Multi-carrier Energy Systems Research Articles

RETRACTED: Probabilistic scheduling of power-to-gas storage system in renewable energy hub integrated with demand response program

• Power-to-gas storage is integrated with energy system based on energy hub concept. • Proposing an incentive-based demand response program via load shifting capability. • Proposing a stochastic approach to handle the system uncertainties. • The introduced stochastic approach is modeled as a mixed-integer linear problem. Reliable energy supply is a significant challenge for the power system operators. The increase of emerging resources, as well as multi-carrier consumers in energy systems, lead to the integration of multi-carrier energy systems. The energy hub (EH) is one of the central infrastructures which smooths the combination and interdependency of various energy carriers to increase the efficiency and reliability. A novel technology, such as power-to-gas (P2G) storage, is a great option for achieving a renewable resources-based integrated energy system with high efficiency. The P2G storage is regarded as a viable energy storage approach to cover ever-increasing renewable energy resources variability in power system operations. The contribution of this paper is to present an optimal stochastic scheduling problem of EH integrated with P2G storage, combined heat and power (CHP) unit, wind power, boiler, electrical storage, and thermal storage to meet electrical, heat, and gas demands considering demand response program (DRP). The load shifting based DRP is applied on the electrical loads to reduce the operation cost of the EH. Also, the P2G storage system is used as a new resource that makes a connection between electrical and natural gas networks by converting the power to hydrogen and after that to natural gas through two processes including electrolysis and mechanization, respectively. A scenario-based stochastic approach is applied to handle the uncertainties related to the electrical loads, wind power, and electricity price. The objective of the proposed problem is to minimize the total operation cost of EH, which is modeled as a mixed-integer linear programming (MILP) problem model. The numerical results are implemented for different cases which demonstrate the effectiveness of the integration of the P2G based multi-carrier energy storage and DRPs on the operation cost of EH. The achieved results confirm the proposed approach by demonstrating the considerable reduction in operating cost of the EHS by approximately 7%.

Distributed robust operational optimization of networked microgrids embedded interconnected energy hubs

An interconnected energy hubs (EHs) framework aims to enhance the efficiency of the multicarrier energy system through realizing optimal coordination among existing players. In this paper, EH concept is studied in networked microgrids (MGs) structure to exploit the potential capabilities of microgrids in satisfying various types of energy demands. In the proposed model, MGs and distribution network are independent entities which have their local scheduling problem. To coordinate the operation of entities, a distributed algorithm based on the alternating direction method of multipliers (ADMM) is exploited to resolve the conflict of exchanged power between multi-MGs and distribution network. Considering the uncertainties, a distributed robust model is employed to precisely analyze the performance of multi-carrier energy networked MGs in different robustness levels. The efficiency of the ADMM model on integrated energy systems is tested on a networked MGs. The achieved results can ensure the light computational burden and convergence of proposed distributed algorithm. The proposed EH optimization problem is solved via Gurobi optimizer packages. According to the results, the ADMM converges to the final solution after 5 iterations, and with increasing the robustness level, the operation costs of EHs increases. The obtained results by Gurobi is more optimal than heuristic algorithms.

Multistage Robust Look-Ahead Unit Commitment with Probabilistic Forecasting in Multi-Carrier Energy Systems

The combined operations of power distribution network (PDN) and district heating network (DHN) can enhance the flexibility and improve the overall energy efficiency of power systems. This article implements a rolling look-ahead unit commitment scheme in a combined PDN and DHN to exploit the operational flexibility of rapid-response combined heat and power (CHP) units under significantly variable renewable energy source (RES) power output. The scheme is formulated as a multistage distributionally robust (DR) unit commitment model that respects the non-anticipativity of decision variables for sequential revelations of uncertainties. In contrast to the moment-based ambiguity sets employed in conventional DR models, the proposed framework constructs an ambiguity set based on probabilistic forecasts. In this regard, a compatibility is achieved between DR approaches and probabilistic forecasts by incorporating comprehensive distribution information of RES power output stemming from probabilistic forecasts into DR models. The computational challenge associated with the proposed multistage DR model is addressed by applying linear decision rules. Moreover, a new constraint reformulation approach is utilized to increase the computational tractability. The proposed model will ultimately cast into a tractable mixed-integer linear programming problem. The effectiveness of the proposed method in capturing a comprehensive distribution of RES power output and reducing the the combined system operation cost is demonstrated by case studies carried out on the Barry Island multi-carrier energy system. Numerical results also validate the proposed model's improved computational performance.

