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ECEEE 2007 SUMMER STUDY SAVING ENERGY JUST DO IT! 31

1,074 Microgrids: An emerging paradigm or meeting building electricity and heat requirements ef ciently and with appro-priate energy quality 1,074 Marnay, Firestone

Microgrids: An emerging paradigm formeeting building electricity and heatrequirements efciently and with appropriateenergy qualityChris MarnayBerkeley Lab MS [email protected]

Ryan FirestoneBerkeley Lab MS [email protected]

Keywords combined cooling, heating and power, commercial buildings,community energy systems, microgrids, engine generators,gensets, on-site generation, photovoltaic, power quality andreliability

AbstractTe rst major paradigm shi in electricity generation, deliv-ery, and control is emerging in the developed world, notably Europe, North America, and Japan. Tis shi will move elec-tricity supply away rom the highly centralised universal serv-ice quality model with which we are amiliar today towards amore dispersed system with heterogeneous qualities o service.One element o dispersed control is the clustering o sourcesand sinks into semi-autonomousgrid s (microgrids). Re-search, development, demonstration, and deployment (RD3)o grids are advancing rapidly on at least three continents,and signi cant demonstrations are currently in progress. Tisparadigm shi will result in more electricity generation closeto end-uses, o en involving combined heat and power applica-tion or building heating and cooling, increased local integra-tion o renewables, and the possible provision o heterogene-ous qualities o electrical service to match the requirements o various end-uses. In Europe,grid RD3 is entering its thirdmajor round under the 7 th European Commission Framework Programme; in the U.S., one speci cgrid concept is undergo-ing rigorous laboratory testing, and in Japan, where the mostactivity exists, our major publicly sponsored and two privately sponsored demonstrations are in progress. Tis evolution poses

new challenges to the way buildings are designed, built, andoperated. raditional building energy supply systems will be-come much more complex in at least three ways: 1. one can-

not simply assume gas arrives at the gas meter, electricity at itsmeter, and the two systems are virtually independent o oneanother; rather, energy conversion, heat recovery and use, andrenewable energy harvesting may all be taking place simultane-

ously within the building energy system; . the structure o en-ergy ows in the building must accommodate multiple energy processes in a manner that permits high overall ef ciency; and3. multiple qualities o electricity may be supplied to variousbuilding unctions.

IntroductionTis paper examines the role o theGrid (microgrid) para-digm in revolutionising the current universal centralised modelo electricity generation and delivery. Ten it provides a survey o several international research projects that pioneer research,development, demonstration, and deployment (RD3) o gridconcepts as an alternative approach to integrating small-scale(< 1 MW) distributed energy resources (DER) into commercialbuildings with peak electrical loads o less than about 2 MWor into multi- amily buildings or housing estates. A grid is agrouping o generating sources and loads operating semi-inde-pendently o the legacy power system, ormacrogrid , typically interconnected at a single point o common coupling (PCC).Te grid may include traditional reciprocating engine gen-erators (gensets), microturbines, uel cells, photovoltaic mod-ules (PV) or other small-scale renewables, heat recovery romthermal generation and use, electrical and heat storage devices,and controllable end-use loads. Tree likely grid eatures are:

1. ef ciently meeting total system energy requirements, o enby including combined heat and power (CHP) technology,especially or building heating and/or cooling, 2. providing

Marnay, ChrisFirestone, Ryan

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32 ECEEE 2007 SUMMER STUDY SAVING ENERGY JUST DO IT!

PANEL 1. THE FOUNDATIONS OF A FUTURE ENERGY POLICY

heterogeneous levels o electricity security, quality, reliability and availability (SQRA) that match the requirements o vari-ous end-uses, thereby potentially lowering expectations orimprovements in the macrogrid to meet the needs o a digitalsociety, and 3. appearing to the macrogrid as a controlled entity,akin to a current local utility customer, or conversely akin toa small embedded generation source, i the grid exports. Te

materials presented are based on presentations at a series o international symposiums held in the U.S. in 005, in Canadain 006, and a third in Nagoya, Japan, in April 007. Materials

rom these events can be ound at http://der.lbl.gov

Dispersed Generation Paradigm Shiftrends emerging in the power system suggest that the highly

centralized paradigm that has dominated power systems or thelast century may eventually be replaced, or at least diluted, by an alternative. In the new paradigm, control is more dispersed,and universal SQRA is replaced by heterogeneous service tai-lored to the requirements o highly diverse classes o end-uses.

