Search

A novel energy storage system based on a SMES cooled by cryogenic fuel has being developed at the Dept. of Electrical Engineering of the University of Bologna. The system (which was patented by the authors) represents an alternative solution with respect to nowadays battery packs for the storage of electrical energy with large specific power. The device may find suitable application on board of road vehicles fed by liquid hydrogen with hybrid power-train (internal combustion engine and electric motor-generation), where a cryogenic tank is already present and no additional cryogenic costs are needed. The housing of the SMES inside the tank used for fuel storage, allows the exploitation of the thermal power required for the continuous evaporation of the fuel for the engine feeding to remove the AC losses from the magnet, thus avoiding the need of external supplied cooling power. In this paper both the design of the magnet and its operation in combination with electronic converter and electric motor during charge/discharge cycles are discussed. Moreover the ongoing activity for the development of a laboratory-scale prototype based on MgB2 superconductor is briefly presented.

Renewable Energy Sources (RES) exploitation for electric energy and hydrogen production has been identified as one of the leading ways towards a future sustainable energy system. Hydrogen can be stored and transported in gaseous (GH2) or liquid form (LH2). When large hydrogen storage is required, liquefaction can be convenient with respect to compression, because of its higher storage density. LH2 can also be used as a coolant for superconducting lines, acting at the same time as energy vector and cryogen. In particular, in this paper we focus on the MgB2 material mainly due to economic considerations and working temperature match with LH2. A system for large scale RES exploitation allowing flexible and controlled delivery of electric energy and LH2 is presented. For the thermo-hydraulic design, a method is proposed which resorts to compressible fluid equations put in a convenient simplified form. A case application with 20 km distance between cooling stations is considered, and the need of taking into account LH2 compressibility for pipeline design is shown.

A superconducting magnet with 200 kJ stored energy and 150 A nominal current has been designed and manufactured. The magnet consists of two coaxial coils, counter-series connected in order to keep the stray field below a given limit. The SC wire is a copper stabilized Ni-Ti strand, coated with an insulating glass yarn. Several copper slabs are placed within the coils in order to permit heat removal deep within the coil, thus allowing the device to operate at high AC losses regime. The device is addressed to innovative power system control aNd stabilization. Several tests with different ramp rate have been carried out at the liquid helium temperature. Design and manufacturing characteristics as well as test results are presented in this paper.

This paper presents the development of a dynamic circuital model suitable for simulation and performance evaluation of Proton Exchange Membrane (PEM) devices. The model directly implements the Butler-Volmer equation for the calculation of the activation potential, and therefore provides consistent results over the whole membrane current density working range, included the open circuit condition. The model is able to take into account relevant effects at low current densities which are due to partial reaction between the cathode catalyst Pt surface and O2, and to fuel crossover through the membrane. The implemented equations keep valid when inverting the current sign, thus allowing the model to simulate a fuel-cell, electrolyzer or regenerative fuel-cell throughout its complete working behavior. The paper shows how the circuital model can be easily implemented in common software environments such as Simulink or EMTP, and validates the results through comparison with available experimental data.

Among the long-term energy scenarios identified by major international organization in order to drastically reduce fossil fuels consumption and set out towards a sustainable energy system within the 21st century, the possibility of remote desert areas exploitation for large scale renewable energy production must be seriously considered. Desert areas are characterized by low cost wide lands with high levels of solar irradiation and wind availability. Interestingly, a little 0.3% of Sahara desert area assigned to solar systems would equal the total installed electrical power of Europe (700 GW). However, apart from generating costs (which should fall down with respect to conventional generation in future), two main technical problems would prevent this scenario. Firstly, fluctuations in the renewable power availability may lead to electric grid instability, reducing the quality of energy supply. Secondly, because deserts are typically far from high density populated and energy demanding areas, very high power lines would be necessary to transport the produced energy towards consumption regions. Hydrogen, produced by water electrolysis, is one of the most promising and studied means for storage and transmission of renewable energy, and is regarded as a possible future replacement of fossil fuels. When liquefied down to 20 K, hydrogen can be used for cooling an MgB2 superconducting line, allowing the design of a combined line for concurrent transport of electrical and chemical power. The feasibility study of a system for large scale energy storage and transport for connecting renewable energy plants sited in North Africa to the European electric grid is presented. The system is aimed at solving the problem of variable renewable energy availability using liquid hydrogen for energy storage. The superconducting MgB2 line could provide a very large power link between North Africa and Europe, through the Gibraltar’s strait, transporting both electrical energy and liquid hydrogen . The main aspects concerning the mechanical and electrical design of the system are examined. The electrical efficiency of the combined line is evaluated in comparison with HVDC conventional technology. The full system simulation during a reference day of solar availability is shown.

