Figure 1: Silicon photovoltaic modules
Project data
Authors James Apple
Nathan Chase
nathan sanger
Completed 2010
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Alternative energy technologies such as photovoltaic modules (Figure 1) are becoming more popular around the world. In 2008, for the first time, worldwide investments in alternative energy sources drew more investors than fossil fuels, netting $155 billion in net capital against $110 billion of new investment in oil, natural gas and coal. Solar power alone generated $6.5 billion in worldwide revenue in 2004, and is expected to almost triple that with projected revenues of $18.5 billion for 2010.

Alternative energy technologies are becoming increasingly popular throughout the world due to greater awareness and concerns regarding pollution, and global climate change. Alternative energy technologies offer a new option for obtaining useful energy from sources that have less environmental impact on the planet. But how much less?

A previous published review of the net energy analysis of silicon-based photovoltaics[1] found that all types of silicon (amorphous, polycrystalline and single crystal)-based PV generated far more energy over their lifetime than is used in their production. All modern silicon PV pay for themselves in terms of energy in less than 5 years - even in highly suboptimal deployment scenarios.

This article explores all of the environmental impacts associated with the production and lifetime use of silicon photovoltaic (PV) panels.

What is a Life Cycle Assessment (LCA)?[edit | edit source]

A Life Cycle Assessment (LCA) evaluates the environmental impacts of a product or process from production to disposal.[2] An LCA investigates the material and energy inputs required to produce and use a product, the emissions associated with its use, and the environmental impacts of disposal or recycling. The LCA may also investigate external costs, such as environmental mitigation, that are made necessary by the production or use of a product.[3]

Silicon PV panel Life Cycle Assessment[edit | edit source]

The following section contains a brief lifecycle analysis of silicon PV panels. The lifecycle factors discussed include: the energy required for production, the lifecycle carbon dioxide emissions, and all of the pollution emissions generated throughout a PV panels useful life from: transportation, installation, operation, and disposal.

Energy requirements for production[edit | edit source]

Manufacturing photovoltaics is overwhelmingly the most energy intensive step of installed PV modules. As seen in Figure 2, large amounts of energy are used to convert silica sand into the high purity silicon required for photovoltaic wafers. The assembling of the PV modules is another resource intensive step with the addition of high energy content aluminum framing and glass roofing.

Figure 2: Energy requirements of production stages in the manufacturing of PV panels as percentages of the Gross Energy Requirement (GER) of 1494 MJ/panel (~ 0.65m2 surface).[4]

The environmental impact of a silicon photovoltaic module involves the production of three main components: the frame, the module, and balance-of-system components such as the rack and inverter.[3] Greenhouse gases are caused mostly by module production (81%), followed by the balance of system (12%) and frame (7%)[3]). Resource requirements of the production cycle are summarized in Figure 3.

Figure 3: The production cycle and required resources of a silicon module.[4]

Lifecycle carbon dioxide emissions[edit | edit source]

Lifecycle carbon dioxide emissions refer to the emissions caused by the production, transportation, or installation of materials related to photovoltaic systems. In addition to the modules themselves, the typical installation includes electrical cable and a metal rack. Ground-mounted photovoltaic systems also include a concrete foundation. Remote installations may require additional infrastructure for transmission of electricity to the local electrical grid. In addition to materials, a life cycle analysis should include carbon dioxide emitted from vehicles during the transportation of photovoltaic modules between the factory, the warehouse, and the installation site. Figure 4 compares the relative contributions of these factors to the lifetime carbon dioxide impacts of five types of photovoltaic modules.[5]

Figure 4: Lifetime carbon dioxide emissions for large-scale photovoltaic installations, categorized according to component. This graph compares typical monocrystalline silicon modules (m-Si(a)), high-efficiency monocrystalline silicon (m-Si(b)), cadmium tellurium (CdTe), and copper indium selenium (CIS) modules. Graph by authors, based on.[5]

Transportation emissions[edit | edit source]

Transportation accounts for about 9% of lifecycle emissions of photovoltaics.[5] Photovoltaic modules, racks, and balance-of-system hardware (such as cables, connectors, and mounting brackets) are frequently produced overseas and transported to the United States by ship.[6]Within the United States, these components are transported by truck to distribution centers and eventually to the installation site.

