Grid Solutions Research Articles

Two-grid finite element method for the dual-permeability-Stokes fluid flow model

In this paper, two-grid finite element method for the steady dual-permeability-Stokes fluid flow model is proposed and analyzed. Dual-permeability-Stokes interface system has vast applications in many areas such as hydrocarbon recovery process, especially in hydraulically fractured tight/shale oil/gas reservoirs. Two-grid method is popular and convenient to solve a large multiphysics interface system by decoupling the coupled problem into several subproblems. Herein, the two-grid approach is used to reduce the coding task substantially, which provides computational flexibility without losing the approximate accuracy. Firstly, we solve a global problem through standard Pk − Pk− 1 − Pk − Pk finite elements on the coarse grid. After that, a coarse grid solution is applied for the decoupling between the interface terms and the mass exchange terms to solve three independent subproblems on the fine grid. The three independent parallel subproblems are the Stokes equations, the microfracture equations, and the matrix equations, respectively. Four numerical tests are presented to validate the numerical methods and illustrate the features of the dual-permeability-Stokes model.

Thirty Years of the Finite Volume Method for Solid Mechanics

Since early publications in the late 1980s and early 1990s, the finite volume method has been shown suitable for solid mechanics analyses. At present, there are several flavours of the method, which can be classified in a variety of ways, such as grid arrangement (cell-centred vs. staggered vs. vertex-centred), solution algorithm (implicit vs. explicit), and stabilisation strategy (Rhie–Chow vs. Jameson–Schmidt–Turkel vs. Godunov upwinding). This article gives an overview, historical perspective, comparison and critical analysis of the different approaches where a close comparison with the de facto standard for computational solid mechanics, the finite element method, is given. The article finishes with a look towards future research directions and steps required for finite volume solid mechanics to achieve more widespread acceptance.

Offshore Wind Farm-Grid Integration: A Review on Infrastructure, Challenges, and Grid Solutions

Recently, the penetration of renewable energy sources (RESs) into electrical power systems is witnessing a large attention due to their inexhaustibility, environmental benefits, storage capabilities, lower maintenance and stronger economy, etc. Among these RESs, offshore wind power plants (OWPP) are ones of the most widespread power plants that have emerged with regard to being competitive with other energy technologies. However, the application of power electronic converters (PECs), offshore transmission lines and large substation transformers result in considerable power quality (PQ) issues in grid connected OWPP. Moreover, due to the installation of filters for each OWPP, some other challenges such as voltage and frequency stability arise. In this regard, various customs power devices along with integration control methodologies have been implemented to deal with stated issues. Furthermore, for a smooth and reliable operation of the system, each country established various grid codes. Although various mitigation schemes and related standards for OWPP are documented separately, a comprehensive review covering these aspects has not yet addressed in the literature. The objective of this study is to compare and relate prior as well as latest developments on PQ and stability challenges and their solutions. Low voltage ride through (LVRT) schemes and associated grid codes prevalent for the interconnection of OWPP based power grid have been deliberated. In addition, various PQ issues and mitigation options such as FACTS based filters, DFIG based adaptive and conventional control algorithms, ESS based methods and LVRT requirements have been summarized and compared. Finally, recommendations and future trends for PQ improvement are highlighted at the end.

Coordinated voltage and reactive power control of offshore HVAC meshed grid and wind power

The Kriegers Flak combined grid solution (KF CGS) is the first hybrid-asset project utilising an offshore high voltage alternating current/high voltage direct current (HVAC/HVDC) interconnector for large offshore wind power plants between Eastern Denmark and Germany in the Baltic Sea. On the Danish side, above 200 km 220 kV cables are arranged into a meshed offshore transmission grid (MOG). In order to maintain good voltages in the MOG and wind power plants, on the Danish side, the control is realised by an automatic voltage regulation and reactive power control (AVR/RPC) of several switchable and variable reactors and transformers with tap-position controllers, and the wind power plant controllers (WPPC); on the German side, the voltage control is achieved by the HVDC back-to-back converter, WPPC, and part of the optimal power flow by the master controller for interconnector operation. This paper presents the proposed coordinated voltage and RPC of the HVAC MOG on the Danish side of the KF CGS interconnector. The efficiency and constraints of the proposed coordinated control scheme of the KF CGS at fluctuating voltage and reactive power on both ends of the MOG are presented by simulations using the entire set up of the 220 kV AC MOG.

