ArticlePDF Available

The Energy and Environmental Performance of Ground-Mounted Photovoltaic Systems—A Timely Update

Authors:

Abstract and Figures

Given photovoltaics’ (PVs) constant improvements in terms of material usage and energy efficiency, this paper provides a timely update on their life-cycle energy and environmental performance. Single-crystalline Si (sc-Si), multi-crystalline Si (mc-Si), cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) systems are analysed, considering the actual country of production and adapting the input electricity mix accordingly. Energy pay-back time (EPBT) results for fixed-tilt ground mounted installations range from 0.5 years for CdTe PV at high-irradiation (2300 kWh/(m2·yr)) to 2.8 years for sc-Si PV at low-irradiation (1000 kWh/(m2·yr)), with corresponding quality-adjusted energy return on investment (EROIPE-eq) values ranging from over 60 to ~10. Global warming potential (GWP) per kWhel averages out at ~30 g(CO2-eq), with lower values (down to ~10 g) for CdTe PV at high irradiation, and up to ~80 g for Chinese sc-Si PV at low irradiation. In general, results point to CdTe PV as the best performing technology from an environmental life-cycle perspective, also showing a remarkable improvement for current production modules in comparison with previous generations. Finally, we determined that one-axis tracking installations can improve the environmental profile of PV systems by approximately 10% for most impact metrics.
Content may be subject to copyright.
energies
Article
The Energy and Environmental Performance of
Ground-Mounted Photovoltaic Systems—A
Timely Update
Enrica Leccisi 1,3, Marco Raugei 2,3 and Vasilis Fthenakis 3,4, *
1Department of Science and Technology, Parthenope University of Naples, Centro Direzionale-Isola C4,
Naples 80143, Italy; enrica.leccisi@uniparthenope.it
2Department of Mechanical Engineering and Mathematical Sciences, Oxford Brookes University,
Wheatley OX33 1HK, UK; marco.raugei@brookes.ac.uk
3Center for Life Cycle Analysis, Columbia University, New York, NY 10027, USA
4Photovoltaic Environmental Research Center, Brookhaven National Laboratory, Upton, NY 11973, USA
*Correspondence: vmf5@columbia.edu; Tel.: +1-212-854-8885
Academic Editor: Gabriele Grandi
Received: 26 May 2016; Accepted: 27 July 2016; Published: 8 August 2016
Abstract:
Given photovoltaics’ (PVs) constant improvements in terms of material usage and
energy efficiency, this paper provides a timely update on their life-cycle energy and environmental
performance. Single-crystalline Si (sc-Si), multi-crystalline Si (mc-Si), cadmium telluride (CdTe)
and copper indium gallium diselenide (CIGS) systems are analysed, considering the actual
country of production and adapting the input electricity mix accordingly. Energy pay-back time
(EPBT) results for fixed-tilt ground mounted installations range from 0.5 years for CdTe PV at
high-irradiation (2300 kWh/(m
2¨
yr)) to 2.8 years for sc-Si PV at low-irradiation (1000 kWh/(m
2¨
yr)),
with corresponding quality-adjusted energy return on investment (EROI
PE-eq
) values ranging from
over 60 to ~10. Global warming potential (GWP) per kWh
el
averages out at ~30 g (CO
2
-eq), with lower
values (down to ~10 g) for CdTe PV at high irradiation, and up to ~80 g for Chinese sc-Si PV at
low irradiation. In general, results point to CdTe PV as the best performing technology from an
environmental life-cycle perspective, also showing a remarkable improvement for current production
modules in comparison with previous generations. Finally, we determined that one-axis tracking
installations can improve the environmental profile of PV systems by approximately 10% for most
impact metrics.
Keywords:
photovoltaic (PV); crystalline Si (c-Si); cadmium telluride (CdTe); copper indium
gallium diselenide (CIGS); life cycle assessment (LCA); net energy analysis (NEA); energy return on
investment (EROI); energy pay-back time (EPBT); environmental performance
1. Introduction
Nowadays, one of the most important environmental challenges is to reduce the use of fossil
fuels, such as coal, oil, and natural gas, and the associated greenhouse gas (GHG) emissions into the
atmosphere. In particular, electricity and heat production accounts for one quarter of the world’s GHG
emissions [
1
]; in parallel with this, United Nations projections show that world population is growing
significantly, as are the related rates of per capita consumption [2].
Meanwhile, the global solar photovoltaic (PV) market has been growing rapidly to address this
issue and to meet the increasing demand for green power; PV’s cumulative installed capacity at the end
of 2015 was 227 GW
p
[
3
], resulting from 100-fold growth over 14 years of development. The compound
annual growth rate (CAGR) of PV installations was 44% between 2000 and 2014. The market in Europe
has progressed from 7 GW
p
in 2014 to around 8 GW
p
in 2015, while in the US it has grown to 7.3 GW
p
,
Energies 2016,9, 622; doi:10.3390/en9080622 www.mdpi.com/journal/energies
Energies 2016,9, 622 2 of 13
with large-scale and third-party ownership dominating. China and Japan have become the biggest PV
markets with annual (2014) deployments of 11 GW
p
and 9.5 GW
p
respectively, and corresponding
cumulative capacities of 28.2 GW
p
and 23.3 GW
p
[
3
]. In addition, several established markets have
confirmed their maturity, including Korea with 1.0 GW
p
, Australia with 0.9 GW
p
, and Canada with
0.6 GWp[3].
PV systems may be classified into first, second, and third generation technologies—first generation
technologies are based on single- and multi-crystalline silicon (c-Si); second generation technologies
consist of thin film technologies such as amorphous silicon (a-Si), multi-junction thin silicon film
(a-Si/
µ
c-Si), cadmium telluride (CdTe), copper indium (di)selenide/(di)sulphide (CIS), and copper
indium gallium (di)selenide/(di)sulphide (CIGS); third generation technologies include concentrator
PVs, organics, and others [4].
Within this variety of technologies, Si-wafer based (first generation) technologies account for
approximately 92% of total production, while CdTe PV represents the largest contributor to non-silicon
based PV systems. Currently, the market for CdTe PV is still virtually dominated by a single producer,
First Solar (Springerville, AZ, USA), with over 10 GW installed worldwide [5].
Generally, PV systems can be mounted on roof tops—commonly named building adapted
photovoltaic (BAPV) systems, and they can be integrated into building facades or roofs—also referred
to as building integrated photovoltaic (BIPV) systems, or they can be mounted on frames directly on
the ground.
There has been constant improvement in the material and energy efficiency of PV cells and
panels [
6
14
]; therefore, an up-to-date estimate of the energy and environmental performance of PV
technologies is of key importance for long-term energy strategy decisions.
This paper provides such an update from both the life cycle assessment (LCA) and net energy
analysis (NEA) perspectives for the main commercially relevant large-scale PV technologies as of
today [3], namely: single-crystalline Si (sc-Si), multi-crystalline Si (mc-Si), CdTe, and CIGS.
2. Methodology
2.1. Life Cycle Assessment
LCA is a discipline widely used in the scientific community and it is considered to be the most
comprehensive approach to assessing the environmental impact and overall efficiency of a product
or a system throughout all stages of its life cycle. LCA takes into account a product’s full life cycle
from the extraction of resources and the production of raw materials, to manufacturing, distribution,
use and re-use, maintenance, and finally recycling and disposal of the final product—including all
transportation and use of energy carriers. Since its inception and first standardization by the society
of environmental toxicology and chemistry (SETAC) [
15
], LCA has become more and more complex,
eventually leading to International Organization for Standardization (ISO) Standards 14040 and
14044 [
16
,
17
]. The latter are followed here, as well as the more PV-specific guidelines provided by the
International Energy Agency (IEA) [18].
Besides addressing a number of environmental impact categories, such as global warming, ozone
depletion, and acidification, LCA also allows the calculation of the total primary energy (PE) harvested
from the environment in order to produce a given amount of end product (i.e., electricity in the case of
PV), commonly named cumulative energy demand (CED) [19].
In the case of a PV system, the CED is thus defined as:
CED “ pPE `Invq{Outel (1)
where PE is the primary energy (sunlight) directly harvested from nature by the PV system and
converted into electricity over its entire lifetime; Inv is the additional PE indirectly “invested” in order
to produce, deploy, maintain, and decommission the PV system; Out
el
is the total energy output over
the PV system’s lifetime, in units of electricity.
Energies 2016,9, 622 3 of 13
The main indication provided by the CED is related to the system’s efficiency in using PE resources.
However, consistent with LCA’s long-term focus, the CED makes no differentiation between the energy
that is directly extracted, delivered, and transformed (PE) and the energy that needs to be invested in
order to do so (Inv).
2.2. Net Energy Analysis
NEA offers an alternative point of view on the performance of energy production systems such as
PVs: it evaluates how effective (as contrasted to efficient) a system is at exploiting PE resources and
converting them into usable energy carriers. In other words, the purpose of NEA is to quantify the
extent to which a given system or process is able to provide a positive energy surplus to the end user,
also referred to as net energy gain (NEG), after accounting for all the energy losses occurring along
process chains (such as extraction, transformation, delivery, and others) as well as for all the additional
energy investments that are required in order to carry out the same chain of processes [2026].
The principle metric of NEA is the energy return on investment (EROI), which is calculated as the
ratio of the energy delivered to society to the sum of energy carriers diverted from other societal uses.
Specifically, for a PV system [27], and using the same nomenclature as in Equation (1):
EROIel Outel{Inv (2)
also:
EROIPE-eq OutPE-eq{Inv “ pOutel{ηGq{Inv (3)
where Out
PE-eq
is the energy delivered to society in units of equivalent PE;
ηG
is the life cycle energy
efficiency of the electricity grid of the country or region where the analysed PV system is deployed
(calculated as the ratio of the yearly electricity output of the entire grid to the total PE harvested from
the environment for the operation of the grid in the same year).
At the very minimum, the EROI
PE-eq
of an electricity production system must be higher than 1,
i.e., the system must ensure the provision of a positive net energy gain (NEG) to the end user:
NEG OutPE-eq ´Inv (4)
In fact, it is actually important that the system has a sufficiently large EROI, beyond unity. In other
words, EROI
PE-eq
> 1 (implying NEG > 0) is a necessary but not sufficient condition, given that
the purpose of an electricity production system is to contribute to the support of the entire energy
metabolism of a modern society, and not just to provide enough net energy to support itself [2830].