Short-Term Self-Scheduling of Virtual Energy Hub Plant Within Thermal Energy Market

Multicarrier energy systems create new challenges as well as opportunities in future energy systems. One of these challenges is the interaction among multiple energy systems and energy hubs in different energy markets. By the advent of the local thermal energy market in many countries, energy hubs' scheduling becomes more prominent. In this article, a new approach to energy hubs' scheduling is offered, called virtual energy hub (VEH). The proposed concept of the energy hub, which is named as the VEH in this article, is referred to as an architecture based on the energy hub concept beside the proposed self-scheduling approach. The VEH is operated based on the different energy carriers and facilities as well as maximizes its revenue by participating in the various local energy markets. The proposed VEH optimizes its revenue from participating in the electrical and thermal energy markets and by examining both local markets. Participation of a player in the energy markets by using the integrated point of view can be reached to a higher benefit and optimal operation of the facilities in comparison with independent energy systems. In a competitive energy market, a VEH optimizes its self-scheduling problem in order to maximize its benefit considering uncertainties related to renewable resources. To handle the problem under uncertainty, a nonprobabilistic information gap method is implemented in this study. The proposed model enables the VEH to pursue two different strategies concerning uncertainties, namely risk-averse strategy and risk-seeker strategy. For effective participation of the renewable-based VEH plant in the local energy market, a compressed air energy storage unit is used as a solution for the volatility of the wind power generation. Finally, the proposed model is applied to a test case, and the numerical results validate the proposed approach.

Preventive maintenance mid-term scheduling of resources in multi-carrier energy systems

Multi carrier energy systems (MCES) have an assortment of energy carriers and production resources. These diverse energy carriers are relatively correlated, complicating the preventive maintenance scheduling of MCES. The complexity is more prominent in mid-term scheduling. The main challenge arises when there are shared units in all energy systems such as combined cooling, heating and power (CCHP) units. To achieve a reliable and optimized maintenance, the correlation between energy carriers should be taken into account. In this paper, a novel model is proposed for optimized maintenance scheduling of generation units in monopoly MCES. Using the proposed model, suitable universal outage time windows are obtained, whereby the total operation and maintenance costs are optimized. As a case study, the proposed model is examined on a test case comprising electrical, thermal, and cooling systems. Simulation results verified the meticulousness of the proposed model in mid-term maintenance scheduling while respecting reliability constraints.

A robust optimization approach for coordinated operation of multiple energy hubs

The energy hub (EH) has become an important concept in terms of optimizing multi-carrier energy systems’ efficiency and flexibility. In this regard, an optimal operation model for managing multiple EHs with electrical and heat energy demands is proposed, which aims to reduce the total cost of the EHs. The components of each EH include the combined heat and power (CHP) unit, gas boiler, heat storage (HS) unit, wind turbine (WT) and photovoltaic (PV) array. A robust optimization approach is then proposed to deal with the uncertainties of renewable distributed energy resources (RDERs) and electricity prices. Meanwhile, both electrical and thermal demand response (DR) programs are considered in the proposed model. Finally, the optimized dispatch results under three different scheduling scenarios, i.e., the independent scenario, and the aggregation scenarios with and without DR programs are discussed. The simulation results show that the proposed multiple EHs optimization model can effectively reduce the total cost of EHs. Meanwhile, the results also reveal that implementing the DR programs can further reduce the consumers’ total costs through load shifting.

Partial surrogate cuts method for network-constrained optimal scheduling of multi-carrier energy systems with demand response

The integration of different energy systems is believed to enable synergy effects such as reducing costs. The concepts of multi-carrier energy systems have critically influenced the investigations of energy management, and their optimal operations with demand response have gained much importance. However, less research has addressed network constraints, which are important, but would transform the overall problem to one of mixed integer nonlinear programming (MINLP) problem, whose solution would be challenging. This paper develops a network-constrained optimal scheduling model for a heating and power energy system with consideration of the demand response and energy storage systems, and detailed constraints such as the maximum number of switching operations for a storage device are considered. To solve this problem, convex relaxations and reformulation techniques are used so that the problem can leverage popular optimization solvers. To further improve the computational efficiency, the partial surrogate cuts (PSC) method is proposed. Its key idea is to partition the continuous variables into linear and nonlinear variables, and then take full advantage of the model structure. Case studies based on practical systems are implemented to evaluate the formulation and demonstrate the effectiveness of the proposed approach.