Installation emissions[edit | edit source]

Emissions associated with installation include vehicle emissions, material consumption, and electricity consumption associated with local construction activities to install the system. These activities generate less than 1% of total lifecycle emissions of the photovoltaic system.[6]

Operation emissions[edit | edit source]

There are no air or water emissions generated during the use of PV modules. Airsheds are impacted during the construction of PV modules from solvent and alcohol emissions that contribute to photochemical ozone formation. Watersheds are impacted by the construction of modules from extraction of natural resources such as quartz, silicon carbide, glass, and aluminum. Overall, replacement of current worldwide grid electricity with central PV systems would lead to 89-98% reductions in greenhouse gas emissions, criteria pollutants, heavy metals, and radioactive species.[7]

Disposal emissions[edit | edit source]

The disposal of silicon photovoltaic modules has not caused significant impacts because large-scale installations have only been in use since the mid-1980's and photovoltaic modules have lifetimes of at least 30 years.[8] Fthenakis et al. (2005)[2] specifically identified a lack of available data on the disposal or recycling of photovoltaic modules, so this topic warrants more thorough investigation.

LCA of photovoltaics compared to other energy sources[edit | edit source]

Total lifecycle emissions associated with photovoltaic energy production are slightly higher (as of 2006, this has significantly lowered now) than those of nuclear power but lower than those of fossil fuel energy production. Lifecycle greenhouse gas emissions of several energy generation technologies are listed below:[3]

  • Silicon PV: 45 g/kWh
  • Coal: 900 g/kWh
  • Natural gas: 400-439 g/kWh
  • Nuclear: 20-40 g/kWh

During their 20-30 year lifetimes, solar modules generate more electricity than was consumed during their production. The energy payback time quantifies the minimum useful life required for a solar module to generate the energy that was used to produce the module. As shown in Table 1, the average energy payback time is 3-6 years.

Table 1: Energy Pay Back Times (EPBT) and Energy Return Factors (ERF) of PV modules installed in various locations around the world.[4]
Country Town Solar radiation
(kWh/m2) 		Latitude Altitude
(m) 		Annual production
(kWh/kWp) 		EPBT
 ERF
Australia Sydney 1614 33.55 1 1319 3.728 7.5
Austria Vienna 1108 48.2 186 906 5.428 5.2
Belgium Brussels 946 50.5 77 788 6.241 4.5
Canada Ottawa 1377 45.25 75 1188 4.14 6.8
Czech Republic Prague 1000 50.06 261 818 6.012 4.7
Denmark Copenhagen 985 55.75 1 850 5.786 4.8
Finland Helsinki 956 60.13 0 825 5.961 4.7
France Paris 1057 48.52 32 872 5.64 5
France Marseille 1540 43.18 7 1317 3.734 7.5
Germany Berlin 999 52.32 35 839 5.862 4.8
Germany Munich 1143 48.21 515 960 5.123 5.5
Greece Athens 1563 38 139 1278 3.848 7.3
Hungary Budapest 1198 47.3 103 988 4.978 5.6
Ireland Dublin 948 53.2 9 811 6.064 4.6
Italy Rome 1552 41.53 15 1315 3.74 7.5
Italy Milan 1251 45.28 103 1032 4.765 5.9
Japan Tokyo 1168 35.4 14 955 5.15 5.4
Republic of Korea Seoul 1215 37.3 30 1002 4.908 5.7
Luxembourg Luxembourg 1035 49.62 295 862 5.705 4.9
The Netherlands Amsterdam 1045 52.21 1 886 5.551 5
New Zeland Wellington 1412 41.17 21 1175 4.185 6.7
Norway Oslo 967 59.56 13 870 5.653 5
Portugal Lisbon 1682 35.44 16 1388 3.543 7.9
Spain Madrid 1660 40.25 589 1394 3.528 7.9
Spain Sevilla 1754 37.24 5 1460 3.368 8.3
Sweden Stockholm 980 59.21 16 860 5.718 4.9
Switzerland Bern 1117 46.57 524 922 5.334 5.2
Turkey Ankara 1697 39.55 1102 1400 3.513 8
United Kingdom London 955 51.3 20 788 6.241 4.5
United Kingdom Edinburgh 890 55.57 32 754 6.522 4.3
United States Washington 1487 38.52 14 1249 3.937 7.1

Examples[edit | edit source]

References[edit | edit source]

