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The progressive increase of renewable energy sources (RES) share during past decade strongly reflects on power system operating conditions. Romania is the South Eastern European country with the largest RES generating capacity. This paper proposes a novel method for assessing the impact on national power systems operation of integrating high shares of RES. Specifically, the method addresses first a variability analysis of RES production, based on historical records over 10 years for the Romanian power system. Wind energy is selected as the RES with the widest confidence interval, thus generating the largest power output fluctuations. Further, different simulation scenarios are defined in terms of variable wind energy share. The values obtained are integrated in a scaled simplified model, implemented in PSS/E. The impact of generating sets based on wind energy employment on voltage magnitude and transient time is assessed in fault conditions. Considering that the simulation scenarios defined comprise variable wind energy generation shares, this study emphasizes the impact of its dynamics on power systems. Simulation results highlight the negative influence of increasing wind energy share on the analyzed quantities. The outcomes of this research can suggest a particular analysis approach useful in studying power systems operation. • Momentary power recordings of a real power system underlie the research. • Different scenarios are defined varying load and wind energy share. • CDF is used to appraise the adequacy of the values selected for simulations. • Wind energy impact at different system loadings is analyzed subsequent faults. • Wind share increase negatively affects voltage evolution and transient time. [ABSTRACT FROM AUTHOR]

District Heating (DH) networks are getting closer to the concept of "Smart Grids" to deal with the contribution of new technologies and paradigms like Renewable Energy Sources, Distributed Generation and Storage, and Low-Temperature District Heating. This requires good anticipation of the system's dynamics with the objective of improving control. This work proposes a model based on the Finite Volumes method for anticipating the dynamics in DH systems. Its application to branched network topologies gives the delay between the change in the settings at the generation points and the time they are perceived by the different substation in the network, which is a prerequisite for system design, operation planning and optimal control. The model is tested in a 6 Node branched network with the main topology elements being represented (junctions, splits, etc.); real demand data is used at the consumption nodes. A comparison between the model developed by the authors and the existing Finite Volumes method is also presented for the proposed topology. These results shed light on the needs and opportunities in DH, mainly for ICT implementation, energy storage location and management, and enhanced control in the smart energy networks context. • New approach to model heat transport in dynamic District Heating networks. • The Electrical Analogy gives robustness to the Finite Volumes method. • The Modified method has better accuracy in variable systems. • Approach is able to evaluate the operation of DH networks in a dynamic environment. [ABSTRACT FROM AUTHOR]

In this paper four different air conditioning systems designed for a building located in Naples, are investigated. The first plant is based on distributed energy conversion systems: twelve boilers and twelve chillers. In the second solution the space heating demand is satisfied by a centralised boiler while the cooling load is met by a centralised chiller. The third option consists of a trigeneration plant. The fourth configuration is composed by an electric heat pump satisfying space heating and cooling and a centralised boiler used for domestic needs. Dynamic simulations have been carried out to compare the energy and environmental performance of the centralised systems with those achieved by the distributed one. Besides, as further loads, for the third option, two electric vehicles charged by the cogenerated electricity surplus are compared to diesel cars. The results show that the best energy and environmental performance are achieved by the cogenerator-based system, with a primary energy demand of 120.6 MWh/y and equivalent dioxide carbon emissions of 25.2 t/y in the configuration without vehicles. This result is also confirmed with electric and diesel vehicles. The energy competitiveness of the plant with the electric heat pump is achieved only in a scenario with a high penetration of renewable energy sources. • Autonomous and centralised air conditioning systems are compared. • Dynamic simulations are performed to carry out energy and environmental analyses. • A multi-purpose block of flats is considered as users simulated. • Electric and diesel vehicles are introduced in the analysis. • A sensitivity analysis is carried out considering the renewable energy sources contribution. [ABSTRACT FROM AUTHOR]

The transition in the energy market and the growing share of renewable energy sources have been boosting the research in new power cycles. For example, the concept of batch evaporation in the Misselhorn Cycle promises to increase the overall efficiency in low-temperature applications and therefore saves resources. In this paper, a dynamic evaporator model was extended in order to prove the feasibility of the Misselhorn Cycle despite its transient character. In this context, the thermal capacity of the wall material as well as the residence time of the heat source medium were added. The previous, underlying model predicted an improved system efficiency for the Misselhorn Cycle of about 50% compared to an Organic Rankine Cycle (ORC) at 100 C ∘ . Initially, the results of the extended model showed a negative influence of the inertial effects on the possible net power output (advantage over ORC only 10%). However, an unheated discharge phase and reduced dimensions of the heat exchanger could compensate these drawbacks and achieved results (about 40% better than ORC) in the same range as the previous, simple model predicted. These findings prove the general practical feasibility of the Misselhorn Cycle. [ABSTRACT FROM AUTHOR]

