The rapid increase in the share of electricity generation from renewable energy sources is having a profound impact on the power sector; one of the most relevant effects of this trend is the increased importance of energy storage systems, which can be used to smooth out peaks and troughs of production from renewable energy sources.\ud \ud Besides their role in balancing the electric grid, energy storage systems may provide also several other useful services, such as price arbitrage, stabilizing conventional generation, etc.; therefore, it is not surprising that many research projects are under way in order to explore the potentials of new technologies for electric energy storage.\ud \ud This paper presents a thermodynamic analysis of a cryogenic energy storage system, based on air liquefaction and storage in an insulated vessel. This technology is attractive thanks to its independence from geographical constraints and because it can be scaled up easily to grid-scale ratings, but it is affected by a low round-trip efficiency due to the energy intensive process of air liquefaction. The present work aims to assess the efficiency of such a system and to identify if and how it can achieve an acceptable round-trip efficiency (in the order of 50–60%)

Abstract:The Information and Communication Technology industry has gone in the recent years through a dramatic expansion, driven by many new online (local and remote) applications and services. Such growth has obviously triggered an equally remarkable growth in energy consumption by data centers, which require huge amounts of power not only for IT devices, but also for power distribution units and for air-conditioning systems needed to cool the IT equipment. Following a previous work where the authors analyzed energy and cost savings that could be achieved in the energy management of data centers by means of a conventional combined cooling, heating and power system based on an internal combustion engine and a LiBr/H 2 O absorption chiller, this paper is dedicated to the economic and energy performance assessment of a CHP system based on a natural gas membrane steam reformer producing a pure hydrogen flow for electric power generation in a polymer electrolyte membrane fuel cell (PEMFC). Heat is recovered from both the reforming unit and the fuel cell in order to supply the needs of an office building located near the data center. In this case, the cooling energy needs of the data center are covered by means of a vapor-compression chiller equipped with a free-cooling unit. Since the fuel cell's output is direct current (DC), rather than alternate current (AC) as in electric generators driven by internal combustion engines, the possibility of further improving data center's energy efficiency by the adoption of DC-powered data center equipment is also discussed.

Besides providing energy for traction, an electric vehicle battery operates on-board auxiliary systems, among which air conditioning features the highest energy consumption and reduces significantly the driving range. Furthermore, electric vehicles heating needs are typically fulfilled through high-consuming resistors. In this respect, heat pumps promise higher energy efficiency and an increase in all-electric range.\ud \ud This paper analyses a reversible heat pump HVAC system equipped with a regenerative heat exchanger for pre-conditioning and hygrometric comfort improvement, and assesses air-conditioning energy loads and their impact on driving range for a vehicle performing daily commutes in different Italian cities. The dynamic model was set up in a Modelica framework. The overall system integrates component models calibrated against experimental data.\ud \ud Results confirm that air conditioning, consuming up to 32% of the energy required for traction on a daily commute, highly impacts on the all-electric range, which can decrease to 72 km from a base value of 94 km. In heating mode, replacing a resistor with a heat pump reduces consumption by 17–52% depending on geographical context, which proves to be highly effective in particularly demanding summer conditions lessening the driving range decrease up to 6%

In this paper, the thermodynamic potentialities and limits of the H2∕O2 turbine cycles (afterward named only H2∕O2 cycles) are investigated. Starting from the conventional gas turbine and steam turbine technology, the paper qualitatively tackles problems related to a change of oxidizer and fuel: from these considerations, an internal combustion steam cycle is analyzed where steam, injected into the combustion chamber together with oxygen and hydrogen, is produced in a regenerative way and plays the important role of inert. A proper parametric analysis is then performed in order to evaluate the influence of the main working parameters on the overall performance of H2∕O2 cycles. All the results are carried out by neglecting the energy requirements for O2 and H2 production systems, but taking into account the work required by the O2 and H2 compression. This choice permits a great freedom in the definition of these thermodynamic cycles; moreover, it is possible to come to some general conclusions because the H2 and/or O2 production systems and their integrations with thermodynamic cycles do not have to be specified. Therefore, this paper can be framed in a context of centralized production of oxygen and hydrogen (by nuclear or renewable energy sources, for example) and their distribution as pure gases in the utilization place. By adopting some realistic assumptions, for example, a top temperature of 1350°C, the potentialities of H2∕O2 cycles are very limited: the net efficiency attains a value of about 50%. Instead, by adopting futurist assumptions, for example, a top temperature of 1700°C, a different H2∕O2 cycle scheme can be proposed and its performance becomes more interesting (the net efficiency is over 60%). The paper tackles the main thermodynamic and technological subjects of the H2∕O2 cycles: for example, it is underlined how the choice of the working parameters of these cycles strongly influences the attainable performance.