How microgrids contribute to the energy transition

07/05/2017
Publication REE REE 2017-2 Dossier Les microgrids
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How microgrids contribute to the energy transition

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REE N°5/2016 Z 35 LES MICROGRIDS DOSSIER 1 Introduction In the early 20th century, the centraliza- tion of electricity production made huge progress, enabling significant economies of scale and improved power plant effi- ciency. Today, decentralization could help tackle the energy challenges of the 21st century by paving the way to an opti- mized access to reliable, green, and resi- lient energy. Microgrids are an emerging energy ecosystem that provides practical answers through a local, interconnected energy system within clearly defined elec- trical boundaries, which incorporate loads, decentralized energy resources, battery storage, and control capabilities. The microgrid concept within clearly defined electrical boun- daries; decentralized energy resources, inclu- ding storage; only; control in both modes; - Microgrid benefits Microgrids contribute to the energy transition by providing practical ans- wers to improve energy reliability, resiliency, energy accessibility, energy independence, green energy safety, energy cost optimization, energy flexi- bility and the ability to participate in demand response or grid-balancing programs. Energy reliability: resiliency through the microgrid ability to isolate itself from the main grid and to be self-sufficient Power outages due to severe weather events are increasing in some regions. In August 2003, a widespread blackout caused power lost to around 55 million people across the northeastern United States and eastern Canada. Many more were affected by the world’s biggest power failure in India in July 2012, which left half of the country without electri- city. Soon after, Hurricane Sandy lashed the eastern U.S., cutting power to eight million customers [1]. According to the Lexington Institute, regarding the resilience of the U.S. elec- trical grid, at least 500,000 people in average were affected daily by power outages, costing $119 billion annually [2]. How microgrids contribute to the energy transition Jean Wild, François Borghese, Veronique Boutin, Jacques Philippe Schneider Electric Industries Microgrid is an emerging decentralized energy ecosystem that incorporates loads, local energy resources, battery storage, and control capabilities within clearly defined electrical boundaries. This paper explains how microgrids could help tackle the energy challenges of the 21st century by improving reliabi- lity and resiliency through their ability to get isolated from the main grid and to be self-sufficient, by providing access to energy at a reasonable cost when the main grid is not accessible, by reducing fossil fuel consumption thanks to a smart integration of renewable generation and enabling energy flexibilities to optimize energy costs. The paper also describes the technical and implementa- tion challenges of microgrids, providing insights on speci- fic constraints for protection, power quality and control, on energy flows optimization or preliminary sizing of equipment. ABSTRACT Les microgrids correspondent à un nouveau modèle de système énergétique décentralisé comprenant des charges, des sources énergétiques locales, du stockage et des capacités de contrôle de l’ensemble. Dans sa première partie, cet article explique comment les microgrids relèvent les défis énergétiques du 21e siècle : en améliorant la fiabilité et la robustesse de l’approvision- nement grâce à leur aptitude à s’isoler du réseau public en cas de problème, en permettant l’accès à l’énergie à un coût raisonnable dans les zones non desservies par un réseau public, en favorisant le déploiement de ressources vertes, tout en optimisant les coûts énergétiques grâce aux capacités de contrôle qui permettent de tirer parti des flexi- bilités énergétiques. Dans une seconde partie, l’article décrit les problématiques techniques spécifiques aux microgrids, ainsi que les ques- tions clés liées à leur mise en œuvre opérationnelle telles que les contraintes liées à la protection, à la qualité et au contrôle de la puissance, à l’optimisation des flux énergétiques ou au dimensionnement des équipements et du système. RÉSUMÉ 36 Z REE N°2/2017 LES MICROGRIDSDOSSIER 1 Resiliency is increased through the microgrid ability to isolate itself from the the main grid encounters a major pro- blem, the microgrid is quickly decoupled and can still continue delivering energy from local sources. There may be limits to this autonomous supply due to local production, storage capability, and ins- tantaneous status. However, with the microgrid local management system, load priorities may be optimally ma- naged and control strategies adjusted accordingly. In addition, when the risk of severe concerns is predictable (for instance in case of a heavy storm forecast), a precautionary strategy may anticipate the microgrid operation, for example by reducing non-vital loads, preparing local generation for dispatch, and char- ging batteries to increase the future resi- lience of the system. - grid itself (for instance, a concern with one of the energy sources or in case of undergoing maintenance), the micro- grid enables