Whereas most lifecycle assessments (LCAs) use one-dimensional indicators and only apply to areas of high solar irradiation, Laleman et al. (2011) used both one-dimensional indicators and the multi-dimensional Eco-Indicator 99 (EI 99) to conduct a broad assessment the environmental impact of various photovoltaic (PV) technologies employed in areas of low solar irradiation such as Canada and Northern Europe. Furthermore, they used these same indicators to compare PV systems to other sources of electricity production. The authors found the energy payback time of PV systems to be less than 5 years, and the global warming potential to be approximately 10 times lower than a coal plant and 4 times higher than a nuclear power plant or wind farm. The authors obtained significantly different results using EI 99 compared to one-dimensional indicators, and thus stressed the importance of carefully evaluating a combination of different environmental impact assessment approaches.—Lucy Block
Laleman, R., Albrecht, J., and Dewulf, J., 2011. Life Cycle Analysis to estimate impact of residential photovoltaic systems in regions with a lower solar irradiation. Renewable and Sustainable Energy Reviews 15, 267-281.
Ruben Laleman, Johan Alrecht, and Jo Dewulf of Ghent University in Belgium used lifecycle data from the Ecoinvent database (v2.0) to assess the environmental impact of six different PV technologies under conditions of low solar irradiation (900-1000 kWh/m2/year). As opposed to only using a one-dimensional indicator such as Cumulative Energy Demand (CED), Energy Payback Time (EPT), or Global Warming Potential (GWP), as many other authors conducting LCAs do, Laleman et al. compared environmental impact findings of these one-dimensional indicators to the multi-dimensional EI 99. The authors also compared their findings of PV environmental impacts to the impact of other electricity sources such as hard coal, natural gas, and the Belgian electricity mix.
The authors’ findings of PV technology’s environmental impact for the one-dimensional indicators—CED, EPT, and GWP—were comparable to previous literature conducted on the subject, but their findings for the EI 99 had very little correlation with the one-dimensional indicators (at most 22%). Therefore, they stress the importance of employing a multi-dimensional indicator, especially alongside one-dimensional indicators, in order to give the most nuanced picture possible of environmental impacts.
Besides assessing environmental impact for various environmental indicators—mineral extraction, fossil fuels, respiratory effects, ozone layer depletion, ionizing radiation, climate change, carcinogenics, land occupation, ecotoxicity, and acidification and eutrophication—EI 99 categorizes those indicators into three main dimensions: human health, ecosystem quality, and the depletion of non-renewable resources, and creates three different “perspectives”—i.e., three different ways to deal with the subjective process of weighting and normalizing results based on different rankings of preferences, values, and attitudes. The three perspectives are Hierarchist, Egalitarian, and Individualist. The Hierarchist represents the view of the “average scientist” who is presumed to follow the IPCC’s (International Panel on Climate Change) assessment reports on the effects of climate change, balance short- and long-term concerns, and bases her views on consensus. The Egalitarian greatly values ecosystem quality, considers the very long term—another way of saying she is concerned with sustainability—and is highly risk-averse, potentially resulting in overestimation of risks. The Egalitarian is prone to consider all possible negative environmental effects of a phenomenon like climate change as definite. This view contrasts with that of the Individualist, who only considers “proven” effects (as opposed to effects based on consensus but around which there remains some doubt). The Individualist does not place any importance in fossil fuel depletion; rather, she only considers the depletion of minerals relevant. Furthermore, the Individualist’s perspective lies within a short-term time frame, whereas the Egalitarian thinks in terms of a very long time frame. Laleman et al. emphasize the need to clarify and outline these different perspectives in LCAs employing EI 99 so as not to cause serious misinterpretations, and for clarity’s sake they also include unweighted results.
First, the authors evaluated environmental impact using one-dimensional indicators for the following six PV technologies: Cadmium Telluride (CdTe), CuInSe2 (CIS), ribbon Si, multi crystalline Si (multi c-Si), mono crystalline Si (mono c-Si) and amorphous (a-Si). The newer technologies are the CdTe, CIS and ribbon Si. Using the same figure for yearly energy output and the same conversion coefficient for electricity generation efficiency, the authors’ calculations for CED and EPT indicators are proportional to one another. Whereas CED measures total energy required to construct the PV system over its lifetime, EPT measures the amount of time until the PV system produces more energy than was required for its construction. In these analyses, the newer technologies were found to be more efficient than older ones, requiring less than 30,000 megajoules equivalent per kilowatt-peak (kilowatt-peak [kWp] is a measure of solar energy output under laboratory conditions; a standard home installation is considered to be 3 kWp in this study) for their construction. All PV types had an EPT of less than 5 years in low irradiation conditions. CdTe, CIS and ribbon Si EPTs were about one year less than those of the other PV systems, though this difference decreased as irradiation conditions increased. In high solar irradiation regions like Spain, EPTs were only 2–3 years.
