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

Performance Increase of a Small-scale Liquefied Natural Gas Production Process by Means of Turbo-expander☆

Abstract In the last years, the growing demand of the energy market has led to the increasing penetration of renewable energy sources in order to achieve the primary energy supply. However, in the next years fossil fuels are expected to remain the dominant energy source, due to the forecasted increase of global energy consumption. In particular, the natural gas is predicted to still play a key role in the energy market, on account of its lower environmental impact than other fossil fuels. Natural gas is currently employed mainly as gaseous fuel for stationary energy generation, but also as liquefied fuel, as an alternative to the diesel fuel, in vehicular applications. Liquefied Natural Gas (LNG) is currently produced in large plants directly located at the extraction sites. The aim of the study is the definition of an optimal small-scale production process for LNG, to be realized – in opposition to the current habit – directly at filling stations. With this purpose, two different LNG production layouts have been proposed and investigated within a thermodynamic analysis: starting from a Joule-Thompson LNG expansion process, a new layout with a turbo-expander has been proposed for the natural gas liquefaction. The carried-out simulations show that the new proposed solution allow to optimize the LNG production process and to minimize the process' energy consumption

Integration of μ-SOFC Generator and ZEBRA Batteries for Domestic Application and Comparison with other μ-CHP Technologies

Abstract This study investigates the possibility to integrate a Solide Oxide Fuel Cell (SOFC) prime mover and ZEBRA batteries, with the aim to fulfill a domestic user energy demand and to reduce the primary energy consumption, thereby, to enhance the total efficiency in a μ-CHP (Combined Heat and Power) application on a yearly basis. A realistic operational sequence of the SOFC-ZEBRA integration has been calculated using simple logic conditions. Both electric and thermal integration have been considered, in order to exploit the SOFC residual heat for the battery stand-by feeding. The key advantage of this system architecture is that the SOFC is operated without major load variations close to constant load, resulting in longer lifetime and thus reducing total costs of operation. Eventually, a comparison with alternative μ-CHP technologies has been carried out, highlighting the SOFC-ZEBRA potential

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

Low-temperature district heating networks for complete energy needs fulfillment

In order to reduce fossil fuels consumption and pollutant emissions, high contribution is given by district heating. In particular, the integration with renewable energy may lead to a significant increase in energy conversion efficiency and energy saving. Further benefits can be achieved with low temperature networks, reducing the heat dissipations and promoting the exploitation of low enthalpy heat sources. The aim of the paper is the analysis of the potential related to the conversion of existing district heating networks, to increase the exploitation of renewables and eliminate pollutant emissions in the city area. Further aim, in this context, is the optimization \u2013 from both energy production and operation management viewpoints \u2013 of a low temperature district heating network for the fulfillment of the connected users\u2019 energy needs. To this respect, a traditional network with a fossil fuel driven thermal production plant has been considered and compared with a low temperature district heating scenario, including geothermal heat pumps, photovoltaic panels and absorption chillers. These scenarios have been analyzed and optimized with a developed software, demonstrating the reduction of primary energy consumption and CO2 pollutant emissions achievable with low temperature networks. In addition, a preliminary economic comparative evaluation on the variable costs has been carried out. Future studies will investigate the economic aspect also from the investment costs viewpoint

Environmental Assessment of Renewable Fuel Energy Systems with Cross-Media Effects Approach☆

Abstract In the last years, the number of installed biofuels power plants is increased in northern Italy, due to favorable legislation on renewable energy sources, posing the issue to assess the resulting environmental effects. The European legislation on emissions for renewable fuels power plants provides guidelines to be integrated in the local regulations; moreover, local authorities have to identify the critical power plants in terms of pollution and the key parameters to grant licenses for the future plants. The aim of this paper is to describe a methodology and the calculation routine developed to assess the environmental effects of biomass plants in terms of simple indexes. The used approach is based on the Cross-Media Effects described by a European Commission Reference Document. In particular, several indexes are introduced to cover the most relevant environmental effects, as: air toxicity, global warming, acidification, eutrophication and photochemical ozone creation. For every considered pollutant (such as NOx, CO, etc.) directly emitted by the power plant, specific factors have been identified, in order to calculate the contribution to the different environmental indexes. Finally, a numerical evaluation of different biomass power plants, installed in Emilia Romagna region, is provided, in order to assess their environmental cross-media potential and to compare such kind of power plants with large scale, fossil-fuelled power plants

Simplified Model for PV Panels Performance Preditcion

Abstract In the last years, the growing global energy demand and the even more strictly pollution regulations have led the research to improve efficiency of conventional technologies and to find out innovative solutions to solve these issues. In this scenario, the renewable energy becomes a fundamental resource, especially in the field of electric energy generation. Problems related to non-programmability and effectiveness of renewables can be minimize through the diffusion of distributed generation and energy storage technologies. In this study, an integrated microgrid, made up of photovoltaic arrays, batteries and a hydrogen generator is presented. The aim of this work is to develop a simplified mathematical model able to describe the behavior of the photovoltaic modules for different operating conditions. On the respect of available literature on this topic, the peculiarity of this model is the possibility of being used simply knowing those parameters usually provided by manufacturers. To validate the model, experimental data recorded during the laboratory tests have been used. Obtained results show that 78 % of the analyzed operating conditions computed using the developed model are within the tolerance range of ± 10 % compared to experimental values

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