Achievements, experiences, and lessons learned from the European research infrastructure ERIGrid related to the validation of power and energy systems

Power system operation is of vital importance and must be developed far beyond today’s practice to meet future needs. Almost all European countries are facing an abrupt and very important increase of renewables with intrinsically varying yields which are difficult to predict. In addition, an increase of new types of electric loads and a reduction of traditional production from bulk generation can be observed as well. Hence, the level of complexity of system operation steadily increases. Because of these developments, the traditional power system is being transformed into a smart grid. Previous and ongoing research has tended to focus on how specific aspects of smart grids can be developed and validated, but until now there exists no integrated approach for analysing and evaluating complex smart grid configurations. To tackle these research and development needs, a pan-European research infrastructure is realized in the ERIGrid project that supports the technology development as well as the roll-out of smart grid technologies and solutions. This paper provides an overview of the main results of ERIGrid which have been achieved during the last four years. Also, experiences and lessons learned are discussed and an outlook to future research needs is provided.

Unified Energy Agents for Combined District Heating and Electrical Network Simulation

A sustainable and climate-friendly energy supply needs flexible and efficient distribution systems. Key factors to implement this kind of systems are intelligent coordination (smart grid approaches) and the integration of different energy sectors. This article introduces the unified energy agent as an agent-based approach for a comprehensive modelling and control of energy conversion systems. This approach enables both the simulation and optimization of coupled energy networks, and then in a next step, the development of corresponding smart grid solutions to be applied in the field. Its applicability for the simulation of coupled networks is presented by a real-world use-case of an innovative combined heat and electrical network, which was implemented for the city of Lemgo, Germany. Preliminary results from the project are discussed and an outlook on future work is given.

An overset RaNS prediction and validation of full scale stern wake for 1,600TEU container ship and 63,000 DWT bulk carrier with an energy saving device

Two merchant ships (1,600TEU container ship, 63,000DWT bulk carrier with a type of pre-swirl duct energy saving device in the stern) are subjected to viscous CFD analysis aiming to investigate the capability of viscous CFD to estimate stern wake in full scale. Rigorous validations are made for the computational results of resistance, propulsion parameters and local flow fields using available measurement data both in model and full scale for the two vessels. The verification study for the container ship in full scale shows the difficulty to achieve grid convergence in propulsion parameters, yet the solution difference for these parameters are mostly below 1.7% of fine grid (~12M cells) solution. The effect of surface roughness becomes apparent not only in powering estimation but also in nominal and total wake distributions. The propeller rotation speed for the container ship in full scale is estimated well by the present CFD within 0.2% of difference compared to the measured data in full scale when the surface roughness is considered in the computation. The total wake in full scale in the vicinity of stern/ESD predicted by the present CFD simulation agree very well to the optical measurement data when the surface roughness is taken into consideration. Investigation of the total wake for the bulk carrier implies that the ESD should be designed based on the flow including both scale effect and the surface roughness. Throughout the validation and investigation of the present computational results in full scale, several common practices are suggested for predicting stern flow using full scale viscous CFD simulation together with the existing recommended procedures and guidelines by the ITTC.

Solar home systems in Ethiopia: Sustainability challenges and policy directions

The current energy access in Ethiopia stands at 44%, where 33% is provided through grid connections and 11% through off grid solutions. In order to increase the electricity access, the Ethiopian government has launched National Electrification Program laying out the country’s ambition towards universal access by 2025 through a combination of 65% grid-connected and 35% off-grid energy systems such as the solar home systems (SHS). With the government’s ambitious plans and increased market diffusion of SHS in the rural communities of Ethiopia, the country requires evidence based comprehensive data on the key challenges of SHS in order to maintain sustainability of the systems. This paper aims to explore the key sustainability challenges associated with the utilization of SHS and provides recommendations to overcome such challenges. This has been achieved through a field questionnaire survey. The study found out that high initial investment cost, lack of local manufacturing, lack of full awareness of the operation, frequent failure of the systems, lack of sufficient maintenance experts, high maintenance and installation costs, lack of spare parts are considered to be the key challenges that are affecting the market diffusion and sustainability of the systems. To overcome these challenges, evidence based policies are recommended.