Tis shi may be thought o as comparable to the replacemento centralised computing by desk and laptop computers, or theswitch rom land based telecommunications to mobile devices.Our current power delivery paradigm has been in place world-wide or a long time, i.e. since the emergence o polyphase ACsystems around the turn o the last century. SQRA targets areconsistent virtually all across vast regions, e.g. all o NorthAmerica, and where standards cannot be met, it is usually theresult o a local technical dif culty and not the outcome o adeliberate attempt to deviate rom the norm. Emerging changeson the demand-side include our seemingly unquenchable thirst

or electricity, in large part driven by the increasingly dominant

role o commercial building use in post-industrial economies,by an emerging digital age that is signi cantly tightening ourSQRA requirements, by the emergence o viable small-scale

ossil generation o en with power electronics and CHP, andby an urgent need to incorporate small-scale renewable gen-eration to abate carbon emissions. Meanwhile, on the supply-side, concerns about terrorism, restrictions on system expan-sion, and the uncertainties o volatile markets in energy-short

times bring our ability to maintain current SQRA standardsinto doubt.

Two Visions of the Future Gridwo alternative visions in current currency o how the power

system might be retooled to provide high SQRA are asuper- grids view and adispersed paradigm. Tese are obviously only two o many possible paths and ull justice cannot be given hereto the technical intricacies o any speci c vision. Te intent isonly to contrast in a comprehensible way the central themeo two divergent alternatives. For more detail on a supergrids view, see Gellingset al ( 004), Amin ( 005), or Amin and Wol-lenberg ( 005). A comprehensible vision or a dispersed grid ispresented by the European Commission (2006), or, or other voices rom the dispersed camp, see Lasseter ( 006) or Marnay and Venkataramanan (2006), but these are by no means theonly contributors to this ongoing debate.

SUPERGRIDS VISION

A supergrids vision is shown in Figure 1. Te x-axis o Figure 1shows the history o the current centralised paradigm, and they-axis reliability expresses as nines, e.g. 3 nines implies 99.9 %availability. Te equivalent annual expected outage times areshown or re erence. Te SQRA o delivered electricity has mul-tiple dimensions, e.g. voltage swells and sags, harmonic distor-tion, etc. Reliability is used here as a representative dimensionbecause it is much more easily comprehended than others,and we have some intuitive sense o its historical trajectory, asshown. In the early days o centralized power systems, electric-ity was supplied by small local stations with only very ew gen-erators to a limited number o customers, in the very early days

using DC. Tese highly unreliable systems were consolidatedby ones covering large areas based on Nikola eslas conceptsor large-scale AC systems. Tis interconnection naturally im-

proved reliability because many more generators were simul-taneously available. Te green arrow shows how this process,together with signi cant and steady technological progress,resulted in steadily improving reliability, reaching the levelsexperienced in North America today; however, note that reli-

1,074 MARNAY, FIRESTONE

Figure 1. Schematic of a Supergrids Vision

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ability is considerably better in western Europe, and better stil lin some Asian countries, notably Japan. Te red arc re ects thegreat concern in North America ollowing the huge New York blackouts o the 1970s that backup gensets or other emergency sources be provided to critical loads, and such requirementsbecame embedded in building codes. Tus, over the last quar-ter century or so, a separate higher reliability service has beenintroduced by installing generation close to sensitive loads.

Te supergrids camp holds that deployment o diverse suites

o new technologies can signi cantly improve the per ormanceo all elements o power systems built around the traditionalparadigm; i.e., delivered SQRA can be dramatically improvedwithin the existing ramework. In the schematic, this is shownby the arcing curves into the uture. While much o the im-provement inevitably must come in the distribution systembecause most outages and power quality problems occur there,over 90 % o interruptions in the case o North America. Distri-bution represents the most vulnerable link in the delivery chainbecause o its sheer size and dispersion, as well as its exposureto the myriad hazards o extreme weather, accidents, and mis-chie . Even in the supergrids view, inevitably there will be end-

uses that require SQRA beyond even the per ormance o themuch enhanced delivery chain, but these can be kept to a mini-mum; i.e., the gap between dashed curves can be kept small.Tis vision imagines massive investments in new technologies

or electricity delivery, such as superconducting lines, etc.