Incentives have played a major role in wind power development in Spain, having allowed the country to reach top worldwide positions in terms of wind power penetration but having also contributed to a structural cost-revenue unbalance. Feed-in tariff and premium schemes had been in force in Spain since the inception of wind power until the adoption of an auction-based support framework in 2016. So far, auctions have resulted in no incentives being allocated to any new wind farm. The present paper analyses the historical evolution of wind power support schemes in Spain and assesses the long run impact of the newly adopted policies on the future evolution of wind capacity and system costs through a behavioral stochastic System Dynamics model. Results show that the current lack of incentives will entail limited wind capacity growth, below the goal set in Spain's Renewable Energy Plan 2011–2020. Incentive levels required to meet specific goals in terms of capacity growth and system costs are computed and discussed. [ABSTRACT FROM AUTHOR]

Future district heating systems (so called 4th Generation District Heating (4GDH) systems) have to address challenges such as integration of (de)centralized renewable energy sources and storage, low system temperatures and high fluctuation of the supply temperature. This paper presents a novel framework for representing and simplifying on-grid energy systems as well as for dynamic thermo-hydraulic simulation and optimization of district heating and cooling systems. We describe physically precise and numerically robust models for simulation and continuous optimization. Furthermore, we propose a novel method to decompose a mixed-integer-optimal control problem into two sub-problems, separating the discrete part from the continuous. Two use cases show the applicability of the framework. An existing district heating system with more than 100 consumers is adapted to test the framework based on simulation requirements of 4GDH systems. The second case presents the continuous optimization of a district heating system in a virtual city district. A main advantage of combining equation-based modelling and nonlinear optimization is the possibility of including model coherences based on physical laws into the optimization formulation. Results show that the framework is well-suited for simulating larger scale 4GDH systems and that the solution time of the continuous optimization problem is sufficiently low for real-time applications. [ABSTRACT FROM AUTHOR]

To achieve the Paris Agreement 1.5 °C target, apart from the obligation for new buildings to be ZEBs, the existing building stock should be retrofitted as well, in order to improve their energy efficiency by using more efficient electromechanical energy systems and envelope materials, whereas RES should cover their energy needs. In this context, Energy Performance Certificates (EPCs) have been institutionalized to certify the energy behavior of buildings. Various types of buildings energy modeling tools and calculation methods have been proposed for EPCs procedures. This study focuses on the energy performance gap between dynamic and quasi steady-state simulation tools. The results from a comparative case study have shown remarkable discrepancies between dynamic and quasi-steady-state simulation processes, for the same building. Indeed, the quasi-steady-state simulation tool estimates 4.5% higher annual electricity consumption per conditioned area for the existing building and approximately 74% less energy savings for the retrofitted one, leading to an overestimation of 85% in CO 2 emissions prediction. Finally, compared to the analysis with the dynamic simulation tool, an increased retrofit cost, approximately by 19.7% (and thus 3 times higher payback period), is needed according to the results of the quasi-steady-state simulation tool, in order to achieve the same Energy classification. • Dynamic simulation tools are the key for accurate and reliable EPCs. • Quasi steady-state tools overestimate the energy consumption of buildings. • Quasi steady-state tools underestimate buildings energy classification. • Quasi steady-state tools perform poor PVs net metering consideration. • Dynamic simulation tools contribute to avoid overestimations in building retrofit. [ABSTRACT FROM AUTHOR]

With the gradual increase of intermittent renewable energy, the coal-fired power generating units must provide flexible peak shaving capabilities. However, the new requirement comes with increasing challenges for the pulverized coal utility boilers, as it tends to have lower combustion efficiency and higher NO x emission at extremely low loads. Accordingly, this work aims at coupling the NO x formation and reduction mechanisms with computational fluid dynamic simulation to thoroughly explore the technology for NO x abatement. The effect of the different primary air equivalence ratios on the Whitehaven bituminous combustion was experimentally and numerically studied. The combustion experiments were performed in a down-fired facility. Moreover, the numerical model validated well with the experimental results. The results reveal that, by reducing the primary air equivalence ratio, the combustion efficiency of pulverized coal stereo-staged combustion increased. Furthermore, the formation and reduction rate of fuel-NO x by HCN decreased but those by NH 3 slightly increased. In addition, the fuel-NO x reaction rates from char-nitrogen decreased. The NH 3 was oxidized to NO x , while HCN mainly played the role of reducing NO x. The primary air equivalence ratio of 0.24–0.28 was found to be the optimal range for the pulverized coal stereo-staged combustion technology. • The HCN and NH 3 formations decreased as the primary air equivalence ratio decreased. • The combustion efficiency increased as the primary air equivalence ratio decreased. • NH 3 was oxidized to NO x and HCN mainly played the role of reducing NO x. • The primary air equivalence ratio of 0.24–0.28 is conducive to lowering NO x. [ABSTRACT FROM AUTHOR]

