II. IMPACTS OF WIND POWER ON GRID OPERATIONS

Transcription

1 IEEE Energy2030 Alana, Georga, USA November 2008 Couplng Wnd Generaors wh eferrable Loads A. Papavaslou, and S. S. Oren UC Berkeley, eparmen of Indusral Engneerng and Operaons esearch, 4141 Echeverry Hall, UC Berkeley, CA, Absrac-- We explore he possbly of drecly couplng deferrable loads wh wnd generaors n order o mgae he varably and randomness of wnd power generaon. Loads engage n a conracual agreemen of deferrng her demand for power by a fxed amoun of me and wnd generaors opmally allocae avalable wnd power wh he objecve of mnmzng he cos of unscheduled and varable supply. We smulae he performance of he proposed couplng n a marke envronmen and we demonsrae s compably wh exsng echnology, grd operaons and economc ncenves. he resuls ndcae ha he combnaon of exsng deregulaed power markes and demand sde flexbly could suppor large scale negraon of wnd power whou sgnfcan mpacs on grd operaons and whou he requremen for prohbve nvesmens n backup generaon. I I. INOUCION s a well known fac ha wnd power has undergone massve growh durng he pas 20 years, o he pon ha large scale negraon of wnd n power sysems s echncally and economcally concevable. Neverheless, he random and varable naure of wnd power supply mposes severe lms o he negraon of wnd power n power sysems. he unpredcable and varable supply of wnd power may resul n balancng acons ha range from rampng oher generaors, load followng, prmary and secondary conrol acons, o he upse of hour-ahead and day-ahead schedules. hese balancng acons are cosly, lead o ar polluon, cause wear and ear o machnery and requre sgnfcan nvesmens n sysem backup. Emprcal and academc sudes have placed an esmae on he coss resulng from wnd varably a a range of 0 o 7 $/MWh [1]-[3]. In addon, wnd s ofen adversely correlaed wh sysem supply and demand paerns, and may be dscarded even when s abundanly avalable [4]. he burden ha wnd power mposes on grd operaons s lkely o ncrease n he fuure due o regulaory commmens for ncreased negraon of wnd power. In he meanme, he exploaon of demand flexbly as an ancllary resource for power sysem operaons s evolvng rapdly. me of use prcng, demand response programs [5] and nerrupble servce conracs [6], [7] are already n place, and he ulzaon of demand n load followng markes s consdered as a vable possbly [8]. I s herefore naural o consder he poenal of flexble loads flucuang accordng o he supply of renewable and non-dspachable energy sources such as wnd power. In order o reap he greaes benefs from demand flexbly, hs flexbly should be explcly modeled n sysem operaor dspach algorhms and remuneraed n he hour-ahead and real-me markes. Ceran marke regulaons such as he Calforna marke redesgn (MU) am a ncorporang demand resources n marke operaons, neverheless demand flexbly s presenly far from fully ulzed [9]. In he meanme, hs paper presens an approach for couplng wnd power supply wh flexble demand whch s compable wh curren grd and power marke operaons, exsng echnologcal nfrasrucure and exsng economc ncenves. In secon II we dscuss he operaonal challenges ha resul from wnd power negraon. In secon III we presen he archecure of he proposed couplng and n secon IV we evaluae s performance. Fnally, we summarze our conclusons n secon V. II. IMPACS OF WIN POWE ON GI OPEAIONS here are wo characerscs of wnd power supply whch presen sgnfcan obsacles o large scale wnd power negraon. Wnd power supply s random and canno be forecas accuraely. In addon, s varable; even f perfec forecass were avalable, wnd would be a problemac power source because vares beyond human conrol. he unpredcably of wnd power supply may cause devaons from hour-ahead dspach schedules. Sarng up uns o compensae for a sudden shorage n wnd power supply may ake hours, lead o addonal ar polluon, resul n wear and he need for frequen manenance of sarup uns, and upse sysem dspach due o he mnmum capacy consrans of sarup uns. Smlar problems are caused by shung down uns o balance an unancpaed ncrease n wnd power supply. he mnue-by-mnue and nra-hour varably of wnd power generaon may also cause sysem mbalances. hs varably mposes a requremen for capacy nvesmens n prmary conrol (spnnng reserve), secondary conrol (nonspnnng reserve), load followng and regulaon uns. he nably o perfecly forecas wnd exacerbaes hs problem. Snce wnd also ends o vary rapdly and n grea magnude, generaors wh suffcen rampng capables are requred. he Calforna ISO (CAISO) has esmaed ha meeng he 20% renewable energy negraon arge n Calforna wll ncrease he regulaon rampng requremen of he sysem by ±10 o ±25 MW/mn, he maxmum load followng rampng requremen by ±30 o ±40 MW/mn, he 3-hour mornng rampng requremen by 926 o 1529 MW, and he 3-hour evenng rampng requremen by 427 o 984 MW dependng on he season [4]. Auhorzed lcensed use lmed o: Unv of Calf Berkeley. ownloaded on March 19,2010 a 18:24:49 E from IEEE Xplore. esrcons apply.