The accurate quantification of the minimum EROI
PE-eq
that makes a technology viable depends
on a number of factors related to the energy supply mix for each country considered, and is beyond the
scope of this paper. In any case, it is important to keep in mind the all-important non-linear relation of
EROIPE-eq to the actual ratio of net–to–gross (NTG) energy output:
NTG “ pOutPE-eq ´Invq{OutPE-eq “ pEROIPE-eq ´1q{EROIPE-eq (5)
The energy pay back time (EPBT) is also calculated for each PV technology considered. EPBT
measures how many years it takes for the PV system to return an amount of electricity that is considered
to be equivalent to the PE invested. In other words, the EPBT is the time after which the system is able
to provide a positive NEG. Operationally:
EPBT Inv{rpOutel{Tq{ηGqs “ T{EROIPE-eq (6)
where Tis the lifetime of the PV system, measured in years.
In this paper, the calculations of EROI
PE-eq
and EPBT are based on a generalized average grid mix
efficiency (
ηG«
0.30), assuming a common grid mix largely reliant on thermal technologies. This is in
order to provide sufficiently generic information and to ensure that the comparison of all the analysed
Energies 2016,9, 622 4 of 13
technologies is consistent both internally and externally with most other literature reviews. In other
words, this means that the two metrics (EROI
PE-eq
and EPBT) do not refer to any specific country
with its own electricity grid mix, but to a theoretical average representative mix, and that in order to
be strictly applicable to a specific country, their values would have to be adapted based on the real
life-cycle efficiency of its grid.
2.3. Data Sources and Scope
In order to carry out the analysis in the most consistent way possible, all the performance
indicators were calculated based on the same underlying inventory data. The main background data
source was the Ecoinvent V3.1 Database (Ecoinvent, Zurich, Switzerland) [
31
]; whenever needed,
the data were adapted to the actual production conditions in order to be as accurate and realistic as
possible. In particular, the latest electricity generation mixes of the countries of production were used.
Regarding the foreground inventory, all the outputs were estimated based on the latest available
data. For CdTe PV, the most up-to-date production data were provided directly by First Solar, who also
provided information on the balance of system (BOS) for typical ground-mounted installations (this same
installation type was extended to apply to all other technologies too). For c-Si PV and CIGS technologies,
the inventory data source was the latest IEA-photovoltaic power systems (PVPS) Task 12 Report [32].
In particular, the latter refers to a literature study published in 2014 but reporting data from
2011 [
33
]. This means that the original inventory database used for our c-Si analysis is ultimately not
very recent—but it is still the most up to date reliable source of information available. Also, in our
analysis, the efficiencies of all the PV technologies as well as the electric mixtures used in the Si supply
chain and for PV module production (Section 3.2) have been updated to reflect the current (2015) situation.
End of life (EOL) management and decommissioning of the PV systems were not included in this
work because these depend of a number of factors and specific conditions, such as the exact location of
the PV plant, the type of PV panel, transport costs, logistic criteria, production quantities, weight per
Wp, and others [
34
]—and making specific assumptions in this regard would not be consistent with the
aim of the paper to provide an average worldwide high-level point of view. However, including EOL
stages may in fact not result in a worsening of the overall energy and environmental performance,
since the recycling of the PV components can often provide environmental and economic benefits,
especially for c-Si PV panels, given the high value of recycled aluminium and silicon [35].
The contribution of energy storage is likewise not included in our analyses. First, since the
main focus is on a high-level comparison between a range of different PV technologies—not an
analysis of specific countries and particular locations—energy storage is beyond the scope of this paper.
Secondly, many electricity production technologies, including but not limited to PVs, are unable to
single-handedly follow the dynamics of societal electricity demand. Hence, energy storage deployment
is required at grid level—rather than for each electricity generation technology taken in isolation [
36
].
Thirdly, even when performing an analysis at grid level, it is recommended to take into account the
smoothing effect produced by the combination of renewable energy sources, such as PV and wind [
37
].
Finally, from a practical standpoint, the analysis was performed using the LCA software
package SimaPro 8 (Pré Consultants, Amersfoort, The Netherlands) [
38
]—and impact assessment was
performed by means of the CML method developed by Leiden University in the Netherlands [39].
3. System Descriptions
3.1. Photovoltaic System Process Stages
The PV systems analysed are composed of PV panels and BOS (mechanical and electrical
components such as inverters, transformers, and cables, as well as system operation and maintenance).
The PV panel technologies considered are: sc-Si, mc-Si, CdTe, and CIGS.
In particular, with regard to c-Si manufacturing, there are more steps to arrive at the final product
in comparison with thin-film PVs (CdTe and CIGS), and a comparatively large amount of energy is
required for the production of crystalline silicon [10,31].
Energies 2016,9, 622 5 of 13
Figures 1and 2show the respective flow diagrams for the c-Si and thin film PV systems.
In particular, Figure 1illustrates each step of the manufacturing chain for sc-Si and mc-Si PV panels.
After the metallurgical (MG) and solar grade (SoG) Si production stages, mc-Si ingots are cast and
sawn into wafers: sc-Si PV cells additionally require an intermediate Czochralski (CZ) recrystallization
step. Then, the individual PV cells are encapsulated between glass panes and assembled into framed
PV panels, and finally the PV system is completed by the addition of the BOS. In contrast, Figure 2
shows that the simpler flow diagrams for CdTe and CIGS technologies. Incidentally, the thin film PV
panels are also glass-glass sandwiches, but devoid of metal frames.
Energies2016,9,6225of13
sawnintowafers:scSiPVcellsadditionallyrequireanintermediateCzochralski(CZ)
recrystallizationstep.Then,theindividualPVcellsareencapsulatedbetweenglasspanesand
assembledintoframedPVpanels,andfinallythePVsystemiscompletedbytheadditionofthe
BOS.Incontrast,Figure2showsthatthesimplerflowdiagramsforCdTeandCIGStechnologies.
Incidentally,thethinfilmPVpanelsarealsoglassglasssandwiches,butdevoidofmetalframes.
Figure1.FlowdiagramforsinglecrystallineSi(scSi)andmulticrystallineSi(mcSi)photovoltaic
(PV)systems.SoG:solargrade;andCZ:Czochralski.
Figure2.Flowdiagramforcadmiumtelluride(CdTe)andcopperindiumgalliumdiselenide(CIGS)
PVsystems.BOS:balanceofsystem
3.2.ProductionSitesandElectricityMixes
EachanalysedPVsystemisalsoclassifiedbycountryofproduction.ThecSiPVproduction
chainisclassifiedintothreemainproducingregions:Europe,China,andtheUSA,accordingtothe
datasourceused[32].ThescSiandmcSiwafersusedinChinesePVmanufacturingareentirely
sourceddomestically;ofthoseusedinUSPVmanufacturing,66%areproducedinChinaand34%
domestically;andforthoseusedinEuropeanPVmanufacturing,89%isproducedlocallyand11%in
China.RegardingCdTePVpanels,thetwoproductioncountriesasof2016areMalaysiaandthe
USA,inaccordancewiththedataprovidedbytheleadingcompanyinthissector(FirstSolar).The
mainproductioncountriesforCIGSPVareJapan(SolarFrontier)[40],towhichouranalysisrefers,
andChina(Hanergy).AllfurtherupstreamstepsintheSisupplychainareanalysedconsidering
theiractualgeographicallocation—forinstance,theproductionofMGSiisdividedamongthemain
globalproducers,i.e.,China,Russia,NorwayandtheUnitedStates[41].
TheindividuallocalupdatedelectricitymixesusedforallPVmodulemanufacturingandfor
theSisupplyingcountriesarealsoconsideredinouranalysis,sincetheyinfluencetheamountofPE
ultimatelyrequiredforeachproductionprocess,aswellastheassociatedenvironmentalimpacts
(NorwegianandJapanesedatafromtheIEA[42];ChineseandUSAdatafromtheU.S.Energy
InformationAdministration(EIA)[43];RussianandEuropeandatafromtheWorldBank(world
Figure 1.
Flow diagram for single-crystalline Si (sc-Si) and multi-crystalline Si (mc-Si) photovoltaic
(PV) systems. SoG: solar grade; and CZ: Czochralski.
Energies2016,9,6225of13
sawnintowafers:scSiPVcellsadditionallyrequireanintermediateCzochralski(CZ)
recrystallizationstep.Then,theindividualPVcellsareencapsulatedbetweenglasspanesand
assembledintoframedPVpanels,andfinallythePVsystemiscompletedbytheadditionofthe
BOS.Incontrast,Figure2showsthatthesimplerflowdiagramsforCdTeandCIGStechnologies.
Incidentally,thethinfilmPVpanelsarealsoglassglasssandwiches,butdevoidofmetalframes.
Figure1.FlowdiagramforsinglecrystallineSi(scSi)andmulticrystallineSi(mcSi)photovoltaic
(PV)systems.SoG:solargrade;andCZ:Czochralski.
Figure2.Flowdiagramforcadmiumtelluride(CdTe)andcopperindiumgalliumdiselenide(CIGS)
PVsystems.BOS:balanceofsystem
3.2.ProductionSitesandElectricityMixes
EachanalysedPVsystemisalsoclassifiedbycountryofproduction.ThecSiPVproduction
chainisclassifiedintothreemainproducingregions:Europe,China,andtheUSA,accordingtothe
datasourceused[32].ThescSiandmcSiwafersusedinChinesePVmanufacturingareentirely
sourceddomestically;ofthoseusedinUSPVmanufacturing,66%areproducedinChinaand34%
domestically;andforthoseusedinEuropeanPVmanufacturing,89%isproducedlocallyand11%in
China.RegardingCdTePVpanels,thetwoproductioncountriesasof2016areMalaysiaandthe
USA,inaccordancewiththedataprovidedbytheleadingcompanyinthissector(FirstSolar).The
mainproductioncountriesforCIGSPVareJapan(SolarFrontier)[40],towhichouranalysisrefers,
andChina(Hanergy).AllfurtherupstreamstepsintheSisupplychainareanalysedconsidering
theiractualgeographicallocation—forinstance,theproductionofMGSiisdividedamongthemain
globalproducers,i.e.,China,Russia,NorwayandtheUnitedStates[41].
TheindividuallocalupdatedelectricitymixesusedforallPVmodulemanufacturingandfor
theSisupplyingcountriesarealsoconsideredinouranalysis,sincetheyinfluencetheamountofPE
ultimatelyrequiredforeachproductionprocess,aswellastheassociatedenvironmentalimpacts
(NorwegianandJapanesedatafromtheIEA[42];ChineseandUSAdatafromtheU.S.Energy
InformationAdministration(EIA)[43];RussianandEuropeandatafromtheWorldBank(world
Figure 2.
Flow diagram for cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS)
PV systems. BOS: balance of system.