Engineering and validation support framework for power system automation and control applications

The rollout of smart grid solutions has already started and new methods are deployed to the power system today. But the complexity is still increasing and the focus is moving from a single system to a system of systems perspective. The results are increasing engineering efforts and escalating costs. To address these challenges, this work proposes the concept of an automated model-based engineering and validation framework that covers the overall development process of smart grid applications from specification and use case design to automatic engineering and validation and, finally, deployment and commissioning. This paper provides an overview of the framework concept and introduces a prototypical implementation. Also, it showcases its potential with the help of some examples.

Smart Grid for Industry Using Multi-Agent Reinforcement Learning

The growing share of renewable power generation leads to increasingly fluctuating and generally rising electricity prices. This is a challenge for industrial companies. However, electricity expenses can be reduced by adapting the energy demand of production processes to the volatile prices on the markets. This approach depicts the new paradigm of energy flexibility to reduce electricity costs. At the same time, using electricity self-generation further offers possibilities for decreasing energy costs. In addition, energy flexibility can be gradually increased by on-site power storage, e.g., stationary batteries. As a consequence, both the electricity demand of the manufacturing system and the supply side, including battery storage, self-generation, and the energy market, need to be controlled in a holistic manner, thus resulting in a smart grid solution for industrial sites. This coordination represents a complex optimization problem, which additionally is highly stochastic due to unforeseen events like machine breakdowns, changing prices, or changing energy availability. This paper presents an approach to controlling a complex system of production resources, battery storage, electricity self-supply, and short-term market trading using multi-agent reinforcement learning (MARL). The results of a case study demonstrate that the developed system can outperform the rule-based reactive control strategy (RCS) frequently used. Although the metaheuristic benchmark based on simulated annealing performs better, MARL enables faster reactions because of the significantly lower computation costs for its own execution.

Validation of lattice Boltzmann method-based large-eddy simulation applied to wind flow around single 1:1:2 building model

This study conducted a validation for the lattice Boltzmann method-based large-eddy simulation (LBM-LES) applied to flow around a single 1:1:2 building. The flow structures and distribution of time-averaged velocity and turbulent kinetic energy (TKE), particularly at pedestrian height, were examined against data obtained by an experiment and finite volume method-based LES (FVM-LES), in addition to checking the grid independence and solution accuracy of LBM-LES. Results of validation metrics showed that the grid resolution of b/16 and b/32 (b: building’s width) achieved similar simulation accuracy and satisfied the acceptance range. However, b/32 gave better reattachment lengths. Furthermore, low accuracies of the velocity and TKE was observed in several areas while using b/16, such as above the roof, around the strong wind area near the sidewall, and in the wake flow area at the pedestrian height. LBM-LES generally showed similar fluctuating velocity characteristics as FVM-LES, including power spectra, and probability densities. However, numerical oscillations probably occurred above the building on the windward side. This study showed that LBM-LES could obtain accurate results for both time-averaged and fluctuating velocities. Moreover, at least b/32 is recommended while simulating pedestrian wind or the reverse flow structures, even though b/16 can obtain satisfactory validation metrics.

A grid function formulation of a class of ill-posed parabolic equations

We study an ill-posed forward-backward parabolic equation with techniques of nonstandard analysis. Equations of this form arise in many applications, ranging from the description of phase transitions, to the dynamics of aggregating populations, and to image enhancing. The equation is ill-posed in the sense that it only has measure-valued solutions that in general are not unique. By using grid functions of nonstandard analysis, we derive a continuous-in-time and discrete-in-space formulation for the ill-posed problem. This nonstandard formulation is well-posed and formally equivalent to the classical PDE, and has a unique grid solution that satisfies the properties of an entropy measure-valued solution for the original problem. By exploiting the strength of the nonstandard formulation, we are able to characterize the asymptotic behaviour of the grid solutions and to prove that they satisfy a conjecture formulated by Smarrazzo for the measure-valued solutions to the ill-posed problem.