  1. ↑ J. Pearce and A. Lau, "Net Energy Analysis For Sustainable Energy Production From Silicon Based Solar Cells", Proceedings of American Society of Mechanical Engineers Solar 2002: Sunrise on the Reliable Energy Economy, editor R. Cambell-Howe, 2002.pdf
  2. ↑ 2.0 2.1 Fthenakis, V. M., E. A. Alsema, and M. J. de Wild-Scholten (2005), Life cycle assessment of photovoltaics: Perceptions, needs, and challenges, IEEE Photovoltaics Specialists Conference, Orlando, Florida.
  3. ↑ 3.0 3.1 3.2 3.3 Fthenakis, V., and E. Alsema (2006), Photovoltaics energy payback times, greenhouse gas emissions and external costs: 2004-early 2005 status, Progress in Photovoltaics, 14, 275-280.
  4. ↑ 4.0 4.1 4.2 Life cycle assessment of photovoltaic electricity generation, A. Stoppato, Energy, Volume 33, Issue 2, February 2008, Pages 224-232
  5. ↑ 5.0 5.1 5.2 Ito, M., K. Kato, K. Komoto, T. Kichimi, and K. Kurokawa (2007), A comparative study on cost and life-cycle analysis for 100 MW very large-scale PV (VLS-PV) systems in deserts using m-Si, a-Si, CdTe, and CIS modules, Progress in Photovoltaics, 16, 17-30
  6. ↑ 6.0 6.1 Ito, M., K. Kato, K. Komoto, T. Kichimi, and K. Kurokawa (2007), A comparative study on cost and life-cycle analysis for 100 MW very large-scale PV (VLS-PV) systems in deserts using m-Si, a-Si, CdTe, and CIS modules, Progress in Photovoltaics, 16, 17-30
  7. ↑ Fthenakis, V., Kim, H., and E. Alsema (2008), Emissions from Photovoltaics Life Cycles. Environmental Science Technology, 42, 2168-2174.
  8. ↑ Luque, A., and S. Hegedus (2003), Handbook of Photovoltaic Science and Engineering, Wiley, Hoboken, NJ.
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Discussion[View | Edit]

Review by James Defenbaugh[edit source]

1. What is the most important strength of this document? The most important strength of this document is the thoroughness of the energy required to produce PV chips.

2. What is the most important aspect to change?

3. How could the navigation of the document be improved? Retitle the “Comparison to Other Energy Sources” maybe tell what you are comparing in the header and retitle “Production” to something like greenhouse gases from production: Retitle “Energy and Material Usage” include greenhouse emissions in there somewhere:

4. Do you have suggestions for improving the headings used in the document? I would like to see the headings be a little more consistent when it comes to formatting. I don’t know why they are different.

5. Are there any topic sentences that should be improved? The topic sentences for “Energy Use in Production and Installation”, “Energy Payback”, is not really a topic sentence.

6. Do all figures have captions, figure numbers and are they referred to in the text? All figures have captions but not all of the figures are numbered or numbered correctly. Also not all the figures are referred to in the text.

7. Is there at least one reference per author? Are the references cited properly and do they use the format described here? https://www.appropedia.org/Help:Footnotes There are more than one reference per author. The references appear to be cited properly, but they do not use the format described by appropedia.

8. Are tables included as text whenever possible? (Appropedia can search text in tables – so Lonny prefers tables to be text rather than images). This page contains information on how to make tables https://www.appropedia.org/Help:Table_examples There is one table and it appears to be an image.

9. Should the document be shortened or lengthened? If so, what suggestions do you have. The length of the document seems reasonable.

10. Any other questions or comments for the authors?


Review by Jeff Evans[edit source]

