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Environmental Impacts of Solar-Photovoltaic and Solar-Thermal Systems with Life-Cycle Assessment

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The demand for clean energy is strong, and the shift from fossil-fuel-based energy to environmentally friendly sources is the next step to eradicating the world’s greenhouse gas (GHG) emissions. Solar energy technology has been touted as one of the most promising sources for low-carbon, non-fossil fuel energy production. However, the true potential of solar-based technologies is established by augmenting efficiency through satisfactory environmental performance in relation to other renewable energy systems. This paper presents an environmental life-cycle assessment (LCA) of a solar-photovoltaic (PV) system and a solar-thermal system. Single crystalline Si solar cells are considered for the solar PV system and an evacuated glass tube collector is considered for the solar thermal system in this analysis. A life-cycle inventory (LCI) is developed considering all inputs and outputs to assess and compare the environmental impacts of both systems for 16 impact indicators. LCA has been performed by the International Reference Life Cycle Data System (ILCD), Impact 2002+, Cumulative Energy Demand (CED), Eco-points 97, Eco-indicator 99 and Intergovernmental Panel on Climate Change (IPCC) methods, using SimaPro software. The outcomes reveal that a solar-thermal framework provides more than four times release to air ( 100% ) than the solar-PV ( 23.26% ), and the outputs by a solar-PV system to soil ( 27.48% ) and solid waste ( 35.15% ) are about one third that of solar-thermal. The findings also depict that the solar panels are responsible for the most impact in the considered systems. Moreover, uncertainty and sensitivity analysis has also been carried out for both frameworks, which reveal that Li-ion batteries and copper-indium-selenium (CIS)-solar collectors perform better than others for most of the considered impact categories. This study revealed that a superior environmental performance can be achieved by both systems through careful selection of the components, taking into account the toxicity aspects, and by minimizing the impacts related to the solar panel, battery and heat storage.
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energies
Article
Environmental Impacts of Solar-Photovoltaic and
Solar-Thermal Systems with Life-Cycle Assessment
M. A. Parvez Mahmud, Nazmul Huda *, Shahjadi Hisan Farjana and Candace Lang
School of Engineering, Macquarie University, Sydney, NSW-2109, Australia;
m-a-parvez.mahmud@mq.edu.au (M.A.P.M.); shahjadi-hisan.farjana@mq.edu.au (S.H.F.);
candace.lang@mq.edu.au (C.L.)
*Correspondence: nazmul.huda@mq.edu.au; Tel.: +61-02-9850-2249
Received: 7 August 2018; Accepted: 1 September 2018; Published: 5 September 2018
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Abstract:
The demand for clean energy is strong, and the shift from fossil-fuel-based energy to
environmentally friendly sources is the next step to eradicating the world’s greenhouse gas (GHG)
emissions. Solar energy technology has been touted as one of the most promising sources for
low-carbon, non-fossil fuel energy production. However, the true potential of solar-based technologies
is established by augmenting efficiency through satisfactory environmental performance in relation
to other renewable energy systems. This paper presents an environmental life-cycle assessment (LCA)
of a solar-photovoltaic (PV) system and a solar-thermal system. Single crystalline Si solar cells are
considered for the solar PV system and an evacuated glass tube collector is considered for the solar
thermal system in this analysis. A life-cycle inventory (LCI) is developed considering all inputs and
outputs to assess and compare the environmental impacts of both systems for 16 impact indicators.
LCA has been performed by the International Reference Life Cycle Data System (ILCD), Impact 2002+,
Cumulative Energy Demand (CED), Eco-points 97, Eco-indicator 99 and Intergovernmental Panel on
Climate Change (IPCC) methods, using SimaPro software. The outcomes reveal that a solar-thermal
framework provides more than four times release to air (100%) than the solar-PV (23.26%), and the
outputs by a solar-PV system to soil (27.48%) and solid waste (35.15%) are about one third that of
solar-thermal. The findings also depict that the solar panels are responsible for the most impact in the
considered systems. Moreover, uncertainty and sensitivity analysis has also been carried out for both
frameworks, which reveal that Li-ion batteries and copper-indium-selenium (CIS)-solar collectors
perform better than others for most of the considered impact categories. This study revealed that a
superior environmental performance can be achieved by both systems through careful selection of
the components, taking into account the toxicity aspects, and by minimizing the impacts related to
the solar panel, battery and heat storage.
Keywords:
solar system; solar-thermal system; photovoltaic panels; life-cycle assessment;
environmental performance; greenhouse gas emission
1. Introduction
The accelerating growth of the world economy and the exponential rise of the global population
have resulted in an increasing demand for traditional fossil-fuel-based power production, resulting
in the emission of record levels of greenhouse gas (GHG) [
1
,
2
]. This burning of fossil fuels usually
causes significant environmental degradations such as air pollution, global warming, ozone-layer
depletion, acid rain, climate change and many more [
3
,
4
]. Therefore, researchers have been trying to
develop alternative sustainable-energy technologies to overcome the challenges of the energy crisis
and its environmental impact [
5
,
6
]. Due to the growing demand for renewable-energy sources in
the last decade, photovoltaic (PV) technologies are getting considerable attention because of their
Energies 2018,11, 2346; doi:10.3390/en11092346 www.mdpi.com/journal/energies
Energies 2018,11, 2346 2 of 21
paramount potential for large-scale sustainable energy generation with higher efficiency and a superior
environmental profile with smaller carbon dioxide (CO
2
) emissions [
7
10
]. It is generally considered
that solar technologies have smaller environmental effects than conventional power generating units,
but between solar-PV and solar-thermal systems which one is more environmentally friendly has not
been explored and compared considering the impacts from each elements production, transportation,
installation, operation and end-of-life recycling.