Abstract: The Ericsson engine is an external combustion engine suitable for the use of certain energy sources such as solar energy, biomass and waste gases at high temperature, and thus contributes to the fight against global warming. Its open cycle configuration considered in this study can achieve good performance in low power range, most particularly in micro-cogeneration applications. The dynamic model of this engine which is the purpose of this study, takes into account both the pressure losses and the variation of the thermophysical properties of the working fluid as a function of the temperature in the system. The coded models are implemented on a Matlab/Simulink platform where the start-up dynamics and performance simulations are conducted. The optimal settings of the expansion cylinder valves, as well as the characteristic parameters of the engine are thus determined. In this configuration the engine develops a power output of 1.72 kW and reacts well when subjected to a selected perturbation. [Copyright &y& Elsevier]

Abstract: The discontinuous nature of the solar energy forces to study the dynamic behavior of solar plants to characterize their operations, to deepen their process understanding and to improve the performance and maintenance. The present paper focuses on the dynamic simulation and control of concentrating solar plants with the aim to define a reasonably simplified layout as well as to highlight the main issues to characterize the process dynamics of these energy systems and their related energy storages. Detailed first-principles mathematical models of key unit operations are developed, implemented, and integrated into commercial codes to improve the reliability of the plant dynamic simulation as well as the prevision accuracy. The case of Archimede concentrating solar power plant with the related two-tanks direct thermal energy storage technology is investigated. [Copyright &y& Elsevier]

Nowadays, the growing availability of renewable energy resources is an opportunity to reduce carbon emissions but also a challenge, as advanced control technologies are required. The new generation of smart district heating and cooling networks, for instance, pledges efficient energy distribution, flexibility and low-carbon energy integration. However, in the literature it is hard to find comprehensive frameworks for the integrated setup and testing of smart control strategies. This paper defines and demonstrates a framework that involves all steps of the controller development for small-scale district heating networks: from conceptualization to prototype testing. The innovative controller prototype, which relies on Model Predictive Control and aims to minimize operating costs and/or energy, is demonstrated in three original case studies, one in a simulation environment and two in real systems of different complexity in operational conditions. Compared to the control approaches previously adopted, based on predefined rules and operator experience, the smart solution achieves 6% reduction in cost and up to 34% reduction in energy consumption while meeting user requirements. The fast replicability of the proposed integrated methodology can foster the transition toward the next generation of smart heating networks. [ABSTRACT FROM AUTHOR]

Combined heat and power generation traditionally allows for higher energy performance than separate production of heat and electricity. However, the significant increase of the renewable energy sources contribution in electricity production has spatially and temporally modified the context in which polygeneration systems operate and the energy and environmental profitability of these technologies could be undetermined. In such a situation it seems interesting to investigate the influence of the power grid efficiency variation on the polygeneration systems performance. For this purpose energy and environmental performance of a proposed system based on combined production are compared to those achieved by a conventional system based on separate production. The primary energy demand of conventional and proposed systems due to electricity depends on the efficiency of the national electric energy system features. In this paper, this efficiency is considered to be time-varying (hour-by-hour) and it is further taken into account that the electric system efficiency changes in different regions of the same Country. According to Italian day ahead market of electricity the national territory is divided in 6 zones; two of them (Centre-North zone and Centre-South zone) will be specifically considered and compared hereinafter. The differences that arise in results are also assessed with respect to the case in which national and local average efficiency is taken into account. The environmental analysis is performed considering the average and the time-varying Italian and local electricity emission factors. The results have highlighted that the cogeneration system feasibility depends upon the variability of these factors. Indeed, referring to thermoelectric-based power grid efficiency, only in Centre-North zone is more energetically convenient to produce heat and power by separate production systems. The environmental analysis outcomes have showed the same trend of energy analysis results in all the considered zones underlining that the evolution towards sustainability in Smart Grids requires an integrated approach. • Separate and combined production of heat and power systems are compared. • Dynamic simulations are conducted to perform energy and environmental analyses. • Time-varying power grid efficiency and emissions factors are considered. • Variable energy and environmental indices in electricity market zones are defined. • Sensitivity analysis is performed considering the indicators provided by regulation. [ABSTRACT FROM AUTHOR]