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The present study concerns with an optimization method of Solid Oxide Fuel Cell (SOFC) systems for electricity generation, directly fed by CH4 (methane) or C2H5OH (ethanol). By considering a detailed thermodynamic analysis, an innovative simulation model, namely THERMAS (THERmodynamic MAthematical Simulation), was designed and implemented. A specific SOFC-based system was selected to be the reference simulation, which is assumed to be equipped with heat exchangers (preheaters), a reformer, a SOFC-stack system and an afterburner. THERMAS allows for an extended parametric analysis in terms of energy and exergy and offers the opportunity to investigate all the operational characteristics that affect system's efficiency. The optimization process relies on the difference between the energy and exergy efficiency, where an OPF (OPtimization Factor) has been introduced and particularly estimated for each simulated scenario, based on several operational parameters, such as fuel composition, extension of chemical reactions and temperatures. The introduction of this OPF is actually an innovative improvement towards an easy-to-use optimization of SOFC systems. It is found that the design of a SOFC-based power plant fueled by pure hydrocarbons, has to be carefully simulated before its, otherwise the purification of fuels sounds meaningless.

This work simulates electricity production in a Solid Oxide Fuel Cell (SOFC)-based power plant, fed by biogas of various compositions. Steam reforming of the gas feed stream is used to produce the required supply for the SOFC. Given the constraints of the feed stream compositions, resulting from the origin of biogas, i.e., by the biomass from which the biogas has been produced as well as by the operating conditions selected for its production, the overall plant performance is modelled in terms of energy and exergy. The model provides results on the efficiency, power output and thermal behavior of the system, thus presenting the potential to offer great advantages in generating electricity from biogas and reducing the environmental impact. This research study presents the efficiency of such a system in terms of energy and exergy, by considering several values of the operational parameters (extensions of reactions that take place in the apparatus, temperatures, feed stream compositions, etc.). It is found that moving towards a methane richer fuel, the energy and exergy efficiency can remain almost constant at high levels (around 70%), while in absolute value the electric energy can increase up to 35% according to the system’s needs. Therefore, under this prospect, the present research study reveals the usefulness of low content methane fuels, which through the optimization process can succeed identical energy management compared to high content methane fuels.

The present research study presents the optimization of Solid Oxide Fuel Cell (SOFC) power plants directly fed by biogas. By considering energy and exergy balances for such a system, a detailed thermodynamic model (THERMAS) was designed and implemented. A specific SOFC-based system was selected as case study, equipped with three heat exchangers (preheaters), a reformer, a SOFC-stack system and an afterburner. The use of the simulation tool THERMAS give us the opportunity to investigate all the appropriate parameters that affect system’s efficiency based on exergy analysis while incorporating a detailed parametric analysis regarding the whole system. The optimization process relies on the difference between the energy and exergy efficiency by considering an innovative Optimization Factor (OPF) for each simulated system, which is dynamically affected by operational parameters, such as fuel composition, extension of chemical reactions and temperatures. It is found that the use of a pure fuels seems to be meaningless without optimization.

We study here the urban use of electric vehicles (EVs), focusing on the electricity production for charging purposes. This work proposes an innovative charging scheme for EVs, by introducing a home-applied power station, consisting of a fuel cell combined with an internal reforming unit, which is fed by natural gas and can thus be directly connected to the already-established natural gas grid. We therefore overcome the barriers posed by hydrogen use (establishment of storage equipment, energy consumption for keeping high pressure, development of supply grid, etc.) while we eliminate the environmental impact, since no fossil fuels are required for electricity production. Furthermore, comparisons against EVs charged by grid and vehicles fueled by petrol, both subjected to urban everyday use, have been carried out here. Precisely, we financially compare the use of an EV charged directly through the national electric grid against our innovative power station. Both options are also compared with the same vehicle, powered by an internal combustion engine fueled by petrol. This study also implements a detailed thermodynamic analysis for this state-of-the-art power station and an additional financial analysis for the everyday use of these vehicles under the three different scenarios. For the sake of equivalence, the new Peugeot 208 was selected as the reference-vehicle, as it is equipped either with a petrol engine or an electric motor, under a roughly identical performance profile. This work also introduces the use of the existing grid of natural gas to produce the necessary electricity for charging EVs, rather than using other renewables (solar, wind, etc.), and could further strengthen the worldwide acceptance of the EVs as a viable and a financially feasible solution for everyday urban transportation.