The research goal of this project is to assess the environmental effects of solar-PV and solar-thermal
frameworks by a systematic life-cycle assessment (LCA) approach and compare the findings for a
better informed choice. Over time, there have been significant advancements achieved by various
research groups in the efficiencies and economic viabilities of PV technologies like solar-PV systems
and solar-thermal systems [
11
13
]. Several research studies have been done in calculating the effects of
a single element of solar technologies like PV panels [
14
17
], batteries [
18
], solar-thermal collectors [
19
],
etc. Some others carried out country-based LCA research [
20
28
] to assess the impacts of solar
technologies; they have not considered a global database, which is required for the consistent global
practice of LCA [
29
] and global policy development [
23
]. Moreover, there are separate LCA analyses
to find the hazards of solar technologies that directly affect the human body [
30
33
], but they have
not measured the rate of energy used from fossil-fuel-based sources in manufacturing solar-PV and
solar-thermal systems. In this study, a literature review on previous studies of LCA-based solar-thermal
and solar-PV systems and the summary is highlighted in Tables 1and 2, respectively. However, very
few studies in the open literature assessed and compared the environmental impacts for the individual
parts of both frameworks, which is required to identify the problematic elements and to replace them
by their equivalent environmentally-friendly options. Therefore, given the remarkable role that solar
technologies have to play in reducing global greenhouse gas (GHG) emissions, it is necessary to
investigate the environmental profiles of both solar PV and thermal systems considering each element
of the system to understand their full potential.
Table 1. Previous studies of life cycle assessment of solar-thermal system and their limitations.
Source Ref. Topic Main Focus of the Work Limitations
[19]
Life cycle
assessment
of a solar
thermal collector.
The environmental
performances of solar
thermal collector
for sanitary warm
water demand has
been studied.
Data source is not global.
It is only applicable for
the plants of Italy.
[25]
Performance of a
PV/T Solar Collector
in a Tropical
Monsoon Climate
City in Brazil.
This work identifies the most
important parameters that affect
the efficiency of the
collector when operating
in a locality of tropical monsoon
climate zone in Brazil.
The estimation of step
by step greenhouse gas
(GHG) emission has not
been undertaken.
[33]
Comparative experimental
Life Cycle Assessment
of two commercial
solar thermal devices
for domestic applications.
The environmental analysis
for Flat Plate Thermos-phonic
Units (FPTU) and Integrated
Collector Storage (ICS) solar
water heaters is carried
out through a Life Cycle
Assessment (LCA) study.
They have not
considered the
end-of-life phase
in assessing
the impacts.
[34]
Life cycle analysis of
a solar thermal system
with thermochemical
storage process.
The LCA technique to study the environmental
impacts associated with
solar thermal system (SOLARSTORE)
is highlighted in this work. The raw
material acquisition and components
manufacturing processes contribute
99% to the total environmental
impacts during the whole life cycle.
The installation and
maintenance processes
are excluded from LCA.
Energies 2018,11, 2346 3 of 21
Table 2. Previous studies of life cycle assessment of solar-PV system and their limitations.
Source Ref. Topic Main Focus of the Work Limitations
[3]
Review of the Life Cycle
Greenhouse Gas Emissions
from Different Photovoltaic
and Concentrating
Solar Power Electricity
Generation Systems.
The cadmium telluride PVs
and solar pond concentrated
solar powers (CSPs) contributed
to minimum life cycle GHGs.
The environmental
contributions from the
solar chimney and solar
pond electricity
generation systems
has not been revealed.
[9]
Life cycle analyses of
organic photovoltaics:
a review.
Discussed the environmental
impacts of organic photovoltaics
(PVs) under several indicators like
cumulative energy demand (CED),
energy payback time (EPBT),
and greenhouse gas (GHG)
emission factor.
Lack of the evolution
of environmental
sustainability
assessment in case
of organic PVs.
[14]
Life Cycle Assessment
of an innovative
recycling process for
crystalline silicon
photovoltaic panels.
It analysed an innovative
process for the recycling
of silicon PV panel.
The end-of-life phase
has been neglected
in this analysis.
[15]
Life Cycle Analysis
(LCA)
of photovoltaic
panels: A review.
It examined the
energy-related indicators
such as EPBT and the indicators
relative to climate change
such as CO2emissions.
The electronic properties
of the panel or balance of system
(BOS) components has not
been evaluated.
[28]
Life cycle assessment
of grid-connected
photovoltaic power
generation
from crystalline
silicon solar modules
in China.
Regardless multi-Si,
mono-Si, large scale photovoltaic
(LS-PV) or distributed PV
system, PV station manufacturing is
responsible for about 84%
or even more of total
energy consumption and
GHG emissions.