2 Wnd power may also cause oversupply problems n sysems whch absorb large amouns of hydroelecrc power, or n sysems where wnd paerns are negavely correlaed wh elecrcy consumpon. Inermency n he presence of hgh wnds s also a sgnfcan drawback of wnd power supply. Snce wnd generaors supply a sgnfcan amoun of power o a sysem durng perods of hgh wnds, here s an ncreased rsk of subsanal supply shorage durng sorms. he end effecs of he problems lsed above whch orgnae from he errac naure of wnd power supply are hgh negraon coss and he dscardng of wnd power. Boh of hese effecs lm our ably o ncrease our relance on wnd power supply. he coss of wnd negraon are capured by marke arffs and may be allocaed o he whole marke or drecly o wnd generaors, dependng on marke regulaons. Sudes have placed an esmae of hese coss beween 0 and 7 $/MWh for negraon levels beween 2.4% o 20%. Wnd energy may be dscarded durng hours of excess wnd power supply f power sysems canno relably absorb hs supply [1], [3]. urng early sprng he Calforna sysem operaor eher splls waer supples from hydroelecrc dams or dscards wnd power [4]. Wnd power s also dscarded under normal operang condons n Calforna whenever forecasng underesmaes he amoun of wnd power supply o he sysem and he excess power canno be sold n he marke. In exas he sysem operaor lms wnd oupu durng load pck-up for relably reasons. In enmark, wnd power s no consumed durng wndy and cold evenngs when combned hea and power hermal uns need o operae [10]. Fg. 1. aa flow of he proposed mplemenaon. III. NEWOK CONFIGUAION AN MOEL he proposed couplng of wnd generaors wh flexble loads s presened n Fg. 1. Loads program asks o be compleed whn a deadlne (e.g. a few hours) and a wnd generaor conrol cener whch conrols he oupu of a large number of wnd generaors swches hese loads remoely and supples power o loads whn he deadlne. ues aggregang from dfferen loads are scheduled accordng o he avalably of wnd power. Meers are nsalled a every load se and a he wnd power plan. he meers monor he oupu of wnd power and he power consumpon of each load. hs nformaon s repored o he ISO and o he power plan conrol cener. A cenral schedulng conroller uses all avalable daa (meered daa, marke prces, load demand, weaher forecass) n order o opmally schedule he allocaon of avalable wnd power for sasfyng ncomng dues. he schedulng conroller can also place bds n he power marke. he conrol cener collecs meered and load demand daa and feeds o he scheduler. Afer he schedulng algorhm deermnes whch loads can consume power n he followng nerval, he conrol cener communcaes hese nsrucons o each load conroller. Load conrollers are nsalled a each load se. hese devces collec meered and power demand daa, communcae hs nformaon o he conrol cener and swch loads. Apar from load flexbly, wnd generaors can ulze an addonal degree of freedom, he hour-ahead marke of elecrcy. In case forecas wnd power supply exceeds he aggregae demand of flexble loads, he excess wnd can be sold n he hour-ahead marke. Smlarly, f aggregae demand s n excess of wnd power supply and wnd supplers rsk mssng load deadlnes, her shor poson can be covered n he marke. Snce loads can be swched o vary accordng o he supply of wnd, he ne power supply of he nework of wnd generaors and flexble loads o he grd remans near zero consanly, hus resulng n mnmal mpacs of wnd power generaon on grd operaons. Moreover, by appropraely combnng supply and demand bds n he marke wnd generaors and flexble loads can overrde he marke prce and effecvely rade he bulk of avalable wnd power blaerally, usng he marke solely for he purpose of resolvng unscheduled devaons and supplyng excessve amouns of wnd power. he welfare ncrease resulng from he proposed couplng can be allocaed among wnd generaors and deferrable loads hrough he desgn of an approprae conracual agreemen. he aforemenoned jon decson process of allocang avalable wnd power and parcpang n he marke s formulaed as an opmzaon problem n (1)-(8). N max E f c c, w, r, B 1 I H s. H 1, - c B 2 N s 1 s (1) 2 { 1... N}, I (2) d 0 I (3) w r W { 1... N} (4) I c C I, {1... N} (5) Auhorzed lcensed use lmed o: Unv of Calf Berkeley. ownloaded on March 19,2010 a 18:24:49 E from IEEE Xplore. esrcons apply.