DISPERSED GRID VISIONIn this view, traditional universal service upstream o the sub-station is not improved signi cantly but rather holds steady at current levels, as seen in Figure asuniversal homogeneousSQRA. In other words, operation o the high voltage transmis-sion system and everything upstream o it are operated as now,with similar rules and conventions,and similar SQRA stan-dards . Sensitive loads are then increasingly served locally intwo ways: rst, improvements in the distribution system are

deployed to improve on the existing systems weakest link; andsecond, widespread use o supply and other resources close tosensitive loads protect them at the levels they demand. Tisis shown in the gure aslocal heterogeneous SQRA. In otherwords, end-uses are serviced with SQRA tailored to their re-quirements. In a sense, this vision is one o increasingly het-erogeneous SQRA downstream in the power system. Te tra-ditional universal SQRA is retained in the high voltage meshedgrid, but the distribution network has di ering levels o invest-

ment in equipment to enhance SQRA, and nally within cus-tomer sites, SQRA is ultimately matched to end-uses by meanso segregated circuits or by provision o high quality service atthe point o end-use, either by microgrids or power condition-ing equipment. In this dispersed paradigm, grids enter in twoways, as coordinated groupings within the distribution net-work that can operate semi-autonomously o the high voltagemeshed grid upstream o substations, and downstream o themeter where sources and sinks are organized to jointly provideheat and electrical energy, as well as heterogeneous SQRA.

EuropeEarly grid RD3 in Europe occurred within the 5th Framework Programme (1998-2002). A Consortium led by the National

echnical University o Athens (N UA) included 14 part-ners rom 7 EU countries, including utilities, e.g. lectricitde France, equipment manu acturers, e.g the German powerelectronics company SMA, and research institutions and uni- versities, e.g. Labein. Te main objectives were to study highrenewable and other microsource penetration into the grid,grid islanding operation, and grid controls. Several levelso centralized and decentralized control were explored at sev-eral laboratories, notably the Institut r Solare Energiever-sorgungs-technik at the University o Kassel, the University o

Manchester, and the National echnical University o Athens. A ollow up project was completed within the 6th Framework Programme ( 00 - 006), again led by N UA but with a some-


Figure 2. Schematic of a Dispersed Vision

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what di erent, although diverse, group o partners. Tis e ortocused on new micro-sources, storage, and control. Tere was

also considerable e ort on network design, protocols, and thebene ts and costs o grids (Hatziargyriou 2006). A new roundo projects will soon begin under the 7th Framework.

Several pilot grid installations have been completed. Asshown in Figure 3, twelve houses in a small valley on Kythnos

Island in the Cyclades Archipelago o Greece are supplied by agrid composed o 10 kW o PV, a 53 kWh battery bank, and a5 kW diesel genset. Te grid includes 3 SMA3.6 kW invertersconnected in parallel to orm one strong single-phase circuit ina master slave con guration. Te most innovative aspect o thissystem is that the battery inverters operate in requency droopmode without ast electrical controls. Tis approach passively allows in ormation ow to grid devices, in a manner similarto the Consortium or Electric Reliability echnology Solutions(CER S) approach used in the U.S. demonstration, describedbelow (Engler 006/7).

A second demonstration has been conducted at the Contin-uon holiday camp in the Netherlands, which has more than 200cottages equipped with a total o 315 kW o PV modules, in-terconnected by inverters. Te cottages are connected to a dis-

tribution trans ormer through our eeders, each about 400 m.Using a power electronic exible AC distribution system andstorage, islanded operation o the grid and power quality con-trol will soon be tested. A third project in Germany, shown inFigure 4, at the 400-inhabitant Am Steinweg residential estatehas 69 kW o DER including a 8 kW CHP plant, 35 kW o PV,and an 880 Ah battery bank. Other projects include an ecologi-

cal estate in Mannheim-Wallstadt, as shown in Figure 4, andprojects in Denmark, Portugal, Spain, and Italy. In addition tothese EC projects, relevant European demonstrations are alsobeing conducted at the national or local government levels.