The solution to
cut down the energy
consumption and
GHG emission
during PV station
manufacturing has
not been discussed.
[30]
Perovskite photovoltaics:
life-cycle assessment
of energy and
environmental impacts.
Compared the results of
Eco-indicator 99, the EPBT,
and the CO2emission factor
among existing PV technologies,
and further perform uncertainty
analysis and sensitivity analysis
for the two modules.
The way to lower the
CO2emission factor
has not been mentioned
and this work lacks information
to improve the system
performance ratio and the
device lifetime.
[35]
Assessing the lifecycle
greenhouse gas emissions
from solar PV and wind
energy: A critical meta-survey.
Physical characteristics
of the solar technologies
are most responsible
for emissions.
The procedure to
lower the greenhouse
gas emission has
not been highlighted.
[36]
The Energy and Environmental
Performance of Ground-Mounted
Photovoltaic Systems
-A Timely Update
One-axis tracking installations
of solar modules can improve the
environmental profile of
PV systems by approximately
10% for most impact metrics.
The benefits of employing
a tracking BOS has not
been explored.
Herein, the ecological impacts incurred by solar-PV and solar-thermal systems are assessed and
compared by LCA approach for each of the elements like solar collector, battery, converter, inverter,
power meter, breaker, flow meter, valve, pump, heat transfer fluid tank etc. In the LCA analysis both
systems are considered for a small residential area. The amount of GHG emissions and fossil-fuel-based
energy consumption by each element of both frameworks is also estimated. Moreover, the sensitivity
analysis of the considered systems is conducted by varying the PV panels and the battery storages to
track the best option in terms of their effects on the environment. Therefore, the key contributions of
this paper can be summarized as follows:
Development of a comprehensive life-cycle inventory (LCI) considering the inputs and outputs of
solar-PV and solar-thermal systems.
Assessment of the environmental impacts for elements of both frameworks from a “cradle to
grave” scheme for 16 impact indicators.
Comparison of the effects from both systems.
Energies 2018,11, 2346 4 of 21
Quantification of the greenhouse gas (GHG) emissions from both systems throughout
their lifetime.
Evaluation of the amount of fossil-fuel-based power consumption during the manufacturing of
elements, installation and operation of the systems, and the waste-management period.
Accomplishment of sensitivity and uncertainty analysis for both systems.
The current study is different from some of the previously reported studies [
3
,
36
38
] and provides
additional information on the impacts associated with each of the elements like PV panel, valve, battery,
converter, controller, flow meter etc. in both solar-PV and thermal systems, which identifies the critical
materials and stages; it is anticipated that by replacing the hazardous materials the environment can
be escaped from long-term dangerous emissions. In the light of the above, the rest of the paper is
arranged as follows. The materials and methods are briefly described in Section 2. The results and
discussions to reveal the environmental performances of solar PV and thermal systems are presented
in Section 3, and concluding remarks on the research outcomes and recommendations are highlighted
in Section 4.
2. Materials and Methods
2.1. Solar-PV and Solar-Thermal System Overview
The solar-PV system consists of a mono-crystalline PV panel, DC-to-DC charge controller,
DC-to-AC inverter, power meter, breaker and battery (Figure 1). The PV panel generates DC electricity
which is controlled by the charge controller (DC/DC) to obtain a regulated DC output. The controlled
DC current is then stored into the battery. The DC output from the battery is inverted to AC by the
DC/AC inverter. A power meter is utilized to measure and record the flow of electricity.
Figure 1. Schematic framework of the solar-PV system.
Figure 2shows the schematic framework of the solar-thermal system. It consists of a solar collector,
flow meter, pump, heat transfer fluid (HTF) tank, ball and check valve, heat storage, temperature gauge,
boiler and reservoir. The PV collector harvests solar energy and converts it into heat, which is utilized
to warm the cold water. The temperature gauge and flow meter measure the water temperature and
flow rate, respectively. The pump is used for circulating the water throughout the system. The heat
storage is between the boiler, the HTF tank and the solar collector. The boiler is a vessel where water
is heated.
Energies 2018,11, 2346 5 of 21
Figure 2. Schematic framework of the solar-thermal system.
2.2. Life-Cycle Assessment Method
The main aim of this research is to find the environmental impacts of solar technologies like
solar-PV and solar-thermal systems, and compare their effects on the environment using sixteen impact
indicators. For that reason, a well-ordered LCA method is used. LCA is a very effective approach
for evaluating the environmental hazards of any device or system [
39
41
]. LCA has been widely
used in impact estimation, sensitivity analysis and sustainability testing [
42
46
]. This LCA has been
accomplished maintaining the ISO (International Organization for Standards) standards 14040:2006
and 14044:2006 [
47
,
48
]. In this study, SimaPro version 8.5 (SimaPro, Amersfoort, The Netherlands) was
used to evaluate the ecological threats of solar technologies. Herein, LCA is carried out by creating a
life-cycle inventory (LCI) considering all of the elements for both solar technologies. The following
four basic steps are maintained in LCA analysis:
1.
Goal and scope definition, where the LCA objective is highlighted and the boundaries are
determined following ISO 14040 [48].
2.