3.2. Production Sites and Electricity Mixes
Each analysed PV system is also classified by country of production. The c-Si PV production
chain is classified into three main producing regions: Europe, China, and the USA, according to the
data source used [
32
]. The sc-Si and mc-Si wafers used in Chinese PV manufacturing are entirely
sourced domestically; of those used in US PV manufacturing, 66% are produced in China and 34%
domestically; and for those used in European PV manufacturing, 89% is produced locally and 11%
in China. Regarding CdTe PV panels, the two production countries as of 2016 are Malaysia and
the USA, in accordance with the data provided by the leading company in this sector (First Solar).
The main production countries for CIGS PV are Japan (Solar Frontier) [
40
], to which our analysis refers,
and China (Hanergy). All further upstream steps in the Si supply chain are analysed considering their
actual geographical location—for instance, the production of MG-Si is divided among the main global
producers, i.e., China, Russia, Norway and the United States [41].
The individual local updated electricity mixes used for all PV module manufacturing and for
the Si supplying countries are also considered in our analysis, since they influence the amount
of PE ultimately required for each production process, as well as the associated environmental
impacts (Norwegian and Japanese data from the IEA [
42
]; Chinese and USA data from the U.S.
Energies 2016,9, 622 6 of 13
Energy Information Administration (EIA) [
43
]; Russian and European data from the World Bank
(world development indicators) [44]; Malaysian data from the Peninsular Malaysia electricity supply
industry outlook [45].)
4. Results and Discussion
4.1. Fixed-Tilt Ground-Mounted Photovoltaic Systems
Figure 3shows the CED of the analysed PV systems, while Figures 46illustrate the respective
LCA impact indicators, namely global warming potential (GWP), acidification potential (AP),
and ozone depletion potential (ODP), all expressed per kW
p
—the stacked bars show the individual
contributions of the main life cycle stages. Each PV technology is also shown separately according
to the country or region in which it was manufactured. The average efficiency for each technology is
assumed in accordance with the latest report by the Fraunhofer Institute for Solar Energy Systems [
40
],
specifically: 17% for sc-Si PV, 16% for mc-Si, 15.6% for CdTe PV, and 14% for CIGS PV.
Energies2016,9,6226of13
developmentindicators)[44];MalaysiandatafromthePeninsularMalaysiaelectricitysupply
industryoutlook[45].)
4.ResultsandDiscussion
4.1.FixedTiltGroundMountedPhotovoltaicSystems
Figure3showstheCEDoftheanalysedPVsystems,whileFigures4–6illustratetherespective
LCAimpactindicators,namelyglobalwarmingpotential(GWP),acidificationpotential(AP),and
ozonedepletionpotential(ODP),allexpressedperkWp—thestackedbarsshowtheindividual
contributionsofthemainlifecyclestages.EachPVtechnologyisalsoshownseparatelyaccordingto
thecountryorregioninwhichitwasmanufactured.Theaverageefficiencyforeachtechnologyis
assumedinaccordancewiththelatestreportbytheFraunhoferInstituteforSolarEnergy
Systems[40],specifically:17%forscSiPV,16%formcSi,15.6%forCdTePV,and14%forCIGSPV.
0
5,000
10,000
15,000
20,000
25,000
30,000
BOS
PVpanel
PVcell
SoGSi
MJPE/kW
p
scSi PV multiSi PV CIGS PV
CdTePV
EU EU USUS CN CN MY US JP
Figure3.Cumulativeenergydemand(CED)perkWpoftheanalysedPVsystems.
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
2,000
BOS
PVpanel
PVcell
SoGSi
kg(CO
2
eq)/kWp
scSi PV multiSi PV CIGS PV
CdTePV
EU EU USUS CN CN MY US JP
Figure4.Globalwarmingpotential(GWP)perkWpoftheanalysedPVsystems.
Figure 3. Cumulative energy demand (CED) per kWpof the analysed PV systems.
Energies2016,9,6226of13
developmentindicators)[44];MalaysiandatafromthePeninsularMalaysiaelectricitysupply
industryoutlook[45].)
4.ResultsandDiscussion
4.1.FixedTiltGroundMountedPhotovoltaicSystems
Figure3showstheCEDoftheanalysedPVsystems,whileFigures4–6illustratetherespective
LCAimpactindicators,namelyglobalwarmingpotential(GWP),acidificationpotential(AP),and
ozonedepletionpotential(ODP),allexpressedperkWp—thestackedbarsshowtheindividual
contributionsofthemainlifecyclestages.EachPVtechnologyisalsoshownseparatelyaccordingto
thecountryorregioninwhichitwasmanufactured.Theaverageefficiencyforeachtechnologyis
assumedinaccordancewiththelatestreportbytheFraunhoferInstituteforSolarEnergy
Systems[40],specifically:17%forscSiPV,16%formcSi,15.6%forCdTePV,and14%forCIGSPV.
0
5,000
10,000
15,000
20,000
25,000
30,000
BOS
PVpanel
PVcell
SoGSi
MJPE/kW
p
scSi PV multiSi PV CIGS PV
CdTePV
EU EU USUS CN CN MY US JP
Figure3.Cumulativeenergydemand(CED)perkWpoftheanalysedPVsystems.
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
2,000
BOS
PVpanel
PVcell
SoGSi
kg(CO
2
eq)/kWp
scSi PV multiSi PV CIGS PV
CdTePV
EU EU USUS CN CN MY US JP
Figure4.Globalwarmingpotential(GWP)perkWpoftheanalysedPVsystems.
Figure 4. Global warming potential (GWP) per kWpof the analysed PV systems.
Energies 2016,9, 622 7 of 13
Figure 5. Acidification potential (AP) per kWpof the analysed PV systems.
Energies2016,9,6227of13
0
2
4
6
8
10
12
14
16
18
20
BOS
PVpanel
PVcell
SoGSi
kg(SO
2
eq)/kWp
scSi PV multiSi PV CIGS PV
CdTePV
EU EU USUS CN CN MY US JP
Figure5.Acidificationpotential(AP)perkWpoftheanalysedPVsystems.
0.0E+00
5.0E05
1.0E04
1.5E04
2.0E04
2.5E04
3.0E04
3.5E04
BOS
PVpanel
PVcell
SoGSi
kgCFC11eq
scSi PV multiSi PV CIGS PV
CdTePV
EU EU USUS CN CN MY US JP
Figure6.Ozonedepletionpotential(ODP)perkWpoftheanalysedPVsystems.
TheresultsclearlyshowthatthemostimpactingstepforcSitechnologiesisfromSoGSisupply
tofinishedPVcells,whichincludesingot/crystalgrowthandwaferandcellproduction,andespecially
sointhecaseofscSiPVsystems(becauseoftheenergyintensiveCZcrystalgrowthprocess).
Figure3highlightsthat,perkWp,cSiPVsystemsareoveralltwiceasenergydemandingto
produceasCdTePVsystems.Figure4illustratestheresultingGWPindicatorperkWp:cSiPV
technologiesgenerallyhavehighervaluesincomparisonwiththinfilmPVpanels,andinparticular,
thelowestGWPvaluesareforCdTePV,especiallywhenproductiontakesplaceinMalaysia.A
similartrendisshowninFigure5,inwhichthelowervaluesofAPperkWparethoseforCdTePV,
andsecondlyforCIGSPV;conversely,scSiPVshowsthehighestAPvalues,followedbymcSiPV.
AlsointermsofODPresults(Figure6),CdTePVisstillthebestperformer,followedbyCIGSPV,
andthenmcSiandscSiPV.
ThesenewresultsshowaremarkableimprovementforcurrentproductionCdTePVmodules
whencomparedtosimilarmodulesproducedin2005(themostrecentproductionyearforwhich
CdTePVinventorydataaredirectlyavailableintheEcoinventV3.1Database).Overonedecade,the
CEDperkWpfortheCdTePVmodulesmanufacturedintheUShasbeenreducedbyapproximately
62%,whiletheGWP,ODP,andAPresultsarealsodownbyrespectively63%,65%,and71%.The
Figure 6. Ozone depletion potential (ODP) per kWpof the analysed PV systems.
The results clearly show that the most impacting step for c-Si technologies is from SoG-Si supply
to finished PV cells, which includes ingot/crystal growth and wafer and cell production, and especially
so in the case of sc-Si PV systems (because of the energy intensive CZ crystal growth process).
Figure 3highlights that, per kW
p
, c-Si PV systems are overall twice as energy-demanding to produce
as CdTe PV systems. Figure 4illustrates the resulting GWP indicator per kW
p
: c-Si PV technologies
generally have higher values in comparison with thin film PV panels, and in particular, the lowest GWP
values are for CdTe PV, especially when production takes place in Malaysia. A similar trend is shown
in Figure 5, in which the lower values of AP per kW
p
are those for CdTe PV, and secondly for CIGS PV;
conversely, sc-Si PV shows the highest AP values, followed by mc-Si PV. Also in terms of ODP results
(Figure 6), CdTe PV is still the best performer, followed by CIGS PV, and then mc-Si and sc-Si PV.
These new results show a remarkable improvement for current production CdTe PV modules
when compared to similar modules produced in 2005 (the most recent production year for which CdTe
PV inventory data are directly available in the Ecoinvent V3.1 Database). Over one decade, the CED
per kW
p
for the CdTe PV modules manufactured in the US has been reduced by approximately 62%,
while the GWP, ODP, and AP results are also down by respectively 63%, 65%, and 71%. The current
CdTe PV systems also show improvements when compared to previously published results [
46
]
referring to more recent (2010–2011) production data; in this case the CED is down by approximately
30%, and the GWP is down by 37%.
Energies 2016,9, 622 8 of 13
It is noted, however, that the CED of complete ground-mounted CdTe PV systems are not much
lower than previously reported values, because the new inventory data for the ground-mounted BOS
provided by First Solar led to a higher energy demand (831 MJ/m
2
) than the previously used data
from the c-Si PV BOS (542 MJ/m
2
, First Solar) [
47
]. The same also applies to the calculated EPBT
values (Table 1).
Table 1.
Energy pay-back time (EPBT) of the analysed PV systems (mean values for the various
production sites), corresponding to the three considered irradiation levels.
Irradiation and Grid Efficiency (η)sc-Si PV mc-Si PV CdTe PV CIGS PV
1000 kWh/(m2¨yr); η= 0.3 2.8 2.1 1.1 1.9
1700 kWh/(m2¨yr); η= 0.3 1.6 1.2 0.6 1.1
2300 kWh/(m2¨yr); η= 0.3 1.2 0.9 0.5 0.8
From a geographical perspective, it is also clear from the results that the considered impact
indicators (GWP, AP, ODP) are generally lower when the manufacturing takes place in Europe in
comparison with the USA and China, and in particular the Chinese production chain consistently
shows the highest indicator values. This is despite the fact that the CED associated to the Chinese
c-Si PV production is actually slightly lower than that for the European and USA manufacturing
chains—this seeming incongruence depends on the large reliance of the Chinese electric grid on
coal [
43
]. The input grid mix composition is also responsible for a significant share of the impacts in
the case of CIGS PV produced in Japan (a country where, after the 2011 nuclear incident in Fukushima,
over 90% of the energy resources used for electricity generation are fossil fuels [42]).