The objective of this work is to investigate, from both experimental and simulation points of view, the feasibility of a flywheel energy storage system (FESS) for buffering energy when implemented in off-grid (autonomous) electricity production. Toward this aim, a prototype FESS was built and measured to identify its optimal design and operational characteristics as they have been obtained theoretically. After simulating two different materials and shapes for the rotating mass, the hollow aluminum cylindrical design found to provide excellent energy storage results. By identifying the storage capacity of a prototype laboratory-scale FESS, it is also found that such a device can be promoted as a uninterruptible power supply system to cover peak loads during limited time periods. Finally, the scale of the project found to be a crucial parameter for its feasibility.

This paper deals with the feasibility of a Renewable Energy Sources (RES)-based stand-alone system for electricity supply based on a Flywheel Energy Storage System (FESS) located on the Greek Island of Naxos. The innovative use of flywheels in parallel connection with electrochemical batteries, as an integrated storage device in the same power plant, was selected to be simulated as it is a necessary buffer covering the load of a typical house. The optimal configuration for the electromechanical connection between the electrochemical batteries and flywheels is also considered in this study. Operational characteristics of the new storage systems were estimated and used in the simulations, while the financial aspects of the projects finalized using hand-made calculations and the HOMER software was used only for the energy calculations. It was found that an off-grid project using advanced and totally “green” technologies is possible and comparable to more conventional RES-based systems, in terms of energy and economical feasibility. Finally, it can be concluded that systems with low price flywheels are equivalent to those with electrochemical batteries.

This paper deals with the feasibility of RES-based systems for electricity supply in four different Greek Islands. Three specific typical loads were selected to be covered, where the grid connection was considered as optional. An optimization procedure in terms of energy efficiency and economical feasibility has also been applied, using the HOMER software for the energy part and a hand-made calculation procedure for the financial aspects. It is found that an off-grid project is not economically feasible and the grid connection is necessary only for the sale of excess electricity (not as a backup source). Finally, the relationship between environmental potential and produced energy is found to be linear, with almost constant behaviour for solar systems.

By using the optimization software tool HOMER, this project aims at the energetic and economical optimization of a RES-based stand-alone system, already installed at Leicestershire, UK. Based on local meteorological data, an optimization strategy has been developed to identify the most economical and efficient scenarios for the generation of electricity to cover the desirable load in annual basis. Furthermore, the environmental-friendly character of the system was highly concerned in terms of emissions reduction, therefore the capability of an off-grid system was also investigated. The simulations show that an off-grid project with zero emissions is feasible, presenting the additional advantage of minimal capital investment costs. Finally, it is found that grid connection corresponds to very high operational costs in a long term.

This work investigates the feasibility of a renewable energy sources (RES)-based stand-alone power system for electricity supply, to several simulated buildings, where energy is stored in a flywheel energy storage system (FESS). The system is assumed to be located on Naxos Island, Greece, due to the island’s high wind and solar potential and was designed to cover both the load of a typical house and a country house, where the excess electricity could be sold to the grid. An innovative storage device type, consisting of flywheels and electrochemical batteries, was selected as the energy buffer. The energy produced by hydrogen used in the proton electrolyte membrane (PEM) fuel cell (FC) charges the flywheel. This apparatus is compared to diesel generators commonly used in stationary applications. Optimization of the system, in terms of energy efficiency and economic feasibility, is also considered. The two systems were simulated using sensitivity, optimization, and simulation modeling software, and ...