Life-cycle inventory, where the energy, material and emission-based input–output flows are
assembled following ISO 14041 [47].
3.
Life-cycle environmental-impact evaluation, where impacts are assessed for sixteen effect
indicators following ISO 14042 [47] .
4.
Impact outcome interpretation, where obtained effects are annotated and examined with the
objective of the LCA, following ISO 14043 [48].
The major LCA steps are explained in the following sections to highlight the LCA approach
carried out in this work.
2.2.1. Goal and Scope Definition
The first step of LCA is goal and scope definition. The main objective of this LCA is to
assess and compare the ecological hazards of solar PV and thermal systems. The LCA is carried
out considering both mid-point (cradle-to-gate) and end-point (cradle-to-grave) aspects for both of
the frameworks
[46,49]
. Therefore, the total LCA takes into account all of the life-cycle stages for
both systems such as raw-material extraction, key element production, transportation, framework
installation, and waste management. The functional unit of the LCA is considered as 1 kWh of energy
production, which determines the reference flow rates [39,41].
Energies 2018,11, 2346 6 of 21
2.2.2. Life-Cycle Inventory
The formation of the life-cycle inventory is the second step of LCA. The input resources like raw
materials and energies and the output emissions per unit process are considered in assembling the
LCA inventory. Figure 3shows the step-by-step energy and material flows for both systems. Both
solar technologies follow the same steps in their lifespan such as raw-material extraction from mines
using resources, raw-material transportation to the plant location for manufacturing key materials,
key-material production at the plant, transportation of the produced materials to the solar plant area,
installation and operation of the plant, and finally the end-of-life waste management. At each step, there
are input and output flows as marked in the figure. We created a comprehensive life-cycle inventory
for both frameworks. Figure 4shows the system boundary considered in this research. The Ecoinvent
database [
50
,
51
] is used to gather the input and output flows, as it has international industrial and
commercial data for material production, transportation, energy consumption etc. [
29
,
50
,
51
]. Table 3
shows the data source for each of the key elements of the frameworks. An assembly is formed using
all the unit processes of the solar-PV system, which is then used to assess the individual impacts of
each process element. Likewise, another assembly is built using all unit processes of the solar-thermal
system to find the effects from each element.
Figure 3. Step-by-step energy and material flows for both systems.
Table 3. Data collection for frameworks in the solar-PV system and the solar-thermal system.
Assembly Unit Process Process Source
Solar-PV system Converter Converter, 500 W, for electric system {GLO}/production/Conseq, U
Battery Battery, Li-ion,rechargeable, prismatic {GLO}/market for/Alloc Def, U
Cable Cable, unspecified, {GLO}/market for/Conseq, U
Breaker Switch, toggle,type, at plant/GLO U/AusSD U
Power meter Electric meter,unspecified {GLO}/production/Conseq, U
Inverter Inverter, 500 W, at,plant/GLO U/I U/AusSD U
PV panel Photovoltaic panel,single-Si, at plant/GLO U/I U/AusSD U
Solar-thermal system Reservoir Tap water, at user/RER U/AusSD U/Link U
Valve Exhaust air valve, {GLO}/ production / Conseq, U
Boiler Hot water tank 200 L, at plant/GLO U /I U/AusSD U
Solar collector Solar collector glass tube, with silver mirror, at plant/GLO U/AusSD U
Heat storage Heat storage 200 L, at plant/GLO U/I U/AusSD U
Temp. gauge Temperature, 500 Degrees F gauge {GLO}/market for/Conseq, U
Pump Pump 40 W, at plant/GLO U/I U /AusSD U
HTF tank Expansion vessel 200 L, at plant /GLO U/I U/AusSD U
Flow meter Flow meters, vortex type, at plant /GLO U/AusSD U
Energies 2018,11, 2346 7 of 21
Figure 4. System boundary of the life-cycle assessment (LCA).
2.2.3. Life-Cycle Impact Evaluation
Life-cycle impact evaluation is the third step of the LCA analysis. The rate of reference flow is
considered for the one functional unit (1 kWh). Impacts were assessed by using the SimaPro software
for both frameworks. The International Reference Life Cycle Data System (ILCD) method is utilized
in evaluating the effects. This approach considers the inputs from the raw-materials extraction to
manufacturing, transportation and usage (cradle-to-gate or mid-point) [
30
], and gives outputs for
sixteen impact indexes. It gives potential environmental impacts under major effect indicators like
global warming, climate change, land use, toxicity, acidification etc. The cradle-to-grave (end-point)
LCA analysis was carried out by the Impact 2002+ approach [
52
] under fourteen impact categories:
carcinogens, non-carcinogens, respiratory inorganics, ionizing radiation, ozone-layer depletion,
respiratory organics, aquatic ecotoxicity, terrestrial ecotoxicity, terrestrial acid, land occupation, aquatic
acidification, aquatic eutrophication, global warming and non-renewable energy, which are further
subdivided into four major indicators, namely human health, ecosystem quality, climate change and
resources. The Raw Material Flows (RMF) method tracks the mass flow of all inputs and outputs based
on adding all the elementary flows available in the Ecoinvent 2.0 database [
53
]. This RMF method is
utilized to find and compare the input materials and output emissions of the systems. The Cumulative
Energy Demand (CED) approach is employed to calculate fossil-fuel-based energy usage amounts for
both of the considered frameworks, as this approach has been extensively used in assessing different
sorts of fuel intakes throughout the lifetime of a unit [
54
]. CED considers various fuel inputs such
as fossil fuels, renewable, nuclear, biomass and embodied energy for the overall lifespan of both
systems [
55
,
56
]. It is important to realize the consumption of carbon-based-fuels to replace them by the
renewable sources for better environmental performance. Moreover, the Intergovernmental Panel on
Climate Change (IPCC) approach is employed to assess the greenhouse gas emission rate. The IPCC
approach reveals the climate change factors by the considered systems with a time frame of 100 years.
