ECOLE POLYTECHNIQUE DE LOUVAIN
LIFE CYCLE ANALYSIS (LCA)
A Life Cycle Assessment (LCA) is a methodology used to
evaluate the environmental impacts associated to the life cycle of a product according to ISO 14040 and ISO14044 standards. In this project the LCA will be applied to perovskite solar cell (PSC) MAPI (Methyl ammonium lead iodide) based. In this study, the first step will be to perform a life cycle thinking in order to identify and understand the system dealing with. Then a simplified LCA of the perovskite solar panel will be done. With 4 months provide to conduct this study, no detailed LCA will be done. The final goal of the study is to compare the results with equivalent LCA study for a traditional solar panel made of silicon in order draw first conclusions concerning the environmental impact of this new technology.
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An LCA is divided in four main steps :
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Goals and Scope
Data Inventory
Impact Assessment
Results Interpretation
GOALS AND SCOPE
1 - Goals
This study aims to quantify environmental impacts generated by a CH3NH3PbI3 perovskite solar
panel. These results aim to be compared with the life cycle of a traditional silicon based solar panel. The study will be done using SIMAPRO software with the "ECOINVENT 3 allocation at point of substitution - system" and "Methods" libraries. Having no access to the MAPI based perovskite LCA, it was necessary to design our own PSC life cycle helped by the assessment of traditional solar cells available on SIMAPRO and the scientific litterature. Hypothesis and assumptions have be done forming then a simplified LCA. The intended audience is the professors and the assistants of the course LMAPR2001.
The results are not intended to be used in comparative assertions to be disclosed to the public. The reason of this choice is because this study will be carried out with many assumptions and simplifica- tions meaning the results will have to be interpreted carefully. The potential transition of this study to a more detailed LCA will definitely be more relevant and accurate and so the access to the public would be justified especially to UCLouvain in the context of "UCLouvain transition"
2 - Scope
The function of the perovskite solar panel is to provide electricity to a student accommodation on the campus of Louvain-La-Neuve by using sunlight.
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The functional unit (FU) is to convert sunlight in electricity in order to provide 6000kWh of electricity per year over a span of 20 years while keeping an acceptable efficiency. This loss should be approximately 0.5% a year, so the acceptable loss of efficiency will be around 10% on the initial efficiency of the solar cells.
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The reference flow would take in account 18 solar panels of 1m² to fulfil the FU. However, wiith a lifespan of 20 years of working, maintenance is necessary to repair and/or replace some elements of the solar panel (such as the solar inverter, which is expected to last 10 to 15 years). The solar panel will also need to be cleaned approximately 40 times in 20 years. Other aspects are considered in the reference flows are the transport, electrical cables, batteries, controller, solar inverter, production of raw materials, recycling.... A "cradle-to-grave" system boundary is selected to obtain the most accurate life cycle of the PSC. This system boundary is taking in account the production and acquisition of the raw materials, the module manufacturing, the installation, the use, the maintenance and all the transport associated. The end of life take in account the recycling of some compounds such as the titanium dioxide, the FTO glass and copper according to litterature, the reuse and waste are included in the analysis.
Data Inventory
In this inventory, the main focus informations are presented. For further information concerning the data, please consult our complete report.
1 - PSC module
The figure 1 below represents the traditional constitution of a perovskite solar panel. The solar cell is consituted of a glass substrate, a transparent conducting layer also known as blocking layer (BL), an eletron transporting layer (ETL), an hole transport layer (HTL), an electrode and the perovskite layer. In order to protect the PSC from moisture and enhance it’s sustainability, the perovskite layer is covered with 2 films of various nature. In this study, the Ethylene Vinyl Acetate (EVA) is selected because it appears to be the most commonly used. The constituent materials of the different layers are inspired from common perovskite solar panel found in the scientific litterature :
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Substrate glass : Glass/Fluorine Doped Tin Oxide (FTO)
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Transparent conducting (Blocking) layer : m-T iO2 (m=mesoporous)
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ETL : c-T iO2 (c=compact)
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Perovskite layer : MAPI based perovskite
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HTL : spiro-OMeTAD
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Top electrode : Copper (Cu)
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Encapsulation : 2 EVA films
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Figure 1 : Schematic representation of a PSC.
2 - Data inventory : Flowsheets
The flowsheets below represent the design of the PSC life cycle. All the data concerning the raw materials and processes are already available in ECOINVENT database. However, some compound of the PSC such as spiro-OMeTAD and HTFSI (HTL), FTO glass (substrate glass), BL-TiO2 (Blocking layer) and MAPI perovskite (perovskite layer) were not available in the database and have been also designed. For quantified values please consult our overleaf for more details.
PSC module life cycle flowsheet
FTO glass synthesis process
HTFSI synthesis process
BL-TiO2 synthesis process
Spiro-OMeTAD synthesis process
MAPI perovskite layer synthesis process
Impact assessment
The data inventory encoded in SimaPro software and the results obtained from the simulation allow us to make first observations and interpretations concerning the environmental impact of our PSC panel life cycle. This analyse is done regarding three different aspects :
The classification characterisation normalisation.
ReCiPe 2016 Midpoint (H) calculation method is used for the assessment.
1 - PSC module and end of life
The figure 2 and 3 below present the main environmental categories which are impacted by the life cycle of our perovskite. The first thing to note is that the end of life do not significantly impact the environnment compared to the entire PSC module manufacturing with the use and maintenance taken in account. In short term emissions, the human carcinogenic toxicity is the category the most impacted. On long term emissions, this category is still dominant but is joined by the freshwater and marine ecotoxicity, plus the ionizing radiation. If PSC panel tend to be popularized i the future it's important to mainly focus on long term emissions.
