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The detailed synthesis/design optimization of a hybrid solid oxide fuel cell–gas turbine (SOFC–GT) power plant is presented in this paper. In the first part of the paper, the bulk-flow model used to simulate the plant is discussed. The performance of the centrifugal compressors and radial turbine is determined using maps, properly scaled in order to match the values required for mass flow rate and pressure ratio. Compact heat exchangers are simulated using Colburn and friction factor correlations. For the SOFC, the cell voltage versus current density curves (i.e. polarization curves) are generated on the basis of the Nernst potential and overvoltages. Validation of the SOFC polarization curves is accomplished with data available from Siemens Westinghouse. Both the steam–methane pre-reforming and internal reforming processes are modeled assuming the water–gas shift reaction to be equilibrium-controlled and the demethanization reactions to be kinetically controlled. Finally, a thermoeconomic model is developed by introducing capital cost functions for each plant component. The whole plant is first simulated for a fixed configuration. Then, a synthesis/design optimization of the plant is carried out using a traditional single-level approach. The results of the optimization are presented and discussed.

In this paper, the optimization of a hybrid solid oxide fuel cell–gas turbine (SOFC–GT) power plant is presented. The plant layout is based on an internal reforming SOFC stack; it also consists of a radial gas turbine, centrifugal compressors and plate-fin heat exchangers. In the first part of the paper, the bulk-flow model used to simulate the plant is presented. In the second part, a thermoeconomic model is developed by introducing capital cost functions. The whole plant is first simulated for a fixed configuration of the most important synthesis/design (S/D) parameters in order to establish a reference design configuration. Next a S/D optimization of the plant is carried out using a traditional single-level approach, based on a genetic algorithm. The optimization determined a set of S/D decision variable values with a capital cost significantly lower than that of the reference design, even though the net electrical efficiency for the optimal configuration was very close to that of the initial one. Furthermore, the optimization procedure dramatically reduced the SOFC active area and the compact heat exchanger areas.

Summary. Background: Low ankle–brachial Index (ABI) identifies patients with symptomatic and asymptomatic peripheral arterial disease. The aim of this study was to correlate ABI value (normal or low) with 1-year clinical outcome in patients hospitalized for acute coronary syndromes or cerebrovascular diseases (CVD). Methods: ABI was measured in consecutive patients hospitalized because of acute myocardial infarction, unstable angina, stroke or transient ischemic attack (TIA). An ABI lower than or equal to 0.90 was considered abnormal. The primary outcome of the study was the composite of non-fatal acute myocardial infarction, non-fatal ischemic stroke, and death from any cause during the year following the index event. Results: An abnormal ABI was found in 27.2% of 1003 patients with acute coronary syndromes, and in 33.5% of 755 patients with acute CVD. After a median follow-up of 372 days, the frequency of the primary outcome was 10.8% (57/526) in patients with abnormal ABI and 5.9% (73/1232) in patients with normal ABI [odds ratio (OR) 1.96; 95% CI 1.36–2.81]. Death was more common in patients with abnormal ABI (OR 2.05; 95% CI 1.31–3.22). Cardiovascular mortality accounted for 81.7% of overall mortality. ABI was predictive of adverse outcome after adjustment for vascular risk factors in the logistic regression analysis (OR 1.93; 95% CI 1.24–3.01). The predictive value of ABI was mainly accounted for by patients hospitalized for acute coronary syndromes (adverse outcome: 12.8% in patients with abnormal ABI and 5.9% in patients with normal ABI, OR 2.35; 95% CI 1.47–3.76). Conclusions: An abnormal ABI can be found in one-third of patients hospitalized for acute coronary or cerebrovascular events and is a predictor of an adverse 1-year outcome.

This work presents a novel renewable trigeneration plant powered by solar, geothermal and biomass energy, producing simultaneously electricity, heat and cool. The developed system includes a 193 m2 photovoltaic field, a 159 kWh lithium-ion battery, a 30 kWe organic Rankine cycle, a 350 kWth biomass auxiliary heater, a geothermal well at 96 °C and a 80 kW single stage H2O/LiBr absorption chiller. The Organic Rankine Cycle is mainly supplied by the geothermal well, producing electricity. An additional amount of electricity is produced by the photovoltaic panels. A detailed dynamic simulation model was developed in TRNSYS environment in order to calculate both energy and economic performance of the plant. The model includes algorithms validated versus literature and experimental data. The model of the renewable trigeneration plant is used for a suitable case study, a residential building in the Campi Flegrei (Naples, South Italy) area, a well-known location for its geothermal sources and good solar availability. The proposed plant exhibits promising energy performance achieving a primary energy saving of 139%, mainly due to the obtained excess energy. From the economic point of view, the proposed plant gets a limited profitability, showing a payback period of about 19 years, mainly due to the high capital cost of the employed technologies. A thermo-economic optimization is also implemented, considering photovoltaic field and battery capacities as independent variables. The results of the optimization suggest increasing the area of the photovoltaic field and to limit the capacity of electric energy storage system, due to the high specific capital cost of the lithium-ion battery. Finally, a multi-objective optimization is also carried out, aiming at calculating the set of the optimal design variables of the proposed trigeneration plant.

