Chris Marnay

Integration of distributed energy resources. The CERTS Microgrid Concept

LBNL-50829 Consortium for Electric Reliability Technology Solutions White Paper on Integration of Distributed Energy Resources The CERTS MicroGrid Concept Prepared for Transmission Reliability Program Office of Power Technologies Assistant Secretary for Energy Efficiency and Renewable Energy U . S . Department of Energy Energy Systems Integration Program Public Interest Energy Research California Energy Commission Prepared by Robert Lasseter, Abbas A k h i l , Chris Marnay, John Stephens, Jeff Dagle, Ross Guttromson, A . Sakis Meliopoulous, Robert Yinger, and Joe Eto A p r i l 2002 The work described in this report was coordinated by the Consortium for Electric Reliability Technology Solutions, and funded by the Assistant Secretary of Energy Efficiency and Renewable Energy, Office of Power Technologies of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098 and by the California Energy Commission, Public Interest Energy Research Program, under Work for Others Contract No. B G 99-39.

Optimal Technology Selection and Operation of Commercial-Building Microgrids

The deployment of small ( < 1-2 MW ) clusters of generators, heat and electrical storage, efficiency investments, and combined heat and power (CHP) applications (particularly involving heat-activated cooling) in commercial buildings promises significant benefits but poses many technical and financial challenges, both in system choice and its operation; if successful, such systems may be precursors to widespread microgrid deployment. The presented optimization approach to choosing such systems and their operating schedules uses Berkeley Labs Distributed Energy Resources Customer Adoption Model (DER-CAM), extended to incorporate electrical and thermal storage options. DER-CAM chooses annual energy bill minimizing systems in a fully technology-neutral manner. An illustrative example for a hypothetical San Francisco hotel is reported. The chosen system includes one large reciprocating engine and an absorption chiller providing an estimated 11% cost savings and 8% carbon emission reductions under idealized circumstances.

A larger role for microgrids

In this paper the technical constraints imposed by the growing needs of distributed generation, DER, and demanding PQR requirements, the microgrid concept is evolving toward a potentially versatile solution. The growing body of technical publications includes analytical modeling that defines the theoretical basis; computer simulation studies that verify operation and performance: and laboratory-scale, community-scale, and utility-scale demonstrations and pilot projects that add field experience to theory and simulation. Similarly, vigorous efforts are underway to expand microgrid economic and regulatory analysis capability, but challenges remain. At the policy level, significant changes will be needed to facilitate capture of the benefits of microgrids.

Policymaking for microgrids

Technically, microgrids are emerging as an outgrowth of dispersed on-site and embedded generation via the application of emerging technologies, especially power electronic interfaces and modern controls, and similarly, microgrid economic and regulatory analysis is generally rooted in the same approaches used to evaluate distributed energy resources (DER). As in the economics of many traditional on-site generation projects, the economics of heat recovery and its application by combined heat and power (CHP) systems is central to the evaluation of microgrids, and integration of this capability is a key requirement whenever CHP appears as an option. The recovery of waste heat offers a key advantage to generation close to loads but at the same time adds significantly to analysis complexity because of the need to simultaneously meet requirements for electricity and heat, plus the inevitability of storage, both active and passive, entering the equation. More novel is the economics of power quality and reliability (PQR), which in microgrids can potentially be tailored to the requirements of end uses in a manner only considered to a limited degree in utility-scale system; e.g., by interruptible tariff options. The economics of microgrids arises from evaluation methods for on-site generation from the customer perspective and from the traditional utility economics of expansion planning from the utility perspective. Both of these areas have received considerable attention, so a growing toolkit exists, but methods need reinforcement in some key regards. Central to public policymaking will be consideration of the societal impact of microgrids, especially since their adoption may change macrogrid requirements.

Energy manager design for microgrids

On-site energy production, known as distributed energy resources (DER), offers consumers many benefits, such as bill savings and predictability, improved system efficiency, improved reliability, control over power quality, and in many cases, greener electricity. Additionally, DER systems can benefit electric utilities by reducing congestion on the grid, reducing the need for new generation and transmission capacity, and offering ancillary services such as voltage support and emergency demand response. Local aggregations of distributed energy resources (DER) that may include active control of on-site end-use energy devices can be called microgrids. Microgrids require control to ensure safe operation and to make dispatch decisions that achieve system objectives such as cost minimization, reliability, efficiency and emissions requirements, while abiding by system constraints and regulatory rules. This control is performed by an energy manager (EM). Preferably, an EM will achieve operation reasonably close to the attainable optimum, it will do this by means robust to deviations from expected conditions, and it will not itself incur insupportable capital or operation and maintenance costs. Also, microgrids can include supervision over end-uses, such as curtailing or rescheduling certain loads. By viewing a unified microgrid as a system of supply and demand, rather than simply a system of on-site generation devices, the benefits of integrated supply and demand control can be exploited, such as economic savings and improved system energy efficiency.

Effect of Heat and Electricity Storage and Reliability on Microgrid Viability:A Study of Commercial Buildings in California and New York States

E RNEST O RLANDO L AWRENCE B ERKELEY N ATIONAL L ABORATORY Effect of Heat and Electricity Storage and Reliability on Microgrid Viability: A Study of Commercial Buildings in California and New York States Michael Stadler, Chris Marnay, Afzal Siddiqui, Judy Lai, Brian Coffey, and Hirohisa Aki Environmental Energy Technologies Division Revised March 2009 http://eetd.lbl.gov/EA/EMP/emp-pubs.html The work described in this paper was funded by the Office of Electricity Delivery and Energy Reliability, Renewable and Distributed Systems Integration Program in the U.S. Department of Energy under Contract No. DE-AC02- 05CH11231.