Reliability evaluation of multi-carrier energy system with different level of demands under various weather situation

Multi-carrier systems enable the cooperation between different energy types to answer the electricity, water, heating and cooling demand together. One of the most important problems related to procuring energy for consumers is the reliability of delivered energy. This paper contributes a framework to assess the reliability of energy hub based on its elements and input energy carriers. Loss of load expectation (LOLE), loss of load probability (LOLP) and expected energy not supplied (EENS) have been employed to determine the reliability of the multi-energy carrier system in two different weather condition. The interactions between different energy carriers have been formed based on the exact model of energy storages. The calculation of the reliability assessment for energy hub has been performed by using MATLAB software. The results of the employment of the presented framework on a case study with various types of energy converters have been illustrated that the reliability of demands has been increased significantly by the use of an energy hub concept. Also, the reliability of energy hub has been imposed based on the size of components to recognize the impacts of each component on the general reliability of the system.

Operation and flexibility contribution of NG tank in the multi-carrier energy systems

Operation and flexibility contribution of NG tank in the multi-carrier energy systems

Transactive Energy Trading in Reconfigurable Multi-carrier Energy Systems

The penetration of multi-carrier energy systems in distribution system gains more and more concerns. In this paper, a bi-level transactive energy trading framework is proposed to improve the energy scheduling and operation efficiency for multi-carrier energy systems which are modeled as energy hubs (EHs). In the upper level, each EH in the distribution system not only makes energy scheduling decisions considering supplies and demands of local energy, but also trades energy with each other to further maximize their social welfare. The associated trading payment among EHs is made in a fair manner by applying Nash bargaining theory. We solve the bargaining problem by decomposing it into two subproblems: operation cost minimization problem and payment bargaining problem. Then, based on the trading decision, the nodal equivalent loads of EHs are sent to the distribution system operator (DSO) without publishing trading details. By applying the second-order cone programming (SOCP), DSO reconfigures the network to reduce the transmission loss of the system in the lower level. The network reconfiguration and the trading behavior of EHs interact and iterate until the convergence. Numerical studies on modified IEEE 33-bus distribution system demonstrate the effectiveness of the proposed framework.

Two-step probabilistic method to enable demand response programs in renewable-based integrated energy systems

This paper presents a two-step procedure to enable residential Demand Response (DR) programs in the Multi-Carrier Energy Systems (MCES), including a combined heat and power generation, renewable resources, a boiler, and energy storage systems. In the first step, an optimization problem is solved to determine the optimal energy cost for each customer. In the second step, the system operator (SO) minimizes the summation of the total loss cost of the electrical distribution system and a designed motivational payment, subject to various operational constraints of the MCES. The motivational payment is the function of deviation of the resulted energy cost of a home in the second step from the desired cost obtained in the first step. The main idea of the proposed procedure is to consider the concerns of customers and the operator, simultaneously. This paper also addresses the uncertainties in renewable resources generation. The proposed procedure is simulated on a test energy system for various cases. The results show that as the level of customer participation in the proposed program is increased, the technical aspects of the integrated energy system are improved. In addition, the customers' costs are decreased by participation in the proposed program.

Standardised modelling and optimisation of a system of interconnected energy hubs considering multiple energies—Electricity, gas, heating, and cooling

The system of interconnected energy hubs (EHs) is a key multi-carrier energy system (MES) model. It is difficult, however, to directly calculate the operational state of the model because of its highly dimensional nonlinear characteristics. To resolve the foregoing problem, a standardised modelling and optimisation method for the system of interconnected EH model is introduced in this paper. In this proposed method, one-dimensional and multi-dimensional piecewise linear approximation methods are adopted to simplify non-convex natural gas transmission functions, generator cost functions, and compressor function. Moreover, a multi-step linearisation method is applied to EHs. The whole system can accordingly be reformulated as a mixed-integer linear programming (MILP) problem. In contrast to the traditional model, the formulated MILP model is effortlessly implemented in the optimisation of the MES with existing advanced optimisation techniques. Finally, the method is verified using a modified three-hub interconnected system. The test results show that the method can save more than 90% computational time with sufficient accuracy. The results also demonstrate that the unified dispatch exploits different energy resources, and the applied energy storage devices can reduce the operational cost from $319,840.267 to $316,382.685.

