Distributed Energy Resources Integration

The development of test plans to validate the CERTS Microgrid concept is discussed, including the status of a testbed. Increased application of Distributed Energy Resources on the Distribution system has the potential to improve performance, lower operational costs and create value. Microgrids have the potential to deliver these high value benefits. This presentation will focus on operational characteristics of the CERTS microgrid, the partners in the project and the status of the CEC/CERTS microgrid testbed.

Application of individual distributed generators can cause as many problems as it may solve. A better way to realize the emerging potential of distributed generation is to take a system approach which views generation and associated loads as a subsystem or a "microgrid". The sources can operate in parallel to the grid or can operate in island, providing UPS services. The system will disconnect from the utility during large events (i.e. faults, voltage collapses), but may also intentionally disconnect when the quality of power from the grid falls below certain standards. Utilization of waste heat from the sources will increase total efficiency, making the project more financially attractive. Laboratory verification of the Consortium for Electric Reliability Technology Solutions (CERTS) microgrid control concepts are included. Index Terms--CHP, distributed generation, intentional islanding, inverters, microgrid, power vs. frequency droop, voltage droop.

There are four realities facing future power systems that require rethinking the distribution system and the use distributed energy resources, DER. These realities require that the T&D system;

- Provide for load grow with enhanced stability with minimal growth of the transmission system.
- Make greater use of renewable such as wind and photovoltaic systems.
- Increase energy efficiency and reduce pollution and greenhouse gas emissions.
- Increase availability of high power quality for sensitive loads.

Economic, technology and environmental incentives are changing the face of electricity generation and transmission. Centralized generating facilities are giving way to smaller, more distributed generation partially due to the loss of traditional economies of scale. Distributed generation encompasses a wide range of prime mover technologies, such as internal combustion (IC) engines, gas turbines, microturbines, photovoltaic, fuel cells and wind-power. Most emerging technologies such as micro-turbines, photovoltaic, fuel cells and gas internal combustion engines with permanent magnet generator have an inverter to interface with the electrical distribution system. These emerging technologies have lower emissions, and have the potential to have lower cost, thus negating traditional economies of scale. The applications include power support at substations, deferral of T&D upgrades, and onsite generation.

The technical and financial feasibility and desirability of microgrids has been shown in simulation and on paper. In order to demonstrate them in practice, an energy manager (EM) for control of microgrid equipment is needed. An all-knowing EM is not possible, an extremely information rich and intelligent but expensive EM might not be the optimal choice, and yet an EM that is too simple threatens several perceived benefits of DER. Both art and science will be required to develop the optimal EM and microgrid for a given site. This report serves to introduce the science. Further work should serve to develop this science and to gain experience on actual systems from which the art will emerge.

The blackouts of summer 2003 underscored the dependence of western economies on reliable supply of electricity with tight tolerances of quality. While demand for electricity continues to grow, expansion of the traditional electricity supply system is constrained and is unlikely to keep pace with the growing thirst western economies have for electricity. Furthermore, no compelling case has been made that perpetual improvement in the overall power quality and reliability (PQR) delivered is possible or desirable. An alternative path to providing for sensitive loads is to provide for generation close to them. This would alleviate the pressure for endless improvement in grid PQR and might allow the establishment of a sounder economically based level of universal grid service.

Providing for loads by means of local power generation is becoming increasingly competitive with central station generation for a number of reasons, four key ones being non-technical constraints on expansion of the grid, improvements in small scale technologies, opportunities for CHP application, and the ubiquitous nature of sensitive loads in advanced economies. Along with these new technologies, concepts for operating them partially under local control in microgrids are emerging, the CERTS Microgrid being one example. It has been demonstrated in simulation, and a laboratory test of a three microturbine system is planned for early 2005, to be followed by a field demonstration. A systemic energy analysis of a southern California naval base building demonstrates a current economic on-site power opportunity.

