Using Microgrids to Integrate Distributed Renewables Into the Grid

Transcription

1 1 Using Microgrids to Integrate Distributed Renewables Into the Grid Bradley Williams, Member, IEEE, and Michael Gahagan, Member, IEEE Abstract This paper explores the structure, use, and value of microgrids as a device to better integrate into the electrical grid small quantities of local, distributed power generated from renewable resources like solar and wind. The paper describes the evolution of microgrids, their potential benefits, their design and structure, and their overall value in moving electricity generation toward a more sustainable model. Index Terms load flow control, networks, network operating systems, power distribution control, power distribution reliability, power system modeling, power system monitoring, software packages, solar power generation, wind power generation. I. INTRODUCTION Electric utilities face a daunting challenge when they address local and regional mandates to increase use of renewables. Large wind farms and solar generators may be located remotely, with limited transmission corridors available to move power from production facility to distribution grid. Even when those corridors are available, moving power long distances incurs substantial loss and high costs. Remote sources are not, of course, the only options for power with which to meet renewables mandates. Local, distributed power generation from solar roofs and small wind turbines may already be available. And utilities may already be paying for that power under regulator-imposed net metering requirements or voluntary local programs for encouraging cleaner energy. Unfortunately, putting these small sources of renewable power to work within the distribution grid is very difficult. The production itself, dependent in many cases on weather conditions and use by the residential or business owner, varies constantly throughout the day. Power arrives unexpectedly in very small quantities. Quality may vary, and utilities frequently have only limited means to ensure that generating equipment is maintained in good order. In most cases, economies of scale dictate that, while utilities count net-metered distributed production toward mandated percentages of a portfolio, these Bradley Williams is vice president, product management for the Tax and Utilities Business Group at Oracle, Redwood Shores, CA USA ( bradley.williams@oracle.com). Michael Gahagan is director, product management for the Tax and Utilities Business Group at Oracle, Redwood Shores, CA USA ( mike.gahagan@oracle.com). odd kilowatts do not contribute to reductions in generation from fossil fuels. One possible solution to this dilemma is the insertion of a new system that can operate a specific geographical area of the utility s distribution grid, in concert with other such systems functioning similarly in other parts of the larger utility operation. These smaller localized operational areas are microgrids, and the new localized systems are microgrid controllers. Microgrids are autonomous electricity environments that operate within a larger electric utility grid. The concept is not new. For years, chemical plants, refineries, military installations and other large facilities have had the ability to generate and manager their own electricity needs while, in addition, remaining connected to centrally located generation for supplemental needs. Today, the promise of clean, locally produced, distributed energy resources from renewables is encouraging expansion of the microgrid concept. Such micro operation within an electric utility has the potential to revolutionize electricity distribution, permitting local renewables to substitute for higher-emitting fuels while also increasing efficiency and environmental sustainability. II. BACKGROUND A. The Development of Centralized Generation The beginning of the 20 th Century saw the advent to electrical consumption on a significant scale. It developed as pockets of consumers connected by wires to electric dynamos (basic electricity generators). Initially, small direct current (DC) electrical generators served the various pockets of new electricity customers. The reason for these local installations was to avoid the large losses that occurred as the demand became more distant geographically from the actual generator. Wiring these pockets together led to the birth of the electric utility. Problems started to arise, however, as utilities strung more overhead wires to reach new electricity customers. Eventually, the maze of wires reached unmanageable proportions. A new approach was needed that could sustain the explosive growth. And one emerged: the alternating current transformer, which permitted utilities to locate generators remotely.