This method usually considers hazardous gas emissions like carbon dioxide, methane, nitrous oxide,
Energies 2018,11, 2346 8 of 21
etc. [
57
]. Uncertainty analysis has been conducted by the ILCD method to check the sustainability for
the environmental-impact indicators of the LCA analysis and to investigate the probability distribution
of both systems following the method described in [
10
,
30
]. Finally, sensitivity analysis is accomplished
using ILCD method considering different PV panels and battery storages to examine their effects.
2.2.4. Life-Cycle Impact Interpretation
The life-cycle impact interpretation is the final stage of the LCA. The impacts are assessed,
compared and interpreted in terms of the main factors responsible for environmental effects of both
solar PV and thermal systems. Moreover, logical judgments are given based on uncertainty and
sensitivity analysis.
3. Results and Discussion
3.1. Environmental Profiles of the Solar-PV System
The overall inputs from nature and outputs to soil, water, air and solid waste scenarios for
each element of the solar-PV system are assessed by the Raw Material Flows (RMF) approach [
53
].
This approach gives output considering the raw material and emission-based mass flow by adding
all elementary flows. The life-cycle inputs and outputs of the elements of solar-PV system such as
PV panel, inverter, power meter, breaker, cable, battery and converter are evaluated considering
step-by-step energy and material flows by the RMF method.
The obtained results are presented in Figure 5for better understanding and comparison. Amounts
are obtained in kilograms and the total amount of each element like converter, battery, cable etc. is set
at 100%. In case of the PV panel, it is clear from the figure that it intakes about 20% from nature during
production and releases equally to air, soil and solid waste (about 30%), but there is no direct release
into water throughout the lifetime of the PV panel. On the contrary, the converter, battery, cable and
power meter of the solar-PV framework release a higher output to water, whilst the inverter, breaker
and PV panel release more output as solid waste (landfill). Therefore, the end-of-life recycling of these
key parts is essential to overcome for the problems associated with their release into water and soil.
Figure 5.
Life-cycle inputs and outputs of the solar-PV system using Raw Materials Flow methodology.
The environmental impacts caused by each element of the solar-PV framework are depicted in
Figure 6, found by the ILCD method [
30
]. The maximum effects occurred for the climate change,
ozone depletion, human toxicity, photochemical ozone depletion, acidification, terrestrial and marine
eutrophication, and water resource depletion impact categories by the PV panel. On the other hand, the
highest impacts from the battery were for the effect indicators of mineral, fossil and renewable resource
depletion, land use, and freshwater eutrophication. As it is not possible to build a battery without
Energies 2018,11, 2346 9 of 21
chemicals, and these chemicals are mostly responsible for the harmful emissions and other effects of the
battery, researchers should rethink the use of environmentally-friendly materials without considering
efficiencies. Furthermore, the power meter is mostly responsible for ionizing-radiation-based impact
because it carries much energy to ionize electrons from atoms during operation. This radiation is a risk
for the human body as it can affect DNA and can damage living cells. Therefore, future research should
be directed toward developing an energy meter with the smallest ionizing-radiation-based impact.
Figure 6. Environmental profiles of the considered solar-PV system.
The results from end-point LCA analysis of the solar-PV system using the Impact 2002+
approach [
52
] are depicted in Figure 7. The PV panels are mostly responsible for affecting human
health and climate change, whereas the battery mostly affects resources. The hazardous fluids used to
transfer heat in solar modules are mostly responsible for the high impacts like toxicity and acidification,
which is still required to be sorted out by the researchers.
Figure 7. Endpoint impacts of the individual components of the solar-PV system.
Energies 2018,11, 2346 10 of 21
3.2. Environmental Profiles of the Solar-Thermal System
In this section, the life-cycle environmental hazards of a solar-thermal system are highlighted .
The total input–output scenarios for each part of the solar-thermal system are evaluated by the RMF
method [
53
]. The life-cycle input–output rates of the solar-thermal framework are depicted in Figure 8.
The solar collector takes 25% of its total inputs from nature and others from other non-nature-based
sources. It releases about 22% to solid waste, about 18% to the soil, about 7% to water and about 18%
to air. On the other hand, the boiler released mostly solid waste (about 48%). Almost 18% of its inputs
comes from nature. However, the pump and valve of the solar-thermal system emitted more output to
water, whilst the boiler, reservoir and temperature gauge emitted significant outputs as solid waste.
Moreover, the solar collector and heat storage released mostly to the air. However, the HTF tank and
flow meter are totally discharged into water at the end-of-life. This happens because in the considered
case these two parts have not been recycled.
