Performance analysis of a polygeneration system in different power grid efficiency scenarios

Combined heat and power generation traditionally allows for higher energy performance than separate production of heat and electricity. However the significant increase of the renewable energy sources contribution in electricity production has spatially and temporally modified the context in which polygeneration systems operate and the energy and environmental profitability of these technologies could be undetermined. In this framework the aim of the paper is to investigate the influence of the power grid efficiency scenarios variation on the polygeneration systems performance. For this purpose the energy and environmental performance of a proposed system based on combined production are compared to those one achieved by a conventional system based on separate production. Both systems satisfy the space heating, cooling and domestic hot water demands of a multipurpose building located in Naples. The primary energy demand of conventional and proposed system due to electricity depends on the efficiency of the national electric energy system features. In this paper, this factor is considered to be time-varying (hour-by-hour) and it is further taken into account that the electric system efficiency changes in the different regions of the same Country. In particular, for the Italian day-ahead market of electricity the national territory is divided in 6 zones; in this analysis two of them will be considered (Centre-North zone and Centre-South zone) and compared. The differences that arise in the results are also assessed with respect to the case in which the national and local average efficiency is taken into account. These considerations also affect the environmental performance of both energy conversion systems. Thus they are compared from an environmental point of view considering the average and the time-varying values of the electricity emission factor referred to Italian, Centre-Nord zone and Centre-South zone thermoelectric plants. The strong variability of these parameters affect the energy and environmental analysis results highlighting the importance of performing detailed analysis with up-to-date actual operation electricity production data, as the evolution towards sustainability in Smart Grids require an integrated approach.