60 years of cyclic monotonicity: a survey

The primary purpose of this note is to provide an instructional summary of the state of the art regarding cyclic monotonicity and related notions. We will also present how these notions are tied to optimality in the optimal transport (or Monge-Kantorovich) problem

Integral estimates for transport densities

The integration-by-parts methods introduced in this paper improve upon the Lp estimates on transport densities given in the recent paper by L. De Pascale and A. Pratelli (Calc. Var. Partial Differential Equations 14 (2002) 249–274)

Storage Solutions for Renewable Production in Household Sector

Abstract The penetration of renewable sources, particularly wind and solar, into the grid has been increasing in recent years. As a consequence, there have been serious concerns over reliable and safety operation of power systems. One possible solution, to improve grid stability, is to integrate energy storage devices into power system network: storing energy produced in periods of low demand to later use, ensuring full exploitation of intermittent available sources. Focusing on stand-alone photovoltaic (PV) energy system, energy storage is needed with the purpose of ensuring continuous power flow, to minimize or, if anything, to neglect electrical grid supply. A comprehensive study on a hybrid stand-alone photovoltaic power system using two different energy storage technologies has been performed. This study examines the feasibility of replacing electricity provided by the grid with hybrid system to meet household demand. This paper is a part of an experimental and a theoretical study which is currently under development at University of Bologna. A test facility is under construction, at the University of Bologna, for the experimental characterization of the cogenerative performance of small scale hybrid power systems, composed of micro-CHP systems of different technologies : a Micro Rankine Cycles (MRC), a Proton Exchange Membrane Fuel Cells (PEM-FC), a battery, an electrolyzer and a heat recovery subsystem. The test set-up is also integrated with an external load simulator, in order to generate variable load profiles. This paper presents the theoretical results of the performance simulations developed considering an hybrid system consisting on a photovoltaic array (PV), electrochemical batteries (B) and electrolyzer (HY) with a H2 tank and a Proton Exchange Membrane Fuel Cell (PEM-FC) stack, in case of a household electrical demand. The performance of this system have been evaluated by the use of a calculation code, in-house developed by University of Bologna; future activities will be the tuning of the software with the experimental results, in order to realize a code able to define the correct size of each sub-system, ones the load profile of the utility is known or estimated

Experimental Analysis of Partial Evaporation Micro-ORC for low -temperature Heat Recovery

In this paper, we present an experimental assessment of the performance of a partial evaporating organic Rankine cycle (PE-ORC) power system. The system converts low temperature heat into electrical energy, with a power size around 1 kW, thus suitable for micro generation in the residential sector. Although the test bench was designed for operating with superheated vapour at the expander inlet, it has demonstrated to be able to work with the expansion occurring entirely in two-phase condition. Since the direct measurement of the vapour quality is not possible using the sensors installed in the test rig, the state of the fluid in the two-phase condition is estimated by means of the thermal balance at the heat exchangers, so the thermodynamic cycle can be evaluated. Temperatures of the heat source in the range between 40 C and 75 C have been tested, and for each temperature value the vapour quality at the expander inlet has been varied by regulating the feed -pump rotating speed. Experimental data are provided regarding the performance of the overall cycle, of the heat exchangers, of the expander and of the feed -pump. It was observed that the effectiveness of the evaporator and the efficiency of the pump are improved with respect to the operation with superheated vapour at the expander inlet. However, the overall performance is lower, especially due to the high ratio of the pump consumption over the expander produced power, commonly called back work ratio (BWR). The latter, under some boundary conditions, has resulted higher than the unit, meaning that the system is not able to produce net electrical power. The aim of the paper is to identify the design characteristics required by a micro -ORC energy system in order to enhance its performance in the PE operating mode

Smart District Heating: Distributed Generation Systems' Effects on the Network☆

Abstract The European strategy 20-20-20 – providing for energy efficiency increase, pollutant emissions reduction and fossil fuel consumption reduction – leads to an increasing attention on the concept of smart cities. In this scenario, it is important to consider a possible integration between networks and distributed generation systems – i.e. to realize a bidirectional energy flux at the utilities, giving rise to the so-called smart grid – not only for the electrical sector, but also for the thermal energy field. Therefore, the concept of smart grid could be extended to the heat sector in relation to District Heating Networks (DHNs) and considering thermal energy distributed generation systems, such as solar thermal panels or micro-Combined Heat and Power (micro-CHP) generators. In this study several different layouts for the utilities substations in smart DHNs will be presented and discussed. These layouts have been developed in order to allow the bidirectional exchange of thermal energy at the utilities, optimizing the thermal exchange as function of network design temperatures (for both the supply and the return), of utilities' thermal power requirement and depending on the characteristics of the production system. Further, in this paper the results obtained from the simulations, carried out with the software Intelligent Heat Energy Network Analysis (I.H.E.N.A.) considering the implementation of the elaborated layouts, will be analyzed

Mars Regolith Simulant Ameliorated by Compost as In Situ Cultivation Substrate Improves Lettuce Growth and Nutritional Aspects