Optimal scheduling of bidirectional energy conversion units in energy and ancillary service markets for system restoration within MCESs

Multi-carrier energy systems (MCESs) can be formed by the integration of various energy infrastructures including power and natural gas systems. The proliferation of bidirectional energy conversion units in an MCES can set the stage for a more resilient and robust system. This study shows how bidirectional energy conversion units and storage devices can be optimally scheduled within an MCES for provision of various regulation services to the grid operator. To that end, a new model is proposed for optimal scheduling of power-to-gas (PtG), gas-fired generation, and gas storage units in an MCES. The model aims to facilitate integration of renewables, utilise gas, and power price arbitrage, provide regulation services to the real-time (RT) market, and contribute to the system restoration. New indices that quantify the contribution of the MCES operator to RT and ancillary service markets are proposed. The proposed model is validated technically and economically by using a test system historical operating data. Numerical results demonstrate that while the proposed model is technically feasible, it also enhances the economic viability of the grid operator.

Robust operation of a multicarrier energy system considering EVs and CHP units

This paper presents the issue of robust operation of a multicarrier energy system (MES) or an energy hub in the presence of electric vehicles (EVs) and combined heat and power (CHP) units. Electrical and gas energies are considered as the inputs of the energy hub whereas electrical and heating energies are the outputs of the MES. In the first step, a deterministic model is developed in the MES that minimizes the energy cost of the energy hub subject to the power flow equation and limits of technical indexes in the MES, EVs parking lots, and CHP constraints. This model is similar to non-linear programming that does not obtain the global optimal point. Hence, in the next step, a linear programming method is used to obtain the global optimal point. In addition, the parameters of electricity, gas, and heating demand, electrical energy price, and EVs parameters are considered as uncertainty sources. This paper presents the bounded uncertainty-based robust optimization for an original deterministic formulation. The case study used in this paper considers 9electrical buses, 4gas nodes, and 7 heating nodes, simultaneously. Finally, the proposed method is implemented in the case study using the GAMS software. Based on numerical results, the linear programming model solves the proposed method with lower calculation time and error. Moreover, the values of parameters including demands, electrical energy, and EVs demand (EVs capacity and charge rate) increase (decrease) in the worst-case scenario (robust model) in comparison to the scenario run with the deterministic method. Additionally, the demand for power decreases at peak load times in the grid with the presence of energy hub units consisting of CHPs and EVs. Finally, because of using energy hub units as reactive power compensators and controlling power, parameters such as pressure, temperature and voltage profiles improve.

Fully-decentralized coordination for simultaneous hydrogen, power, and heat interaction in a multi-carrier-energy system considering private ownership

This paper focuses on a multi-agent system-based fully-decentralized coordination approach over a multi-carrier energy system comprising of thermal, electrical, and hydrogen loads. The system has a connection with up-stream electricity network. All agents in the proposed approach such as photovoltaic agent, electrolyzer agent, and fuel cell agent are active in thermal, electrical, and hydrogen interactions, influencing the clearing price of those simultaneous interactions. Furthermore, in this cooperative model, each agent has a private ownership; thus, in addition to social welfare optimization, each agent also tries to maximize its own profit via communication with the rest of agents. Since all agents try to satisfy the power balance constraint and their own local constraints through this communication, the need for a central agent is obviated for the balance of power. To evaluate the proposed multi-agent-based model, simulations were carried out in ‘Any Logic.’ Then, the effect of load-shedding by demand response program in simultaneous thermal, electrical, and hydrogen interactions of multi-carrier energy system was investigated. Finally, the obtained simulation results of the proposed decentralized model were compared with those of the centralized model. The obtained results demonstrated the validity of the proposed model.

Modeling of the Enthalpy Transfer Using Electric Circuit Equivalents: Theory and Application to Transients of Multi-Carrier Energy Systems

Analogies between electric, hydraulic, and thermal quantities do exist for developing various circuit models that involve quantities such as currents and voltages, flows and pressures, and heat transfers and temperatures. With the increasing interest in multi-carrier energy systems, it would be beneficial to extend the scope of analogies to the enthalpy transfer by advection. The presentation of the concept and the realization of this analogy extension are the purpose of this paper. It is shown how the enthalpy transfer is formulated using circuit equivalents and how they can be used in the modeling of components such as junctions and pipes of multi-carrier energy systems. The theoretical considerations are complemented by validation through comparison with software models and physical experiment. The value of implementing the enthalpy transfer using circuit equivalents is illustrated by the modeling of a combined heat and power multi-carrier energy system implemented in a nodal-analysis-based network simulator of the EMTP type.