North AmericaTe U.S. has a slowly expanding grid research program, sup-ported both by the U.S. Department o Energy under the Of ceo Electricity Delivery and Energy Reliability, and by the Cali-

ornia Energy Commission through its Public Interest Energy Research Program. Te most well known e ort has been pur-sued under the Consortium or Electric Reliability Solutions(CER S, http://certs.lbl.gov ), which was established in 1999 toexplore implications or power system reliability o emerging


Figure 3. The Kythnos Microgrid

Figure 4. Mannheim-Wallstadt Microgrid

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technological, economic, regulatory-institutional, and environ-mental in uences. From its inception, the likely emergence o DER was recognized as an important actor a ecting reliabil-ity, and it has consistently been a eature o the CER S RD3port olio.

Te speci c concept o the CER S Microgrid (CM) shownin Figure 5 was ully developed by 00 , and was described in awhite paper presented at a CEC workshop on May 00 , a erwhich building physical examples was undertaken (Lasseteret al 2003). As with most grid paradigms, the CM is intendedto seamlessly separate rom normal utility service at a single

point of common coupling (PCC) during a disruption and con-tinue to serve its critical internal loads until acceptable utility service is restored. As in the Kythnos demonstration, the CMprovides this unction or relatively small sites without need orcostly ast electrical controls or expensive site speci c engineer-ing. Unlike Kythnos, no single device is essential or operation,creating a robust system. o the utility, the CM appears as asingle controlled load, and it is explicitly designed to provideheterogeneous SQRAas varying reliability on circuits. In theevent o a grid disturbance, a static switch opens and the CMserves critical loads in islanded operation until grid power isagain adequate, and reconnection occurs. Tis switching tech-nology is critical to the CM and many other grid concepts,and has been the ocus o intensive RD3 in the past ew years(Lynch, et al, 006). Several technologies are available or astswitching, but at considerable cost. Te CM is also a dispersed plug-and-play system, i.e. no custom engineering is required

or interconnection o any single device, as long as it has CMcapability, making system con guration exible and variable.Sources may not only be spread across circuits, they may bephysically placed around the site, quite possibly co-located withconvenient heat sinks that o er economically attractive CHPopportunities. Finally, the CM has generic slow controls. TeCM is currently undergoing testing at the Dolan echnology Center in Columbus, OH, using three reciprocating engine

gensets as prime movers, as shown in Figure 6. I this test issuccess ul, a ull-scale eld demonstration will ollow.

One notable eature o the CM project has been simultane-

ous RD3 into necessary tools or grid deployment, other thanthe actual electrical hardware. wo major products o this uni-ed approach are the Grid Analysis ool, under development

at the Georgia Institute o echnology, and the Distributed En-ergy Resources Customer Adoption Model (DER-CAM) in useat Berkeley Lab and several other R&D acilities worldwide.DER-CAM is discussed urther below. Te CM is quite explic-itly designed around CHP applications and hence analysis o CHP applications in buildings is a central part o the CER SRD3 program.

In Canada, grid RD3 activities concentrate on the medium- voltage ( 5-170 kV) distribution network (Katiraei and Iravani

007). For example, the Fortis, Alberta, distribution system isa grid-inter ace microgrid composed o a 25 kV distributionnetwork that is normally connected to the substation. One ap-


Figure 5 Schematic of the CERTS Microgrid

Figure 6. Layout of the CERTS Microgrid Test at the DolanTechnology Centre

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proach to maintain the supply during substation maintenance

periods or subsequent to aults in the main grid is to tempo-rarily connect the distribution system to an alternative 5 kVeeder. Another approach to supply the load is to orm an is-

land on either the entire or a portion o the distribution eeder,depending on adequate availability o power rom local DERunits. At a notable example in British Columbia, the HydroBoston Bar system uses a planned islanding option.