This report describes the tests conducted to determine the behavior of two Capstone 30 kW microturbines connected in parallel with some impedance between them. This test was meant to simulate the operation of two microturbines at nearby customer facilities. This arrangement also constitutes a simple microgrid. The goal of this test was to investigate if any voltage and power instabilities exist between the two microturbines.

Two test sequences were conducted. The first test sequence operated two microturbine/ load bank pairs using manual control of the microturbine and load bank set points. The second test sequence used the Capstone Load Following mode of operation to control generation levels of one of the microturbines. The two microturbine/ load bank sets were connected together through a 300 foot long, four conductor, #12 cable so that the impedance between them would cause up to a 5% voltage drop (depending on the load balance between the two sets). Data was collected from both Capstone microturbines, two power quality instruments and a power monitor.

Application of individual distributed generators can cause as many problems as it may solve. A better way to realize the emerging potential of distributed generation is to take a system approach which views generation and associated loads as a subsystem or a "microgrid". During disturbances,the generation and corresponding loads can separate from the distribution system to isolate the microgrid's load from the disturbance (providing UPS services) without harming the transmission grid's integrity. This ability to island generation and loads together has a potential to provide a higher local reliability than that provided by the power system as a whole.In this model it is also critical to be able to use the waste heat by placing the sources near the heat load. This implies that a unit can be placed at any point on the electrical system as required by the location of the heat load.

Deregulation is haltingly changing the United States electricity markets. The resulting uncertainty and/or rising energy costs can be hedged by generating electricity on-site and other benefits, such as use of otherwise wasted heat, can be captured. The Public Utility Regulatory Policy Act (PURPA) of 1978 first invited relatively small-scale generators (≥1 MW) into the electricity market. The advent of efficient and reliable small scale and renewable equipment has spurred an industry that has, in recent years, made even smaller(business scale) electricity generation an economically viable option for some consumers.On-site energy capture and/or conversion, known as distributed energy resources (DER),offers consumers many benefits, such as economic savings and price predictability,improved reliability, control over power quality, and emissions reductions. Despite these benefits, DER adoption can be a daunting move to a customer accustomed to simply paying a monthly utility bill.

A microgrid is defined as an aggregation of electrical loads and generation. The generators in the microgrid may be microturbines, fuel cells, reciprocating engines, or any of a number of alternate power sources. A microgrid may take the form of shopping center, industrial park or college campus. To the utility, a microgrid is an electrical load that can be controlled in magnitude. The load could be constant, or the load could increase at night when electricity is cheaper, or the load could be held at zero during times of system stress.

The microgrid utilizes waste heat from the generators to improve overall efficiency. The purpose of the Energy Management System (EMS) is to make decisions regarding the best use of the generators for producing electric power and heat. These decisions will be based upon the heat requirements of the local equipment, the weather, the price of electric power, the cost of fuel and many other considerations. The EMS will dispatch the generators and provide an overview of the Combined Heat and Power (CHP) system.

Since initiating research on integration of distributed energy resources(DER) in 1999, the Consortium for Electric Reliability Technology Solutions (CERTS) has been actively assessing and reviewing existing DER test facilities for possible demonstrations of advanced DER system integration concepts. This report is a compendium of information collected by the CERTS team on DER test facilities during this period.

The Consortium for Electric Reliability Technology Solutions (CERTS)MicroGrid concept assumes an aggregation of loads and microsources operating as a single system providing both power and heat. The majority of the microsources must be power electronic based to provide the required flexibility to insure operation as a single aggregated system. This control flexibility allows the CERTS MicroGrid to present itself to the bulk power system as a single controlled unit that meets local needs for reliability and security.

This report examines the protection problems that must be dealt with to successfully operate a microgrid when the utility is experiencing abnormal conditions. There are two distinct sets of problems to solve. The first is how to determine when an islanded microgrid should be formed in the face of the array of abnormal conditions that the utility can experience. The second is how to provide segments of the microgrid with sufficient coordinated fault protection while operating as an island separate from the utility.

