[below is a very short excerpt of this 22 page paper, I was interested in how much recycling can contribute to a high EROI but there are many other important points made in this paper]
Davidsson, S., Höök, M., Wall, G. 2012. A review of life cycle assessments on wind energy systems. The International Journal of Life Cycle Assessment.
http://www.diva-portal.org/smash/get/diva2:435510/FULLTEXT01.pdf
Energy systems based on wind, as well as other renewable energy sources, are often automatically assumed to be sustainable and environmental-friendly sources of energy in much of the mainstream debate.
However, all systems for converting energy into usable forms have various environmental impacts, not to mention a requirement of natural resources. It is essential to have consistent evaluation methods for analyzing all aspects of a given energy source.
Without such methods, it is difficult to compare them and make the right decisions when planning and investing in energy systems for the future.
Future growth of any new energy systems, in this case wind power, will require energy, as well as other resources during the expansion phase, and these implications need to be considered when planning future developments. A need for meticulous environmental impact assessments and energy performance evaluations can be seen here.
It could be questioned how certain it is that the materials will in fact be recycled in 20 years, or more. For some materials making up large parts of a wind turbine, i.e. steel, copper, aluminum and other metals, it is highly likely that the materials will be recycled in the future, but it is not certain. The economics of recycling scrapped wind plants are also uncertain and it is entirely possible that the cost of dismantling and extracting the recyclable parts will be prohibitively high in the future, especially for wind farms located in remote or off-shore areas. For example, the Tehachapi Pass in California contains “bone yards” of abandoned wind turbine hardware that has been lying around without being recycled (Pasqualetti et al., 2002).
Even if decommission is usually mandatory in operating permits, the total costs of decommissioning may not be covered due to price inflation, low capacity, unexpected circumstances (e.g., hurricane destruction), or a combination of such events (Kaiser and Snyder, 2012). It is possible that recycling can become uneconomic compared to abandonment under certain conditions, which is important to remember as decommissioning is dependent on a number of highly uncertain parameters that can have significant direct or indirect impacts on cost.
Material recovery at the end of the life cycle cannot be guaranteed as expressed by Crawford (2009), who also stresses that the environmental credit should rather be given to products using the recycled material.
Jacobson and Delucci (2011) states that Earth has somewhat limited reserves of economically recoverable iron ore, over a 100–200 year perspective at current recovery rates, but also mention that most of the steel will be recycled. What is not mentioned is that the steel consumption is already rising fast. ESTP (2009) projects the global steel consumption to be over 2000 Mt by 2050, compared to just below 1400 Mt in 2010. This growth, coupled with the fact that recyclable steel has often been held up for many decades before finally being recycled, makes the total part of steel production coming from recycled steel is fairly low, only around 45% in Europe (ESTP, 2009).
Such real world recycling shares appears to be in significant disagreement with some of the very high recycling percentages used in the reviewed studies.
Kubiszewski et al. (2010) compiled 50 EROI studies and found values ranging from 1.0 to 125.8 with an average of approximately 18.
It is difficult to see how the higher figures could be using the same concepts and parameters as the lower ones. It should be added that many of the results in these studies are old, and that LCA methodology has evolved since they were done. However, a large spread in results is still seen in the fairly new studies reviewed in this paper (Table 3).
Improving the treatment of energy
There is significant problem that EROI or EPBT is sometimes presented as primary energy using thermal equivalents, and sometimes using direct equivalents, making comparisons very difficult, especially since is sometimes difficult to even interpret if the conversion were done. As an example, Lee et al. (2006) and Lee and Tzeng (2008) presents an EPBT of 1.3 months – equivalent an EROI of 185 – far superior to all other reviewed studies. It seems like they use direct energy payback time without any conversion to thermal equivalents, but still compare their result to Schleisner (2000), who converts produced electricity to primary energy. It is quite odd that an energy performance many times better than Schleisner (2000) – and literally all other previous LCAs on wind energy –is not reflected upon. Instead, it is claimed that performance of wind power systems implemented in Taiwan is among the best in the world (Lee et al. 2006). Drawing these conclusions without analyzing other reasons for the variations, such as methodological differences, should be considered highly questionable.
This is just one of example how a LCA study can make flawed and even misleading comparisons and conclusions.
Regarding energy use during the life cycle, we find no consensus on how different energy carriers should be treated. How this is done is generally not clearly described in published studies either. The total amount of primary energy used is often presented, and in some cases this is also divided into different energy carriers. However, energy carriers used varies between studies making comparisons difficult. For electricity, national generation mixes are typically used, if anything is mentioned at all. How much of the total energy used was originally electrical energy is not plainly presented in any of the reviewed studies, making it difficult to investigate the impact of using of different electricity mixes. Guezuraga et al. (2012) showed that switching generation mix could alter the results by around 50%, indicating the importance of this factor.
Improved handling of non-energy resources
The need for non-energy resources does not seem to be seen as an important factor in most studies, and is usually not considered or discussed in any detail. When they are, intricate impact methods expressing resource depletion in antimony equivalents per kg is sometimes used even though this likely will be challenging to grasp for laymen and planners. Material resource use is a trivial issue for LCA according to Weidema (2000). In contrast, Finnveden (2005) suggests that resource use, although it should not be included as an impact factor in the LCIA, could be included in the LCA and states that LCA potentially can be a useful tool for discussing both environmental and resource aspects of products. Another significant problem is the use of end-of-life recycling crediting. It can be argued, for many reasons, that environmental effects of recycling that may occur in 20 years should not be credited the environmental impacts apparent today. However, most of the reviewed studies credit future recycling in some way. The implications of the recycling crediting on the results are often difficult to interpret, but for some of the results, the effect appears to be significant. For instance, energy use in Guezuraga et al. (2012) is increased by 43.3% when no recycling of materials is considered.
Final recommendations
The most troublesome part we found is the lack of transparency regarding fundamental and underlying assumptions, calculations and conversions done in the reviewed LCAs. Mitigating this issue will not only improve clarity, but is also likely to strengthen the credibility of LCA methodology. The LCA society should clearly strive for better agreement on which methods are to be used for evaluating renewable energy resources. This is not just desirable, but crucial, to be able to accurately evaluate and present the environmental performance of wind energy. Also, the use of natural resources, like REEs, should be clearly mentioned in the assessments to enable evaluating of possible bottlenecks in future production.
Kubiszewski I, et al (2010) Meta-analysis of net energy return for wind power systems. Renewable Energy. 35(1): 218-225, DOI: http://dx.doi.org/10.1016/j.renene.2009.01.012