would be highlymitigated. On theother hand, from the perspective of the environmental protectionof the whole world, it was better to install PV systems in China thanto export them.

The transportation of PV modules didn't contribute much(less than 3%) to the total primary energy demand and envi-ronmental impacts. In addition, areas with high solar radiation,such as the Tibet Autonomous Region, northeastern Qinghai, andwestern borders of Gansu, were most suitable for installing thePV systems from the perspective of environmental protection. Inthe future, we will discuss the PV systems produced and locatedin any other regions in China in depth and study the environ-mental impacts of improved PV technologies and productionlocated in Tibet and Beijing was 2.69E-04 kg SO2-e/kWh and 3.44E-04 kg SO2-e/kWh, and the AP of transport accounted for 1.33% and0.33%, respectively. The environmental impacts of the total PVsystem and transportation per kWh were shown in Table 5.

Obviously, in terms of all the environmental impacts, themodule transportation from Jiangsu to Tibet was larger than thatfrom Jiangsu to Beijing because the distance from Jiangsu to Tibet ismuch longer. However, even if considering the transportation ofmodules, all of the environmental impacts per kWh of PV systemslocated in Tibet were less than those in Beijing due to the bettergenerating capacity of the PVs located in Tibet, which has greatersolar irradiation. In addition, the environmental impacts of PVlocated in Beijing were less than those in Jiangsu, which werefourth-class areas. Therefore, considering the impact of long-distance transportation, the rst-class areas represented by Tibetwere still the most suitable place for the installation of multi-Si PVsystems, with the least environmental impacts.

Furthermore, life cycle environmental burden of high-concentration PV systems was much lower than that of the at-plate c-Si systems operating in the same high-insolation regions(Fthenakis and Kim, 2013). Therefore, itll be more environmentallyfriendly to develop the high-concentration photovoltaic systems.Now the grid in China is ready for large scale PV production, and thedevelopment of intelligent electric grid will promote the gridconnection of PV system. After gird connected operation of PV,there is capacity for transporting electricity throughout the countryby the grid. But the economic cost of PV is higher than electricitygenerated by coal-red power plants now. Thus, Chinese govern-ment is committed to grid parity of PV by subsidy and technologicalinnovation.

oduction 86 (2015) 180e190 189processes.

Acknowledgments

This research was nancially supported by the Natural ScienceFoundation of China (41222012), the Public Welfare Project of the

Jungbluth, N., 2005. Life cycle assessment of crystalline photovoltaics in the swissecoinvent database. Prog. Photovolt. 13, 429e446.

Kannan, R., Leong, K.C., Osman, R., Ho, H.K., Tso, C.P., 2006. Life cycle assessmentstudy of solar PV systems: an example of a 2.7 kW(p) distributed solar PVsystem in Singapore. Sol. Energy 80, 555e563.

Kato, K., Murata, A., Sakuta, K., 1998. Energy pay-back time and life-cycle CO2emission of residential PV power system with silicon PV module. Prog. Photo-volt. 6, 105e115.

Y. Fu et al. / Journal of Cleaner Production 86 (2015) 180e190190Ministry of Environmental Protection (201009058), the Program forNew Century Excellent Talents in University (NCET-11-0244), andthe Fundamental Research Funds for Central Universities(1124021114).

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.jclepro.2014.07.057.

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Life-cycle assessment of multi-crystalline photovoltaic (PV) systems in China1. Introduction2. Materials and methods2.1. System boundary and description2.2. Data sources and LCA inventory2.3. Life-cycle impact assessment (LCIA)

3. Results3.1. Primary energy demand and energy payback time (EPBT)3.2. Environmental impacts3.3. Normalization3.4. Sensitivity analyses

4. Discussion4.1. Comparison with other power generation systems in China4.2. Location and transportation effect

5. ConclusionsAcknowledgmentsAppendix A. Supplementary dataReferences