Heavy payloads in future shuttle journeys to Mars present limiting factors, making self-sustenance essential for future colonies. Therefore, in situ resources utilization (ISRU) is the path to successful and feasible space voyages. This research frames the concept of planting leafy vegetables on Mars regolith simulant, ameliorating this substrate’s fertility by the addition of organic residues produced in situ. For this purpose, two butterhead lettuce (Lactuca sativa L. var. capitata) cultivars (green and red Salanova®) were chosen to be cultivated in four dierent mixtures of MMS-1 Mojave Mars simulant:compost (0:100, 30:70, 70:30 and 100:0; v:v) in a phytotron open gas exchange growth chamber. The impact of compost rate on both crop performance and the nutritive value of green- and red-pigmented cultivars was assessed. The 30:70 mixture proved to be optimal in terms of crop performance, photosynthetic activity, intrinsic water use eciency and quality traits of lettuce. In particular, red Salanova® showed the best performance in terms of these quality traits, registering 32% more phenolic content in comparison to 100% simulant. Nonetheless, the 70:30 mixture represents a more realistic scenario when taking into consideration the sustainable use of compost as a limited resource in space farming, while still accepting a slight significant decline in yield and quality in comparison to the 30:70 mixture

Thermodynamic Evaluation of Repowering Options for a Small-size Combined Cycle with Concentrating Solar Power Technology☆

Abstract The increasing penetration of low-carbon technologies and enhancements in fossil-fuelled power plants efficiency are some of the most important and up to date research topics. Renewable energy, in particular solar, has the potential of meeting the world energy needs while addressing environmental concerns, but technological advances in renewable energy electricity production are necessary to become competitive with conventional technologies. New opportunities to increase the penetration of renewables energies, smoothing out renewables variability and intermittency problems, come out from the hybridization concept. Hybrid renewable-fossil fuel systems join the advantages of both renewable energies and programmable devices. Among all the renewable technologies available for hybridization, Concentrating Solar Power (CSP) with parabolic trough is the most diffused because of its relatively conventional technology and ease of scale-up. CSP hybrids are well established worldwide, predominantly with natural gas: the hybridization options for CSP ranging from feed water heating, reheat steam, live steam to steam superheating. Based on a detailed thermodynamic cycle model of a reference small-size one pressure level Combined Cycle (CC) plant, the impact of CSP addition is thoroughly evaluated. Different hybrid schemes are evaluated and compared considering CC off-design operation. The goal of this study is to evaluate, from a thermodynamic point of view, three repowering options of a small-size CC with a CSP system in a hybrid system configuration and to quantify their potential benefits in terms of system's performance increase. In particular, the optimal size of CSP plant is shown for each investigated hybrid repowering options. The changes in CC steam cycle operating parameters are presented together with CC performance increase. It is shown that solar hybridization into an existing CC plant may give rise to a substantial benefit from a thermodynamic point of view

Pump Hydro Storage and Gas Turbines Technologies Combined to Handle Wind Variability: Optimal Hydro Solution for an Italian Case Study☆

Abstract Load and wind energy profiles are totally uncorrelated, therein lies the problem of variable energy sources. Managing load with increasing wind penetration may call for operational ranges that conventional systems cannot readily access. Storage technologies could allow tolerating the unsteadiness of renewable sources with smaller fossil fuel plants capacity. Pumped Hydro Storage (PHS) is a crucial technology for balancing large steam power plants and may become increasingly important for storing renewable energies. Hence capacity ranges of PHS as well as its dynamic response to renewable power variability, will become progressively relevant. An integrated system made of a wind farm, a PHS plant and a set of gas turbines (GTs), as programmable fossil fuel devices, to handle renewable variability and maximize renewable energy exploitation, is studied in this paper. A specific case study is analyzed: a wind farm with a nameplate capacity equal to that installed in Sardinia is considered. To match the power output requested by the region with the integrated systems different configurations of PHS plant will be investigated. The impact of reversible or separate Francis machines with constant or variable speed will be analyzed in order to minimize electric power output overproduction and GTs fuel consumptions. Minimum and maximum capacity range for reversible or separate machines will be considered. The aim of the study is the optimum sizing and design of a PHS unit in a hybrid wind-hydro-gas turbine power plant to match the load request. Results in terms of PHS operation, water height behavior in upper and lower reservoirs, GT units power output, natural gas consumed and electric power output overproduction will be presented for each analyzed case

Complex energy networks: Energy-ecological efficiency based evaluations towards the sustainability in energy sector

In the last years, international programs in diverse sectors and national frameworks have been driven by the need of a sustainable growth, in a green economy perspective. In order to reduce the energy losses/dissipations, as well as the fossil fuels employment and related pollutant emissions, indeed, the spread of combined heat and power units and/or renewable sources generators is promoted into both the electrical grids and the thermal networks but are often in conflict with the economic aspects. In this context, the optimal management of complex energy networks - including, in particular, smart district heating - may lead to the achievement of important goals from the environmental and sustainability viewpoints. The aim of this paper is to develop a preliminary methodology for the complete evaluation of complex energy networks, considering energy, economic and environmental aspects. With this purpose, a case study consisting in a network for the fulfillment of electrical and thermal needs of the connected users will be analyzed, considering different scenarios in terms of energy generation mix and operation and applying different optimization software. In addition, the carried out evaluations will allow to set the basis for the discussion about the future of energy policies and possible incentives towards the sustainable development of the energy sector