back-up and automated reconfiguration possibilities. Let’s consider the example of the Oncor campus microgrid (figure 1): Profile: 100+ acre system operating services facility. Challenge: - nology; - gy resources (DERs); turbine, two energy storage systems, four legacy generators. Solution: Oncor’s innovative system comprises four interconnected microgrids and uses nine different DERs, including inverter and non-inverter-based resources that can disconnect from–and reconnect to–the main utility grid. The microgrid controller and operations software pro- vide the information, communications and control to monetize the energy flexi- bility value by optimizing coordination of loads, generation, and storage. Results: and facilitates switching from a grid- connected mode to an off-grid mode to ensure reliable power for critical loads; individual microgrids to a configuration that leverages multiple microgrids wor- king together as needed; - vices to store energy either from the utility feed or any of the facility’s gene- ration sources; dispatch and DER forecasting provides an additional layer of optimization and intelligence. Multiple use cases are supported and the connection between microgrid and utility can be implemented using industry standard communication protocols. Let’s consider now the example of a mission-critical microgrid (figure 2): Profile: 3500 acre Marine Corps Air Station Miramar operation and mainte- nance facility. Challenge: continue uninterrupted, even if uti- lity power grid is compromised or damaged; Figure 1: Oncor campus Microgrid, USA. REE N°2/2017 Z 37 How microgrids contribute to the energy transition power the installation and manage electricity during peak usage; resources, advanced smart grid control systems and demand response capa- bilities; zero energy installation,” which entails producing as much energy as it uses over the course of one year. Solution: Miramar’s innovative system consist of existing energy resources such as landfill gas, solar photovoltaic and energy storage systems, along with an upgraded gas). The microgrid controller and ope- rations software provide situational awa- reness, communications, and control to monetize the energy flexibility value by optimizing coordination of loads, gene- ration, and storage. The system includes updating of the energy control systems and integrated microgrid controls. Expected Results: - ted by July 2018; - crogrid will be capable of powering microgrid will smartly interact with the grid through demand response; the functionality of existing onsite gas; renewable energy and is targeting the ultimate goal of net zero energy status. Energy accessibility: provide access to energy at a reasonable cost when the main grid is not accessible Microgrids could drastically speed up the deployment of smart grids and increase access to energy in developing countries. Smart grid implementation is com- plex and calls for substantial adaptation of grid infrastructure. This will take time and require a significant capital invest- ment. Microgrids could be a simple alternative to demonstrate the potential of smart, smaller-scale, more economi- cal energy systems. In developing countries where there is no energy network, the massive de- centralization of local renewable sources could be inspired by the example of mo- bile communications, which overcame the obstacle of investment in heavy infrastructure. Similarly, in the short term, low-power microgrids can provide pragmatic solutions for producing and delivering energy. Let’s consider now the example of a rural electrification project for villages in Tonga (figure 3): Profile: 60 remote off-grid villages, from 80 up to 520 households per vil- lage, with no access to electricity. Challenge: - nable way; Figure 3: Islands of Tonga rural electrification project for villages. Figure 2: Marine Corps Air Station Miramar mission-critical Microgrid. 38 Z REE N°2/2017 LES MICROGRIDSDOSSIER 1 maintenance of generators. Solution: Off-grid solar and battery storage systems, allowing access to energy day and night. Results: renewable without diesel dependence is available. Energy independence: Reduce fossil fuel consumption by integrating more renewable generation For example, islands of Tonga, in addi- tion to the challenge of improving energy accessibility, must also work toward ener- gy independence. National energy needs are met by imported petroleum to sup- ply 15,000 customers on the four larger main island of Tongatapu. 20000 m3 of diesel fuel were used for electricity gene- ration in the Tonga islands in 2012. About afforded by diesel engines, the rest being generated by solar energy. Energy cost optimization: Utilize energy flexibility to optimize energy mix and grid balancing Let’s consider the Syndicat dépar- temental d’énergies du Morbihan (SDEM), a utility in the Brittany region of France. The main office of the SDEM is a 3 200 m² building, housing 80 people approximately (figure 4). A microgrid system was set up to optimize the electricity demand during consumption peaks and smooth the building’s load curve as well. This microgrid is connec- ted to the public, low-voltage distribu- tion network, and is used to reinforce the network and augment the availabi- lity of energy. During times of high ener- gy demand or reduced grid functionality