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The necessary integration of renewable based technologies in the current energy systems is leading to a faster development of energy storage technologies. As widely known, renewables suffer for unpredictability, and their massive utilization is significantly affecting grid stability and management. In this framework, the development of efficient and large electrical storage systems is becoming a pivotal point to achieve a stable electrical network based on renewables. This paper proposes a novel approach to reduce the energy excesses exported to the grid by a residential user equipped with a100 kW solar photovoltaic field. In particular, the electricity is stored as hydrogen by means of a 50 kW reversible solid oxide fuel cell. A comprehensive energy and economic simulation model of the system is proposed. In particular, a model of the reversible solid oxide fuel cell is developed in MatLab® and then integrated in TRNSYS17 for dynamic simulation purpose. Results showed that using the plant waste heat is crucial for improving fuel cell efficiency and plant energy performance. The proposed system achieves a reduction of the primary energy consumption by 74%. However, the proposed plant exhibits a poor economic profitability, with a payback period of 15 years.

The anaerobic digestion of the organic fraction of municipal solid waste and the biogas production obtained from its stabilization are becoming an increasingly attractive solution, due to their beneficial effects on the environment. In this way, the waste is considered a resource allowing a reduction in the quantity of it going to landfills and the derived greenhouse gas emissions. Simultaneously, the upgrading process of biogas into biomethane can address the issues dealing with decarbonization of the transport. In this work, the production of biogas obtained from the organic fraction of municipal solid wastes in a plug flow reactor is analyzed. In order to steer the chemical reactions, the temperature of the process must be kept under control. A new simulation model, implemented in the MatLab® environment, is developed to predict the temperature field within the reactor, in order to assess how the temperature affects the growth and the decay of the main microbial species. A thermal model, based on two equilibrium equations, is implemented to describe the heat transfer between the digester and the environment and between the digester and the internal heat exchanger. A biological model, based on suitable differential equations, is also included for the calculation of the biological processes occurring in the reactor. The proposed anaerobic digestion model is derived by the combination of these two models, and it is able to simultaneously simulate both thermal and biological processes occurring within the reactor. In addition to the thermal energy demand, the plant requires huge amounts of electricity due to the presence of a biogas upgrading process, converting biogas into biomethane. Therefore, the in-house developed model is integrated into a TRNSYS environment, to perform a yearly dynamic simulation of the reactor in combination with other renewable technologies. In the developed system layout, the thermal energy required to control the temperature of the reactor is matched by a solar thermal source. The electrical demand is met by the means of a photovoltaic field. In this work, a detailed thermoeconomic analysis is also proposed to compare the environmental impact and economic feasibility of a biomethane production plant based on a plug flow reactor and fed by renewables. Several economic incentives are considered and compared to determine the optimal solution, both in terms of energy and economic savings. The plant is designed for the treatment of a waste flow rate equal to 626.4 kg/h, and the biomethane produced, approximately 850 tons/years, is injected into the national gas grid or supplied to gas stations. In the proposed plant, a solar field of an evacuated tube collector having a surface of approximately 200 m2 is able to satisfy 35% of the thermal energy demand while over 50% of the electric demand is met with a photovoltaic field of 400 m2. A promising payback time of approximately 5 years was estimated.

In the current energy and environmental framework, the environmental impact of the road transport sector and the urban waste management and disposal are extremely important for highly crowded cities. This work assesses the energy, economic and environmental performance of an innovative paradigm for the full decarbonisation of the road transport sector. This problem is integrated with the management of the organic fraction of municipal solid waste. In particular, the proposed technology is based on an anaerobic digestion plant coupled with a biogas upgrading unit, for the production of biomethane. In addition, photovoltaic panels and solar thermal collectors are also considered for matching electrical and thermal demands, in order to achieve a fully-renewable system. To this scope, the system also includes suitable thermal and electric storages. The economic analysis also considers specific public funding policies, currently available for this technology. This system aims to be a novel paradigm in the energy scenario of waste disposal and road transport sector refurbishment. TRNSYS software was adopted to perform an accurate dynamic simulation for a one-year operation of the system. The anaerobic digestion model is developed by the authors in MatLab and integrated in TRNSYS, for dynamic simulation purpose. Results show that the plant is almost self-sufficient due to the integration of storage systems for both the thermal and electric energy. The photovoltaic system is able to reduce by 45% the energy dependence from the grid. Energy and environmental analyses show a Primary Energy Saving of 126% and a reduction of CO(2) equivalent emissions by 112%. The economic feasibility analysis shows a promising Simple Payback period of 6 years.

This paper presents a thermoeconomic analysis of a polygeneration system based on solar-assisted desiccant cooling. The overall plant layout supplies electricity, space heating and cooling, domestic hot water, and freshwater for a residential building. The system combines photovoltaic/thermal collectors, photovoltaic panels, and a biomass boiler coupled with reverse osmosis and desiccant air conditioning. The plant was modeled in TRNSYS and simulated for 1 year. A parametric study defined the system’s setup. A thermoeconomic optimization determined the set of parameters that minimize the simple payback period. The optimal structure showed a total energy efficiency of 0.49 for the solar collectors and 0.16 for the solar panels. The coefficient of performance of the desiccant air conditioning was 0.37. Finally, a sensitivity analysis analyzed the influence of purchase electricity and natural gas costs and the electricity sell-back price on the system. The optimum simple payback was 20.68 years; however, the increase in the energy cost can reduce it by up to 85%.

The production of biogas by means of the anaerobic digestion process is becoming increasingly attractive in the green economy context. When municipal organic waste is used to produce biogas, a further positive effect on urban waste disposal is obtained. Starting from the anaerobic digestion model n.1, an accurate analysis of the temperature effects on the anaerobic digestion process in a plug flow reactor is performed. This paper aims at presenting a comprehensive and integrated one-dimensional biological and thermal model for a plug flow reactor. Partial differential equations with respect to time and space are considered to model the heat transfer between the reactor and the internal heat exchanger and between the reactor and the environment. In this scope, a suitable simulation code was developed in MATLAB and validated using the data available in literature. The results of the calculations show that temperature plays a crucial role in the anaerobic digestion process, since it strongly affects the kinetic rates of the microbial species and the methane production. The results obtained in terms of temperature fields and biogas production are compared with the ones available in literature, dealing with a continuously stirred tank reactor. The comparison is conducted considering that both reactors process a volumetric waste flow rate of 20 m3/d and have the same structural characteristics. The plug flow reactor resulted better performance with a produced biogas flow rate equal to 2300 Nm3/year.