Figure 8.
Life-cycle inputs and outputs of the solar-thermal system using Raw Materials
Flow methodology.
The cradle-to-gate (mid-point) environmental effects of each part of the solar-thermal system are
highlighted in Figure 9, obtained by the ILCD approach [
30
]. Among sixteen impact types, the highest
impacts are occurred to climate change, ozone depletion, human toxicity, acidification, terrestrial
eutrophication, ecotoxicity, water resource depletion and land use from the solar collector. However,
the maximum hazards from the valve were to freshwater eutrophication and mineral, fossil and
renewable resource depletion. Furthermore, the other parts of the framework showed minor impacts.
Overall, most of the impact from the solar-thermal system occurred for the solar collector and heat
storage (about 90% for the 14 impact categories) because of the use of hazardous materials and
chemicals in their manufacturing, operation and recycling.
Energies 2018,11, 2346 11 of 21
Figure 9. Environmental profiles of the considered solar-thermal system.
The end-point LCA analysis of the solar-thermal system was done by the Impact 2002+
method [
52
]. The end-of-life results depicted in Figure 10 reveal that the solar collector and the
heat storage are the critical components in terms of the environment, as they are mostly responsible
for damaging the ecosystem, climate and human health. Moreover, the boiler and HTF tank affect
resources to a great extent in comparison with other parts of the framework.
Figure 10. Endpoint impacts of the individual components of the solar-thermal system.
Energies 2018,11, 2346 12 of 21
3.3. Impacts Comparison between Solar-PV System and Solar-Thermal System
The input–output comparison between the solar-PV system and the solar-thermal system is
highlighted in Table 4, which shows that a higher input from nature is taken by the solar-thermal
system than by the PV system. However, the outputs to the air, soil and solid waste are a greater
from the solar-thermal system than from the PV system, whilst outputs to water are mostly by the
PV system.
Table 4.
Life-cycle inputs and outputs comparison between the solar-PV system and the
solar-thermal system.
Label Solar-PV System (%) Solar-Thermal System (%)
Inputs from nature 20.80 100
Outputs to air 23.26 100
Outputs to water 100 0.43
Outputs to soil 27.48 100
Outputs solid waste 35.15 100
The life-cycle comparative environmental impacts of the solar PV and thermal systems are
depicted in Figure 11, as estimated by the ILCD method. The results show that the solar-thermal
system emits more hazardous materials and is highly responsible for more of the impact categories like
land use, freshwater ecotoxicity, marine and terrestrial eutrophication, acidification, photochemical
ozone formation, ionizing radiation, particulate matter, human toxicity and climate change than the
solar-PV system.
Figure 11. Comparison of environmental impacts from the solar-PV and the solar-thermal system.
Energies 2018,11, 2346 13 of 21
The cradle-to-grave effect outcome comparison between the solar PV and thermal frameworks
is obtained by the Impact 2002+ method under four major indicators, as demonstrated in Figure 12.
The outcome shows that the solar-thermal system is more dangerous for human health, climate change
and the ecosystem than a solar-PV system of equivalent rate. However, the impacts to resources by the
solar-PV system are ten times as high as for the solar-thermal framework.
Figure 12. Endpoint impact comparison of the systems using Impact 2002+ methodology.
3.4. GHG Emission Factor Estimation
The well-known IPCC method [
57
] is used to evaluate and compare the greenhouse gas emissions
of the solar PV and thermal systems. Figures 13 and 14 show GHG releases by the solar-PV and
thermal frameworks. Clearly, the maximum amount of dangerous nitrous oxide and carbon dioxide
emission were the responsibility of the cable and inverter, respectively. However, the converter, battery
and power meter are mostly responsible for land transformation. The valve, flow meter and HTF
tank released the maximum to the land from the solar-thermal system. The solar collector, boiler, heat
storage, temperature gauge of the solar-thermal system emitted a higher amount of nitrous oxide to
the environment. The comparative GHG release obtained by the IPCC approach is demonstrated as
Figure 15, which shows that solar-thermal framework releases about five times as much carbon dioxide
as the solar-PV. The nitrous oxide emission is doubled for the solar-thermal system in comparison to
the solar-PV. However, other GHGs were emitted mostly by the solar-PV system. Overall, the obtained
outcomes of this research confirm that cautious selection of a less toxic solar panels, battery and heat
storage is a prerequisite to achieve a superior environmental performance by both systems.
Energies 2018,11, 2346 14 of 21
Figure 13. Greenhouse gas (GHG) emission of the solar-PV system with a time period of 100 years.
Figure 14. GHG emission of the solar-thermal system with a time period of 100 years.
Energies 2018,11, 2346 15 of 21
Figure 15.
GHG emission comparison of the systems using Intergovernmental Panel on Climate
Change (IPCC) methodology.
3.5. Fossil-Fuel-Based Energy Consumption Evaluation
The comparative amounts of fossil-fuel-based energy consumption by the solar PV and thermal
systems are demonstrated in Figure 16, which is found by the CED approach [
54
] of LCA. Clearly,
the outcome shows that solar-thermal installations consume higher power than solar-PV systems.