3 c 0 I, a 1 (6) w, c 0 I, {1... N } (7) r 0 { 1... N} (8) Wnd generaors supply power o a se of flexble consumers I over a se of en-mnue me nervals { 1... N}. he se H consss of hose en-mnue nervals belongng o he - h hour. Wnd generaors agree o supply power o deferrable loads a a fxed prce f. hs fxed prce should only be a fracon of he hour-ahead marke prce of elecrcy n order o be aracve o flexble. Generaors ncur an hourly devaon penaly for devang from her marke bd, and a en-mnue rampng penaly for varaons of her ne supply o he marke. A each en-mnue nerval generaors deermne he amoun of power c, suppled o user ; he amoun of wnd power w, allocaed o user ; and he amoun of wnd power r suppled o he marke. A each hourly nerval generaors bd a quany B of power o he hour-ahead marke. I s assumed ha bds are placed wo hours n advance of he acual operang nerval. Hence he bd a hour comms he suppler for perod 2 and s rewarded he prce 2. he erms n he objecve funcon of (1) nclude revenues for supplyng power o deferrable loads, revenues for energy bds n he hour-ahead marke devaon penales and rampng penales. he generaor ne supply o he marke a each en-mnue nerval s max s B 2 H s r ( c w, ). Hence I s he maxmum devaon of he ne supply o he marke from he scheduled quany B 2 over he course of hour. Expecaon n he objecve funcon s aken over he jon dsrbuon of he wnd power supply and prce processes. he remanng energy requred o complee he reques of user s, n perod and evolves accordng o (2). Equaon (3) mposes he consran ha he reques of user mus be compleed by he deadlne d. Accordng o (4) he oal amoun of wnd power suppled o flexble consumers and he spo marke canno exceed he amoun of avalable wnd power W. Equaon (5) models he capacy consran C of user and accordng o (6) power canno be suppled a o he ask of user pror o he arrval me. he devaon penaly erm n (1) s nended o model he coss assocaed wh he unpredcably of wnd power supply, whle he rampng penaly erm s nended o model varably coss. Apar from her modelng nerpreaon, hese erms also have an economc meanng n he conex of power markes. he devaon penaly erm can be nerpreed as a capacy cos resulng from he requred nvesmen n load followng generaon whch can neuralze wnd generaor devaons from her scheduled oupus n he nra-hour me scale. Lkewse, he rampng penaly erm can be nerpreed as a capacy cos resulng from requred upgrades n he rampng requremens of load followng uns. hese nvesmen coss are dscussed n secon II. I should be noed ha he model n (1)-(8) does no accoun for ransmsson consrans. As such, s a bes-case scenaro for explong demand-sde flexbly, snce he presence of ransmsson consrans wll boh lm and complcae he soluon o he problem. he hardware nfrasrucure requred for mplemenng he archecure of Fg. 1 s lmed o one-way meerng devces, communcaon lnks and load conrollers whch are used exensvely n power sysem operaons. Insead, s he avalably of flexble power consumers whch s n queson. here s a varey of large scale ndusral and commercal loads whch are promsng canddaes for he proposed couplng. Such loads nclude ndusral elecrc heaers, hermal sorage, HVACs, pumps, agaors, smelers, refrgeraors, and poenally programmable hermosas and daa ceners. An emergng source of flexbly whch wll probably revoluonze our ably o ncorporae wnd power n power sysems are plug-n elecrc vehcles. Usng wnd power supply o power elecrc vehcles s n he process of mplemenaon n enmark, and a plo program n Calforna s also beng consdered. he couplng whch s advocaed n hs paper can equally well be appled o mgae he varably and randomness of any renewable energy source whch s beyond human conrol. In parcular, solar power s a promsng area of applcaon for hs concep especally n Calforna where solar power supply s complemenary o wnd power. he reason ha we have decded o focus on wnd power n he presen paper s ha wnd power s currenly he prmary renewable energy source n Calforna, and we have