2 2 Alternating current and remote generation rapidly became the predominant form of the electric utility because this model solved such problems as: Too many overhead wires in urban areas. Growing urban air pollution from increased coal burning. Traffic density resulting from the need to haul fuel to each generator. Economies of scale and operational complexity. The AC utility was not, however, without problems. It increased the potential for: Large-scale interruptions of electrical service (blackouts). Voltage spikes and extreme oscillations can severely damage computer and other advanced technology equipment. Standards and regulations have helped keep these problems at bay. However, nothing has prevented significant demand increases. As more and more electricity is being required and consumed, the electrical system is reaching capacity. And the potential addition of millions of plug-in electric vehicles (PHEVs) demands consideration of new approaches. B. The Potential Benefits of Microgrids Microgrids have the potential to better accommodate new demands for electricity by shifting the electricity paradigm away from an exclusive model of centralized, remote generation to one in which distributed generation from local, clean resources supplements centralized generation. Microgrids are typically small electrical areas embedded inside of a single electrical utility s service territory. 1 Examples of these smaller areas could be neighborhood(s), retail shopping areas, or commercial parks. The necessary elements of a microgrid are: Embedded distributed energy resources. Advanced energy storage. Flexible demand. Each of these will be discussed in some detailed later in this paper. One of the primary aims of introducing microgrids into a typical utility s service territory today is to promote the use of new technologies that are becoming available for both electrical based transportation (electric autos) and advanced electrical energy storage. Without a more localized focus, electric utilities will need to attempt to upgrade their transmission and distribution facilities (a very difficult and costly regulatory and legal proposition) in order to accommodate these new items. As anyone in the utility business today knows, building new major transmission lines is next to impossible. Getting the necessary approvals for such things for such things as land siting / right away and environmental impacts involves a lengthy hearing process and numerous public meetings. An extensive amount of time is required and there is no guarantee of success. Due to that risk, utilities have increasingly shied away from new transmission line construction. Only a handful 1 Though single-utility microgrids are typical, nothing precludes a microgrid from overlapping two or more utilities. of new major construction projects have occurred in the past almost 40 years. The same is true for new major new generation projects. The trend in the past 20 years has been to build smaller steam generation plants fueled by natural gas. However, if the intelligence is provided in a local micro grid to manage the available local energy resources and serve the local demand, then utilities should be able to meet the growing demand without building major new infrastructure. They will be able to provide the improved electrical energy quality needed for the new technologies as they emerge. And these new technologies will become a reality. This requires utilities to plan today so that they can meet tomorrow s challenges. III. MICROGRID DESIGN A. Accommodating Demand The microgrid contains many individual points of demand. Some are traditional: electricity consumed as called for and needed. Others are intelligent : the electrical connection to the customer uses one or more of the following: A smart meter and advanced metering interface (AMI) to record consumption in intervals and to enable utilities to vary electricity prices according to the interval in which power was consumed. A home area network (HAN) that connects most if not all of their electrical apparatus together and is managed by a home controller. This network would generally be capable of turning on and off devices based on the personal profile of the consumer, using real time pricing information received from the utility or some other provider, such as a load aggregator. On-site power sources, such as advanced energy storage (batteries using highly advance storage techniques), personnel generators ( rotating generation, such as a motor-generator pair or a small wind generator) and/or passive generation (photovoltaic arrays). These may or may not be linked to the utility s distribution system.