CHECK LIST RESPONSE TO INCLUDE ON APPROPEDIA
1. What is the most important strength of this document? Emissions and efficiency comparison to other energy generation methods.
2. What is the most important aspect to change? Some of your carbon dioxide production percentages refer to the particular process and some refer to the LCA as a whole for example your production percentages add to 100 % for production but give no reference to the percentage of the life cycle while the transportation is per life cycle.
3. How could the navigation of the document be improved? Navigation is good you might add a sentence in each section introduction stating what subsections will be found for each section.
4. Do you have suggestions for improving the headings used in the document? Just make sure they are consistent one state lifecycle of energy then the next one is lifecycle of carbon dioxide for Photovoltaics.
5. Are there any topic sentences that should be improved? See above just add a sentence giving section outlines.
6. Do all figures have captions, figure numbers and are they referred to in the text? No some of the Figures are missing numbers.
7. Is there at least one reference per author? Are the references cited properly and do they use the format described here? https://www.appropedia.org/Help:Footnotes The last reference could have link even if it is just a journal source just to be consistant.
8. Are tables included as text whenever possible? (Appropedia can search text in tables – so Lonny prefers tables to be text rather than images). This page contains information on how to make tables https://www.appropedia.org/Help:Table_examples One is a figure of a table however it looks to be a fairly extensive table. Suggestion: copy individual columns into Microsoft onenote and use the convert picture to text command then copy the column to excel should be able to create the actual table quickly.
9. Should the document be shortened or lengthened? If so, what suggestions do you have. When more research is available on waste and recycling then it could be extended for now its good.

Review by Lisa Hockaday[edit source]

CHECK LIST RESPONSE TO INCLUDE ON APPROPEDIA
1. What is the most important strength of this document? I liked the section on energy payback. You guys did a good job illustrating the important point that payback occurs before the lifetime of the panels.
2. What is the most important aspect to change? I would do some proof reading of the text. I found errors like this: “installation and transportation of the final produce.” Where “produce” should have been “product.” (This was in the Energy Use in Production and Installation section.)
3. How could the navigation of the document be improved? I can’t think of how improvement could occur for this part. I had no trouble finding my way around the page. Some reorganization could occur, like with the sections for manufacturing (mentioned in #9).
4. Do you have suggestions for improving the headings used in the document? Main headings (the ones that have the dividing lines between the sections) should be in bold. Right now, the subsections underneath them are competing for much of the reader’s attention – my eye got drawn in by the bold letters first even though they were smaller.

Some of the subheadings are different font sizes. Make sure that this is what you intended to do.

5. Are there any topic sentences that should be improved? I think that the following sentence should be the topic sentence in the Energy Use in Production and Installation section: “Manufacturing photovoltaics is overwhelmingly the most energy intensive step of installed PV modules.”
6. Do all figures have captions, figure numbers and are they referred to in the text? The introductory photo of panels has a caption but no reference in the text, but it is obvious that this is just a picture to give the reader and idea of what this type of panel looks like, so I don’t think it needs to be referred to in the text.

Figure 1 has a caption and a reference in the text, but “figure” should be capitalized in the text.

Figure 2 has both caption and text reference.

The bar graph, which is the figure just after Figure 2, has a caption, but does not have a figure number. The text does refer to it, but it would be easier to make the reference if the figure was numbered. The flow chart, which is labeled as Figure 2, should be labeled Figure 3 and be referenced in the text.

7. Is there at least one reference per author? Are the references cited properly and do they use the format described here? https://www.appropedia.org/Help:Footnotes One thing to improve is to make all of the references hyperlinked so that they just show up at the bottom. As a reader of material on the web, I didn’t expect to see in-text citations like we do with what we write for school. On the web, it just makes it appear cluttered.
8. Are tables included as text whenever possible? (Appropedia can search text in tables – so Lonny prefers tables to be text rather than images). This page contains information on how to make tables https://www.appropedia.org/Help:Table_examples There is a table for energy payback times included on the page, but it is not included as text. It could potentially be quite laborious to transfer it all into text as it is a large table with statistics for different countries and cities on solar power. In this case, I think it would not be all that beneficial to transfer it into text form.
9. Should the document be shortened or lengthened? If so, what suggestions do you have. I think that the length is appropriate, but you could elaborate on the manufacture of the panels. For instance, in the Energy and Materials Usage section, you talk about the carbon emissions being generated during the lifecycle of the PV panel by the transportation and installation, but are there any generated during the manufacturing process too? Perhaps this small “Production” section could be merged with the text earlier that talks about manufacturing.
10. Any other questions or comments for the authors? In the Brief History of Solar Power, you mention that the pn-junction was accidentally developed. I wanted to hear more about that – the idea that this was not deliberate was intriguing to me.

Change “overtime” to “over time”. This occurs in the first sentence in the Lifecycle of Energy section.

In the Lifecycle of Energy section, you talk about the section looking into the energy side of the lifecycle analysis, without mentioning what the other side is. Perhaps you should first tell the reader that there are two sides of the story (is the other one the carbon analysis?), then it would make more logical sense to focus on the energy side.

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