JapanWorldwide, grid RD3 is most active in Japan. o increasepotential renewable energy harvesting near demand centres,Japans grid RD3 ocuses on utilising controllable prime mov-ers, such as natural or biogas red gensets, to compensate or variable demand and local small-scale intermittent renewablesupply. Te New Energy and Industrial echnology Develop-ment Organisation (NEDO), the research unding arm o theMinistry o Economy, rade and Industry, has started ourdemonstrations, as shown in Figure 7 (Funabashi and Yokoya-ma 006).

As shown in Figure 8, the rst o Japans grid demonstra-tion projects started during the 2005 World Exposition, us-ing a combination o varied chemistry uel cells, 70 kW and300 kW Molten Carbonate Fuel Cells (MCFC), our 200 kWPhosphoric Acid Fuel Cells, and a 25 kW Solid Oxide FuelCell (SOFC). Te MCFCs use a gas derived rom wood wasteand plastic bottles. Experimental intentional islanding has also

been conducted. Recently, the system was permanently movedto the Central Japan Airport City in Nagoya, where it will sup-ply a okoname City of ce and a sewage treatment plant usinga private eeder.

Te Hachinohe, Aomori Pre ecture, project began operationin October 005 and is being evaluated or SQRA, cost e ec-tiveness, and carbon emissions reduction over its demonstra-tion period stretching through March 008. Te grid has PVand wind turbines totalling 100 kW, 510 kW o controllableengine gensets supplied by digester gas rom a sewage plant,and a 100 kW lead-acid battery bank. Seven Hachinohe City buildings are supplied via a private 6 kV, 5.4 km distribution

eeder, with the whole system connected to the commercialgrid at a single point. est islanding operation is also planned

or this project.In a third NEDO project, the municipal government o Kyo-

tango City, north o Kyoto, leads a virtual grid demonstration.Te DER included are 50 kW each o PV and wind turbines,

ve 80 kW biogas engines, a 250 kW MCFC, and 100 kW o battery back-up. In this project, an energy centre communi-cates with the DER over the existing utility network to coor-dinate demand and supply. Imbalances between supply anddemand are resolved within ve minutes.

Finally, NEDO sponsors an ambitious and interesting multi-ple SQRA demonstration project in Sendai, Miyagi Pre ecture,

shown in Figure 9. Tis grid demonstrates multiple SQRA onadjoining rest home, high school, university, and waste treat-ment acilities. Te energy centre and a dedicated distributionline are connected at a single PCC. Te main DER are a 250 kWMCFC, two 350 kW natural gas- red gensets, 50 kW o PV,and batteries. Tese should be apparent in the gure. Te leadorganization or this project is N Facilities, an arm o Japanstelecom giant. Because o this industrys expertise in the high


Figure 7. Locations of the NEDO Microgrid DemonstrationProjects

Figure 8. The Aichi Microgrid Installed at the 2005 World Exposition

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SQRA DC systems that have always powered telephone serviceworldwide, the Sendai demonstration eatures direct service toDC telecom loads. As well as DC, multiple qualities o stand-ard AC service are delivered rom the clean power buildingmarked in the rear o the compound, creating an outstandingexample o heterogeneous SQRA. In act, this grid suppliesAC to the nearby buildings at four di erent service qualities.A premium quality A service or critical loads is never inter-rupted, and wave orm correction is per ormed on it. When theutility grid has a momentary voltage sag or outage, the threeB quality circuits receive SQRA. Te B service is urther sub-

divided into three di erent types. During outages, the higherquality B1 service is backed up by storage, while B is backedup by distributed power, i.e. slower responding backup, whileB3 service is not backed up and experiences grid SQRA (Hiroseet al 006). Note the similarity between this arrangement andthe multiple SQRA on the various circuits o the CM

In addition to the government-sponsored projects describedabove, there are signi cant research activities in Japans privatesector. Shimizu Corporation, a large construction company, isdeveloping a grid control system at its okyo test acility. Also,

okyo Gas, together with the University o okyo, plans to es-tablish a grid to supply three-level power quality to a buildingo the Yokohama Research Institute.