The BOS contribution is generally fairly low, with the partial exception of the AP results, which are
negatively affected by the comparatively large amounts of copper and aluminium required.
Figures 710 then illustrate the same results (CED, GWP, AP and ODP) expressed per kWh
el
.
These results are computed assuming a performance ratio of 0.8 and a lifetime of 30 years [
18
].
Also, in order to provide results applicable to different contexts, three different irradiation levels are
used, which are respectively representative of irradiation on a south-facing, latitude-tilted plane in
Central-Northern Europe (1000 kWh/(m
2¨
yr)), Central-Southern Europe (1700 kWh/(m
2¨
yr)), and the
Southwestern United States (2300 kWh/(m
2¨
yr)). In the figures, different symbol sizes (small, medium,
and large, respectively) are used to refer to these three specific irradiation levels.
Energies2016,9,6228of13
currentCdTePVsystemsalsoshowimprovementswhencomparedtopreviouslypublishedresults
[46]referringtomorerecent(2010–2011)productiondata;inthiscasetheCEDisdownby
approximately30%,andtheGWPisdownby37%.
Itisnoted,however,thattheCEDofcompletegroundmountedCdTePVsystemsarenotmuch
lowerthanpreviouslyreportedvalues,becausethenewinventorydataforthegroundmounted
BOSprovidedbyFirstSolarledtoahigherenergydemand(831MJ/m2)thanthepreviouslyused
datafromthecSiPVBOS(542MJ/m2,FirstSolar)[47].ThesamealsoappliestothecalculatedEPBT
values(Table1).
Fromageographicalperspective,itisalsoclearfromtheresultsthattheconsideredimpact
indicators(GWP,AP,ODP)aregenerallylowerwhenthemanufacturingtakesplaceinEuropein
comparisonwiththeUSAandChina,andinparticulartheChineseproductionchainconsistently
showsthehighestindicatorvalues.ThisisdespitethefactthattheCEDassociatedtotheChinese
cSiPVproductionisactuallyslightlylowerthanthatfortheEuropeanandUSAmanufacturing
chainsthisseemingincongruencedependsonthelargerelianceoftheChineseelectricgridoncoal
[43].Theinputgridmixcompositionisalsoresponsibleforasignificantshareoftheimpactsinthe
caseofCIGSPVproducedinJapan(acountrywhere,afterthe2011nuclearincidentinFukushima,
over90%oftheenergyresourcesusedforelectricitygenerationarefossilfuels[42]).
TheBOScontributionisgenerallyfairlylow,withthepartialexceptionoftheAPresults,which
arenegativelyaffectedbythecomparativelylargeamountsofcopperandaluminiumrequired.
Figures7–10thenillustratethesameresults(CED,GWP,APandODP)expressedperkWhel.
Theseresultsarecomputedassumingaperformanceratioof0.8andalifetimeof30years[18].Also,
inordertoprovideresultsapplicabletodifferentcontexts,threedifferentirradiationlevelsareused,
whicharerespectivelyrepresentativeofirradiationonasouthfacing,latitudetiltedplanein
CentralNorthernEurope(1000kWh/(m2yr)),CentralSouthernEurope(1700kWh/(m2yr)),andthe
SouthwesternUnitedStates(2300kWh/(m2yr)).Inthefigures,differentsymbolsizes(small,
medium,andlarge,respectively)areusedtorefertothesethreespecificirradiationlevels.
3.5
4.0
4.5
5.0
MJ
PE
/kWh
el
scSi PV mcSi PV CdTe PV CIGS PV
EU US CN EU US CN MY US JP
Figure7.CEDperkWheloftheanalysedPVsystems,underthreeirradiationlevels.Smallsymbols:
1000kWh/(m2yr);mediumsymbols:1700kWh/(m2yr);andlargesymbols:2300kWh/(m2yr).
Unsurprisingly,thebestenergyandenvironmentalperformanceasmeasuredbyallconsidered
metricsisthatofCdTePVsystemsinstalledintheSouthwesternUS,withCIGSPVasaclosesecond.
Attheotherendofthescale,thehighestimpactintermsofGWPandAParethosefortheChinese
producedscSiPV,mainlyduetothistechnology’shigherdemandforinputelectricity,coupled
withtheprominenceofcoalintheChineseelectricitygridmix.
Figure 7.
CED per kWh
el
of the analysed PV systems, under three irradiation levels. Small symbols:
1000 kWh/(m2¨yr); medium symbols: 1700 kWh/(m2¨yr); and large symbols: 2300 kWh/(m2¨yr).
Unsurprisingly, the best energy and environmental performance as measured by all considered
metrics is that of CdTe PV systems installed in the Southwestern US, with CIGS PV as a close second.
Energies 2016,9, 622 9 of 13
At the other end of the scale, the highest impact in terms of GWP and AP are those for the Chinese
produced sc-Si PV, mainly due to this technology’s higher demand for input electricity, coupled with
the prominence of coal in the Chinese electricity grid mix.
Energies2016,9,6229of13
0
10
20
30
40
50
60
70
80
90
100
g(CO
2
eq)/kWh
el
scSi PV mcSi PV CdTe PV CIGS PV
EU US CN EU US CN MY US JP
Figure8.GWPperkWheloftheanalysedPVsystems,underthreeirradiationlevels.Smallsymbols:
1000kWh/(m2yr);mediumsymbols:1700kWh/(m2yr);andlargesymbols:2300kWh/(m2yr).
0.0
0.2
0.4
0.6
0.8
1.0
g(SO
2
eq)/kWh
el
scSi PV mcSi PV CdTe PV CIGS PV
EU US CN EU US CN MY US JP
Figure9.APperkWheloftheanalysedPVsystems,underthreeirradiationlevels.Smallsymbols:
1000kWh/(m2yr);mediumsymbols:1700kWh/(m2yr);andlargesymbols:2300kWh/(m2yr).
0
1
2
3
4
5
6
7
8
µgCFC11eq
scSi PV mcSi PV CdTe PV CIGS PV
EU US CN EU US CN MY US JP
Figure10.ODPperkWheloftheanalysedPVsystems,underthreeirradiationlevels.Smallsymbols:
1000kWh/(m2yr);mediumsymbols:1700kWh/(m2yr);andlargesymbols:2300kWh/(m2yr).
AsillustratedinTable1,theenergypaybacktimesoftheanalysedPVtechnologieswerefound
torangefrom6months(forCdTePVinstalledintheUSSouthWest)toapproximately2–3years(for
cSiPVinstalledinCentralNorthernEurope).
Figure 8.
GWP per kWh
el
of the analysed PV systems, under three irradiation levels. Small symbols:
1000 kWh/(m2¨yr); medium symbols: 1700 kWh/(m2¨yr); and large symbols: 2300 kWh/(m2¨yr).
Energies2016,9,6229of13
0
10
20
30
40
50
60
70
80
90
100
g(CO
2
eq)/kWh
el
scSi PV mcSi PV CdTe PV CIGS PV
EU US CN EU U S CN MY US JP
Figure8.GWPperkWheloftheanalysedPVsystems,underthreeirradiationlevels.Smallsymbols:
1000kWh/(m2yr);mediumsymbols:1700kWh/(m2yr);andlargesymbols:2300kWh/(m2yr).
0.0
0.2
0.4
0.6
0.8
1.0
g(SO
2
eq)/kWh
el
scSi PV mcSi PV CdTe PV CIGS PV
EU US CN EU US CN MY US JP
Figure9.APperkWheloftheanalysedPVsystems,underthreeirradiationlevels.Smallsymbols:
1000kWh/(m2yr);mediumsymbols:1700kWh/(m2yr);andlargesymbols:2300kWh/(m2yr).
0
1
2
3
4
5
6
7
8
µgCFC11eq
scSi PV mcSi PV CdTe PV CIGS PV
EU US CN EU US CN MY US JP
Figure10.ODPperkWheloftheanalysedPVsystems,underthreeirradiationlevels.Smallsymbols:
1000kWh/(m2yr);mediumsymbols:1700kWh/(m2yr);andlargesymbols:2300kWh/(m2yr).
AsillustratedinTable1,theenergypaybacktimesoftheanalysedPVtechnologieswerefound
torangefrom6months(forCdTePVinstalledintheUSSouthWest)toapproximately2–3years(for
cSiPVinstalledinCentralNorthernEurope).
Figure 9.
AP per kWh
el
of the analysed PV systems, under three irradiation levels. Small symbols:
1000 kWh/(m2¨yr); medium symbols: 1700 kWh/(m2¨yr); and large symbols: 2300 kWh/(m2¨yr).
Energies2016,9,6229of13
0
10
20
30
40
50
60
70
80
90
100
g(CO
2
eq)/kWh
el
scSi PV mcSi PV CdTe PV CIGS PV
EU US CN EU U S CN MY US JP
Figure8.GWPperkWheloftheanalysedPVsystems,underthreeirradiationlevels.Smallsymbols:
1000kWh/(m2yr);mediumsymbols:1700kWh/(m2yr);andlargesymbols:2300kWh/(m2yr).
0.0
0.2
0.4
0.6
0.8
1.0
g(SO
2
eq)/kWh
el
scSi PV mcSi PV CdTe PV CIGS PV
EU US CN EU US CN MY US JP
Figure9.APperkWheloftheanalysedPVsystems,underthreeirradiationlevels.Smallsymbols:
1000kWh/(m2yr);mediumsymbols:1700kWh/(m2yr);andlargesymbols:2300kWh/(m2yr).
0
1
2
3
4
5
6
7
8
µgCFC11eq
scSi PV mcSi PV CdTe PV CIGS PV
EU US CN EU US CN MY US JP
Figure10.ODPperkWheloftheanalysedPVsystems,underthreeirradiationlevels.Smallsymbols:
1000kWh/(m2yr);mediumsymbols:1700kWh/(m2yr);andlargesymbols:2300kWh/(m2yr).
AsillustratedinTable1,theenergypaybacktimesoftheanalysedPVtechnologieswerefound
torangefrom6months(forCdTePVinstalledintheUSSouthWest)toapproximately2–3years(for
cSiPVinstalledinCentralNorthernEurope).
