1,721,010 research outputs found
Heat pumps to upgrade existing CHP-DHN systems towards new generation thermal networks
Full text linkDistrict heating networks with combined heat and power systems and renewable energies are one of the most promising solutions for efficient and sustainable energy supply. In many cases, however, especially for district heating networks prior to the 4th generation, significant renovations are required to meet decarbonization targets. In this paper a study is proposed to evaluate the integration of high temperature heat pumps in an existing combined heat and power - district heating plant to reduce fossil fuel consumption and increase the exploitation of renewable energy sources. The plant is currently operating in central Italy and connects more than 1250 users. The identified solution implies lowering the district heating networks operating temperature and supplying power peaks with a high temperature heat pump acting as a booster. Results showed significant improvements in system performance especially in the winter months, due to the greater impact of lowering the temperature level of the district heating network during these months. Overall, the updated scenario allows the overall demand and ground heat losses to be reduced annually by 5.3 % and 13.5 % respectively. This reduces natural gas consumption by 13.3 % and avoids the emission of about 836 tCO2. The analysis provides guidelines for the upgrade of 3rd generation district heating network that can be useful for planning improvements towards newest generation thermal networks
Managing plug-in electric vehicles in eco-environmental operation optimization of local multi-energy systems
No full textLocal multi-energy systems (LMES) have been recently recognized as a promising alternative to centralized energy supply systems to meet local energy needs, since they promote efficient use of the available energy thanks to the coordination of heat and power technologies, storage, flexible demand and plug-in electric vehicles (PEVs). In this framework, PEVs represent loads to satisfy in the grid-to-vehicle (G2V) mode, while also serving as distributed storage when equipped with vehicle-to-grid (V2G) technology, and can provide both economic and environmental benefits if properly managed. The contribution of this paper is to present a comprehensive multi-objective optimization model for the energy management of an LMES in the presence of PEVs, with the aim to combine maximization of LMES operator's profit with the minimization of CO2 emissions. The LMES supplies electricity, heat and cooling to a building cluster with PEVs, which can operate in both G2V and V2G modes. The problem consists of dispatching technologies in the LMES and finding the optimized charging/discharging strategies of PEVs in order to maximize the operator's profit while also reducing CO2 emissions, and it is addressed by formulating a multi-objective linear programming problem with the detailed modeling of interdependencies among energy carriers. The weighted sum method is used to represent the eco-environmental optimization problem, and it is solved by using CPLEX solver and considering a cluster of office buildings located in Italy as end-user of the LMES with PEVs owned by the offices’ employees. Testing results demonstrate the effectiveness of the optimization framework to maximize the operator's profit while also reducing the CO2 emissions, thanks to the optimal coordination of the multiple energy carriers in the LMES and the effective management of the flexibility collected at both supply and demand sides. Moreover, it is found that through the optimized charging and discharging strategies, the PEVs, acting as distributed energy storage, allow the provision of demand response services by also complementing renewable power to improve energy efficiency. In detail, under the economic optimization, most of flexibility collected from PEVs is sold into the wholesale market in order to maximize the operator's profit, whereas, under the environmental optimization, the power discharged from PEVs is exploited for self-use in the LMES to minimize environmental impacts by using a carbon-free source
A review on liquid air energy storage: History, state of the art and recent developments
No full textLiquid air energy storage (LAES) represents one of the main alternatives to large-scale electrical energy storage solutions from medium to long-term period such as compressed air and pumped hydro energy storage. Indeed, characterized by one of the highest volumetric energy density (≈200 kWh/m3), LAES can overcome the geographical constraints from which the actual mature large-scale electrical energy storage technologies suffer from. LAES is based on the concept that air can be liquefied, stored, and used at a later time to produce electricity. Although the liquefaction of air has been studied for over a century, the first concept of using cryogenics as energy storage was proposed for the first time in 1977 and rediscovered only in recent times. Indeed, the need for alternative energy vectors in the energy