access o a more dealed daabase for our smulaon model. I could be argued ha he proposed couplng s redundan n he presence of an ancllary servces marke where he prce sgnal would be suffcen o acvae he necessary responses whch would balance he mpac of wnd power varaons on sysem relably. However, desgnng a marke whch s fas and accurae enough o ensure grd relably s a challengng ask. Hence, an a pror conracual agreemen of he sor descrbed n hs paper may be an aracve alernave o ensurng relably n he presence of large amouns of wnd power. In order o demonsrae he ncenve compably of he proposed couplng for boh wnd power supplers and flexble consumers, he proposal mus be compared o a benchmark of exsng pracces. We wll consder a baselne scenaro n whch wnd generaors bd he forecas wnd supply n he hour-ahead marke and supply all wnd power as becomes avalable. Hence wnd generaors receve he marke prce for he full amoun of avalable wnd power, however hey ncur sgnfcan devaon and rampng charges. Auhorzed lcensed use lmed o: Unv of Calf Berkeley. ownloaded on March 19,2010 a 18:24:49 E from IEEE Xplore. esrcons apply.

4 Fg. 2. A snapsho of load schedulng for 1500 users and 18 hours of avalable me for processng jobs. o argue ha deferrable loads have an ncenve o couple, we wll conen ourselves o demonsrang ha wnd power supplers are able o provde power o flexble consumers below he average marke prce. We wll herefore refran from explcly modelng consumer uly funcons, and he resulng dscomfor of posponng elecrcy consumpon. o demonsrae ha supplers have an ncenve o couple, we wll show ha s possble o use he flexbly of deferrable users n combnaon wh marke bddng o mgae boh rampng and devaon penales. he savngs n devaon and rampng penales, as compared o he baselne case, wll exceed he revenue losses resulng from sellng power a a dscouned prce o deferrable loads nsead of he hour-ahead marke. IV. SIMULAION ESULS aher han provdng an exac assessmen of he negraon coss of wnd power n he presence of demandsde flexbly, he smulaons presened n hs secon am a esmang a wha pon hs proposal becomes an economcally vable alernave o exsng pracces. In addon, he smulaons analyze he sensvy of he proposed couplng o ceran sgnfcan problem parameers, such as he number of avalable deferrable loads and he deadlnes of he deferrable asks. Such an analyss s nmaely relaed o he queson of how much flexbly s nheren n our consumpon paerns: f ndeed a sgnfcan proporon of he power we consume can be deferred for only a few hours a a mnmal mpac and f hese few hours of flexbly can be opmally rescheduled so as o mgae he coss of wnd power negraon, hen here s good reason o pursue he roue of demand-sde managemen as an avenue of addressng our dependence on fossl fuels and mgang he envronmenal mpacs of elecrcy generaon. he assumpons ha are employed n he smulaons are lsed n appendx A. he algorhm ha s used for schedulng loads and parcpang n he hour-ahead marke s descrbed n appendx B. Fg. 3. Profably of he proposed couplng as a funcon of he number of deferrable loads for varous levels of consumer flexbly. A. An Example un Fg. 2 s a 24-hour snapsho of he load schedulng for he case of 1500 users, each of whch provdes an 18-hour me wndow for processng a ask whch would normally requre 7 hours (see appendx A). he sold lne s he oal amoun of avalable wnd energy, and he broken dark lne represens he consumpon profle of ncomng blocks of perfecly nflexble loads. he broken lgh lne s he power consumpon of hese loads, as adjused by he schedulng algorhm. he frs block of ncomng dues s sasfed upon arrval, as plenful wnd power s avalable n he ngh me. A approxmaely 6 a.m., wnd power supply drops sharply, a he same me when he second block of loads arrves. If hese loads were rgd, he power suppler would face a severe defc from 8 a.m. up unl 10 p.m. n he evenng of he same day. However, he suppler s able o pospone he power consumpon of he second block of