During the past few years a significant effort has been performed in order to promote the use of renewable energy sources. However, one of the main barriers for a mature commercialization is due to the unpredictability of the renewable power production, mainly in case of wind and solar energy. Unfortunately, electric storage devices are often poorly profitable. Therefore, some more stable renewable energy systems must be designed. In this framework, this paper presents a novel hybrid renewable system consisting of Building Integrated PhotoVoltaic panels and small-scale Wind Turbines and double-stage heat pumps. This combination is very promising since it reduces the typical fluctuations of solar or wind systems, achieving a more stable profile of the overall power production. A detailed dynamic simulation model is developed in TRNSYS environment, including validated models for all the components and a suitable thermoeconomic analysis. A case study is implemented for a hotel building, where the space heating and cooling energy is supplied by an electrically driven reversible air-to-water Heat Pump, supplied by the electricity produced by Building Integrated PhotoVoltaic panels and Wind Turbines. the thermal energy recovered from the HP desuperheater is coupled with the thermal energy produced by a two-stage cascade cycle Heat Pump to produce domestic hot water. Results are presented in terms of hourly, monthly and yearly system performance data as well as by discussing the results of a detailed sensitivity analysis performed to detect the optimum configuration and weather zone of this hybrid renewable system. An analysis of the building envelope features is also performed, according to the nearly zero energy buildings target. Results showed that the combination of photovoltaic and wind technologies allows one to significantly enhance the stability of the renewable power production. Results also show that the use of heat pumps leads to a reduction of the primary energy demand for building space heating/cooling and domestic hot water by 30%. A payback period of about 5.2 years is obtained and the optimum configuration suggests adopting one 20 kW Wind Turbine for the selected case study.

District Heating and Cooling is considered an efficient solution to address the thermal energy demand of the building sector and reduce its environmental impact. In this paper, a 5th generation bidirectional heating/cooling network is designed and modelled. The network is coupled with water-to-water heat pumps, ground heat pumps and a photovoltaic field and is designed to meet the energy requirements of a 50-building district in the city of Leganes (Madrid). All components are modelled in TRNSYS 18. The studied network achieves a primary energy saving index of 64% and reduces the CO2 emissions by 76% relative to the current situation. The economic analysis of the system results in the relatively long payback period of 33 years, mainly due to the high costs of excavation and the installation of the heat pumps and pipes. With the current design, the photovoltaic field meets only 30% of the electricity demand of the district. However, additional energy storage could help align the power production with the actual power demand better and avoid grid balancing issues. The inclusion of other types of thermal energy consumers would also enhance the performance of the network by increasing the simultaneity between cooling and heating demands.

Anaerobic Digestion (AD) is a well-established process that is becoming increasingly popular, especially as a technology for organic waste treatment, the process produces biogas, which can be upgraded to biomethane, which can be used in the transport sector or injected into the natural gas grid. Considering the sensitivity of Anaerobic Digestion to several process parameters, mathematical modeling and numerical simulations can be useful to improve both design and control of the process. Therefore, several different modeling approaches were presented in the literature, aiming at providing suitable tools for the design and simulation of these systems. The purpose of this study is to analyze the recent advancements in the biomethane production from different points of view. Special attention is paid to the integration of this technology with additional renewable energy sources, such as solar, geothermal and wind, aimed at achieving a fully renewable biomethane production. In this case, auxiliary heat may be provided by solar thermal or geothermal energy, while wind or photovoltaic plants can provide auxiliary electricity. Recent advancements in plants design, biomethane production and mathematical modeling are shown in the paper, and the main challenges that these fields must face with are discussed. Considering the increasing interest of industries, public policy makers and researchers in this field, the efficiency and profitability such hybrid renewable solutions for biomethane production are expected to significantly improve in the next future, provided that suitable subsidies and funding policies are implemented to support their development.