due to network or generation faults, the site can relieve stress on the grid by ser- ving its own load. The microgrid consists of the fol- lowing components: - tion network; of Li-ion batteries and power electro- nic converters; placed at the low voltage service en- trance, provides energy security and stabilizes the voltage and frequency of the building’s electrical network in off- grid mode; and therefore contribute to the balance between production and consumption. Current and future technologies Architecture Microgrids result from the association of subsystems acting in a coordinated manner, rather than from independent functional components (figure 5). Practically, they are often composed of: includes equipment for energy gene- ration (usually multiple Distributed Energy Resources), energy distribution network(s) and energy users/consu- mers exhibiting different profiles and levels of criticality; Resource (DER) level; - vel, aiming to optimize the entire system; quisition (SCADA) system to interface with microgrid operators; tariff management, demand charge optimization, demand response, self- consumption, blackout management, carbon dioxide (CO2 ) reduction, etc. Microgrids are implemented to ful- fill global energy expectations such as resiliency, economy, security, and CO2 reduction. The relative importance of Figure 4: SDEM Syndicat Départemental d’Energies du Morbihan, France. REE N°2/2017 Z 39 How microgrids contribute to the energy transition these expectations depends on the microgrid category and the related tech- nical features whose components might differ accordingly. However, in every case, specific performance objectives have to be solved through technical advances in system control and protec- tion innovations so that cooperation of distributed energy resources towards a shared objective can be fulfilled. Ensuring safe and reliable operation Specific constraints for the protection strategy In microgrids, the association of local distributed generation and capability to isolate from the main grid brings up new challenges for the protection sys- tem design. Microgrids are characterized by varying operating modes, according to the real-time production of distributed generation, the microgrid configuration (grid-connected or isolated), and the real-time power demand (load profiles), as shown in sub-cases of figure 6. As microgrid operating conditions change, the network topology also changes. Consequently, the short-cir- cuit current capacity may vary both in magnitude and direction. Protection systems have to be carefully designed in a way that secures people and equip- ment from all possible types of fault in each operating mode, while avoiding downtime due to errant protection dis- crimination. Particular attention should be paid to the fact that microgrids are often multi- source systems with both rotating and power electronics-based sources. The protection system design is getting more complex because these sources can operate both in parallel and individually. For these reasons, project-specific electrical engineering studies are requi- red to specify in detail the protection and metering devices to be used. Specifics related to power quality Microgrids are balancing energy gen- eration and demand in real time. This Figure 5: Microgrid functional architecture, from the grid to the cloud. A. Supplied by the grid only B. Supplied by the grid and a local energy source in parallel, storage is recharged C. Supplied by a local energy source and storage (isolated mode) Figure 6: Examples of Microgrid operating modes. 40 Z REE N°2/2017 LES MICROGRIDSDOSSIER 1 requires fast and accurate measure- ments of active and reactive powers, frequency, current and voltage levels in order to enable proper power quality control and automated operation. Power quality measurements be- come even more important in microgrid applications. The following particular power quality issues should be moni- tored, analyzed and kept within their normal operating range (figure 7). Harmonics: the presence of harmo- nics and their interactions are more important than in traditional networks where the major sources of harmonics are typically the electronic loads and equipment. In microgrids, inverter- based DERs generate additional har- monic pollution and harmonic levels can potentially rise much higher if not monitored and treated properly. Frequency variations: usually, when connected to the main grid, the micro- grid frequency is stable and frequen- cy variations are rare, especially in countries where the grid is strong and meshed. However, when a microgrid becomes isolated, frequency varia- tions can become more critical due to less stiff generating sources in the system, and subsequently should be closely monitored. Transients: during configuration and operating mode changes, transients may occur. They should be captured and analyzed for any potential root cause. causes of unplanned downtime both in traditional networks and in microgrids. Sags and swells should be monitored, recorded, and localized through ade- quate monitoring functions, such as dis- turbance direction detection features. Microgrid implementation challenges Preliminary sizing Based on the typical architecture and technology challenges presented earlier, and once the business model to follow has been