As used in this discussion, the term microgrid refers to conventional distribution systems with distributed resources (DR) added. This is not to imply that the simple addition of DR to a distribution system creates a microgrid. In a microgrid the DR(s) has sufficient capacity to carry all, or most, of the load connected to that portion of the distribution system that houses the DR. In addition, a microgrid can operate as an electrical island in times of disturbance to the main utility system. Thus, there will be a well-defined interconnection point where the microgrid can be disconnected from the bulk of the electric utility system if so desired.

The following report summarizes the benefits of introducing Distributed Resources within an industrial site. A detailed description of the factory is followed by steady state analysis of the system. This industry has an overall demand of 1MW and is connected to the main grid with a series of transformers. Within the plant there are three main buildings: the factory, the warehouse and the offices. The grid supplies also another plant in the immediate vicinity of the one under study. Each parameter of the system is found from tables available from the literature. Steady state analysis is used to obtain voltage profiles and power flows for the system in the following scenarios: without units, with DR's with grid connection and with DR's in isolation mode, when the connection to the main grid fails.

Distributed technologies are slated to represent a substantial portion of future additions in power generation capacity. Modern distributed generation technologies such as microturbines, fuel cells, wind turbines and photovoltaic systems invariably employ several power electronic converters such as rectifiers and inverters in them in order to provide utility grade ac power. The cost of power electronic systems represent a substantial portion of overall installation costs. This has been due to the complexity of the engineering and realization of power electronics system packaging.

It is common for families of power converter products today to be custom designed. This results in sub-optimal economic performance in terms of engineering design, packaging, manufacturing, etc. Substantial opportunity exists for wide spread application of electrical power converters if they can be made low cost, reliable, rugged,serviceable, and interchangeable. Inspiration for a new, high level approach to power converter design is found in the areas of digital electronics and computer architectures.

This report presents the results of ongoing investigations on development of high power electronic systems for distributed generation systems using standardized approaches for integrating the components that comprise a power converter. The investigations have focused on developing a modular architecture that would allow using pre-engineered and mass-produced components to develop power electronic solutions in a systematic manner.

The term "Distributed energy resources" or DER refers to a variety of compact, mostly self-contained power-generating technologies that can be combined with energy management and storage systems and used to improve the operation of the electricity distribution system, whether or not those technologies are connected to an electricity grid. Implementing DER can be as simple as installing a small electric generator to provide backup power at an electricity consumer's site. Or it can be a more complex system, highly integrated with the electricity grid and consisting of electricity generation, energy storage, and power management systems. DER devices provide opportunities for greater local control of electricity delivery and consumption.They also enable more efficient utilization of waste heat in combined cooling, heating and power (CHP) applications—boosting efficiency and lowering emissions. CHP systems can provide electricity, heat and hot water for industrial processes, space heating and cooling, refrigeration,and humidity control to improve indoor air quality.

This report describes test measurements of the behavior of two microturbine generators (MTGs)under transient conditions. The tests were conducted under three different operating conditions: grid connect;stand-alone single MTG with load banks; and two MTGs running in parallel with load banks. Tests were conducted with both the Capstone 30-kW and Honeywell Parallon 75-kW MTGs.All tests were conducted at the Southern California Edison /University of California, Irvine (UCI) test facility. In the grid- connected mode, several test runs were conducted with different set-point changes both up and down and a start up and shutdown were recorded for each MTG. For the standalone mode, load changes were initiated by changing load-bank values (both watts and VARs). For the parallel mode, tests involved changes in the load-bank settings as well as changes in the power set point of the MTG running in grid-connect mode. Detailed graphs of the test results are presented. It should be noted that these tests were done using a specific hardware and software. Use of different software and hardware could result in different performance characteristics for the same units.

This report defines two distributed energy application scenarios with the necessary models for micro-turbines, fuel cells, inverters and induction machines. The two scenarios described in Section 1 are distribution support and a sensitive load. Each of the scenario descriptions begins with a list of objectives and constraints. There are essentially two components that are required in developing the scenarios of interest; the use of appropriate models and associated parameters for studying phenomenon of interest, and the criteria and methods for evaluation of performance.