The influence of urban form on the grid integration of renewable energy technologies and distributed energy systems

Standard and newly designed building blocks for complex urban sites– also designated by urban archetypes - are used in this study to quantify the influence of urban forms on their energy demand and energy systems design. An energy hub, which consists on a multi-carrier energy system involving multiple energy conversion, storage and/or network technologies, is employed to quantify the impact of the urban morphology on the energy system requirements. This study reveals that urban archetypes have a notable influence on the heating and cooling energy demands of city districts that can be characterized using form factors and floor area ratio. However, the influence on demand profiles cannot be assessed based on the aforementioned indicators. The cost of energy systems can increase up to 50% due to the impact of urban forms that are well beyond the increase of peak and/or annual energy demands. In addition, renewable energy integration to the grid as well its utilization in districts is influenced by urban forms. This makes it essential to consider energy system design as a part of the urban planning process moving even beyond building simulation.

The Dual Control With Consideration of Security Operation and Economic Efficiency for Energy Hub

This paper proposes a dual control of energy hub considering security operation and economic efficiency which is constituted by the control of energy hub outputs and inner devices. As security operation is a significant requirement of multi-carrier energy system (MCES) with energy hubs, it is necessary for MCES to regulate the outputs of hubs which highly influence the performance. The control approach of energy hub outputs can proportionally allocate the electricity and heat outputs of energy hubs. Meanwhile, the decentralized control of energy hubs can be realized to eliminate the impact of communication on security operation by implementing the proposed method. Furthermore, in view of the characteristics of energy hub, the elements in hubs also need to be regulated to reduce energy consumption. The control of inner devices based on the improved equal incremental consumption principle can reach to the minimal loss of the energy. Numerical simulations demonstrate the effectiveness of the proposed method.

Day‐ahead energy management framework for a networked gas–heat–electricity microgrid

The integration of various energy supplying systems increases the energy efficiency and energy system reliability. Smart microgrids are an ideal area to use multi-carrier energy systems. In this context, this study presents a novel modelling framework for optimal day-ahead scheduling of a networked multi-carrier energy microgrid (NMCEMG) system. The NMCEMG system in this study is composed of heat, gas, and power supply networks. The presented framework has enhanced the multi-carrier microgrid modelling against the previous works that modelled the multi-carrier microgrid as an energy hub due to difficulties in the energy flow analysis of heat and gas networks. The proposed framework optimises the day-ahead operating cost of the NMCEMG system considering nodal and energy flow constraints of each network. The proposed microgrid includes various energy interdependent equipment such as combined heat and power units, gas-fired boilers, power to gas units, electrical and heat storages and electric heat pumps. This study presents a new optimisation algorithm named self-adaptive modified whale optimisation algorithm based on wavelet theory to solve the day-ahead optimal scheduling of the NMCEMG problem. The numerical results corroborate the proposed modelling framework as superior over conventional hub-based multi-carrier microgrid models in terms of energy system security.

Flexibility Services to Minimize the Electricity Production from Fossil Fuels. A Case Study in a Mediterranean Small Island

The design of multi-carrier energy systems (MESs) has become increasingly important in the last decades, due to the need to move towards more efficient, flexible, and reliable power systems. In a MES, electricity, heating, cooling, water, and other resources interact at various levels, in order to get optimized operation. The aim of this study is to identify the optimal combination of components, their optimal sizes, and operating schedule allowing minimizing the annual cost for meeting the energy demand of Pantelleria, a Mediterranean island. Starting from the existing energy system (comprising diesel generators, desalination plant, freshwater storage, heat pumps, and domestic hot water storages) the installation of solar resources (photovoltaic and solar thermal) and electrical storage were considered. In this way, the optimal scheduling of storage units injections, water desalination operation, and domestic hot water production was deduced. An energy hub model was implemented using MATLAB to represent the problem. All equations in the model are linear functions, and variables are real or integer. Thus, a mixed integer linear programming algorithm was used for the solution of the optimization problem. Results prove that the method allows a strong reduction of operating costs of diesel generators also in the existing configuration.