Estimating carbon dioxide emission factors for the California electric power sector

The California Climate Action Registry ( Registry ) was initially established in 2000 under Senate Bill 1771, and clarifying legislation (Senate Bill 527) was passed in September 2001. The Ernest Orlando Lawrence Berkeley National Laboratory (Berkeley Lab) has been asked to provide technical assistance to the California Energy Commission (CEC) in establishing methods for calculating average and marginal electricity emissions factors, both historic and current, as well as statewide and for sub-regions. This study is exploratory in nature. It illustrates the use of three possible approaches and is not a rigorous estimation of actual emissions factors. While the Registry will ultimately cover emissions of all greenhouse gases (GHGs), presently it is focusing on carbon dioxide (CO2). Thus, this study only considers CO2, which is by far the largest GHG emitted in the power sector. Associating CO2 emissions with electricity consumption encounters three major complications. First, electricity can be generated from a number of different primary energy sources, many of which are large sources of CO2 emissions (e.g., coal combustion) while others result in virtually noCO2 emissions (e.g., hydro). Second, the mix of generation resources used to meet loads may vary at different times of day or in different seasons. Third, electrical energy is transported over long distances by complex transmission and distribution systems, so the generation sources related to electricity usage can be difficult to trace and may occur far from the jurisdiction in which that energy is consumed. In other words, the emissions resulting from electricity consumption vary considerably depending on when and where it is used since this affects the generation sources providing the power. There is no practical way to identify where or how all the electricity used by a certain customer was generated, but by reviewing public sources of data the total emission burden of a customers electricity supplier can be found and an average emissions factor (AEF) calculated. These are useful for assigning a net emission burden to a facility. In addition, marginal emissions factors (MEFs) for estimating the effect of changing levels of usage can be calculated. MEFs are needed because emission rates at the margin are likely to diverge from the average. The overall objective of this task is to develop methods for estimating AEFs and MEFs that can provide an estimate of the combined net CO2 emissions from all generating facilities that provide electricity to California electricity customers. The method covers the historic period from 1990 to the present, with 1990 and 1999 used as test years. The factors derived take into account the location and time of consumption, direct contracts for power which may have certain atypical characteristics (e.g., green electricity from renewable resources), resource mixes of electricity providers, import and export of electricity from utility owned and other sources, and electricity from cogeneration. It is assumed that the factors developed in this way will diverge considerably from simple statewide AEF estimates based on standardized inventory estimates that use conventions inconsistent with the goals of this work. A notable example concerns the treatment of imports, which despite providing a significant share of Californias electricity supply picture, are excluded from inventory estimates of emissions, which are based on geographical boundaries of the state.

Distributed energy resources customer adoption modeling with combined heat and power applications

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 Labs 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 (mGrid). Current work focuses on the implementation of combined heat and power (CHP) capability. A mGrid 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 mGrid 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 mGrid is meant to optimize the overall energy system requirements of participating customers rather than the objectives and requirements of the macrogrid.

On voltage standards for DC home microgrids energized by distributed sources

Owing to the increasing prevalence for DC home appliances and distributed energy resources, the concept of a DC home microgrid is attracting considerable attention. This paper is to investigate voltage standards for DC home microgrids. First, a DC home microgrid configuration is proposed. All home loads are divided into five groups for separate connection to a common DC bus. An alternative path is designed to supply the high-power load groups through the public AC grid with less power conversion stages, when local sources are deficient. Second, voltage levels and wire cross-sections for different load groups are discussed, according to line thermal limits, power losses, and voltage drops. The results show that, if 120 volts is chosen for the DC bus, higher voltage standard over 120 volts could not bring loss savings for load groups. It can also be concluded that, 24 V DC could be a standard only for extra-low power appliances in a small house or single room, because of big losses; instead, 48 V DC may be better suitable for lighting and low-power appliances, especially when most of them could be working on 48 V DC in future.

Modeling of customer adoption of distributed energy resources

This report describes work completed for the California Energy Commission (CEC) on the continued development and application of the Distributed Energy Resources Customer Adoption Model (DER-CAM). This work was performed at Ernest Orlando Lawrence Berkeley National Laboratory (Berkeley Lab) between July 2000 and June 2001 under the Consortium for Electric Reliability Technology Solutions (CERTS) Distributed Energy Resources Integration (DERI) project. Our research on distributed energy resources (DER) builds on the concept of the microgrid ({mu}Grid), a semiautonomous grouping of electricity-generating sources and end-use sinks that are placed and operated for the benefit of its members. Although a {mu}Grid can operate independent of the macrogrid (the utility power network), the {mu}Grid is usually interconnected, purchasing energy and ancillary services from the macrogrid. Groups of customers can be aggregated into {mu}Grids by pooling their electrical and other loads, and the most cost-effective combination of generation resources for a particular {mu}Grid can be found. In this study, 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 {mu}Grid) in a specified test year. DER-CAMs 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 under the second year of CEC funding. The key accomplishments of this years work were the acquisition of increasingly accurate data on DER technologies, including the development of methods for forecasting cost reductions for these technologies, and the creation of a credible example California {mu}Grid for use in this study and in future work. The work performed during this year demonstrates the viability of DER-CAM and of our approach to analyzing adoption of DER.