Figure 10.
ODP per kWh
el
of the analysed PV systems, under three irradiation levels. Small symbols:
1000 kWh/(m2¨yr); medium symbols: 1700 kWh/(m2¨yr); and large symbols: 2300 kWh/(m2¨yr).
Energies 2016,9, 622 10 of 13
As illustrated in Table 1, the energy pay-back times of the analysed PV technologies were found to
range from 6 months (for CdTe PV installed in the US South-West) to approximately 2–3 years (for c-Si
PV installed in Central-Northern Europe).
Figure 11 illustrates the positioning of the analysed PV systems along the curve defined by the
non-linear relation of EROI
PE-eq
to NTG (often referred to as the “net energy cliff” [
48
]). This figure
makes it abundantly clear that, while the individual EROI
PE-eq
values for the different PV systems
over the three considered irradiation levels span a comparatively large range—from ~10 for sc-Si PV at
1000 kWh/(m
2¨
yr) to ~60 for CdTe PV at 2300 kWh/(m
2¨
yr)—in fact, all data points sit on what may
be considered the “safe”, quasi-horizontal portion of the “cliff”. In other words, all PV systems afford
the benefit of over 90% of their gross energy output being available as net usable energy to the end
user (NTG > 0.9).
Energies2016,9,62210of13
Table1.Energypaybacktime(EPBT)oftheanalysedPVsystems(meanvaluesforthevarious
productionsites),correspondingtothethreeconsideredirradiationlevels.
IrradiationandGridEfficiency(η)scSiPV mcSiPV CdTePVCIGSPV
1000kWh/(m2yr);η=0.32.82.11.11.9
1700kWh/(m2yr);η=0.31.61.20.61.1
2300kWh/(m2yr);η=0.31.20.90.50.8
Figure11illustratesthepositioningoftheanalysedPVsystemsalongthecurvedefinedbythe
nonlinearrelationofEROIPEeqtoNTG(oftenreferredtoasthe“netenergycliff”[48]).Thisfigure
makesitabundantlyclearthat,whiletheindividualEROIPEeqvaluesforthedifferentPVsystems
overthethreeconsideredirradiationlevelsspanacomparativelylargerange—from~10forscSiPV
at1000kWh/(m2yr)to~60forCdTePVat2300kWh/(m2yr)—infact,alldatapointssitonwhatmay
beconsideredthe“safe”,quasihorizontalportionofthe“cliff”.Inotherwords,allPVsystems
affordthebenefitofover90%oftheirgrossenergyoutputbeingavailableasnetusableenergytothe
enduser(NTG>0.9).
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
010203040506070
NTG
EROI
PEeq
NetEnergyCliff scSiPV mcSiPV CdTePV CIGSPV
Figure11.PositioningoftheanalysedPVsystemsonthe“netenergycliff”(illustratingthe
nonlinearrelationofthenettogrossenergyoutputratiototheenergyreturnoninvestment
(EROIPEeq)),underthreeirradiationlevels.Smallsymbols:1000kWh/(m2yr);mediumsymbols:1700
kWh/(m2yr);andlargesymbols:2300kWh/(m2yr).
4.2.AComparisonto1AxisTrackingInstallations
Generally,trackingPVsystemsprovidethebenefitofboostingtheenergyyieldincomparison
withfixedtiltinstallationsbecausethepanelsaremountedonastructurethatfollowsthe
movementofthesun.Inparticular,oneaxistrackershaveonedegreeoffreedom(themovement
occursalongasingleaxisofrotation).Theresultsshownbelowcorrespondtoahorizontalrotational
axisintheNorthSouth(NS)directionwiththepanelsfacingEastinthemorningandfacingWestin
thelateafternoon.Trackingcouldbefurtheroptimizedwiththehorizontalrotationalaxistilted
southifthetopographyallows,whichwouldgivethebenefitofaflatterprofilethroughouttheday.
Ononehand,theinvestedenergy(andassociatedenvironmentalimpacts)forbuildingthe
trackingBOSarehigherthanforconventionalfixedtiltPVsystems,sincetrackinginstallations
requirelargeramountsofstructuralsteelandcoppercabling;also,theyuseelectricityduringthe
usagephasefortrackingactuators.Ontheotherhand,thekeyadvantageoftrackingsystemsisthe
abilitytoharvestmoredirectbeamirradiance,therebyrequiringfewerPVmodulesperkWh
producedincomparisonwithfixedtiltinstallations.
Theenergyandenvironmentalperformanceoftrackingsystemsarehighlyinfluencedbysite
latitudeanddiffusedlightconditions;inparticular,siteswithlower(<40%)diffusedlightbenefit
Figure 11.
Positioning of the analysed PV systems on the “net energy cliff” (illustrating the non-linear
relation of the net-to-gross energy output ratio to the energy return on investment (EROI
PE-eq
)),
under three irradiation levels. Small symbols: 1000 kWh/(m
2¨
yr); medium symbols: 1700 kWh/(m
2¨
yr);
and large symbols: 2300 kWh/(m2¨yr).
4.2. A Comparison to 1-Axis Tracking Installations
Generally, tracking PV systems provide the benefit of boosting the energy yield in comparison
with fixed-tilt installations because the panels are mounted on a structure that follows the movement
of the sun. In particular, one-axis trackers have one degree of freedom (the movement occurs along
a single axis of rotation). The results shown below correspond to a horizontal rotational axis in the
North-South (N-S) direction with the panels facing East in the morning and facing West in the late
afternoon. Tracking could be further optimized with the horizontal rotational axis tilted south if the
topography allows, which would give the benefit of a flatter profile throughout the day.
On one hand, the invested energy (and associated environmental impacts) for building the
tracking BOS are higher than for conventional fixed-tilt PV systems, since tracking installations require
larger amounts of structural steel and copper cabling; also, they use electricity during the usage phase
for tracking actuators. On the other hand, the key advantage of tracking systems is the ability to
harvest more direct beam irradiance, thereby requiring fewer PV modules per kWh produced in
comparison with fixed-tilt installations.
The energy and environmental performance of tracking systems are highly influenced by site
latitude and diffused light conditions; in particular, sites with lower (<40%) diffused light benefit more
Energies 2016,9, 622 11 of 13
from tracking systems. Also, the gain in PV yield is reported to range from +10% to +24% over tropical
and subtropical latitudes (0˝–40˝) [49].
Table 2shows the maximum achievable variations in LCA impact assessment results (GWP, AP,
OPD) and EPBTs for a range of one-axis tracking PV systems, expressed as relative to the corresponding
values for fixed-tilt PV installations, assuming a best-case scenario of 2300 kWh/(m
2¨
yr) irradiation,
and +24% enhanced capture efficiency with respect to latitude tilt fixed installations.
Table 2.
Life cycle impact assessment (LCIA) and EPBT results for one-axis tracking PV system
installations, per kWh
el
and relative to fixed-tilt installations. Assumed irradiation: 2300 kWh/(m
2¨
yr);
assumed energy harvesting gain due to tracking: +24%.
Indicator sc-Si PV mc-Si PV CdTe PV CIGS PV
GWP ´14% ´11% ´1% ´6%
AP ´12% ´9% ´7% ´16%
ODP ´13% ´11% ´4% ´9%
EPBT ´13.2% ´10.5% ´2.3% ´7.8%
In general terms, the c-Si PV systems were found to benefit the most from tracking installations
(over
´
10% impact). Instead, the advantage from tracking for CdTe PV (and also to a lesser extent for
CIGS PV) appear to be much smaller, due to the very good performance of these thin film technologies
in the first place, and hence the comparatively larger share of their overall impacts are due to the
BOS itself.
5. Conclusions
Overall, the ongoing improvements in terms of material usage for and energy efficiency of the
range of commercially-available PV technologies have been shown to be paralleled by correspondingly
better life-cycle energy and environmental performance. The most remarkable achievements have
been obtained by CdTe PV, which can boast a two-thirds reduction in environmental impacts over
the decade since its introduction to the market. Also importantly, our results definitively put to rest
the often voiced concerns about PV not providing large-enough net energy returns per unit of energy
invested: all analysed PV technologies have been shown to be able to afford a >90% net-to-gross
energy return ratio, even when deployed in less-than-optimal locations (e.g. at Central-Northern
latitudes). On the other hand, the additional benefit of employing a tracking BOS is not as clear-cut,
and depends on the individual PV technology as well as on specific local conditions (high irradiation,
low diffused light).
Acknowledgments:
The authors gratefully acknowledge the supply of up-to-date inventory information on CdTe
PV production by First Solar, Inc.
Author Contributions:
Vasilis Fthenakis conceived and designed the study; Enrica Leccisi performed the
experimental work; Enrica Leccisi and Marco Raugei analyzed the data; Vasilis Fthenakis contributed materials
and analysis insight; Enrica Leccisi and Marco Raugei wrote the paper.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Intergovernmental Panel on Climate Change (IPCC). Climate Change 2014: Mitigation of Climate Change;
Cambridge University Press: New York, NY, USA, 2014.
2.
World Population Prospects: The 2015 Revision, Key Findings and Advance Tables; Working Paper
No. ESA/P/WP.241; United Nations Department of Economic and Social Affairs, Population Division:
New York, NY, USA, 2015.
3.
Snapshot of Global Photovoltaic Markets; Report IEA PVPS T1-29:2016; International Energy Agency (IEA):
Paris, France, 2015.
Energies 2016,9, 622 12 of 13
4.
Global Market Outlook for Solar Power 2015–2019; Solar Power Europe, European Photovoltaic Industry
Association: Brussels, Belgium, 2015.
5.
First Solar. Taking Energy Forward, Providing Comprehensive Solar Solutions to Diversify Your Energy
Portfolio, 2016. Available online: http://www.firstsolar.com/ (accessed on 10 May 2016).
6.
Alsema, E. Energy requirements of thin-film solar cell modules—A review. Renew. Sustain. Energy Rev.
1998
,
2, 387–415. [CrossRef]
7.
Alsema, E. Energy pay-back time and CO
2
emissions of PV systems. Prog. Photovolt.
2000
,8, 17–25.
[CrossRef]
8.
Alsema, E.; Nieuwlaar, E. Energy viability of photovoltaic systems. Energy Policy
2000
,28, 999–1010.
[CrossRef]
9.
Fthenakis, V.M. Life cycle impact analysis of cadmium in CdTe PV production. Renew. Sustain. Energy Rev.
2004,8, 303–334. [CrossRef]
10.
De Wild-Sholten, M.; Alsema, E. Towards cleaner solar PV: Environmental and health impacts of crystalline
silicon photovoltaics. Refocus 2004,5, 46–49. [CrossRef]
11.