The GWP measures quantity of greenhouse gases emitted over the lifecycle of a PV system. As with CED and EPT indicators, the GWP indicator showed the three newer PV technologies, along with multi c-Si, to have less impact than the three older ones (approximately 5000 kg of CO2 equivalent compared to approximately 6000 kg of CO2 equivalent).
The EI 99 results differed significantly from the one-dimensional indicators. Using the Hierarchist perspective, CdTe was found to have the highest impact score, and greatly exceeded the scores of the other newer technologies (450 compared to 317 and 353). A breakdown of impact scores according to individual environmental indicators shows that most impact originates from fossil fuels and respiratory effects. The authors note that reducing the energy input of PV production will decrease the impact related to fossil fuel extraction, respiratory effects, climate change, acidification and carcinogenics as they all relate to one another.
In order to compare the environmental impact of PV technology to other sources of electricity, the authors selected the multi c-Si system, as it has the largest market share. They employed both a pessimistic (20 year) and optimistic (30 year) lifespan estimate for the PV system, and using both GWP and EI 99 indicators they compared the impact for 1 kWh (kilowatt-hour) produced by the various electricity sources.
The GWP analysis showed PV electricity to have a markedly lower impact than fossil fuel based sources (even with an expected lifespan of 20 years, the PV’s GWP was 0.12 kg of CO2 equivalent per kWh (kgCO2-eq/kWh) compared to 0.53 for natural gas). The Belgian mix is surprisingly low, at 0.33 kgCO2-eq/kWh, due to the high (55%) proportion of nuclear energy contribution. The GWP of PV electricity was found to be approximately four times higher than nuclear and wind and ten times lower than coal (the authors claim their impact assessment for nuclear takes into account the impact of radiation on human health).
The EI 99 results for compared environmental impact across electricity sources varied greatly depending on the perspective used. Because the Individualist perspective does not “value” fossil fuel extraction as having an environmental impact, the mineral extraction associated with PV construction is weighted very highly and thus the total impact of PV is very high for the Individualist compared to the Egalitarian and Hierarchist perspectives. Since PV technology requires a significant level of aluminum, iron, and copper, the Individualist finds PV to be much more impactful than natural gas, whereas the Egalitarian and Hierarchist find natural gas to be significantly more impactful. In the unweighted category of ecosystem quality, PV is about twice as impactful as natural gas (and both are small compared to coal). In the category of human health and resource depletion, PV impacts are negligible, natural gas impacts are small, and coal impacts are high. Though a comparison of mineral ore extraction across electricity sources show that PV requires a relatively large amount of mineral ore, an EI 99 assessment of overall resource depletion shows mineral extraction associated with PV to be negligible compared to the fossil fuel extraction required for other electricity sources. With regards to the issue of mineral ore required for PV construction, the authors indicate that the removal of the aluminum frame used for PV panel installations would greatly reduce overall environmental impact, and they recommend an efficient recycling program for the ores.
The authors conclude that PV systems have a relatively low environmental impact even in areas of low solar irradiation, especially compared to fossil fuel based sources of electricity, though mineral extraction requirements should be taken into consideration. Lifetime energy production ranged from 4-6 times lifetime energy consumption, and could reach 12 times lifetime energy consumption in sunny regions. Lifetime greenhouse gas emissions were significantly lower than fossil fuel based sources of electricity production. The EI 99 analysis showed that when fossil fuels were considered to have a negative impact on the wellbeing of future generations, PV systems were found to be less impactful than natural gas, coal, and the Belgian electricity mix. The weighting step of EI 99 analysis greatly affected results, making the Individualist perspective consider PV more impactful than natural gas—as the authors point out, many would consider the large weight the Individualist assigns to mineral extraction to be illogical or irrational in this case. The authors suggest this implies a need for great care and consideration of complexities in conducting a LCA. Furthermore, due to low correlation of EI 99 results with one-dimensional indicators, Laleman et al. recommend the use of various indicators for a thorough and comprehensive LCA.