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In this paper, we assess using two alternative allocation schemes, namely exergy and primary energy saving (PES) to compare products generated in different combined heat and power (CHP) geothermal systems. In particular, the adequacy and feasibility of the schemes recommended for allocation are demonstrated by their application to three relevant and significantly different case studies of geothermal CHPs, i.e., (1) Chiusdino in Italy, (2) Altheim in Austria, and (3) Hellisheidi in Iceland. The results showed that, given the generally low temperature level of the cogenerated heat (80–100 °C, usually exploited in district heating), the use of exergy allocation largely marginalizes the importance of the heat byproduct, thus, becoming almost equivalent to electricity for the Chiusdino and Hellisheidi power plants. Therefore, the PES scheme is found to be the more appropriate allocation scheme. Additionally, the exergy scheme is mandatory for allocating power plants’ environmental impacts at a component level in CHP systems. The main drawback of the PES scheme is its country dependency due to the different fuels used, but reasonable and representative values can be achieved based on average EU heat and power generation efficiencies.
Daniele Fiaschi; Giampaolo Manfrida; Barbara Mendecka; Lorenzo Tosti; Maria Parisi. A Comparison of Different Approaches for Assessing Energy Outputs of Combined Heat and Power Geothermal Plants. Sustainability 2021, 13, 4527 .
AMA StyleDaniele Fiaschi, Giampaolo Manfrida, Barbara Mendecka, Lorenzo Tosti, Maria Parisi. A Comparison of Different Approaches for Assessing Energy Outputs of Combined Heat and Power Geothermal Plants. Sustainability. 2021; 13 (8):4527.
Chicago/Turabian StyleDaniele Fiaschi; Giampaolo Manfrida; Barbara Mendecka; Lorenzo Tosti; Maria Parisi. 2021. "A Comparison of Different Approaches for Assessing Energy Outputs of Combined Heat and Power Geothermal Plants." Sustainability 13, no. 8: 4527.
Industrial anaerobic digestion requires low temperature thermal energy to heat the feedstock and maintain temperature conditions inside the reactor. In some cases, the thermal requirements are satisfied by burning part of the produced biogas in devoted boilers. However, part of the biogas can be saved by integrating thermal solar energy into the anaerobic digestion plant. We study the possibility of integrating solar thermal energy in biowaste mesophilic/thermophilic anaerobic digestion, with the aim of reducing the amount of biogas burnt for internal heating and increasing the amount of biogas, further upgraded to biomethane and injected into the natural gas grid. With respect to previously available studies that evaluated the possibility of integrating solar thermal energy in anaerobic digestion, we introduce the topic of economic sustainability by performing a preliminary and simplified economic analysis of the solar system, based only on the additional costs/revenues. The case of Italian economic incentives for biomethane injection into the natural gas grid—that are particularly favourable—is considered as reference case. The amount of saved biogas/biomethane, on an annual basis, is about 4–55% of the heat required by the gas boiler in the base case, without solar integration, depending on the different considered variables (mesophilic/thermophilic, solar field area, storage time, latitude, type of collector). Results of the economic analysis show that the economic sustainability can be reached only for some of the analysed conditions, using the less expensive collector, even if its efficiency allows lower biomethane savings. Future reduction of solar collector costs might improve the economic feasibility. However, when the payback time is calculated, excluding the Italian incentives and considering selling the biomethane at the natural gas price, its value is always higher than 10 years. Therefore, incentives mechanism is of great importance to support the economic sustainability of solar integration in biowaste anaerobic digestion producing biomethane.
Lidia Lombardi; Barbara Mendecka; Simone Fabrizi. Solar Integrated Anaerobic Digester: Energy Savings and Economics. Energies 2020, 13, 4292 .
AMA StyleLidia Lombardi, Barbara Mendecka, Simone Fabrizi. Solar Integrated Anaerobic Digester: Energy Savings and Economics. Energies. 2020; 13 (17):4292.
Chicago/Turabian StyleLidia Lombardi; Barbara Mendecka; Simone Fabrizi. 2020. "Solar Integrated Anaerobic Digester: Energy Savings and Economics." Energies 13, no. 17: 4292.