Building CHPWhile this paper has ocused on grid demonstrations aroundthe world, and primarily on their SQRA aspects, equally im-portant rom the buildings perspective is the CHP opportuni-ties that grids will create. Te importance o the commercialsector in electricity consumption in developed countries can beseen by three multiplicative actors. 1. Te share o all energy being consumed as electricity increases, e.g. in the U.S. rom13 % in 1980 to about 20 % today. 2. Te commercial sectoruses a growing share o all electricity, e.g. in the U.S. rom 7 %

in 1990 to 35 % in 005. And 3., typically an increasing share o electricity is generated thermally as carbon- ree hydro sourcesare ully exhausted, although the shares o carbon- ree nuclear

vary widely across grids. Te product o these actors meansthe carbon ootprint o commercial buildings can grow rapidly,but changes in the uel mix, e.g. more natural gas red genera-tion, can also have a big e ect. Further, in warm climates suchas most o the U.S. and Japan, and or an increasing share o Europe, commercial sector cooling is a key driver o peak loadgrowth, and hence the stress to and investment in the widerpower system. Consequently, deployment o grids to servebuildings, especially ones applying CHP technologies or cool-ing, is central to containing the growth o electricity consump-tion and its associated carbon emissions. DER-CAM has been

developed as part o the CM RD3 project speci cally to analyzethe economics o building-scale grids.

DER-CAMDER-CAM identi es optimal technology-neutral grid invest-ments and operating schedules at a given site, based on availableequipment options and their associated capital and O&M costs,customer load pro les, energy tari structures, and uel prices.Te Sankey (Spaghetti) diagram in Figure 10 shows partially disaggregated site end-uses on the right-hand side, and energy inputs on the le . As an example, the re rigeration and coolingload may be met in one o multiple ways, including standard

electrically powered compressor cooling, direct re or wasteheat activated cooling, or direct engine powered compressorcooling. DER-CAM solves this entire problem optimally andsystemically. Figure 11 shows a high level schematic o inputsto and outputs rom the model.

As can be seen in Figure 11, DER-CAM picks its optimalcombination o grid equipment using hourly building end-use loads and care ul consideration o the detailed tari s thebuilding aces. Te choice o technologies can include a broadrange o grid technologies. DER-CAM is particularly suitedto evaluating grid CHP opportunities since it selects the op-timal combination o investment options, ully taking their

interdependence into account; e.g., i there is a trade-o be-tween thermally activated cooling and on-site genset capacity,DER-CAM obtains the combination o the two that minimizes


Figure 9. The Sendai Multiple SQRA Microgrid Demonstration

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Te area underneath the solid black line in these gures isthe hourly energy demand. Area above the solid black line in-dicates storage charging. Te various patterns in the graphsindicate the source o the energy. For electrical loads the lowerpro le indicates the portion o the electric load that can be metby only electricity, whereas the solid line above it is the totalelectric load, including cooling. Note that electric cooling loadscan be o set by the absorption chiller. For thermal loads, thelower line indicates the heat required or heating, whereas thesolid black line indicates the total thermal load, including heatrequired or the absorption chiller.

ConclusionsResearchers worldwide are recognizing the promise o gridsto provide heterogeneous SQRA to serve sensitive loads, toimprove energy ef ciency by moving thermal generation closeto possible uses. Tis would permit waste heat recovery anduse, and better integration o small-scale dispersed renewablesinto the energy supply in rastructure. Nonetheless, it is alsoclear that development o grid concepts and capabilities willrequire considerable RD3 resources, and e orts are currently underway, in Europe, North America, and Japan, intended todemonstrate grid concepts, operation, and economic viability.Close cooperation and exchange o in ormation among these

disparate activities can deliver the most ef cient RD3 agendaoverall. Te international Microgrids Symposiums held so arhave o ered a highly bene cial orum or exchange o relevant

research results. Further, coordinated joint RD3 e orts amongthe major countries are emerging and are expected to provideurther mutual bene ts in the historic e ort to achieve the big-

gest paradigm shi in electricity generation and delivery in acentury or so, one that can accelerate lowering the carbon oot-print o electricity supply and simultaneously meet developedcountries growing requirements or high SQRA service.