system attracted many researchers to discover the potential of the use of cryogenic media. This has brought the realization of a first LAES pilot plant and a growing number of studies regarding LAES systems. The main drawback of this technology is the low round-trip efficiency that can be estimated around 50–60% for large-scale systems. However, due to its thermo-mechanical nature, LAES is a versatile energy storage concept that can be easily integrated with other thermal energy systems or energy sources in a wide range of applications. Most of the literature published is based on thermodynamic and economic analysis focusing on different LAES configurations. This paper provides a collection of the papers published on LAES and it classifies the various studies conducted in different categories. Future perspectives show that hybrid LAES solutions with efficient design of the waste energy recovery sections are the most promising configuration to enhance the techno-economic performance of the stand-alone system
Day-ahead optimal scheduling of smart electric storage heaters: A real quantification of uncertainty factors
Full text linkOptimized controls are particularly promising for flexible and efficient management of space heating and cooling systems in buildings. However, when controls are based on predictive models, their effectiveness is affected by the reliability of the models used. In this paper we propose a quantification analysis of some of the main uncertainty factors that can be observed in an optimal control really implemented in a building. A day-ahead optimal scheduling was applied to the heating system (composed of smart electric heaters with thermal storage) of a single room in an office building located in Osimo (Italy). The control algorithm is formulated to determine the charging periods of the heaters with the objective of minimizing the withdrawal of energy from the grid. The control takes into account the electricity produced by a photovoltaic plant and must maintain the internal air temperature close to an imposed setpoint.
Firstly, the actual application of the control is shown during two selected days. Secondly, the analysis is extended to quantify the impact on the control performance of the prediction uncertainty of the input variables. The variable that has the greatest impact is the weather forecast and, specifically, the cloudiness index, which determines the solar gains. The different moment in time in which the weather forecast is predicted has proved to have a significant impact on the charging periods of the heaters (expected variation ranges from -50% to + 100%) and on the prediction of the indoor air temperature (variations observed up to 40%)
Renewables self-consumption potential in districts with high penetration of electric vehicles
Full text linkThe need to act on the challenges brought by climate change calls for an increasing penetration of renewable energy sources (RES) in our society's energy supply, but such integration can be challenging. This study analyzes the impact of large numbers of smart electric vehicles (EVs) in a real urban district, using the Italian town Osimo as a case study, to determine the achievable degree of RES self-consumption and CO2 emission reductions. Osimo features a multi-energy system with electricity, natural gas, district heating, and a 23% share of non-controllable RES capacity, mostly photovoltaics. The presence of EVs is evaluated in the present conditions and in scenarios with an increasing capacity of non-controllable RES. The case study is modeled in the deterministic hourly energy systems simulation model EnergyPLAN, which for these analyses is embedded within a framework aimed at enhancing its capabilities to consider the impact of uncertainties and obtain more robust results. The results show that a 10% EV penetration with vehicle-to-grid (V2G) capability can eliminate the need to export electricity surplus at the current PV capacity, lowering Osimo's CO2 emissions by 3.5%. A 30% penetration achieves the same with twice the PV capacity, reducing the emissions of 17.6%
New parametric performance maps for a novel sizing and selection methodology of a Liquid Air Energy Storage system
No full textLiquid Air Energy Storage is one of the most promising novel energy storage concept that guarantees at the same time viable capital cost, high energy density and no geographical/geological constrains. Considering the complexity of the plant, composed by three different phases (charge, discharge and storage), thermodynamic modelling could be a challenging undertaking. Making use of the strong similitude with gas turbine technology, this paper aims to deliver new generalized performance maps for Liquid Air Energy Storage system. The performance maps, validated against the experimental results of Highview Power pilot plant, have been modelled by means of a comprehensive sensitivity analysis carried out considering three macro-scenarios imposing the storage pressures and the turbomachinery performance (design/off-design conditions). By means of the performance maps, the impact