defined, some preliminary sizing is necessary to understand and define the economic viability of the pro- ject, then propose appropriate technical solutions. Each microgrid project varies in size, power and voltage levels, number and type of electrical sources, as well as the number, type, and criticality of electrical loads, etc. The environment information (such as location, climate, standards and regulations, local energy pricing, physical layout, main drivers and cost criteria, etc.) is always pro- ject-specific and highly influences the design of the solution. Therefore, the preliminary sizing step aims to model the actual physi- cal and economic environment and context in order to help the enginee- ring team determine the types and power ratings of the microgrid com- ponents minimizing a given cost cri- terion. This step generally requires a micro- grid sizing software tool that enables the following: Figure 7: Power quality measurements are key to assure microgrid control, reliability, and standard compliance. REE N°2/2017 Z 41 How microgrids contribute to the energy transition 1 , CO2 emissions, REN penetration rate, and sometimes a mixture of them; (assess the list of available compo- nents and level of details in the entity’s existing computer models); - base of typical parameters (physical and commercial); evaluate their benefits. Several tools for this exercise are available. A common critical limita- tion of these tools is the fact that they do not allow the user to define global control strategies. In parallel, more open approaches are being studied by some academic and industrial research cen- ters or start-ups. Design engineering challenges Once one or several economically viable scenarios have been determined in the preliminary sizing phase, some project-specific engineering studies are required. These will both specify equip- ment details and guarantee the correct behavior of the microgrid in operation. Below is a list of the main calculations and studies to be performed. 1. Identification and detailed descrip- tion of the operating philosophy with all the operating modes of the microgrid: every source-versus-load scenario shall be identified and des- cribed, even the temporary configura- tions, for example when switchovers or emergency shedding are required. This step is particularly important 1 The levelized cost of electricity (LCOE) is a measure of a power source that attempts to compare different methods of electricity gener- ation on a comparable basis. It is an economic assessment of the average total cost necessary to build and operate a power-generating asset over its lifetime divided by the total energy out- put of the asset over that lifetime. because microgrids generally involve - by definition - many types of elec- trical sources of different natures and behaviors. 2. Load flow calculations in all possible operating configurations: the aim of this iterative process is to evaluate the current flows and the voltage levels in the microgrid power system while in operation, allowing: - the identification of any risk of equip- ment overload; - the identification (and forbidding, whenever relevant) of any configu- ration non compatible with the cur- rent and voltage constraints; - the recommendation of any prefer- red transformer taps and/or size of any power factor correction (PFC) equipment in order to achieve an acceptable voltage plan (according to self-operation requirements and grid code requirements as well, whenever applicable). In microgrids, establishing a rele- vant load list and assessing the load criticality levels and load consump- tion profiles are sometimes a chal- lenge. 3. Short-circuit current calculations: The goal is to determine the mini- mum and maximum short-circuit current levels that may occur in the power system in case of a fault. The use of international and local applicable standards is highly recom- mended (e.g. IEC, EN, IEEE, etc.). Those short-circuit current values allow to determine: - the correct sizing of the power sys- tem equipment in terms of thermal and dynamic current withstand; - the definition, settings, and coordi- nation of the power system’s pro- tection relays. In microgrids, as described previous- ly, short-circuit currents are likely to vary substantially between different operating configurations. 4. Protection philosophy and coordi- nation study: Considering the low and variable short-circuit currents of microgrids, the protection study is a key engineering step. This study is de- signed to ensure personnel safety and equipment protection and coordinate the protection tripping sequences and curves as well. As explained previous- ly, the traditional protection principles may become inapplicable in the con- text of microgrids. 5. Neutral earthing system manage- ment: Linked to the protection study, this technical topic is crucial to ensure the correct operation of microgrids, especially because microgrids often switch over from one source to ano- ther and combine electrical supplies from the main power grid, rotating generators and static converters. Because electrical installation rules are often specific to local regulations, the management of how the neutral is connected to earth then distributed within the microgrid is an important topic that can become challenging. 