To calculate the social costs and benefits, Gulli [43] takes into account effects such as the impact on public health, agriculture, the ecosystem in general and pollution emissions. The value of such effects are calculated in monetary terms, measured via a ‘willingness to pay or accept’ measure. The results suggest that even when such social externalities are taken into account, the DG project, in general, is still more costly than the conventional centralised systems (with the exception of two cases): a gas engine CHP system in Palermo (for the hospital case), and a gas turbine CHP system in Milan (also for the hospital case). The author finds that the efficiency benefits associated with CHP use and the avoidance of transmission costs are not sufficient to compensate for higher investment costs of the DG applications. However, the author notes that the methodologies used to evaluate the external costs are imperfect, and also that technological developments in the efficiency of dispersed energy systems (with specific reference to the development of fuel cells) could increase DG performance. Additionally, in this paper the author attaches a higher environmental impact coefficient to emissions that occur in urban areas than to emissions that occur in non-urban areas. The DG systems are located in urban areas, necessarily close to demand, and therefore, in relative terms, the CHP systems are associated with higher emission costs. The appropriateness of such an assumption should perhaps be considered, and sensitivity analysis around this assumption would be informative