of the main LAES operative parameters, as well as the effect of the cold/warm thermal energy storage utilization factor, over the key performance indicators has been assessed and analysed. The analysis shows that at design condition the higher is the value of the high grade cold thermal energy storage utilization factor, the lower is the positive impact of charge pressure over the specific consumption. For off-design condition of the main turbomachinery, the negative effect of lower isentropic efficiency of the main turbomachinery on the round trip efficiency is amplified by the choice of the charge pressure. At high value of the warm energy storage utilization factor, this negative effect can be partially offset by the higher Turbine Inlet Temperature available for the expansion process of the discharge phase
Criticalities of district heating in Southern Europe: Lesson learned from a CHP-DH in Central Italy
No full textEnergy recovery in gravity adduction pipelines of a water supply system (WSS) for urban areas using Pumps-as-Turbines (PaTs)
No full textEnergy recovery solutions reduce considerably the carbon footprint of Water Supply Systems (WSSs), which accounts for a large share of the energy demand in urban areas. The evaluation of the potential saving requires the availability of water flow rate and net head values in WSSs pipelines; however, this task is not always achievable since flow meters are costly and not installed in all the pipelines. In this paper, a novel methodology to predict the yearly average flow rate in gravity adduction pipelines is presented and validated using measured data coming from a WSS in Italy. A methodology already developed by some of the authors of this work was used to select Pump-as-Turbines (PaTs) and evaluate their Best Efficiency Point (BEP) to maximize the energy recovery. Two different installation layouts were investigated, namely one PaT and two PaTs in parallel, to be installed in the selected branches. The first one showed the best economic profitability, leading to a saving of 1325 €/year and a PayBack Period (PBP) of 11 years. The branch with the highest energy recovery potential led to a saving of 4915 €/year and a PBP of 6 years. Energy Efficiency Certificates (ECCs) were considered, highlighting their pivotal role to lower PBPs
Influence of users type on costs and primary energy savings potential for decentralized energy systems
No full textDecentralization of the energy production system is emerging as one of the best strategies to achieve and increased system resiliency and a reduction of carbon emissions through a more rational use of primary energy resources: both of which are mandatory traits for the energy systems of the upcoming future. Smart grids and specifically microgrids are able to deal in an effective way with distributed energy systems, thus emerging as a technology able to fill such gap. Microgrids can serve several types of users, both in rural off-grid settings and in highly urbanized areas. With this study we aim to understand how the type of user affects the potential for primary energy resources savings in an highly urbanized scenario. Specifically the effects of a decentralization strategy are confronted between a purely residential user, a tertiary user and a mix of the two; with the users represented by both simulated and measured data for a university campus in Singapore. The analysis is carried out by confronting the optimal set of technologies needed to meet the users demand, where such configuration is determined following a minimal life cycle cost criteria. Results show the potential savings in costs and primary energy usage for the proposed scenarios
District heating potential in the case of low-grade waste heat recovery from energy intensive industries
Full text linkWaste Heat Recovery (WHR) from energy intensive industries has a great potential in curbing CO2 emissions. Among the different solutions, District Heating (DH) is considered of major interest, satisfying the heating demand of users in the proximity of power plants. Considering the energy intensity of the pulp and paper industry, a method for evaluating the recovery potential of its low-grade waste heat from cogeneration plants in DH is presented. The proposed method allows to evaluate the thermal power from cogeneration plants to end users and to assess the potential maximum number of residential buildings that could be connected to each DH network. Based on the proposed method, the benefits of the WHR are evaluated from both energy and environmental points of view. More precisely, considering 50 pulp and paper mills in Italy under investigation in the present analysis, a yearly natural gas saving corresponding to 143.76 kTonnes of Oil Equivalent (TOE) and 333.11 ktCO2 is obtained. In case of WHR, the average Primary Energy Saving (PES) of the cogeneration plants increases from 0.14 up to 0.22. In particular, cogeneration units based on steam turbine technology show the greatest improvement, since its average PES moved from 0 up to almost 0.1
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