Fthenakis, V.M.; Kim, H.C.; Alsema, E. Emissions from photovoltaic life cycles. Environ. Sci. Technol.
2008
,
42, 2168–2174. [CrossRef] [PubMed]
12.
Fthenakis, V.M.; Held, M.; Kim, H.C.; Raugei, M.; Krones, J. Update of energy payback times and
environmental impacts of photovoltaics. In Proceedings of the 24th European Photovoltaic Solar Energy
Conference and Exhibition, Hamburg, Germany, 21–25 September 2009.
13.
Raugei, M.; Fullana-i-Palmer, P.; Fthenakis, V.M. The energy return on energy investment (EROI) of
photovoltaics: Methodology and comparisons with fossil fuel life cycles. Energy Policy
2012
,45, 576–582.
[CrossRef]
14.
Dale, M.; Benson, S.M. The energy balance of the photovoltaic (PV) industry—Is the PV industry a net energy
provider? Environ. Sci. Technol. 2013,47, 3482–3489. [CrossRef] [PubMed]
15.
Consoli, F.; Allen, D.; Boustead, I.; De Oude, N.; Fava, J.; Franklin, R.; Jensen, A.A.; Parrish, R.; Perriman, R.;
Postlethwaite, D.; et al. Guidelines for Life-Cycle Assessment: A “Code of Practice”; Society of Environmental
Toxicology and Chemistry: Sesimbra, Portugal, 1993.
16.
Environmental Management—Life Cycle Assessment—Principles and Framework; ISO 14040:2006; International
Standardization Organization: Geneva, Switzerland, 2010.
17.
Environmental Management—Life Cycle Assessment—Requirements and Guidelines; ISO 14044:2006; International
Standardization Organization: Geneva, Switzerland, 2010.
18.
Fthenakis, V.; Frischknecht, R.; Raugei, M.; Kim, H.C.; Alsema, E.; Held, M.; De Wild-Scholten, M.
Methodology Guidelines on Life Cycle Assessment of Photovoltaic Electricity; Report IEA-PVPS T12-03:2011;
International Energy Agency (IEA): Paris, France, 2016.
19.
Frischknecht, R.; Wyss, F.; Büsser Knöpfel, S.; Lützkendorf, T.; Balouktsi, M. Cumulative energy demand in
LCA: The energy harvested approach. Int. J. Life Cycle Assess. 2015,20, 957–969. [CrossRef]
20. Leach, G. Net energy-is it any use? Energy Policy 1975,3, 332–344. [CrossRef]
21.
Chambers, R.S.; Herendeen, R.A.; Joyce, J.J.; Penner, P.S. Gasohol: Does it or doesn’t produce positive net
energy? Science 1979,206, 789–795. [CrossRef] [PubMed]
22.
Herendeen, R. Net energy considerations. In Economic Analysis of Solar Thermal Energy Systems; West, R.,
Kreith, F., Eds.; MIT Press: Cambridge, MA, USA, 1988; pp. 255–273.
23.
Cleveland, C.J.; Costanza, R.; Hall, C.A.S.; Kaufmann, R. Energy and the U.S. economy: A biophysical
perspective. Science 1984,225, 890–897. [CrossRef] [PubMed]
24.
Cleveland, C.J. Energy quality and energy surplus in the extraction of fossil fuels in the U.S. Ecol. Indic.
1992
,
6, 139–162. [CrossRef]
25.
Herendeen, R. Net Energy Analysis: Concepts and Methods. In Encyclopedia of Energy; Elsevier: Amsterdam,
The Netherlands, 2004; pp. 283–289.
26.
Carbajales-Dale, M.; Barnhart, C.; Brandt, A.R.; Benson, S. A better currency for investing in a sustainable
future. Nat. Clim. Chang. 2014,4, 524–527. [CrossRef]
27.
Raugei, M.; Frischknecht, R.; Olson, C.; Sinha, P.; Heath, G. Methodological Guidelines on Net Energy
Analysis of Photovoltaic Electricity; Report IEA-PVPS T12-071:2016; International Energy Agency (IEA):
Paris, France, 2016.
Energies 2016,9, 622 13 of 13
28.
Hall, C.A.S.; Balogh, S.; Murphy, D.J.R. What is the minimum EROI that a sustainable society must have?
Energies 2009,2, 25–47. [CrossRef]
29.
Lambert, J.C.; Hall, C.A.S.; Balogh, S.; Gupta, A.; Arnold, M. Energy, EROI and quality of life. Energy Policy
2014,64, 153–167. [CrossRef]
30.
Raugei, M.; Leccisi, E. A comprehensive assessment of the energy performance of the full range of electricity
generation technologies deployed in the United Kingdom. Energy Policy 2016,90, 46–59. [CrossRef]
31. Ecoinvent Database, 2016. Available online: http://www.ecoinvent.org/ (accessed on 10 May 2016).
32.
Frischknecht, R.; Itten, R.; Sinha, P.; de Wild-Scholten, M.; Zhang, J.; Fthenakis, V.; Kim, H.C.; Raugei, M.;
Stucki, M. Life Cycle Inventories and Life Cycle Assessment of Photovoltaic Systems; Report IEA-PVPS T12-04:2015;
International Energy Agency (IEA): Paris, France, 2015.
33.
De Wild-Scholten, M. Life Cycle Assessment of Photovoltaics Status 2011, Part 1 Data Collection; SmartGreenScans:
Groet, The Netherlands, 2014.
34.
Sander, K.; Schilling, S.; Reinschmidt, J.; Wambach, K.; Schlenker, S.; Müller, A.; Springer, J.; Fouquet, D.;
Jelitte, A.; Stryi-Hipp, G.C. Study on the Development of a Take Back and Recovery System for Photovoltaic Products;
Institut für Ökologie und Politik GmbH: Wuppertal, Germany, 2007.
35.
Corcelli, F.; Ripa, M.; Leccisi, E.; Cigolotti, V.; Fiandra, V.; Graditi, G.; Sannino, L.; Tammaro, M.; Ulgiati, S.
Sustainable urban electricity supply chain—Indicators of material recovery and energy savings from
crystalline silicon photovoltaic panels end-of-life. Ecol. Indic. 2016. [CrossRef]
36.
Carbajales-Dale, M.; Raugei, M.; Barnhart, C.J.; Fthenakis, V.M. Energy return on investment (EROI) of solar
PV: An attempt at reconciliation. Proc. IEEE 2015,103, 995–999. [CrossRef]
37.
Nikolakakis, T.; Fthenakis, V.M. The optimum mix of electricity from wind- and solar-sources in conventional
power systems: Evaluating the case for New York State. Energy Policy 2011,39, 6972–6980. [CrossRef]
38.
Pre Consultants 2014. SimaPro 8 LCA Software. Available online: https://www.pre-sustainability.com/
simapro (accessed on 10 May 2016).
39.
CML-IA Characterisation Factors, 2016. Available online: http://www.universiteitleiden.nl/en/research/
research-output/science/cml-ia-characterisation-factors (accessed on 10 May 2016).
40. Photovoltaics Report; Fraunhofer Institute for Solar Energy Systems: Freiburg, Germany, 2016.
41.
Silicon, 2016. Available online: http://minerals.usgs.gov/minerals/pubs/commodity/silicon/mcs-2016-
simet.pdf (accessed on 10 May 2016).
42.
Statistics Search, 2016. Available online: http://www.iea.org/statistics/statisticssearch/ (accessed on 10
May 2016).
43.
EIA U.S. Energy Information Administration. Today in Energy, 2016. Available online: http://www.eia.gov
(accessed on 10 May 2016).
44.
Breakdown of Electricity Generation by Energy Source. The Shift Project Data Protal, 2014.
Available online: http://www.tsp-data-portal.org/Breakdown-of-Electricity-Generation-by-Energy-
Source#tspQvChart (accessed on 10 May 2016).
45.
Suruhanjaya Tenaga Energy Commission. Peninsular Malaysia Electricity Supply Industry Outolook 2014.
Available online: http://www.st.gov.my/index.php/en/component/k2/item/606-peninsular-malaysia-
electricity-supply-industry-outlook-2014.html (accessed on 10 May 2016).
46.
De Wild-Scholten, M. Energy payback time and carbon footprint of commercial photovoltaic systems.
Sol. Energy Mater. Sol. Cells 2013,119, 296–305. [CrossRef]
47.
Mason, J.; Fthenakis, V.M.; Hansen, T.; Kim, C. Energy pay-back and life cycle CO
2
emissions of the BOS in
an optimized 3.5 MW PV installation. Prog. Photovolt. Res. Appl. 2006,14, 179–190. [CrossRef]
48.
Murphy, D.; Hall, C.A.S. Year in review—EROI or energy return on (energy) invested. Ann. N. Y. Acad. Sci.
2010,1185, 102–118. [CrossRef] [PubMed]
49.
Sinha, P.; Schneider, M.; Dailey, S.; Jepson, C.; De Wild-Scholten, M. Eco-efficiency of CdTe photovoltaics
with tracking systems. In Proceedings of the 39th IEEE Photovoltaic Specialists Conference (PVSC), Tampa,
FL, USA, 16–21 June 2013.
©
2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
... The rates of progress in improving the key metrics module efficiency h, degradation rate, and system costs are essential for past economic successes and the prospects of photovoltaics. Moreover, improvements in energy payback time (EPBT) of photovoltaic modules (Bermudez and Perez-Rodriguez, 2018;Fu et al., 2018;Feldman et al., 2012;SETO, 2017;Leccisi et al., 2016;IEA, 2020aIEA, , 2020bBMU, 2021;Li et al., 2020) and reductions in the global warming potential of the energy mix in PV module producing-and installing countries (Bloomberg, 2021;UN, 2020) affect key sustainability metrics like the ability of a PV module to displace greenhouse gases (GHG), on which we focus in this publication. Past developments and future projections for these metrics are shown in Figure 1. ...
... We find that the Figure 1. Development of the most relevant technical, economic, and sustainability parameters of PV modules over time Data for module efficiency (h), degradation rate (deg), and cost until 2020 were taken from (ISE, 2020;Bermudez and Perez-Rodriguez, 2018;Fu et al., 2018;Feldman et al., 2012;SETO, 2017;Leccisi et al., 2016), future projections until 2050 are based on (IEA, 2020;BMU, 2021;Li et al., 2020) or were extrapolated were data was not available (marked gray). Energy payback time values were calculated using data from (Bermudez and Perez-Rodriguez, 2018;Fu et al., 2018;Feldman et al., 2012;SETO, 2017;Leccisi et al., 2016;IEA, 2020;BMU, 2021;Li et al., 2020) and the greenhouse gas emissions associated with electricity generation in Germany and China was taken from (Bloomberg, 2021;UN, 2020 iScience Article economically ideal operation period for this scenario in the year 2000 was 23 years. ...