This project evaluates what $/kW subsidy on microturbines (MT's) makes them economically competitive with natural gas internal combustion engines (ICE's). The Distributed Energy Resources Customer Adoption Model (DER-CAM) is used to determine least cost solutions, including distributed generation (DG) investment and operation, to sites' energy demands.

The first site considered is a hospital in New York City. The small hospital (90 beds) has a peak electric load (including cooling) of 1200 kW, with heat loads comparable to electric loads. Consolidated Edison electricity and natural gas tariffs for 2003 are used. A 60% minimum DG system efficiency is imposed on DG operation to avoid the standby tariff, which is less amenable to DG than the parent tariff.

The second site considered is the Naval Base Ventura County commissary in Southern California. The commissary has 13,000 m² of floor space and contains a large retail store, supermarket, food court, and other small businesses. The site peak electric load (including cooling) is 1050 kW. Electricity and natural gas supply are from direct access contracts, and delivery service is provided by Southern California Edison and Southern California Gas, respectively. 2003 supply and delivery rates are used.

In this report, an economic model of customer adoption of distributed energy resources (DER) is developed. It covers progress on the DER project for the California Energy Commission (CEC) at Berkeley Lab during the period July 2001 through Dec 2002 in the Consortium for Electric Reliability Technology Solutions (CERTS) Distributed Energy Resources Integration (DERI) project. CERTS has developed a specific paradigm of distributed energy deployment, the CERTS Microgrid (as described in Lasseter et al 2002). The primary goal of CERTS distributed generation research is to solve the technical problems required to make the CERTS Microgrid a viable technology, and Berkeley Lab's contribution is to direct the technical research proceeding at CERTS partner sites towards the most productive engineering problems. The work reported herein is somewhat more widely applicable, so it will be described within the context of a generic microgrid (µGrid). Current work focuses on the implementation of combined heat and power (CHP) capability. A µGrid as generically defined for this work is a semiautonomous grouping of generating sources and end-use electrical loads and heat sinks that share heat and power. Equipment is clustered and operated for the benefit of its owners. Although it can function independently of the traditional power system, or macrogrid, the µGrid is usually interconnected and exchanges energy and possibly ancillary services with the macrogrid. In contrast to the traditional centralized paradigm, the design, implementation, operation, and expansion of the µGrid is meant to optimize the overall energy system requirements of participating customers rather than the objectives and requirements of the macrogrid.

This report describes a Berkeley Lab effort to model the economics and operation of small-scale(<500 kW) on-site electricity generators based on real-world installations at several example customer sites. This work builds upon the previous development of the Distributed Energy Resource Customer Adoption Model (DER-CAM), a tool designed to find the optimal combination of installed equipment, and idealized operating schedule, that would minimize the site's energy bills, given performance and cost data on available DER technologies, utility tariffs, and site electrical and thermal loads over a historic test period, usually a recent year. This study offered the first opportunity to apply DER-CAM in a real-world setting and evaluate its modeling results.

DER-CAM has three possible applications: first, it can be used to guide choices of equipment at specific sites, or provide general solutions for example sites and propose good choices for sites with similar circumstances; second, it can additionally provide the basis for the operations of installed on-site generation; and third, it can be used to assess the market potential of technologies by anticipating which kinds of customers might find various technologies attractive.

A list of approximately 90 DER candidate sites was compiled and each site's DER characteristics and their willingness to volunteer information was assessed, producing detailed information on about 15 sites of which five sites were analyzed in depth. The five sites were not intended to provide a random sample; rather they were chosen to provide some diversity of business activity,geography, and technology. More importantly, they were chosen in the hope of finding examples of true business decisions made based on somewhat sophisticated analyses, and pilot or demonstration projects were avoided. Information on the benefits and pitfalls of implementing a DER system was also presented from an additional ten sites including agriculture, education, health care, airport, and manufacturing facilities.