This work presents a dynamic analysis of an anaerobic digestion plant, in which concentrating photovoltaic/thermal collectors are used to match a part of both heating and power demand of the process. The system is supplied by the organic fraction of municipal solid waste. The system also includes a thermal storage tank and an auxiliary heating system. An up-grade section is also included, to produce biomethane, suitable for injection into the natural gas pipeline network. For such hybrid solar-biomass system, a comprehensive simulation model was developed in MATLAB®, calculating the time-dependent production of biomethane as a function of the operating temperature within the digester. The model, based on differential equations and thermal balances, accounts for both thermal and biological phenomena occurring within the process, taking into consideration the geometrical and structural characteristics of the system. The consistent Anaerobic Digestion Model 1 is used to model the biological process, evaluating the biogas production as a function of a series of operating variables: the digester operating temperature, mass flowrate and temperature of the hot water entering the digester, ambient temperature, mass flowrate and composition of the organic waste in input. The model also calculates the electric consumption of the upgrading process, used to convert the biogas into biomethane. Such model was integrated into the simulation platform of the overall plant, developed in TRNSYS, evaluating the energy, environmental and economic performance of the entire system. A case study is presented, showing the dynamic performance of the system under evaluation: for such case, a primary energy saving of 24% was found, with respect to a conventional digester; around 20% of the overall thermal energy demand is met by solar energy; finally, a promising payback time of about 3 years was estimated.

The production of “green hydrogen” is currently one of the hottest topics in the field of renewable energy systems research. Hydrogen storage is also becoming more and more attractive as a flexible solution to mitigate the power fluctuations of solar energy systems. The most promising technology for electricity-to-hydrogen conversion, and vice versa, is the reversible solid-oxide cell (SOC). This device is still very expensive, but it exhibits excellent performance under dynamic operating conditions compared to the competing devices. This work presents the dynamic simulation of a prototypal renewable plant combining a 50 kW photovoltaic (PV) field with a 50 kW solid-oxide electrolyzer cell (SOEC) and a compressed hydrogen tank. The electricity is used to meet the energy demand of a dwelling located in the area of Campi Flegrei (Naples). The SOC efficiency is simulated by developing a mathematical model in MATLAB®. The model also calculates the cell operating temperature as a function of the input current. Once the optimal values of the operating parameters of the SOC are calculated, the model is integrated in the transient system simulation tool (TRNSYS) for dynamic analysis. Furthermore, this work presents a parametric analysis of the hydrogen storage system (HSS). The results of the energy and environmental analyses show that the proposed system can reach a primary energy saving by 70% and an amount of saved CO2 of 28 tons/year. Some possible future market scenarios are considered for the economic analysis. In the most realistic case, the optimal configuration shows a simple pay back lower than 10 years and a profit index of 46%.

Hospitals are very attractive for Combined Heat and Power (CHP) applications, due to their high and continuous demand for electric and thermal energy. However, both design and control strategies of CHP systems are usually based on an empiric and very simplified approach, and this may lead to non-optimal solutions. The paper presents a novel approach based on the dynamic simulation of a trigeneration system to be installed in a hospital located in Puglia (South Italy), with around 600 beds, aiming to investigate the energy and economic performance of the system, for a given control strategy (electric-load tracking). The system includes a natural gas fired reciprocating engine (with a rated power of 2.0 MW), a single-stage LiBr-H2O absorption chiller (with a cooling capacity of around 770 kW), auxiliary gas-fired boilers and steam generators, electric chillers, cooling towers, heat exchangers, storage tanks and several additional components (pipes, valves, etc.). Suitable control strategies, including proportional–integral–derivative (PID) and ON/OFF controllers, were implemented to optimize the trigeneration performance. The model includes a detailed simulation of the main components of the system and a specific routine for evaluating the heating and cooling demand of the building, based on a 3-D model of the building envelope. All component models were validated against experimental data provided by the manufacturers. Energy and economic models were also included in the simulation tool, to calculate the thermoeconomic performance of the system. The results show an excellent economic performance of the trigeneration system, with a payback period equal to 1.5 years and a profitability index (ratio of the Net Present Value to the capital cost) equal to 3.88, also due to the significant contribution of the subsidies provided by the current Italian regulation for CHP systems (energy savings certificates).