IoVT: Internet of Vulnerable Things? Threat Architecture, Attack Surfaces, and Vulnerabilities in Internet of Things and Its Applications towards Smart Grids

In recent years, people have witnessed numerous Internet of Things (IoT)-based attacks with the exponential increase in the number of IoT devices. Alongside this, the means to secure IoT-based applications are maturing slower than our budding dependence on them. Moreover, the vulnerabilities in an IoT system are exploited in chains to penetrate deep into the network and yield more adverse aftereffects. To mitigate these issues, this paper gives unique insights for handling the growing vulnerabilities in common IoT devices and proposes a threat architecture for IoT, addressing threats in the context of a three-layer IoT reference architecture. Furthermore, the vulnerabilities exploited at the several IoT attack surfaces and the challenges they exert are explored. Thereafter, the challenges in quantifying the IoT vulnerabilities with the existing framework are also analyzed. The study also covers a case study on the Intelligent Transportation System, covering road transport and traffic control specifically in terms of threats and vulnerabilities. Another case study on secure energy management in the Smart Grid is also presented. This case study covers the applications of Internet of Vulnerable Things (IoVT) in Smart energy Grid solutions, as there will be tremendous use of IoT in future Smart Grids to save energy and improve overall distribution. The analysis shows that the integration of the proposed architecture in existing applications alarms the developers about the embedded threats in the system.

Assessing uncertainty in the timing of energy use during cost-optimal distributed energy technology selection and sizing

This paper empirically derives uncertainty ranges in cost-optimal solar PV and storage sizing by comparing results from the REopt Lite optimization platform from metered data and a set of simulated Department of Energy Commercial Reference Building (CRB) profiles at 65 sites. We find load profile shape alone does not explain a site’s optimal configurations (i.e., PV, Storage, PV and Storage, No System). Still, load profile shape does introduce uncertainty to optimal PV and storage capacities. Across all cases where PV is part of an optimal configuration, we find the average ratio of power capacities derived from metered loads to capacities derived from CRB profiles to be 0.97 (and as high as 1463), where 1 would be a perfect match in system size. For storage, the ratio is 1.6 (and as high as 42). We also assess how, in the absence of complete metered data, a CRB profile can be selected that would be expected to yield the most similar solar PV and storage capacities. From those metrics that can be available from billing data (i.e., peak demand, monthly load totals), we find that uncertainty is most reduced by selecting the CRB’s with an annual peak occurring at the most similar time, or those with the lowest average root mean square error (RMSE) among monthly peak loads. This research can help improve the implementation and interpretation of results derived from simulated load profiles and is an important next step in advancing smart grid solutions.

A Novel Methodology for the Scalability Analysis of ICT Systems for Smart Grids Based on SGAM: The InteGrid Project Approach

Information and Communication Technology (ICT) infrastructures are at the heart of emerging Smart Grid scenarios with high penetration of Distributed Energy Resources (DER). The scalability of such ICT infrastructures is a key factor for the large scale deployment of the aforementioned Smart Grid solutions, which could not be ensured by small-scale pilot demonstrations. This paper presents a novel methodology that has been developed in the scope of the H2020 project InteGrid, which enables the scalability analysis of ICT infrastructures for Smart Grids. It is based on the Smart Grid Architecture Model (SGAM) framework, which enables a standardized and replicable approach. This approach consists of two consecutive steps: a qualitative analysis that aims at identifying potential bottlenecks in an ICT infrastructure; and a quantitative analysis of the identified critical links under stress conditions by means of simulations with the aim of evaluating their operational limits. In this work the proposed methodology is applied to a cluster of solutions demonstrated in the InteGrid Slovenian pilot. This pilot consists of a Large Customer Commercial Virtual Power Plant (VPP) that provides flexibility in medium voltage for tertiary reserve and a Traffic Light System (TLS) to validate such flexibility offers. This approach creates an indirect Transmission System Operator (TSO)—Distribution System Operator (DSO) coordination scheme.

Economics of Smart Grids Technologies Towards Sustainability

The aim of this paper is to identify challenges and solutions for the energy grids and economics of the future. Smart grids are perceived as a key building block for a sustainable energy future with less emissions and better quality of service. Energy efficiency is at the heart of any strategy to guarantee secure, sustainable and inclusive economic growth. It is one of the most cost-effective ways to enhance security of energy supply, to boost competitiveness and welfare, and to reduce the environmental footprint of the energy system. The anticipated growth of cities creates unprecedented sustainability challenges. Increasing demands for energy, water, sanitation, education, healthcare, housing, transport and public service are testing the limits of city infrastructures. Six million new people move to such housing every year, thus ever increasing the demand for services. Cities are responsible for 67 percent of the global energy demand and consume 40 percent of world’s energy overall. Energy intensity improves in the Stated Policies Scenario by 2.3% annually to 2040. Smart electric grids are vital to success in the new energy landscape. Smart grids are shaping opportunities for a new energy age: They automatically balance demand and generation, handle multi-directional power flows and ensure the energy transition to seamlessly incorporate photovoltaic and other renewables.