The five sites are:

1. A&P Waldbaum's Supermarket: A Long Island supermarket that has installed a microturbine with CHP for desiccant dehumidification.
2. Guarantee Savings Building: An historic office building in California's central valley that has undergone a major remodel and will house two federal agencies. Three fuel cells with an absorption chiller are being installed.
3. The Orchid: A Hawaiian resort that has installed propane fired reciprocating engines and an absorption chiller.
4. BD Biosciences Pharmingen: A San Diego biotech company that is installing reciprocating engines with heat recovery for the almost constant space heating required because of frequent air changes needed for laboratories.
5. USPS San Bernardino: A postal sorting facility in southern California that is considering a reciprocating engine, possibly with absorption cooling.

All of these sites provided enough information on their loads, the tariffs they face, any subsidies or incentives they expected, and their analysis of their project for a parallel DER-CAM analysis to be completed. However, their various projects were at different stages of completion, so that the accuracy of available data was not consistent. For example, the Guarantee Savings Building remodel that was in progress at the time of this study was so major that historic energy use data was of no use and had to be replaced by simulation.

Scenarios were modeled to show the potential options and the financial value of different energy system designs such as the base case energy consumption with no DER installation, unrestricted installation of DER technologies, and a replication of the site's DER installation decision. The modeling results also emphasized the importance of DER grants and included sensitivity analyses on important parameters such as the spark-spread rate, standby charges, and general tariff structures.

This study accomplished the following goals: DER site project experience was analyzed, described,and disseminated; real-world problems involved with DER adoption decision-making and system design were described; DER-CAM financial estimates and technology adoption decisions were validated; the accuracy of DER-CAM was improved and its capabilities were expanded based on real-world experience; contacts were established with relevant DER sites for future research.The results of this case study report provide information on DER system costs and benefits that can be used to analyze the financial value of the DER project using tools such as net present value(NPV) and payback analysis. Important results in the report are the head-to-head comparison of DER technologies chosen at the site and the technologies recommended by DER-CAM. Typically the DER-CAM solution involves a higher capacity installation than that chosen by the site. Some sites' technology adoption decisions differed from DER-CAM due to factors not included in the model. Comparisons of DER-CAM results to the sites' estimates of DER system costs and benefits are presented. Note that most projects were in the installation or initial operation stage and actual costs could diverge significantly because of unanticipated operating conditions.

The key results are:

• Calculating financial costs and benefits of each DER system and using this information to validate DER-CAM's estimates.
• In general, DER-CAM and Berkeley Lab staff were able to reproduce energy bills and other key data with reasonable accuracy, typically within about 10%.
• DER-CAM generally found reciprocating engines often with absorption cooling to be the most attractive technology and, consequently, fairly accurately predicted its adoption for those sites installing engines. In one notable case where DER-CAM chose a reciprocating engine, the Guarantee Savings Building, the developers have adopted fuel cells in large part for reasons not incorporated into DER-CAM.
• DER-CAM tends to choose higher capacities than sites themselves choose. This seems to suggest a quite reasonable conservatism and risk averseness on the part of customers.
• This project has provided an excellent opportunity for Berkeley Lab to exercise DER-CAM, to learn about real world DER installations, and to develop a base of data and personal contacts that will be invaluable in future research on DER adoption.

In this study, the Distributed Energy Resources Customer Adoption Model (DER-CAM), an economic model of customer DER adoption implemented in the General Algebraic Modeling System (GAMS) optimization software is used, to find the cost-minimizing combination of on-site generation customers (individual businesses and a µGrid) in a specified test year. DER-CAM s objective is to minimize the cost of supplying electricity to a specific customer by optimizing the installation of distributed generation and the self-generation of part or all of its electricity. Currently, the model only considers electrical loads, but combined heat and power (CHP) analysis capability is being developed.