This work presents a dynamic simulation model of a prototypal renewable plant producing electricity, heat and cool. The hybrid system consists of a 6 kWe Organic Rankine Cycle (ORC), a 17.1 kWf absorption chiller, a geothermal well, a 25 m2 evacuated solar collector field, a 200 kWt biomass heater and a 45.56 kWh electric energy lithium-ion storage system. The geothermal well at 96 °C, in combination with the solar field, supplies the thermal energy driving the ORC. This simulation model is implemented in TRNSYS environment. In order to evaluate the thermoeconomic performance of this renewable trigeneration plant, a suitable case study is analysed: a bar and soccer centre in the area of Campi Flegrei (Naples). By the simulation, interesting results in terms of energy and environmental performance are obtained. The proposed renewable power plant achieves a primary energy saving of 94.54% and a reduction of CO2 emissions equal to 97.36%. The high total capital cost of the plant significantly affects the payback period of 16.7 years. However, in the future European energy scenarios, where a full decarbonization will be achieved and the capital cost of the renewables will significantly decrease, the use of these technologies will be pivotal and significantly profitable.

The paper presents an in-depth analysis of a novel scheme for the sustainable mobility, based on electric vehicles, photovoltaic energy and electric energy storage systems. The work aims to analyse such innovative system, putting in evidence its advantages in comparison to a conventional one, based on the grid-to-vehicle technology. The study also provides interesting guidelines for potential users and system designers. Two case studies are presented: i) the taxi fleet of the city centre of Naples and ii) the cargo vans of the city of Salerno; both towns are in Southern Italy. For each case, the hourly power consumption of the vehicles was evaluated, as a function of the daily trip length. An accurate procedure was implemented to select the sites suitable for the installation of the charging stations, including a photovoltaic field and an electric storage system. A comparison was also performed between two different electric storage technologies: lead-acid and lithium-ion battery. The case studies were analysed by means of a detailed dynamic simulation model, developed in TRNSYS. A sensitivity analysis was also performed, to evaluate how different values of the most important design and operating parameters affect the system overall performance. It was found that the results are mostly affected by solar field area, capacity of the energy storage system and investment cost. The comparison between the two selected storage technologies did not exhibit significant differences. For both the cases investigated, it was found that, during the summer, solar energy covers an important amount of the total energy demand. On the contrary, in winter the amount of energy provided by the public electric grid was high. From an economic point of view, assuming a lithium-ion battery capital cost equal to 90 €/kWh, acceptable pay-back periods (about 6 years) were obtained, for both the applications considered.

This work presents a thermoeconomic comparison between two different solar energy technologies, namely the evacuated flat-plate solar collectors and the photovoltaic panels, integrated as auxiliary systems into two renewable polygeneration plants. Both plants produce electricity, heat and cool, and are based on a 6 kWe organic Rankine cycle (ORC), a 17-kW single-stage H2O/LiBr absorption chiller, a geothermal well at 96 °C, a 200 kWt biomass auxiliary heater, a 45.55 kWh lithium-ion battery and a 25 m2 solar field. In both configurations, electric and thermal storage systems are included to mitigate the fluctuations due to the variability of solar radiation. ORC is mainly supplied by the thermal energy produced by the geothermal well. Additional heat is also provided by solar thermal collectors and by a biomass boiler. In an alternative layout, solar thermal collectors are replaced by photovoltaic panels, producing additional electricity with respect to the one produced by the ORC. To reduce ORC condensation temperature and increase the electric efficiency, a ground-cooled condenser is also adopted. All the components included in both plants were accurately simulated in a TRNSYS environment using dynamic models validated versus literature and experimental data. The ORC is modeled by zero-dimensional energy and mass balances written in Engineering Equation Solver and implemented in TRNSYS. The models of both renewable polygeneration plants are applied to a suitable case study, a commercial area near Campi Flegrei (Naples, South Italy), a location well-known for its geothermal sources and good solar availability. The economic results suggest that for this kind of plant, photovoltaic panels show lower pay back periods than evacuated flat-plate solar collectors, 13 years vs 15 years. The adoption of the electric energy storage system leads to an increase of energy-self-sufficiency equal to 42% and 47% for evacuated flat-plate solar collectors and the photovoltaic panels, respectively.