Figure 2. Normalisation results of the PSC module with 30% recycling in short term emissions
Figure 3. Normalisation results of the PSC module with 30% recycling in long term emissions
2 - PSC module impact
If we focus on the PSC module only as shown by figure 4, we can observe that the inverter production is the most impacting compound in the 3 mains environmental categories ( Freshwater ecotoxicity, marine ecotoxicity, human carcinogenic toxicity). The controller and the battery manufacturing also play a major role. The PSC panel manufacturing is clearly negligible with a slight impact on human carcinogenic toxicity
Figure 4. Normalisation results of the individual compound of the PSC module in long term emissions
3 - PSC panel impact
Focusing on the PSC panel itself presented by figure 5, electricity consumption and FTO synthesis are the main factors impacting the environment in long term emissions. Copper production and EVA synthesis can also be noticed. In agreement with the previous observations, human carcinogenic toxicity, freshwater, ecotoxicity and ionizing radiation are highlighted.
Figure 5. Normalisation results of the PSC panel in long term emissions
4 - Impact of electricity consumption
By looking at figure 6, the PSC panel manufacturing seems to be highly energivore which would explain the reason why the electricity consumption play the major role in the negative effect on the environment. Human health is the main affected by that and the increase of ionizing radiation can also reinforce this problem.
Figure 6. Normalisation results of the electricity production in long term emissions
5 - Impact of FTO synthesis
As second main factor impacting the environment, FTO synthesis touches the same environmental categories enonced before, but unlike electricity, it doesn't affect the ionizing radiation according to figure 7. All the processes for the FTO glass manufacturing play their part. Tin and soda ash production as long as transport mainly touch the freshwater and marine ecotoxicity. The human carcinogenic toxicity is mostly dependent of aluminium oxide production, but soda ash, silica sand, tin production with the transport play also a significant part.
Figure 7. Normalisation results of the FTO synthesis in long term emissions
6 - Impact of panel recycling
As presented by figure 8, a 30% recycling of our PSC panel seems to have a slight impact on human carcinogenic toxicity. But by increasing this ratio to a 100% recycling, the effect is amplified.
30% recycling
100% recycling
Figure 8. Normalisation results of PSC panel recycling at 30 and 100% ratio in long term emissions
By looking in details to understand the reason of this increase, we can see that the end of life is actually impacting numerous of categories with human carcinogenic toxicity still dominant (Figure 9). But it can be possibly explained by the wastes. If we focus only on the recycling process (Figure 10), we can observe that the solvents needed for the recycling, ethanol and N,N-dimethylformamide, as long as electricity present negative effect on human toxicity. We can see the benefit of the recycling with a decrease of the impact of all the processes needed for the production of copper, TiO2 and especially FTO. But these benefits are not enough to compensate the impact of the recycling process itself. Figure 11 is a resume of the different scenarios of the recycling process to illustrate the damage caused by this process.
Figure 9. Normalisation results of PSC panel end of life in long term emissions
Figure 10. Normalisation results of PSC panel 100% recycled in long term emissions
Figure 11. Normalisation results of different PSC panel recycling scenarios in long term emissions
7 - Comparaison between PSC and Silicon solar cell
The figure 12 shows the comparaison between a traditional silicon solar cell and the PSC designed. We can observe that in long term, the PSC is largely more impactant than the traditional solar cell especially in human toxicity. However, it's important to note that many assumptions and simplificiations have been made in our PSC panel manufacturing design while the production of the traditional solar cell is the fruit of a deep and complete analysis. Plus, PSC manufacturing is still in a lab scale production and a lot of research and optimisation need to cover this field in order to develop an industrial scale production more relevant to comparaison.
Figure 12. Normalisation results of PSC with traditional silicon solar cell production comparaison in long term emissions
Results interpretation
The life cycle of the solar panel in perovskite gives us some first conclusions about this type of panel. This product has significant impact in human carcinogenic toxicity, freshwater and marine ecotoxicity and also ionizing radiation. These environmental impacts are caused by the FTO synthesis, the main compound of the panel, but essentially by the electric consumption necessary for the PSC panel manufacturing. However, the others elements composing the entire module such as inverter presents a more significant impact than the PSC panel itself, meaning that the PSC panel is not currently the main problem in photovoltaic installation in terms of environmental impacts. The current recycling solution for PSC does not seem to be a solution to reduce the environmental impact of the panel. The recycling process unfortunately causes much damage than it prevents. But this field is still under
study and we can still by hopefull for the future.
The main focus of this study, the perovskite, presents a low environmental impact due to it’s low contribution in the entire manufacturing process. The comparaison of a traditional silicon solar panel LCA with the PSC panel LCA done in this study shows that the PSC panel seems to be much more impactful on the environment. but this comparison should be taken carefully because significant difference in the design of those LCA could largely impact the results even if some results tend to show that the 2 designs present similarity on some aspects. It is important to keep in mind that this study was carried out with many assumptions inaccurate and imprecise while the traditional design was deeply studied on site and complete.
By only interpreting the results obtained in this study, the PSC panel are not attractive compared to traditional silicon solar panel in an environmental point of view. However, this technology is still under study, discoveries and optimisations facing the 21st century challenges will be carried out in the future. A more deeper LCA should and must be done on PSC panel after more knowledge gathered in order to obtain more relevant results and draw the first conclusions.