The interaction of a technology with its environment is very complex. In general it can be stated that a technology may have impacts on the natural or physical as well as on the economic and sociocultural environment. The ways in which this interaction takes place may be diverse, depending on the kind of technology. However, every technology has a reason for its application, which ultimately is to deliver either a product or a service to society. This function — if it meets the demands of the final consumer — is what makes a new technology enter the market and consequently drives its impact on the environment. This idea of the interaction of technology with its environment through a function that needs to be fulfilled is shown in Fig. 3.1 (Balkema et al, 2002).

Consequently, the impact of a technology is always assessed taking into account its function. This is what makes it possible to compare a novel technology to ‘old’ technologies or to compare different alternatives for shaping a technology to each other. It is even possible to compare different technologies to services provided that the function for the user remains the same. Although the motivation to compare is very important, if not the most widespread one for sustainability assessment, it may also be interesting to assess one technology on its own. This motivation is encountered mostly in cases where the term technology designates not a single device, process or service, but rather a far reaching change in the sense of systems innovation which usually encompasses technology as well as organizational and social

innovation; a well-known example of this is the internet. Here, often the term technology assessment (TA) is used, which covers a wide procedural approach encompassing many methodological tools in order to explore and assess a multitude of possible and maybe interacting consequences on the natural or social environment (van den Ende, 1998; Butschi et al., 2004).

In contrast, the term sustainability assessment of technologies in the literature is rather used for a more focused assessment and comparison of specific technologies and their interaction with their environment. Keeping in mind that the impact of a technology is always connected to its function, one generic approach of assessment has become most popular: the methodology of life cycle assessment (LCA). It mirrors the view of the function as driving force for the use of a technology and as a point of reference for assessment. Most approaches to sustainability assessment of technologies are based on this method, either exclusively or by incorporating it in a wider framework. This notion is also true when looking at the assessment of technologies for energetic or material use of biomass (Dewulf and van Langenhove, 2006). Consequently, in order to reduce the plethora of names and single approaches, this chapter will be restricted to life cycle assessment as the most widespread concept for sustainability assessment of technologies.