The realization and connection to the electrical grid of large scale renewable generating plants exploiting sources such as solar or wind can be prevented by problems of grid stability and power management due to fluctuating and poorly predictable resource availability. One of the most promising and studied means for long storage of energy in chemical form is the production of hydrogen by electrolysis of water, which can be stored in liquid form when large storage is required. The liquefaction process is high power consuming, but part of the energy consumption can be recovered if the Liquid Hydrogen (LH2) is used in order to improve the performance of some of the devices which make part of the global system. This paper describes advanced systems for reconversion of LH2 into Gaseous Hydrogen (GH2) at the end of the transport chain, which is necessary if end-users actually requires GH2 or if the LH2 has to be converted into electric energy. Working with Liquid Hydrogen (LH2) at 20 K as cold sink and making use of MHD generator with high combustion temperatures, these systems achieve very high thermodynamic efficiencies, actually allowing the recovering of part of liquefaction energy when compared with traditional systems. Different Gas Turbine, MHD, and combined systems are proposed and compared with available conventional thermo-electric and fuel cell systems in terms of output electric energy and Gaseous Hydrogen (GH2) for unit mass of input LH2. The higher electric energy output for the same consumed hydrogen can be seen as the re-covering of part of the energy spent for liquefaction.

Large scale Renewable Energy Sources (RES) exploitation has been indicated as one of the leading ways in order to drastically reduce fossil fuels consumption and develop a sustainable energy system within the 21st century. Often, suitable areas for RES power plants are remotely located, hence efficient large power transmission systems are needed for energy transport to-wards consumption sites. Moreover, apart from hydroelectric power, RES power is characterized by fluctuating and poorly predictable availability. When a significant part of total power generation is produced by fluctuating sources, storage systems are required in order to match end-users requirements and guarantee grid stability. Hydrogen, produced by water electrolysis, is today the most promising and studied mean of storage and transmission vector of renewable energy in chemical form. Usually, large hydrogen transport is considered to be feasible whether in gaseous form (GH2) through pipeline, or in liquid form (LH2) through truck cryotanks. This paper presents the design of a combined MgB2-superconducting/LH2-cryogenic pipeline. The line is designed for the concurrent transport of multi-GW electric power and liquid hydrogen up to 7 kg/s. Two scenarios are proposed for the application of the system. First, it is shown that the line could transport the electric power produced by the “Three Gorges” hydroelectric plant, replacing the several planned traditional lines with higher efficiency and lower environmental impact. Second, an hypothetical very large solar plant located in the Chinese Gobi desert is considered.

The problem of deposition on sensitive surfaces of eroded material from the discharge chamber ceramic walls of Hall thrusters is one of the main concerns which still prevent the wide diffusion of these devices to commercial satellite applications. This paper describes the experimental activity performed using a Quartz Crystal Microbalance for deposition measurements. A QCM is a sensor which can detect very small changes in the mass of its sense quartz crystal, providing a real-time measurement of deposited material with a sensitivity of the order of an atomic layer. This paper describes the preparation work performed for the use of the QMC and the collected experimental results.

A circuit scheme of a Magnetic Shield Type Superconducting Fault Current Limiter is developed. The circuit parameters are determined by means of the energy conservation law after the discretized field problem inside the device is solved. In order to validate the model a basic prototype of the limiter is tested. Experimental and numerical waveforms of current and voltage across the device under different operating conditions are compared. The equivalent circuit obtained can be introduced in a power system simulator to evaluate how a Magnetic Shield Type SCFCL interacts with a power network.

BackgroundMetabolic dysfunction-associated fatty liver disease (MAFLD) represents a new inclusive definition of the whole spectrum of liver diseases associated to metabolic disorders. The main objective of this study was to compare patients with MAFLD and non-MAFLD with hepatocellular carcinoma (HCC) included in a nationally representative cohort.MethodsWe analysed 6882 consecutive patients with HCC enrolled from 2002 to 2019 by 23 Italian Liver Cancer centres to compare epidemiological and future trends in three subgroups: pure, single aetiology MAFLD (S-MAFLD); mixed aetiology MAFLD (metabolic and others, M-MAFLD); and non-MAFLD HCC.ResultsMAFLD was diagnosed in the majority of patients with HCC (68.4%). The proportion of both total MAFLD and S-MAFLD HCC significantly increased over time (from 50.4% and 3.6% in 2002–2003, to 77.3% and 28.9% in 2018–2019, respectively, pConclusionsThe prevalence of MAFLD HCC in Italy is rapidly increasing to cover the majority of patients with HCC. Despite a less favourable cancer stage at diagnosis, patients with MAFLD HCC have a lower risk of HCC-related death, suggesting reduced cancer aggressiveness.