Tis power supply evolution poses new challenges to the way buildings are designed, built, and operated. raditional build-ing energy supply systems will become much more complexin at least three ways. First, architects and building engineerscannot assume that as now gas will arrive at the gas meter, elec-tricity at its meter, and within the structure, the two systems are virtually independent o one another. Rather, energy conver-sion, heat recovery and use, and renewable harvesting may allbe taking place simultaneously at various locations within thebuilding energy system. Second, the structure o energy owsin the building must accommodate multiple energy processesin a manner that permits high overall ef ciency. In other words,the building must be designed around its energy ows and en-ergy equipment to ensure ef ciency. And third, multiple quali-ties o electricity may be supplied to various building unctions,and there placement and supply must be considered.

DER-CAM, developed as part o the CER S Microgrid RD3programme is intended to permit economic analysis o possi-

ble building grids. DER-CAM nds the optimal combinationo equipment to install in a building-scale grid, given the re-quirements or use ul energy services in the building, the local


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economic environment, e.g. utility tari s, and a menu o avail-able equipment. Tis approach allows a quite new type o build-ing energy analysis that directly delivers a desirable equipmentchoice taking the potential interactions between heat (includ-ing cooling) and on-site generating equipment into account.

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and Must Modernize the Grid, IEEE Power & Energy Magazine, March-April 005.

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Lasseter, Robert, Abbas Akhil, Chris Marnay, John Stevens,Je Dagle, Ross Guttromson, A. Sakis Meliopoulos, Rob-ert Yinger and Joe Eto, 003, Integration o DistributedEnergy Resources: Te CER S Microgrid Concept, CEC,P500-03-089F, October.

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Lynch, Jonathan, V. John, S.M. Danial, E. Benedict, I. Vi-hinen, B. Kroposki, and C. Pink, 006, Flexible DER Util-ity Inter ace System: Final Report, National RenewableEnergy Laboratory, NREL/ P-560-39876, August.

Marnay, Chris and Giri Venkataramanan, 006, Microgridsin the Evolving Electricity Generation and Delivery In ra-structure, paper presented at the IEEE Power Engineer-ing Society General Meeting, Montral, June.

AcknowledgementsTe work described in this report was unded by the Of ce o Electricity Delivery and Energy Reliability, Distribution SystemIntegration Program o the U.S. Department o Energy underContract No. DE-AC02-05CH11231, and by the Cali ornia En-ergy Commission, Public Interest Energy Research Program,under Work or Others Contract No. 500-03-0 4. Te author

recognizes the signi cant contributions o the group that inpart organized the Microgrids Symposiums and have providedmuch o the material used in this paper, Hiroshi Asano, Univer-sity o okyo, Nikos Hatziargyriou, National echnical Univer-sity o Athens, and Reza Iravani, University o oronto. Te au-thor also thanks the many participants in the three completedMicrigrids Symposiums. Te paper also builds on prior work the author has completed together with Giri Venkataramanan,University o Wisconsin, Madison, A zal S Siddiqui, University College, London, Michael Stadler, Center or Energy and Inno- vative echnologies, Yspertal, Austria, plus Kristina HamachiLaCommare, and Judy Lai o Berkeley Lab.

GlossaryAC alternating currentBerkeley Lab Ernest Orlando Lawrence Berkeley National

Laboratory, Berkeley CACER S Consortium or Electric Reliability echnology

SolutionsCHP combined heat and powerCM CER S MicrogridDC direct currentDER distributed energy resourcesDER-CAM DER Customer Adoption Model

genset traditional reciprocating engine poweredgenerator

ISE e.V. Institut r Solare Energieversorgungstechnik,Kassel, Germany

kV kilovoltkW kilowattMCFC molten carbonate uel cellMW megawattNAS sodium-sulphur (battery)NEDO New Energy and Industrial echnology

Development Organisation, RD3 branch o theJapans economy ministry

NREL National Renewable Energy Laboratory,Golden CO

N Nippon elegraph and elephone Corp., thedominant Japanese telecom

N UA National echnical University o AthensO&M operating and maintenancePAFC phosphoric-acid uel cellPCC point o common couplingPV photovoltaicRD3 research, development, demonstration, and

deploymentSMA SMA echnologie AG, a power electronics

manu acturer based in Niestetal, Germany SOFC solid oxide uel cellSQRA security, quality, reliability, and availability


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