The gas-based fossil-fuel consumption rate is the maximum power usage by the solar-PV system. On
the other hand, biomass-based energy is the lowest amount of energy consumption by the solar-PV
framework. Therefore, regarding a smaller amount of fossil-fuel consumption, the solar-PV installation
is a better choice than the solar-thermal installations.
Figure 16.
Comparative required energy from different sources to build, operate and waste
management of both the systems.
Energies 2018,11, 2346 16 of 21
3.6. Sensitivity and Uncertainty Analysis
Two sensitivity analyses have been conducted to examine the environmental performance of
the solar-thermal systems and solar-PV systems for different PV panels and batteries to discover the
superior one in terms of the environment. Table 5reveals the impacts of a solar-thermal framework for
five different solar collectors: Amorphous silicon (a-Si), Copper indium selenide (CIS), multi-Si, ribbon
Si and single Si. The analysis outcome shows that single Si is highly accountable for climate change,
whereas the CIS collector is the least hazardous to the climate. The solar collector made of a-Si is largely
liable for human toxicity and the multi-Si-based collectors are mostly responsible for water resource
depletion. Overall, the solar collectors made from CIS provided a superior environmental profile.
Various types of batteries such as lithium-ion (Li-ion), sodium chloride (NaCl) and Nickel–metal
hydride (NiMH) are used in the sensitivity analysis of a solar-PV framework.
Table 5.
Sensitivity analysis outcome based on different solar collector types for the
solar-thermal system.
Impact Category a-Si
[mPt]
CIS
[mPt]
Multi-Si
[mPt]
Ribbon-Si
[mPt]
Single-Si
[mPt]
Climate change 0.31 0.13 1.86 1.62 2.55
Ozone depletion 0.002 0.001 0.18 0.17 0.1837
Human toxicity, cancer effects 9.71 1.56 8.46 3.76 8.90
Particulate matter 0.11 0.03 0.61 0.51 0.707
Ionizing radiation-Human Health (HH) 0.09 0.03 0.16 0.12 0.156
Ionizing radiation-Ecosystem (E) 0.19 0.13 0.14 0.35 0.527
Photochemical ozone formation 0.10 0.04 1.01 0.92 1.28
Acidification 0.10 0.04 0.67 0.59 0.835
Terrestrial eutrophication 0.10 0.04 0.80 0.71 1.105
Freshwater eutrophication 0.001 0.002 0.09 0.09 0.094
Marine eutrophication 0.05 0.02 0.47 0.43 0.649
Freshwater ecotoxicity 0.41 0.09 1.68 1.50 1.767
Land use 9.9 ×1053.7 ×1055.1×1054.2×1055.9 ×105
Water resource depletion 0.06 0.02 3.28 1.50 2.94
Mineral, fossil & renewable resource depletion 5.16 ×1011 4.95 ×1011 1.23 ×1089.36 ×1091.2 ×108
The analysis outcome based on different battery types for the solar-PV system highlighted in
Table 6shows that a NiMH-based framework provides higher impacts for indicators like acidification,
particulate matter, ozone depletion, ionizing radiation, eutrophication, freshwater toxicity, water
resource depletion, and climate change. The NaCl-battery-based solar-PV system had a maximum
for the human-toxicity category. Overall, the Li-ion type battery-based solar-PV framework showed
the best environmental profile at the sensitivity analysis outcome. Therefore, stakeholders should
consider CIS as a solar collector and a Li-ion battery as the energy storage device in building solar
systems. The main implication of this result is in the solar-pv and solar-thermal plant industry, in
which investors should use environmentally-friendly parts to reduce the environmental impacts.
The probability distributions of the solar-PV and thermal systems are demonstrated in Figures 17
and 18, which are obtained by using the Eco-Indicator 99 approach of LCA. The bars with smaller rate
depict higher probabilities of getting identical impacts from the installations. The lower bars of the
probability distributions for the single-score impact category of the solar-PV System with a rate of
approximately 90% of the total probabilities indicate that this system is environmentally highly viable.
Furthermore, about 70% of the small bars of the probability distributions for the single-score impact
category of the solar-thermal system reveal that this system is also environment friendly and robust.
Energies 2018,11, 2346 17 of 21
Table 6. Sensitivity analysis outcome based on different battery types for the solar-PV system.
Impact Category Li-ion
[mPt]
NaCl
[mPt]
NiMH
[mPt]
Climate change 0.0559 0.0558 0.1813
Ozone depletion 0.0072 0.0053 0.5297
Human toxicity, non-cancer effects 1.8839 1.3667 1.093
Human toxicity, cancer effects 1.0477 2.6478 2.2411
Particulate matter 0.123 0.455 1.045
Ionizing radiation-Human Health (HH) 0.068 0.174 0.174
Ionizing radiation-Ecosystem (E) 0.015 0.227 0.871
Photochemical ozone formation 0.040 0.092 0.208
Acidification 0.114 0.757 1.753
Terrestrial eutrophication 0.037 0.044 0.092
Freshwater eutrophication 0.058 0.045 0.054
Marine eutrophication 0.017 0.019 0.041
Freshwater ecotoxicity 0.258 0.260 0.383
Land use 0.00049 0.00051 0.00084
Water resource depletion 0.287 0.658 0.912
Mineral, fossil &renewable resource depletion 0.806 0.670 2.111
Figure 17. Probability distribution for the single-score impact category of the Solar-PV System.