6. Dynamic stability studies: as ex- plained and detailed previously, it is very important to evaluate, predict and monitor the dynamic behavior of the microgrid power system with regard to transient events. Those events can come from: - normal operation: load step, trans- former inrush, motor starting, load shedding, transfer between one operating mode to another, source switchover, etc. - unexpected disturbances: loss of a power source, or short-circuit fault on a power system component. Microgrids generally include a mix of power generation, storage and conversion technologies. The chal- lenge is to ensure stable conditions not only with rotating inertia given by traditional generators, but also - 42 Z REE N°2/2017 LES MICROGRIDSDOSSIER 1 power electronic-based generation as well as new types of converters be carried out with close links with the designers of the static converters’ control system 7. Electrical equipment specifications and Single-Line Diagram (SLD): these deliverables are the main out- puts of the power systems enginee- ring studies. They are key elements required to order equipment, and they are complementary to item 1: explaining and illustrating the micro- grid operating philosophy. 8. Microgrid control systems – func- tional analysis and design: As explained previously, the control systems are an essential element to make microgrids fully operatio- nal. From the detailed description of the operating modes (see item 1), functional analysis, complete deve- lopment (or adaptation) then confi- guring the microgrid control system are required. These control systems shall integrate all possible control schemes and operating scenario ma- nagement. 9. Microgrid testing and commission- ing: A comprehensive testing and validation specification shall also be written so as to check that, in any real situation, the microgrid controller pro- vides the expected decision based on the selected criteria and the ac- tual constraints. Interoperability with upper- and lower-layer systems must be specified and tested prior to final starting. Conclusion Energy decentralization is a major development that could help tackle the energy challenges of the 21st century. Major technical and economic changes continue to occur. There is substan- tial progress regarding decentralized LES AUTEURS Jean Wild is the R&D program manager at Schneider Electric for microgrid and smart grid solutions. He is specialized in power quality issues and electrical dis- tribution, and specifically in smart energy systems in order to incorporate more renewable energies within distribution grids and microgrids. He has managed many international collaborative projects for Schneider Electric. Veronique Boutin is a graduated engineer from Ecole supérieure d’électricité. She wrote her PhD thesis on an experimental project with a thermodynamic solar power plant. At Schneider Electric, she designed a number of automatic systems in various industrial contexts. She then focused on innovation and has been involved in several large cooperative programs such as HOMES, dedica- ted to energy efficiency in buildings, and Arrowhead, dedicated to cooperative automation for industry, buildings, and infrastructures. She belongs to the Analy- tics, Applications & Programs team, where she is in charge of Proof-of-Concept demonstrations. François Borghese is global marketing lead for the commercial and industrial energy flexibility management offers of Schneider Electric. He is an expert in the building control market and has managed numerous projects, acquisi- tions, and market strategies. He led the definition and launch of the company’s - ment of successful projects in France and the USA. Jacques Philippe is the Power Systems Competency Domain Leader for Schnei- der Electric, and is also in charge of a power system expertise team at Schneider Electric’s regional execution center for the EMEAS region. He holds two master - he has been involved in various customer project tendering and execution in a core team composed of representatives and experts from the whole Schnei- der organization and localizations, he leads the roadmap definition for Schneider Electric in the power systems domain. REE N°2/2017 Z 43 How microgrids contribute to the energy transition energy resources, such as solar energy and battery storage. Internet of Things (IoT) is also operational, driving new cooperation and optimization capabili- ties. Microgrids are one answer to the energy transition challenge and their benefits encompass energy reliabi- lity, energy accessibility, independence through renewable generation and energy cost optimization. Future of microgrids is difficult to pre- dict at this stage, but it looks possible that we move into an era where microgrids will be the norm and not the exception. Prospective studies show that this future is technically feasible and could be a way to introduce widespread adoption of intermittent generation such as solar or wind [1]. Microgrids could be one of the keystones for energy transition. Références [1] How Prosumers Leverage 4 Techno- logiesforGreener,Reliable,Economical Energy by François Borghese, Schnei- der Electric. [2] S. Bhattacharyya, S.Cobben, “Con- sequences of Poor Power quality – an Overview”, Power Quality, book edited by Andreas Eberhard (Ed.), ISBN: 978- 953-307-180-0, InTech, 2011.