Generalized Multiscale Finite Element Method for the poroelasticity problem in multicontinuum media

In this paper, we consider a poroelasticity problem in heterogeneous multicontinuum media that is widely used in simulations of the unconventional hydrocarbon reservoirs and geothermal fields. Mathematical model contains a coupled system of equations for pressures in each continuum and effective equation for displacement with volume force sources that are proportional to the sum of the pressure gradients for each continuum. To illustrate the idea of our approach, we consider a dual continuum background model with discrete fracture networks that can be generalized to a multicontinuum model for poroelasticity problem in complex heterogeneous media. We present a fine grid approximation based on the finite element method and Discrete Fracture Model (DFM) approach for two and three-dimensional formulations. The coarse grid approximation is constructed using the Generalized Multiscale Finite Element Method (GMsFEM), where we solve local spectral problems for construction of the multiscale basis functions for displacement and pressures in multicontinuum media. We present numerical results for the two and three dimensional model problems in heterogeneous fractured porous media. We investigate relative errors between reference fine grid solution and presented coarse grid approximation using GMsFEM with different numbers of multiscale basis functions. Our results indicate that the proposed method is able to give accurate solutions with few degrees of freedoms.

Decentralized heating grid operation: A comparison of centralized and agent-based optimization

Abstract Moving towards a sustainable heat supply calls for decentralized and smart heating grid solutions. One promising concept is the decentralized feed-in by consumers equipped with their own small production units (prosumers). Prosumers can provide an added value regarding security of supply, emission reduction and economic welfare, but in order to achieve this, in addition to advanced hydraulic control strategies also superordinate control strategies and appropriate market models become crucial. In this article we study methods to find a global optimum for the local energy community or at least an acceptable approximation to it. In contrast to standard centralized control approaches, based either on expert rules or mixed integer linear optimization, we adopt an agent-based, decentralized approach that allows for incorporation of nonlinear phenomena. While studied here in small-scale systems, this approach is particularly attractive for larger systems, since with an increasing number of interacting units, the optimization problem becomes more complex and the computational effort for centralized approaches increases dramatically. The agent-based optimization approach is compared to centralized optimization of the same prosumer-based setting as well as to a purely central setup. The comparison is based on the quality of the optimization solution, the computational effort and the scalability. For the comparison of these three approaches, three different scenarios have been set up and analysed for four seasons. In this analysis, no approach has emerged as clearly superior to the others; thus each of them is justified in certain situations.

EVALUATION OF DISTRIBUTED ENERGY RESOURCE INTERCONNECTION CODES AND GRID ANCILLARY SERVICES OF PHOTOVOLTAIC INVERTERS: A CASE STUDY ON DUBAI SOLAR PROGRAMME

This paper evaluates the technical aspects of grid-connected photovoltaic (PV) systems and distributed energy resources (DERs) interconnection grid codes. The advanced functions of smart PV inverters and smart grid solutions are discussed as well as the gaps of the existing grid codes that hinder DER ancillary services. An online survey targeted the key stakeholders and industry experts have been conducted to investigate advanced inverters potential of providing DER ancillary services to distribution grids. The survey results are discussed in details and recommendations for the reactive power support of DER inverters and DER interconnection codes enhancements are presented. Keywords: Distributed Energy Sources, Distributed Energy Resource Interconnection Grid Codes, Distributed Energy Resource Ancillary Services, Distributed Energy Resource Integration, Advanced Inverters Capabilities, Volt/Var Control JEL Classifications: P48, Q42, Q48 DOI: https://doi.org/10.32479/ijeep.8758

A Toolchain for the Development of Agent-Based Smart Grid Control Solutions

The energy transition necessitates a variety of control solutions to integrate renewables-based energy generation and unlock demand-side flexibility. To contribute to solving this challenge, the authors built a toolchain for developing smart grid control solutions. This toolchain consists of methodological, conceptual and technological components. In this contribution, we detail the way in which the toolchain facilitates the continuous utilization of control software artifacts across simulations, testbeds and deployment. This capability has the potential to significantly reduce engineering effort and build trust in agent-based control solutions for smart grids.