The electricity supply system is undergoing major regulatory and technological change with significant implications for the way in which the sector will operate (including its patterns of carbon emissions) and for the policies required to ensure socially and environmentally desirable outcomes.One such change stems from the rapid emergence of viable small-scale (i.e., smaller than 500 kW)generators that are potentially competitive with grid delivered electricity, especially in combined heat and power configurations. Such distributed energy resources (DER) may be grouped together with loads in microgrids. These clusters could operate semi-autonomously from the established power system, or macrogrid, matching power quality and reliability more closely to local end-use requirements. In order to establish a capability for analyzing the effect that microgrids may have on typical commercial customers, such as office buildings, restaurants, shopping malls, and grocery stores, an economic model of DER adoption is being developed at Berkeley Lab. This model endeavors to indicate the optimal quantity and type of small on-site generation technologies that customers could employ given their electricity requirements. For various regulatory schemes and general economic conditions, this analysis produces a simple operating schedule for any installed generators. Early results suggest that many commercial customers can benefit economically from on-site generation, even without considering potential combined heat and power and reliability benefits, even though they are unlikely to disconnect from the established power system.

This effort represents a contribution to the wider distributed energy resources (DER)research of the Consortium for Electric Reliability Technology Solutions (CERTS, http://certs.lbl.gov) that is intended to attack and, hopefully, resolve the technical barriers to DER adoption, particularly those that are unlikely to be of high priority to individual equipment vendors. The longer term goal of the Berkeley Lab effort is to guide the wider technical research towards the key technical problems by forecasting some likely patterns of DER adoption. In sharp contrast to traditional electricity utility planning, this work takes a customer-centric approach and focuses on DER adoption decision making at,what we currently think of as, the customer level. This study reports on Berkeley Lab's second year effort (completed in Federal fiscal year 2000, FY00) of a project aimed to anticipate patterns of customer adoption of distributed energy resources (DER). Marnay,et al., 2000 describes the earlier FY99 Berkeley Lab work. The results presented herein are not intended to represent definitive economic analyses of possible DER projects by any means. The paucity of data available and the importance of excluded factors, such as environmental implications, are simply too important to make such an analysis possible at this time. Rather, the work presented represents a demonstration of the current model and an indicator of the potential to conduct more relevant studies in the future.

The goal of this work is to develop an integrated framework for distributed energy resource (DER) deployment forecasting. Results for the Customer Adoption Model developed by this project show strong potential for future DER adoption. Factors that benefit DER include locally high electric rates or low natural gas prices. Although current regulations often prohibit the installation of small-scale generation for anything other than for emergency purposes, the strong interest in DER could soon remove this barrier. Environmental siting concerns are also an important consideration, the studied area, southern San Joaquin Valley (SJV), is under strict air quality restrictions. Siting DER in such locations is an environmental challenge, requiring proper selection of the DER technology, and, possibly, mitigation measures. The potential of GIS to geographically display numerous constraints associated with DER deployment in specified siting locations make it a powerful tool for anticipating potential barriers.Together, this work creates a framework for assessing customer adoption for DER deployment.

Distributed energy resources (DER) are in transition from the lab to the marketplace. The defining characteristic of DER is that they are active devices installed at the distribution system level, as opposed to the transmission level. While no specific size range has been defined, most distribution systems would have difficulty accommodating distributed generating resources larger than 10 MW/MVA at any single location and many systems may have even lower limits. Distributed energy resources include generation resources such as fuel cells, micro-turbines, photovoltaics, and hybrid power plants or storage technologies such as batteries, flywheels, ultra capacitors and superconducting magnetic energy storage. They may also consist of dynamic reactive power control devices and possibly customer end-use load controls.

This paper summarizes technical requirements for large-scale integration of active devices into the existing distribution infrastructure to maintain or enhance reliability. The paper is intended to lay the groundwork for a multi-year program of research necessary to facilitate the transition to such a system. The scope of the research includes consideration of control systems, including the sensors and instruments necessary to gather intelligence for real-time power management, and dispatch or coordination among distributed generation resources and with utility distribution systems. It also includes improved modeling techniques to better characterize the technologies and their impacts on the distribution (and ultimately the transmission) system.