... Development of the most relevant technical, economic, and sustainability parameters of PV modules over time Data for module efficiency (h), degradation rate (deg), and cost until 2020 were taken from (ISE, 2020;Bermudez and Perez-Rodriguez, 2018;Fu et al., 2018;Feldman et al., 2012;SETO, 2017;Leccisi et al., 2016), future projections until 2050 are based on (IEA, 2020;BMU, 2021;Li et al., 2020) or were extrapolated were data was not available (marked gray). Energy payback time values were calculated using data from (Bermudez and Perez-Rodriguez, 2018;Fu et al., 2018;Feldman et al., 2012;SETO, 2017;Leccisi et al., 2016;IEA, 2020;BMU, 2021;Li et al., 2020) and the greenhouse gas emissions associated with electricity generation in Germany and China was taken from (Bloomberg, 2021;UN, 2020 iScience Article economically ideal operation period for this scenario in the year 2000 was 23 years. The ideal operation period reduces to 17 years for modules installed in 2010 and slightly increased again to 19 years for modules installed around 2020. ...
Article
Full-text available
The role of innovation for the success of photovoltaics cannot be overstated. Photovoltaics have enjoyed the most substantial price learning of any energy technology. Innovation affects photovoltaic performance in more ways, though. Here, we explore the role of innovation for economics and greenhouse gas savings of photovoltaic modules using replacement scenarios. We find that the greenhouse gas displacement potential of photovoltaic modules has improved substantially over the last 20 years - fourfold for the presented example. We show that the economically ideal time for repowering is after around 20 years, but that repowering may reduce greenhouse gas savings. Expanding photovoltaic installations is generally preferable, economically and sustainably, to repowering. We argue that: i) we should maximize the greenhouse gas saving potential of each module, which requires a global strategy ii) tandem solar cells should aim for stability, and iii) efforts to continue and accelerate innovation in photovoltaic technology are needed.
... One key indicator in this regard is the Energy Payback Time (EPBT) which describes how many years a system must operate in order to recover the lifetime energy. EPBT-values are dependent on different factors, e.g., module technology, nominal module power and local solar irradiation but commonly range between 1 and 4 years [1][2][3], thus easily falling below the usual lifetime and providing a significant net energy gain. From an economic standpoint a similar trend can be observed, although to a lesser degree, meaning the payback time is longer but still below the expected lifetime [4,5]. ...
Conference Paper
Cracked backsheets have become an increasing problem for the reliability of photovoltaic modules. These defects can cause insulation faults and accelerate degradation, therefore leading to a significant shortening of the module lifetime. Repair solutions based on coatings have been developed to counteract this problem and ensure that modules reach their expected lifetime. Besides the technical suitability of these repair solutions, questions of environmental and economic feasibility should also be considered in regard to the implementation potential of these measures. In this work, models assessing the repair process from an environmental and economic standpoint have been developed and applied to several case studies representing a broad spectrum of potential use cases. Results show that the repair process, when comparing it to disposal with and without module replacement, is highly advantageous regarding the environmental performance in almost every case while also providing good results from an economic standpoint. 1 INTRODUCTION Photovoltaics (PV) is widely regarded as one of the critical technologies in enabling a sustainable energy transition. Although the lifecycle of a PV system is associated with environmental impacts (mostly from module production incl. upstream processes), the long lifetime of the system (25 years and more) along with the fact that basically no impacts are caused during the use phase, make this form of power generation environmentally-friendly. One key indicator in this regard is the Energy Payback Time (EPBT) which describes how many years a system must operate in order to recover the lifetime energy. EPBT-values are dependent on different factors, e.g., module technology, nominal module power and local solar irradiation but commonly range between 1 and 4 years [1-3], thus easily falling below the usual lifetime and providing a significant net energy gain. From an economic standpoint a similar trend can be observed, although to a lesser degree, meaning the payback time is longer but still below the expected lifetime [4,5]. Several failure modes for PV modules are known from literature [6], with backsheet failures (especially cracking but also delamination and discolouration) being identified as one of the most relevant issues over the last years [7]. Cracked backsheets (see Figure 4) lead to insulation failures and can also cause accelerated degradation in modules. These defects result in performance loss over time and, in the worst case, can make the module unusable because of safety risks [8]. When dealing with this problem the disposal of the faulty modules (with or without replacement) can be seen as the current standard. In view of a more sustainable approach, the topic of backsheet repair has garnered increasing interest in the PV industry over the last years. Some companies already provide solutions, based mostly on repair tapes, with evaluations of solutions based on coatings also ongoing. Besides the technical suitability and long-term stability of such repair solutions, questions about environmental and economic aspects are also important in order to assess whether an implementation on a large scale can be achieved successfully. Therefore, the goal of this work is to assess and compare repair solutions with other options (disposal with and without replacement) of dealing with defective modules with cracked backsheets from an environmental and economic standpoint.
Article
Replacing fossil fuels with solar photovoltaics (PV) has proven to be a viable option for transitioning the global economy to a low-carbon future. However, although the power generation from solar PV systems is often considered carbon-free by society, they have several potential adverse effects on the environment during different stages of their value chain. Furthermore, various factors significantly affect electricity generation through solar PV modules, such as their orientation angle relative to the sun. In this context, this paper aims to assess the environmental impacts of fixed and single-axis tracking systems (SATS) from a solar PV power plant composed of multi-crystalline silicon (multi-Si) PV modules in Northeast Brazil. For this purpose, our analysis explores their environmental performance against global warming, land use, and water consumption from a life cycle perspective. It includes the production of solar PV modules, transport activities, and the construction, operation, maintenance, and end-of-life of the solar PV power plant, using the Ecoinvent database and the ReCiPe 2016 method. According to our results, the most environmentally sound option is the solar PV system using SATS since it is, on average, 17% less impactful in all three impact categories considered than the other solar PV system installed on fixed structures. Hence, prioritizing SATS on the current solar PV generation expansion in Brazil can reduce GHG emissions, land use, and water consumption by up to 17%, 15%, and 7%, respectively. Furthermore, minor changes not exceeding 1.5% were observed by analyzing the nationalization of the solar PV modules, reducing GHG emissions and land use, and increasing water consumption.
Article
Photovoltaic installed cumulative capacity reached 849.5 GW worldwide at the end of 2021, and it is expected to rise to 5 TW by 2030. The sustainability of this massive deployment of photovoltaic modules is analysed in this article. A literature review, completed with our own research for emerging technologies has been carried out following life cycle assessment (LCA) methodology complying with ISO 14040 and ISO 14044 standards. Different impact categories have been analysed for five commercial photovoltaic technologies comprising more than 99% of current market (crystalline silicon ~94% and thin film ~6%) and a representative of an emerging technology (hybrid perovskite). By using data from LCA inventories, a quantitative result for 15 impact categories has been calculated at midpoint and then aggregated in four endpoint categories of damage following ReCiPe pathways (global warming potential, human health damage, ecosystems damage and resources depletion) in order to enable a comparison to other renewable, fossil fuel and nuclear electricity production. In all categories, solar electricity has much lower impacts than fossil fuel electricity. This information is complemented with an analysis of the production of minerals with data from the British Geological Survey; the ratio of world production to photovoltaic demand is calculated for 2019 and projected to 2030, thus quantifying the potential risks arising from silver scarcity for c‐Si technology, from tellurium for CdTe technology and from indium for CIGS and organic or hybrid emerging technologies. Mineral scarcity may pose some risk for CdTe and CIGS technologies, while c‐Si based technology is only affected by silver dependence that can be avoided with other metals replacement for electrodes. When the risks grow higher, investment in recycling should boost the recovery ratio of minerals and other components from PV module waste. Life cycle assessment of 15 midpoint impact categories and their aggregation in four endpoint categories of damage (global warming potential, human health damage, ecosystems damage and resources depletion) demonstrate that solar electricity has much lower impacts than fossil fuel electricity. For future IEA scenarios (NZE2050) mineral scarcity may pose some risk for CdTe and CIGS photovoltaic technologies, while c‐Si‐based technology is only affected by silver dependence. Better recycling strategies will contribute to reduce these risks in the future.
Article
Land utilisation by the solar energy industry and other sectors, such as residential and agriculture, has become increasingly competitive in recent years. Therefore, space optimisation is essential to reduce greenhouse gas (GHG) emissions while optimising electricity generation and profiting from the solar power plant. This article aims to discuss the different configurations of integrated photovoltaic (PV) systems, which combine the requirement features of a ground-mounted photovoltaic farm (GMPV) grouped into three systems: PV-wind, building integrated- or applied- PV (BIPV/BAPV) and agrophotovoltaic (agroPV). These systems generate electricity but differ because PV–wind systems generate electricity from two energy sources, whilst BIPV/BAPV systems utilise existing building space. Improving these systems, the agroPV system combines the benefits of producing power and using the vacant ground beneath the PV panels by cultivating crops. As a result, the BIPV system possesses the lowest emission rate with a range of −0.906–0.071 kgCO2eq/kWh. The manufacturing PV system's emission rate for these systems is highly affected. Meanwhile, the longest energy payback time (EPBT) is 6.3 years (BAPV), and the shortest is 0.5 years (GMPV). GMPV has the lowest EPBT due to the high electricity production of the plant, which allows the immediate repayment of the primary energy consumed. GMPV system has the lowest levelised cost of energy (LCOE) with the range of $0.04–$0.13/kWh. Meanwhile, the agroPV system has a good performance with an emission rate of 0.02 kgCO2eq/kWh, comparable to GMPV systems and lower than other integrated systems in terms of emission. The system has the LCOE of ∼$0.1/kWh, which is slightly higher than GMPV systems due to the system's higher cost but still provides monetary benefit.
Article
Full-text available
Combining solar photovoltaic panels with agricultural crops on the same land were recently proposed as to maximise land use. However, most researchers were based on temperate climate whereas studies in the tropics have yet to be initiated. Thus, this study investigates the microclimate properties and soil properties for potential agricultural crops to be planted. We monitored photosynthesis active radiation (PAR), light intensity (LI), air humidity (RH), air temperature (AT), and wind speed (WS) in outskirt panels, under panels and row between panels at three different locations: highest point area, moderately sloped area and lowest point area. We also sampled the soil for analyses of chemical and physical properties. We found that PAR, LI, and WS remained low beneath the panels at all locations. Interestingly, no significant difference was detected in AT at different treatments. The accumulation of organic matter, moisture content, and soil bulk densities showed similarities between different treatments irrespective of locations. Soil infertility is reflected by low pH, CEC, exchangeable bases, available phosphorus. Besides, the result showed almost no amount of carbon, sulphur and nitrogen was found. This research might be the starting point of a potential agrivoltaic system in Malaysia that will benefit both farmers and engineers.
