explorative attempts at quantification are frequently the first step in generating the societal discussion processes that lead with time to more widely accepted systems for cost accounting one need but think of accounting for c emissions and subsequently to better forms of internalisation a good conceptual understanding is the essential condition for any attempt at quantification this is why the following discussion of the different items of the system cost matrix distinguishes clearly between gridlevel system costs which are the subset of system costs which can be usefully quantified in the context of this study and total system costs which include external effects where quantification and monetisation in the present context would not add any value