Influence of power grid efficiency variability on the support mechanisms for high efficiency cogeneration: an Italian case study

In Europe, economic support mechanisms have been developed to promote high-efficiency cogeneration systems because of their potential role in primary energy saving, network losses reduction, greenhouse gases emissions mitigation and energy supply security increase. Following the implementation of the Directive 2004/8/EC, in Italy new constructed or refurbished high-efficiency cogeneration plants are recognized the access to the White Certificates scheme, and they are allocated Type II Energy Efficiency Certificates proportionally to the energy savings provided with respect to separate electric and thermal energy supply. However, for the evaluation of the primary energy savings, constant parameters are adopted as reference values, and the average conventional efficiency of the Italian power grid is considered in relation to the separate supply of electric energy. As a result, although being capable of greatly affect the context in which the adoption of cogeneration systems is encouraged, the time variability of the electricity production mix and its effects on the power grid operation are undetermined. Therefore, to have a more accurate estimation of the feasibility and the profitability of combined heat and power production plants, this work aims at assessing the impact of using time varying power grid efficiency indicators for the evaluation of the primary energy savings due to the installation of two micro-cogenerators for polygeneration purposes in a multi-storey building. Unlike what the regulatory framework suggests, hourly-based power grid efficiency values will be used. The main findings have shown that the increased time resolution leads to greater energy savings and, in turn, to major economic revenues.