Article
Thin-film photovoltaics (PV) cells offer several benefits over conventional first-generation PV technologies, including lighter weight, flexibility, and lower power generation cost. Among the competing thin-film technologies, chalcogenide solar cells offer promising performance on efficiency and technological maturity level. However, in order to appraise the performance of the technology thoroughly, issues such as raw materials scarcity, toxicity, and environmental impacts need to be investigated in detail. This paper therefore, for the first time, presents a cradle to gate life cycle assessment for four different emerging chalcogenide PV cells, and compares their results with copper zinc tin sulfide (CZTS) and the commercially available CIGS to examine their effectiveness in reducing the environmental impacts associated with PV technologies. To allow for a full range of indicators, life cycle assessment methods CML 2001, IMPACT 2002+, and ILCD 2011 were used to analyse the results. The results identify environmental hotspots associated with different materials and components and demonstrate that using current efficiencies, the environmental impact of copper indium gallium selenide (CIGS) for generating 1kWh electricity was lower than that of the other studied cells. However, at comparable efficiencies the antimony-based cells offered the lowest environmental impacts in all impact categories. The effect of materials used was also found to be lower than the impact of electricity consumed throughout the manufacturing process, with the absorber layer contributing the most to the majority of the impact categories examined. In terms of chemicals consumed, cadmium acetate contributed significantly to the majority of the environmental impacts. Stainless steel in the substrate/insulating layer and molybdenum in the back contact both contributed considerably to the toxicity and ozone depletion impact categories. This paper demonstrates considerable environmental benefits associated with non-toxic chalcogenide PV cells suggesting that the current environmental concerns can be addressed effectively using alternative materials and manufacturing techniques if current efficiencies are improved.
Article
Full-text available
We performed a comprehensive and internally consistent assessment of the energy performance of the full range of electricity production technologies in the United Kingdom, integrating the viewpoints offered by net energy analysis (NEA) and life cycle assessment (LCA). Specifically, the energy return on investment (EROI), net-to-gross energy output ratio (NTG) and non-renewable cumulative energy demand (nr-CED) indicators were calculated for coal, oil, gas, biomass, nuclear, hydro, wind and PV electricity. Results point to wind, and to a lesser extent PV, as the most recommendable technologies overall in order to foster a transition towards an improved electricity grid mix in the UK, from both points of view of short-term effectiveness at providing a net energy gain to support the multiple societal energy consumption patterns, and long-term energy sustainability (the latter being inversely proportional to the reliance on non-renewable primary energy sources). The importance to maintain a sufficient installed capacity of readily-dispatchable gas-fired electricity is also recognised.
Technical Report
Full-text available
Life Cycle Assessment (LCA) is a structured, comprehensive method of quantifying material- and energyflows and their associated impacts in the life cycles of products (i.e., goods and services). One of the major goals of IEA PVPS Task 12 is to provide guidance on assuring consistency, balance, transparency and quality of LCA to enhance the credibility and reliability of the results. The current report presents the latest consensus LCA results among the authors, PV LCA experts in North America, Europe and Asia. At this time consensus is limited to five technologies for which there are well-established and up-to-date LCI data: mono- and multi-crystalline Si, CdTe CIGS, and high concentration PV (HCPV) using III/V cells. The LCA indicators shown herein include Energy Payback Times (EPBT), Greenhouse Gas emissions (GHG), criteria pollutant emissions, and heavy metal emissions. Life Cycle Inventories (LCIs) are necessary for LCA and the availability of such data is often the greatest barrier for conducting LCA. The Task 12 LCA experts have put great efforts in gathering and compiling the LCI data presented in this report. These include detailed inputs and outputs during manufacturing of cell, wafer, module, and balance-of-system (i.e., structural- and electrical- components) that were estimated from actual production and operation facilities. In addition to the LCI data that support the LCA results presented herein, data are presented to enable analyses of various types of PV installations; these include operational data of rooftop and ground-mount PV systems and country-specific PV-mixes. The LCI datasets presented in this report are the latest that are available to the public describing the status in 2011 for crystalline Si, 2010-2011 for CdTe, 2010 for CIGS, and 2010 for HCPV technology. This report provides an update of the life cycle inventory data in Section 5 of the previous report: V. Fthenakis, H. C. Kim, R. Frischknecht, M. Raugei, P. Sinha, M. Stucki , 2011, Life Cycle Inventories and Life Cycle Assessment of Photovoltaic Systems, International Energy Agency(IEA) PVPS Task 12, Report T12-02:2011. Updates are provided for the crystalline silicon PV global supply chain (Section 5.1), thin film PV module manufacturing (Sections 5.2-5.3), PV mounting structures (Section 5.5), and country-specific electricity grid mixes (Section 5.9). Other sections of this report are the same as in the previous report. Electronic versions of the updated tables in Section 5 are available at IEA PVPS (http://www.iea-pvps.org; select Task 12 under Archive) and treeze Ltd (http://treeze.ch; under Publications).
Article
Full-text available
Examines the importance of energy return on investment (EROI) as a useful metric for assessing long-term viability of energy-dependent systems. Here, focuses on the methods, applications, and analyses for determining EROI for solar power and solar energy technologies.
Conference Paper
Full-text available
Eco-efficiency is a management practice based on creating more value with less environmental impact. Tracking systems provide the benefit of boosting the specific yield (kWh/kWp/yr) of photovoltaic (PV) systems, therefore requiring fewer modules per kWh produced than fixed-tilt systems. Although life cycle balance of system (BOS) environmental impacts for tracking systems are higher per kWh produced than for fixed-tilt systems, this difference is counteracted by tracking systems requiring fewer modules manufactured upstream and decommissioned downstream per kWh produced than fixed-tilt systems. The life cycle carbon footprint and energy payback time/non-renewable energy payback time (EPBT/NREPBT) of utility-scale cadmium telluride (CdTe) PV systems in the U.S. Southwest range from 16-17 g CO2e/kWh and 0.6-0.7 yr, respectively, with impacts for tracking systems slightly (1-3%) lower than for fixed-tilt systems. Similarly, although tracking systems have slightly higher construction and operations and maintenance (O&M) costs per watt than fixed-tilt systems, these costs are counteracted by the improved specific yield of tracking systems, resulting in lower cost per kWh in the U.S. Southwest case study considered in this evaluation (global horizontal irradiation of 1952-2094 kWh/m2/yr). Because tracking systems have the potential to create more value (kWh/$) with less life cycle environmental impact, they provide an eco-efficient strategy for improving the sustainability of PV systems. A key factor influencing the eco-efficiency of tracking systems is the tracking energy gain relative to fixed-tilt systems, which generally ranges from 10-24% over tropical and subtropical latitudes and is determined by project design, site latitude, and the proportion of diffuse horizontal insolation to global horizontal insolation at the site.
Article
Full-text available
Net energy analysis should be a critical energy policy tool. We identify five critical themes for realizing a low-carbon, sustainable energy future and highlight the key perspective that net energy analysis provides.
Article
Solar photovoltaic (PV) electricity has the potential to be a major energy solution, sustainably suitable for urban areas of the future. However, although PV technology has been projected as one of the most promising candidates to replace conventional fossil based power plants, the potential disadvantages of the PV panels end-of-life (EoL) have not been thoroughly evaluated. The current challenge concerning PV technology resides in making it more efficient and competitive in comparison with traditional fossil powered plants, without neglecting the appraisal of EoL impacts. Indeed, considering the fast growth of the photovoltaic market, started 30 years ago, the amount of PV waste to be handled and disposed of is expected to grow drastically. Therefore, there is a real need to develop effective and sustainable processes to address the needed recycle of the growing number of decommissioned PV panels. Many laboratory-scale or pilot industrial processes have been developed globally during the years by private companies and public research institutes to demonstrate the real potential offered by the recycling of PV panels. One of the tested up lab-scale recycling processes – for the crystalline silicon technology – is the thermal treatment, aiming at separating PV cells from the glass, through the removal of the EVA (Ethylene Vinyl Acetate) layer. Of course, this treatment may entail that some hazardous components, such as Cd, Pb, and Cr, are released to the environment, therefore calling for very accurate handling. To this aim, the sustainability of a recovery process for EoL crystalline silicon PV panels was investigated by means of Life Cycle Assessment (LCA) indicators. The overall goal of this paper was to compare two different EoL scenarios, by evaluating the environmental advantages of replacing virgin materials with recovered materials with a special focus on the steps and/or components that can be further improved.
Article
Purpose Environmental life cycle assessment (LCA) is today an important methodology to quantify the life cycle based environmental impacts of products, services or organisations. Since the very first LCA studies, the cumulative energy demand CED (also called ‘primary energy consumption’) has been one of the key indicators being addressed. Despite its popularity, there is no harmonised approach yet and the standards and guidelines define the cumulative energy demand differently. In this paper, an overview of existing and applied life cycle based energy indicators and a unifying approach to establish characterisation factors for the cumulative energy demand indicator are provided. The CED approaches are illustrated in a building’s LCA case study. Methods The five approaches are classified into two main concepts, namely the energy harvested and the energy harvestable concepts. The two concepts differ by the conversion efficiency of the energy collecting facility. A unifying ‘energy harvested’ approach is proposed based on four theses, which ensure consistent accounting among renewable and non renewable energy resources. Results and discussion The indicator proposed is compared to four other CED indicators, differing in the characterisation factors of fossil and biomass resources (upper or lower heating value), the characterisation factor of uranium and the characterisation factors of renewable energy resources (amount harvested or amount harvestable). The comparison of the five approaches is based on the cumulative energy demand of a newly constructed building of the city of Zürich covering the whole life cycle, including manufacturing and construction, replacement and use phase, and end of life. The cumulative energy demand of the life cycle of the building differs between 336 MJ oil-eq/m2a (‘CED uranium low’) and 836 MJ oil-eq/m2a (‘CED energy statistics’). The main differences occur in the use phase. The main reason for the large differences in the results are the different concepts to determine the characterisation factors for renewable and nuclear energy resources. Conclusions The energy harvested approach ‘CED standard’ is a consistent approach, which quantifies the energy content of all different (renewable and non-renewable) energy resources. The ‘CED standard’ approach and the impact category indicator results computed with this approach reflect the safeguard subject ‘energy resources’ but not (no other) environmental impacts. The energy harvested approach proposed in this paper can readily be implemented in different contexts and applied to various data sets.