3 3 Demand control for specific devices that permit electricity flow only under specific conditions, such as time of day and/or price level. Such control is a probable requirement for utilities to manage the recharging of very large numbers of electric vehicles distributed throughout its territory. Complicating this picture is the fact that changes will take place over time. Initially, smart homes will be minimal in number. Some neighborhoods will continue as they are today. Others will change more rapidly. Utilities will need to: Handle various amounts and locations of real-time data and information processing in constantly changing and largely unpredictable patterns. Make operational changes needed to maintain optimal electric reliability while insuring the quality required by highly technical equipment. Requiring human operators to make and implement all of the necessary decisions is simply not feasible. Utilities need a new type of automated controller that can provide the necessary split-second analysis and immediate application in this very dynamic environment. B. Microgrid Controllers A new type of controller is needed that can manage this diverse set of equipment effectively while providing the new services envisioned. One of the new services will be the improve management of the reactive power supply of the microgrid area using advance optimization techniques. Another service involves lowering customer costs by responding automatically to real-time price signals and varying operating conditions. distribution areas to supply all parts of the network that need additional energy. The DMS may have to adjust energy needs to accommodate excess electricity from distributed resources. It could route this excess to another adjacent distribution area. In addition, each MMC will have a direct connection to all of those devices (distributed energy resource, advanced energy storage, dynamic demand, reactive power supply devices, and any smart switching equipment) that it has responsibility to coordinate and potentially operate. Smart meters will have to facilitate communication between HANs and the Microgrid Controller so that demand pricing is viable. New, smart electrical switching throughout the microgrid will accommodate new demand. This new smart switching will replace the old arrangement of automatic reclosers working in conjunction with fixed fusing typically dispersed today throughout the distribution area. This new smart switching equipment will be able, during an unplanned event, to reconfigure portions of the distribution network automatically, so that the greatest number of customers continues to receive electricity. Initially, microgrids will use the interface between the DMS and the utility s prevalent SCADA system for all SCADA-related events. However, as experience with these microgrid controllers grows, and as they evolve over time, direct communications and operation without the intervention of the SCADA system should be possible. In the future, SCADA will focus on the transmission system, and microgrid controllers will handle all distribution related control and data acquisition. The Microgrid Master Controller and its related field devices would communicate via either dedicated communication circuits utilizing protocols such as the Internet Protocol (IP) and / or applicable wireless capabilities. Additionally, the communication mechanism between the Microgrid Controllers and the DMS would most likely be IP based utilizing the existing utility communications infrastructure. Since these devices and their associated communication infrastructure will be critical to the reliable supply of electricity, redundancy will be necessary for both. Conceptually, a utility s distribution system could have any number of Microgrid Master Controllers (MMCs). The actual number would be dictated by those areas that have a preponderance of distributed energy resources, advanced energy storage facilities, and smart consumers (residential customers or light commercial customers, but not large industrial enterprises, which would likely have individual arrangement with the utility and with designated energy providers). In this type of design, MMCs communicate and take direction from the overarching Distribution Management System (DMS). The DMS has overall knowledge of all IV. RESULTS The introduction of microgrids promises: Additional reliability. New services. Lower costs to the utility customer. These benefits arise from the ability to localize the evaluation and application of proven optimization techniques to a prescribed area of a utility s distribution system. Additionally, the installation and operation of new energy sources and battery technologies permit microgrids to be largely self-sufficient. Without the introduction of microgrids, utilities will face the impossible challenge of managing effectively all of the new advances and providing the inherent

