1,721,041 research outputs found
A novel stochastic method to dispatch microgrids using Monte Carlo scenarios
Full text linkStochastic operating strategies have proven to achieve cheaper resource scheduling both in large power systems and microgrids, but suffer from high computational requirements with respect to traditional deterministic approaches; therefore, using stochastic formulations in advanced infra-daily operating strategies is quite challenging, especially in isolated energy systems with limited computational assets. This paper proposes a dispatching methodology for microgrids based on a novel two-stage formulation that decomposes the stochastic problem into several deterministic subproblems, whose solutions are afterwards aggregated by the aggregator using simulations and a cost-based rule. In the first stage, every subproblem is solved, then each optimal dispatching is simulated in the second stage to evaluate the corresponding expected operating cost, which is used by the aggregator to select the final optimal scheduling. When compared to traditional methods for a rural microgrid in Uganda, the proposed approach not only achieves interesting savings in operational costs, up to 5%, but also sharply reduces the computational requirements, even more than 5–100 times with respect to traditional stochastic approaches. The paper also proposes a review and first classification of this kind of methodologies, to highlight the novelties of the approach
Optimal sizing of microgrids: On the design equivalences of different objective functions
No full textDecentralized energy systems have risen attention of policy makers and academia for their potentiality to improve the electricity service, reduce costs and foster the rural electrification in developing countries. Several design methodologies have been proposed to optimize the size of different components, which is crucial especially in off-grid configurations. Given the interests of private companies, profitability aspects are becoming the major focus; nevertheless, there is no general agreement on the best indicator to use to assess if and how much the microgrid is cost effective. Moreover, different economic indicators can correspond to several sizing solutions, which makes the selection of the objective function a very critical aspect. In this study, we propose a comparison between main indicators used to optimize off-grid microgrids, including theoretical and numerical comparisons. Equivalences and inequalities among typical economic criteria are considered, including formulations accounting for the cost of the energy-not-served. Numerical case studies supporting the analysis are provided
Rolling-horizon scheduling strategies for off-grid systems: On the optimal redispatching frequency and the effects of forecasting errors
No full textAchieving universal electricity access is a serious challenge that developing countries are facing with. Decentralized systems are widely recognized as part of the solution, especially for remote areas where traditional approaches would be too expensive. In particular, mini-grids, which are local systems conceived to produce and distribute electricity, can provide good quality electricity enabling the development of basic industrial and commercial activities. Unfortunately, the significant business risks in that areas are hampering private companies in developing initiative in many areas of the world; hedging risks and reducing costs by achieving the optimal design and operation of mini-grids is then crucial. Advanced rolling-horizon operating strategies can lead to interesting savings in operating costs, which can improve the profitability of the project. In fact, predictive strategies advance the system's requirements and, by re-dispatching the system infra-daily, can better cope with load and RES uncertainties. In the present study, we investigate the effect of both the redispatching frequency and the forecasting errors into the operating costs, in order to help practitioners and researchers in identifying the best parameters to use in design and operation of mini-grids. A numerical case study is proposed for a mini-grid in Soroti, Uganda
Optimal design of renewable energy communities (RECs) in Italy: Influence of composition, market signals, buildings, location, and incentives
No full textIn Europe the concept of Renewable Energy Communities (RECs) renovates the need for decentralized energy generation among citizens and companies. The corresponding legal framework enables the creation of business models that shall support environmental, economic and social benefits, provided that adequate planning accounting for the local conditions is executed. The present work is focused on a thermal-electric co-simulation approach for the analysis of the energy exchanges within an Italian REC, aimed at sizing photovoltaics (PV) and energy storage systems. EnergyPlus is used to estimate the thermal and electric needs of the community, whose results are fed into the “EnergyCommunity.jl” tool for the design of the local power system. The influence of REC composition (prosumers/consumers), the building energy demands for heating, cooling, and appliances, the geography of the REC in Italian regions, the market data, and the total peak power of PV are examined. The self-consumed electricity, the energy shared among the community, and the social costs are evaluated in different scenarios, suggesting significant environmental and economic benefits for Energy Communities
Development of an Energy Management System for AC/DC hybrid networks: From abstract functional requirements to the flexible tool
No full textAlternating Current (AC) networks are the predominant technologies used to transmit and distribute electricity worldwide. However, the penetration of renewable sources and the decreasing costs in power electronics are making Direct Current (DC) systems a promising approach to increase energy efficiency, reliability, and resilience, while exploiting synergies with AC systems. Therefore, appropriate Energy Management Systems (EMS) are mandatory for achieving energy efficiency and economic profitability, which shall account for both AC and DC components and networks. Moreover, in practical applications, multiple different control methodologies have been proposed to manage power systems, with different simulation tools, development platforms and software tools, which rarely have the same interface. This study aims at proposing the generalized framework and the tool for the development of a flexible EMS, which could be easily interfaced with standard commercial tools, e.g. NEPLAN or PowerFactory. The theoretical and functional requirements of the methodology can lay the foundations for further research studies and the proposed results confirm the robustness of the methodology
Fairness and reward in Energy Communities: Game-theory versus simplified approaches