Figure 18. Probability distribution for the single-score impact category of the solar-thermal system.
4. Limitations of This Study
The key limitations of this study are summarised as follows:
The LCA of solar technologies other than solar-PV and solar-thermal have not been studied in
this research.
Energies 2018,11, 2346 18 of 21
The LCA analysis of this study is completely dependent on the Ecoinvent 2.0 global database.
Sensitivity analysis has been accomplished for the battery and the solar collector alone due to the
lack of data sources.
The replacement of elements that are responsible for hazardous emissions without considering
the efficiencies and robustness of the systems has not been studied in this research.
The ways to reduce the consumption of fossil-fuels during the manufacturing of elements,
installation and operation of the systems, and the waste-management periods have not been
tracked in this work.
Determination of the energy payback period and an economic estimation of the considered solar
systems have not been accomplished.
The future studies should be directed toward the overcoming of the above-mentioned limitations
of this work. Thus, solar systems can eliminate many long-term dangerous emissions.
5. Conclusions
In this paper, the systematic LCA-based environmental effects of a solar-PV and a solar-thermal
system are evaluated and compared. To assure the effectiveness of this research, (i) a comprehensive
system boundary is developed for both of the considered solar technologies, (ii) a life-cycle assessment
is carried out for both systems by multiple methods to assess the environmental profiles, (iii) the
greenhouse gas emission rates are estimated for both of the systems, and (iv) a sensitivity and
uncertainty analysis is conducted to examine the environmental performance of both systems
more critically. The well-known SimaPro software and renowned Ecoinvent global database are
used for assessing the life-cycle environmental impacts by multiple methods such as ILCD for
mid-point analysis, Impact 2002+ for end-point analysis, CED for fossil-fuel-based energy consumption
estimation, Eco-points 97 for metal and gas-based emission assessment, Eco-indicator 99 for uncertainty
analysis and IPCC for GHG emission evaluation. The outcome of this research provides valuable
information on the environmental impacts of each elements of the considered solar technologies and
identifies the better environmentally-friendly option in the case of battery energy storage and solar
collectors. The results highlight that the solar-PV framework performs environmentally superior than
the solar-thermal framework for most of the impact indicators such as land use, freshwater ecotoxicity,
marine and terrestrial eutrophication, acidification, photochemical ozone formation, ionizing radiation,
particulate matter, human toxicity and climate change. The outcomes also reveal that the solar-PV
system is less impactful for human health, climate change and the ecosystem than the solar-thermal
system. Sensitivity analysis shows that CIS-solar collectors and Li-ion batteries perform better than
others for the solar-thermal and solar-PV system, respectively. However, the main limitation of this
work is that a sensitivity analysis for all considered elements has not been carried out. Thus, the future
direction of this work is to track the unsafe components and check their possible replacements for
more environmentally-friendly solar systems. Overall, it is recommended that, in order to protect the
environment from hazardous emissions by the solar technologies, future research should be directed
toward finding replacements for hazardous parts or processes by others that have a superior profile in
terms of the environment.
Author Contributions:
M.A.P.M. and N.H. conceived and designed the project; M.A.P.M. and S.H.F. performed the
LCA simulations; N.H. and M.A.P.M. analyzed the outcome; C.L. contributed database and software management;
M.A.P.M. and S.H.F. drafted the manuscript; N.H. and C.L. performed the overall supervision in this research.
Funding: This research received no external funding.
Acknowledgments:
This work is part of a PhD research funded by Macquarie University’s iMQRTP scholarship
scheme. The authors gratefully acknowledge the English editing service provided by Keith Imrie and the
anonymous reviewers who helped in improving the manuscript.
Conflicts of Interest:
The authors declare no conflict of interest. The founding sponsors had no role in the design
of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the
decision to publish the results.
Energies 2018,11, 2346 19 of 21
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This paper contains an extensive review of life cycle assessment (LCA) studies on greenhouse gas emissions (GHG) from different material-based photovoltaic (PV) and working mechanism-based concentrating solar power (CSP) electricity generation systems. Statistical evaluation of the life cycle GHG emissions is conducted to assess the role of different PVs and CSPs in reducing GHG emissions. The widely-used parabolic trough and central receiver CSP electricity generation systems emitted approximately 50% more GHGs than the paraboloidal dish, solar chimney, and solar pond CSP electricity generation systems. The cadmium telluride PVs and solar pond CSPs contributed to minimum life cycle GHGs. Thin-film PVs are also suitable for wider implementation, due to their lower Energy Pay-Back Time (EPBT) periods, in addition to lower GHG emission, in comparison with c-Si PVs.
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This paper presents the comparative study of two commercially available types of solar water heaters for domestic applications: Flat Plate Thermosyphonic Units (FPTU) and Integrated Collector Storage (ICS) solar water heaters. The conducted analysis initially focuses on the experimental investigation of the thermal behaviour and proceeds to the detailed holistic environmental analysis for both systems through a completed Life Cycle Assessment (LCA) study (i.e. throughout their fabrication, installation and operation phases).