2. Materials and methods2.1. Emergy analysisEmergy accounting is a methodology introduced by Howard T.Odum (see for example Odum, 1996). It considers the total amountof available energy (exergy) of one kind (in particular solar), directlyor indirectly required to make a product or to support a process.Emergy flows are expressed in units of solar equivalent joules (seJ)(Sciubba and Ulgiati, 2005).In order to account for the different transformations of solarenergy, a factor called solar transformity () is defined as emergyinput per unit of available energy output. Emergy flows and trans-formities are linked by the following relationship:
EM
=
n
i=1
Eii
where EM is the emergy use (seJ) of a product or a process withn input components, Eiis the available energy (J) in component iand iis the corresponding transformity (seJ J−1). A more completetreatment of the formulas that link emergy flow and transformitycan be found in Bastianoni et al. (2011).