No full textThe energy transition requires huge investments. However, increasing citizen participation in the energy system by providing flexibility and decentralized generation and storage could provide relief and reduce the total system costs. In this regard, several governments are promoting the development of aggregations of users, sometimes in the form of Energy Communities, to foster the desired socio-economic and environmental goals. Energy Communities are expected to attract local investors and induce positive behavioural change that lowers the burden on the power grid. However, business models and fairness in the reward schemes are matters of concern that cannot be disregarded in the optimal planning of Energy Communities. In this framework, this paper proposes a comparison of different schemes that can be used to share revenues and rewards among the members of a Community. The cooperative optimization problem, calculated using Mixed-Integer Linear Programming (MILP), is compared to non-cooperative approaches where users do not cooperate. Simple rewarding schemes, e.g. proportional to the shared energy and investment costs, are compared to game-theory approaches using Shapley Value, Nucleolus, and VarLeast-Core. A numerical case study suggests that the procedure can be implemented in practice and suggests approximate techniques to address reward distribution schemes for Energy Communities
Fault localization to improve power system quality in distribution networks: a greedy approach to optimize the switching sequence of remotely-controlled devices
No full textThe developments in Information and Communication Technology (ICT) and electronic sectors have enabled regulators to set strict Power Quality targets, especially regarding the continuity of supply, such as the System Average Interruption Duration Index (SAIDI), that distributors must comply with to avoid penalties. Accordingly, distribution system operators (DSOs) have started introducing remote control and automation on the power system, but accurate and robust methodologies are required to identify where the fault occurred. When a fault happens, an entire feeder goes off-service, however by operating the remotely-controlled disconnectors and switchgears along the feeder, the distributor can speed up the system restoration process, thus avoiding the manual intervention by maintenance teams. In this paper, we describe an iterative heuristic-aided methodology to locate of the fault in a distribution network by acting on remote-controlled switches. In every iteration, all the possible actions aimed to quickly locate the fault are evaluated and the corresponding impact of the reliability indicator (SAIDI) is calculated. Then, the action with the lowest SAIDI is selected. The proposed methodology is flexible and can be generalized to any topology, including the restoration by an adjacent feeder. A numerical case study is proposed and discussed
Modelling lithium battery packs from single cell electro-Thermal equivalent circuit model
No full textModelling thermal behaviour of battery packs in pure electric vehicles (BEVs) is one of the most demanding tasks in powertrain design activities. The complexity is given by the need of considering several aspects like internal geometry, cooling circuit, etc. for which the standard approach based on equivalent circuit model seems not to be adequate. The aim of this paper is instead to demonstrate how it is possible to maintain the equivalent circuit model approach, by making minimal changes and by using data from vehicle CAN network. Then, the model can be used to correctly achieve battery pack temperature under different realistic use conditions
On the impact of different electricity markets on the operation of a network of microgrids in remote areas
No full textThe development of distributed energy generation, often aggregated to form micro- or nano- grids based on power generation from renewable sources, or small-size generators make it easier to electrify remote and isolated areas. In addition to privately owned generation capacities, it could be feasible and profitable to sell/buy the excess energy to/from the closest neighbors, giving rise to “peer-to-peer” forms of energy trades. Despite that peer-to-peer trading has been widely discussed in the literature, the organization of isolated markets with limited small capacities is still a subject of study and discussion in the power community. In this paper, we evaluate the functioning of an alternative shorter market scheme characterized by only one bidding period, closer to the delivery time, which is convenient as it profits from more accurate forecasts. Then, the final balancing is performed internally within the same microgrids. Feasibility and cost-effectiveness of the proposed market is assessed for an isolated cluster of microgrids and compared with the currently operating markets, modelled as a day-ahead and real-time balancing markets. Two-stages stochastic optimization is implemented to compare the two market options. For this purpose, a grid of five villages is considered as a case-study and simulations are performed under two possible sets of installed capacities, including both diesel generators and renewable energy sources, to operate in either a dependent or a self-sufficient regime. Simulation results show that both markets succeed in supplying the required power demand, but the proposed simpler type of market may also be cost effective with a cost reduction up to 20%
Multi-year stochastic planning of off-grid microgrids subject to significant load growth uncertainty: overcoming single-year methodologies
No full textThe optimal design of off-grid microgrids in developing countries is difficult to achieve, as several political and socio-economic risks can hamper investments of private companies. Estimating the energy demand and its growth is a challenging task, subject to high uncertainty that rarely have been accounted for in multi-year simulations at hourly resolution. Besides, from a long-term perspective, the assets degradation can significantly affect the performance of stand-alone hybrid energy systems. In this paper, we address these challenges and propose a novel stochastic dynamic method to size microgrids, simulating with accuracy the system operation and considering the unavoidable uncertainty in load growth and the components ageing. A predefined scenario tree structure allows capturing the load growth uncertainty and obtaining different capacity expansion strategies for each scenario. An illustrative case study for an isolated power system in Kenya using data collected in 23 Kenyan microgrids is shown. The proposed stochastic formulation results in a considerable reduction of the size of components with respect to traditional single-year approaches. Savings in terms of Net Present Cost (NPC) are beyond 16-20% and the effects of assets degradation are about 6%. Results lead to recommend multi-year optimization tools, as single-year methodologies can hardly achieve the same performances
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