A dynamic simulation model of a novel solar–geothermal polygeneration system and the related exergetic and exergoeconomic analyses are presented in this paper. The plant is designed in order to supply electrical, thermal and cooling energy and fresh water for a small community, connected to a district heating and cooling network. The hybrid system is equipped with an Organic Rankine Cycle fueled by medium-enthalpy geothermal energy and by a Parabolic Trough Collector solar field. Geothermal brine is also used for space heating and cooling purposes. Finally, geothermal fluid supplies heat to a Multi-Effect Distillation unit, producing also desalinized water from seawater. Dynamic simulations were performed in order to design the system. The overall simulation model, implemented in TRNSYS environment, includes detailed algorithms for the simulation of system components. Detailed control strategies were included in the model in order to properly manage the system. An exergetic and exergoeconomic analysis is also implemented. The exergetic analysis allows to identify all the aspects that affect the global exergy efficiency, in order to suggest possible system enhancements. The accounting of exergoeconomic costs aims at establishing a monetary value to all material and energy flows, then providing a reasonable basis for price allocation. The analysis is applied to integral values of energy and a comparison of results between summer and winter season is performed. Results are analyzed on different time bases presenting energetic, exergetic, economic and exergoeconomic performance data. Results show that global exergy efficiency varies between 40% and 50% during the “Thermal Recovery Mode” operation and between 16% and 20% during the “Cooling mode” operation. It was also found that electricity, chilled water, cooling water and desalinated water exergoeconomic costs vary respectively in the ranges 0.1475–0.1722 €/kW h, 0.1863–0.1888 €/kW hex, 0.01612–0.01702 €/kW hex and 0.5695–0.6023 €/kW hex.

A great interest has recently arisen for the sustainable supply of energy and fresh water, due to the growing demand from developing countries. Facing this demand by traditional technologies implies evident risks related with the high cost of fossil fuels and their environmental impact. Then, alternative solutions based on the use of renewable sources and innovative technologies must be considered. In this paper a renewable polygeneration system is examined, which includes a solar field based on parabolic trough photovoltaic/thermal collectors, a biomass heater, an absorption chiller and a Multiple Effect Distillation desalination unit. Plant operation under dynamic conditions has been analysed in previous papers; in this paper an exergetic and exergoeconomic analysis is carried out. The exergetic analysis is intended to identify the steps that mostly affect the overall plant exergy efficiency, so as to propose possible improvements. The exergoeconomic cost accounting is aimed at assigning a monetary value to each energy or material flow, thus providing a rational basis for price assignment. Both the exergetic and exergoeconomic analyses are applied to integral values of energy flows, comparing the results obtained in the summer and winter season. Finally, economic viability of the system in different context scenarios is discussed.

During the last years, special attention has been paid to renewable polygeneration technologies, able of simultaneously producing thermal, cooling, electrical energy and desalinated water from seawater. This paper focuses on an innovative polygeneration system driven by renewable energy sources, including the following technologies: hybrid photovoltaic/thermal collectors, concentrating parabolic trough (CPVT), a biomass heater, a single-stage absorption chiller and a multiple-effect distillation desalination system. The system is designed to cover the base load of an isolated small community. In previous papers, the dynamic simulation model about plant operation is discussed. In this paper, a detailed exergy, economic and environmental analysis of the plant is presented. In addition, the plant was optimized using different objective functions, applying the Design of Experiment (DoE) methodology which evaluates the sensitivity of the different objective functions with respect to the selected design parameters. The results show that an increase of the storage volume is generally negative, whereas increasing the solar field area involves an increase of the exergy destruction rate, but also an improvement of the CPVT exergy output provided, the final result is an increase of both the exergy efficiency and the economic profitability of the polygeneration system.

This paper investigates the integration of solar and geothermal energy in a novel polygeneration system producing simultaneously: electricity, thermal energy, cooling energy and fresh water. The polygeneration system under analysis includes concentrating photovoltaic/thermal solar collectors (CPVT), a Geothermal Well (GW) a multi-effect distillation (MED) system for seawater desalination, a single-stage LiBr–H2O absorption chiller and additional components, such as: storage tanks, heat exchangers and balance of plant devices. The CPVT produces simultaneously electrical energy and thermal energy, at a maximum temperature of about 100 °C. The electrical energy is delivered to the grid, whereas the thermal energy can be used for different scopes. First, the thermal energy can be used for heating purposes and/or Domestic Hot Water production. As an alternative, solar thermal energy can be used to drive an absorption chiller, producing chilled water for space cooling. Finally, solar energy, in combination with the thermal energy produced by low-enthalpy (about 80 °C) geothermal wells, may be used by the MED system to convert seawater into desalinated water. Geothermal energy is also used to produce Domestic Hot Water at 45 °C. The system is dynamically simulated by means of a zero-dimensional transient simulation model. The simulation model also includes detailed control strategies, for the management of the different technologies included in such a complex system. The system is assumed to be operated in some of the several small volcanic islands in the Mediterranean Sea, assuming Pantelleria (Trapani, Italy) as main case study. Here, the availability of solar and geothermal energy is high whereas the availability of fresh water is scarce and its cost consequently high. Results show an excellent energetic performance of the system under investigation. From the economic point of view, the profitability of the system dramatically increases when user Domestic Hot Water demand is high.