Page 255 - Materials Chemistry, Second Edition

Hydropower Life-Cycle Inventories 245

Although there are some studies using a life-cycle perspective to evaluate
hydropower, most of them are limited to a few environmental impacts, mainly
GHG emissions and the energy pay-back (ORNL 1994; IEA 2000; Carrignton
2000). Other studies are focused on establishing monetary values to environmental
impacts (ORNL 1994; EUROPEAN COMMISSION 1995); and very few are
designed to produce a complete LCI dedicated to hydropower (Brännstrom-Nor-
berg et al. 1996; Vattenfall 1999). Evaluating those studies, the most relevant
findings are presented in the following.

3.1 Product System Modeling

As already commented, many initiatives have been taken to define a ‘‘typical’’
process for hydropower construction and operation. However, local and techno-
logical differences between plants make the results of those attempts inaccurate.
It was verified that all the founded hydropower LCI studies first obtain the
inventory of a single plant, generally the one with the higher installed power, and
then, the whole system was approximated by an extrapolation of its results. As a
second step, those analyses develop LCIs for other plants, combining them in order
to obtain an average inventory, based on installed power acting as a weighting
factor.
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Only one of the found studies went beyond this, using two LCI s for different
dams installed on the same river, in order to establish an average between them,
representing an improvement over the present situation (Swedish Environemntal
Management Council 2002a, 2002b). However, criteria used to perform the
average were not deeply described. Studies performed for hydropower generation
systems have the tendency to follow the LCA’s attributional approach. This focus
can be justified due to the fact that it generally makes part of broader projects
focused on electricity database development.

3.2 Function and Functional Unit

Even though some hydropower plants use their reservoirs to purposes other than
electricity generation, all the LCA consider this as the single function of an energy
production unit. Because of this, no allocation was made on any case.
Taking into account both requirements—the electricity generation as the only
function of the product system, and the attributional approach of LCA—the
Functional Unit (FU) of an LCA study for hydropower generation should neces-
sarily match ‘‘to generate a certain amount of energy’’. In general, the amount of
energy produced by the system is expressed either in Megawatt–hour (MWh), or
Mega joule (MJ). It seems in fact that MWh is preferable because it is more
familiar in electricity studies.