4 4 benefits without the full utilization of labor- and money-saving technology. There are additional benefits when the industry implements multiple microgrids through a region and beyond. These include: More complete use of generation. Today s 500 KV transmission line more than 100 miles in length operating at maximum capacity may see losses as high as 5 to 8 percent. In other words, 1000 MW electricity flow over 50 MWs power that could supply 50,000 homes with electricity is lost due solely to transmission. Microgrids, which can supply energy closer to the demand, avoid this loss. The postponement (or at least considerable delay) in the construction of new major transmission facilities. If microgrids can supply most residential and commercial needs with distributed energy resources located in close proximity to the demand, no (or little) additional high voltage transmission capacity will be necessary. Enhanced transmission grid reliability. Coordination among microgrids means that, whenever a disturbance occurs (manmade or natural), the Microgrid Master Controllers can respond accordingly. By reducing demand, adding more generation, and undertaking intelligent switching, the controllers can prevent an escalation that results in large-scale system blackouts. If enough demand can be quickly removed from the overall grid, cascading events do not occur or diminish to a ripple. V. CONCLUSION The concept of microgrids has been around for some time at such enterprises as military bases and petro chemical installations. However, with the advent of new technologies such as computers, smart meters and advanced energy resources, the wide application of microgrids across utility s distribution systems becomes very feasible and beneficial. Microgrids hold out the promise of increased reliability and new services (dynamic pricing, distributed energy resource management) to the customer. In addition to these localized consumer benefits, microgrids benefit the overall power system by reducing the need for more high voltage transmission capacity and lowering the losses that occur today due to the large distances between generation sources and demand they serve. They also have the strong potential to enhance overall system reliability through the ability to respond quickly and in a localized fashion to maintain the required power balance during minor and major disturbances. And their ability to integrate small amounts of locally produced power from renewable sources will help utilities meet clean energy goals and mandates. VI. BIOGRAPHIES Bradley Williams, P.E., is Vice President of Oracle Utilities Global Business Unit s Product Strategy responsible for Outage Management, Distribution Management, Mobile Workforce Management, Work and Asset Management, and Load Analysis utility applications and Smart Grid Strategy. Williams has more than 24-years utility technology innovation experience. Prior to Oracle, Williams was a Research Director in Gartner s Energy & Utilities Industry Advisory Services focusing on utility applications of GIS, SCADA/EMS/DMS, Outage and Work Management, and Transmission & Distribution Asset Management research. Prior to being a Research Analyst, Williams directed PacifiCorp s T&D Asset Management responsible for long-term asset strategies and Business Technology that developed and implemented comprehensive IT investment programs. As Director of T&D Infrastructure Planning, Williams was responsible for PacifiCorp s Subtransmission Planning, Telecommunications, and operations Technology Development groups. Williams also worked at Southern California Edison for 10-years where he was involved in transmission system planning, distribution automation, and reliability programs. Williams earned BSEE and MBA degrees from Cal Poly, holds 4 US patents on smart grid technologies, is a registered professional engineer in the State of California, and member of IEEE PES, UCA International Users Group, and CIM Users Group. Williams was awarded an IEEE PES Prize Paper for co-authoring Transmission Voltage Recovery Delayed by Stalled Air Conditioner Compressors, IEEE Transactions on Power Systems, August 1992, Paper No A1.1, pp Williams also authored Distribution Capacitor Automation Provides Integrated Control of Customer Voltage Levels and Distribution Reactive Power Flow, IEEE Proceedings of the 1995 IEEE Power Industry Computer Applications Conference, /95, May 1995, pp Michael Gahagan directs the Operational Product Management focus for the Oracle Utilities Global Business Unit. In that capacity, he has focused on the technology needed to support successful Smart Grid / Microgrid strategies in the areas of distribution, work and asset management and mobile workforce management. Prior to this position, Gahagan was consulting with many companies in the utility industry with focus on Utility Operations, Business Customer Facing Services, Business Continuity including Disaster Recovery, Sarbanes Oxley IT compliance, Outsourcing and all aspects of utility technologies. Previously, he was Vice President, CIO and Chief Strategy Officer for the Midwest Independent Transmission Operator (MISO). The Midwest ISO is one of the entities formed in the deregulated U.S. utility sector that provides air traffic control like operational services for the overall transmission network located in the Midwestern U.S. and central Canada. The ISO operates one of the largest energy markets in the world. Prior to the Midwest ISO, Gahagan was the Chief Operating Officer for the Mid-continent Area Power Pool (MAPP), a regional North American Reliability Council (NERC) oversight association for electrical utilities in the upper Midwest. He directed the tactical, day-to-day operations and managed the entire technical infrastructure. Gahagan s experience prior to MAPP included successfully directing the development and delivery of computer products globally for Siemens AG. He has also held various management, technical consulting and engineering jobs at Control Data Corporation, the Salt River Project, and the Montana Power Company. Gahagan holds a Master of Science degree in Electrical Engineering from Montana State University; completed the executive MBA program at the Carlson School of Business, University of Minnesota; and holds undergraduate degrees in Mathematics, Physics, and Electrical Engineering. He is a registered Professional Engineer in the state of Minnesota, a member

5 of the Institute of Electrical and Electronic Engineers, and the Project Management Institute. He has published papers in the IEEE on such subjects as power system modeling and energy management systems installations. 5