the “hybrid” LCA, attempts to address this issue by combining aspects of both techniques: using the PA approach where specific data are available and the EIO method where such data are not available.

To provide a coherent and consistent framework for LCAs, various agencies have compiled life-cycle inventory (LCI) databases that list the materials and energy inputs required for various technologies. For example, ECLIPSE (Frankl et al., 2004) is a LCI assessment project developed in Europe that looks at emissions and resource consumption. Other PA-type LCI databases include DEAM (Ecobilan, 2001), Franklin (Franklin Associates, 2008), and Ecoinvent (Pre Consultants, 2007b). EIO analyses typically rely on economic databases that are compiled by governmental bodies. For example, in the United States, the Department of Commerce generates data on air emission and water and energy use for 485 commodity sectors from various data sources.

Beyond the choice of LCA method and LCI database, there are any number of other factors that can affect LCA results and cause discrepancies among analyses. Assumptions about power plant capacity (or lifetime output), plant life expectancy, and energy infrastructure influence LCA results. In general, when comparing installations of the same energy technology, those with longer plant life expectancies and greater electrical output to the grid will have lower lifetime emissions per unit of electricity.

The nature of the underlying energy structure that supports the manufacture, operation, and dismantling of a given facility are also quite important. For example, the construction of a wind turbine in Sweden where much of the energy is produced using renewable sources will generally have less embedded CO2 emissions than the same turbine produced in the United States, where coal-fired power plants generate a significant fraction of the electricity available on the grid.

A further source of discrepancies for LCAs arises from the fact that these assessments are aimed at technologies that are often undergoing continuous modification and improvement. Comparisons cited here of an LCA for a given technology may differ because the technology under consideration evolved over the period from one LCA to another. This is especially true for solar and wind technologies where the ongoing rate of innovations is quite rapid. A further complication arises from the fact that some LCAs assess impacts for a hypothetical, future installation of the technology.

Another shortcoming of LCA is that it addresses only a single environmental impact. If one is in the position of choosing one technology over another, it would be desirable to have a more integrated understanding of the overall environmental



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