Emission Assessment of Distributed Generation in Urban Areas

The increasing diffusion of distributed generation within urban areas calls for deeper analyses aimed at evaluating the sustainability of energy generation and its environmental impact. In particular, cogeneration technologies enable enhanced energy efficiency and thus CO₂ emission saving with respect to the conventional separate production of heat and electricity. However, the distributed cogeneration production could dramatically worsen the air quality on a local level, due to emissions of various hazardous pollutants such as NO₂, CO, and so on. In addition, in urban areas the air quality regulation could be quite stringent, thus calling for a thorough environmental impact assessment at the planning stage. In this paper, the emission characteristics of distributed cogeneration are evaluated with respect to the conventional separate production of heat and electricity on the global and local levels through the emission balance approach. The analysis is carried out with reference to small-scale (below 1 MW_e) distributed generation technologies available on the market, such as microturbines and internal combustion engines. In particular, after evaluating the emission break-even conditions for equivalence between distributed and centralized generation, it is shown how the specific results may depend upon the plant operation characteristics (at partial load) and upon the reference values for emission assessment. These aspects could be particularly relevant for energy policy formulations.