loads unl abou 8 p.m., by whch me he suppler needs o sar feedng power o he loads from he marke n order o sasfy he 18-hour deadlne. B. Opmal Choce of Consumers Fg. 3 demonsraes he performance of he proposed couplng as a funcon of he number of deferrable loads, for varous levels of consumer flexbly (measured n erms of he avalable me wndow o sasfy he asks a hand). he parameers used o derve hese resuls were f 30$ / MWh, 100$ / MWh, and 100$ / MWh. We conclude ha he opmal choce of conraced deferrable loads depends on he processng me ha hese loads offer o wnd power supplers. he longer he me wndow, he greaer he number of loads whch supplers can accommodae, and he greaer he profably of he supplers. For a 10-hour me wndow, s opmal for supplers o conrac wh 500 users per day, for a 14-hour wndow wh 1000 users per day and for an 18-hour wndow wh 1500 users. Moreover, he profably s sensve o he number of served loads, herefore he decson Auhorzed lcensed use lmed o: Unv of Calf Berkeley. ownloaded on March 19,2010 a 18:24:49 E from IEEE Xplore. esrcons apply.

5 of an opmal mx of flexble consumers s crcal o he performance of he proposed couplng. Wnd power supply paerns can vary from season o season, whch mposes a challenge of dynamcally adjusng he mx of flexble consumers and/or he qualy of servce o deferrable loads so as o accommodae hese seasonal varaons. C. Economc Performance In order o assess he economc performance of he couplng, s necessary o compare he coss under he couplng wh he baselne negraon scenaro descrbed n secon III. However, assessng he coss of wnd power varably s a challengng ask, snce he resul depends on numerous facors whch are unque o each sysem under consderaon, such as he supply mx, he consumpon paerns, he ransmsson consrans and oher facors whch are ndependen from wnd power supply. herefore, a model such as he one descrbed n (1) (8) whch consders he sysem of wnd generaors and deferrable loads n solaon from he remanng power sysem canno be used o accuraely assess he coss of wnd power varably. A proper assessmen of he cos mplcaons would requre smulang he performance of he couplng n a un commmen model n order o evaluae he resulng savngs n ancllary servces requremens. hs s a drecon whch wll be pursued by he auhors n fuure work. Insead, n he presen paper we make a prelmnary assessmen by employng an nverse approach o he one oulned above: nsead of assessng coss and deermnng wheher he couplng ouperforms curren pracce, we wll nqure wha level of capacy charges would jusfy he ulzaon of hs couplng. If hese prces are suffcenly lower han he exsng capacy charges for load followng reserves and rampng upgrades, hen hs s an ndcaon ha couplng s jusfable n economc grounds. energy prce f whch yeld he same profs as he baselne case for a fxed rampng capacy charge of 100$ / MW. hese graphs are drawn for four separae cases. he bold sold lne refers o he case of 500 users wh a 10-hour me wndow and he bold broken lne refers o he case of 1500 users wh an 18-hour me wndow. In order o evaluae he conrbuon of bddng n he hour-ahead marke o he performance of he couplng, he counerpars of he wo cases above are drawn n lgh sold and lgh broken lnes respecvely. he furher lef ha he graphs le n he plane, he beer he performance of he correspondng case. herefore, Fg. 4 confrms he concluson drawn from Fg. 3 ha he profably of he couplng ncreases as me wndows ncrease. However, performance s no sgnfcanly beer, whch s farly surprsng gven ha consumers are offerng an exra 8 hours of flexbly o complee asks. On he oher hand, bddng n he hour-ahead marke can lead o sgnfcan gans for he case of a 10-hour me wndow, bu o sgnfcan losses for he case of an 18-hour wndow, whch mples ha he employed bddng sraegy performs poorly n erms of mgang devaons. akng no accoun he fac ha he average spo prce of elecrcy for hese smulaons s 83.4 $/MWh, all cases bu one are compeve o exsng pracces. hs can be deduced from Fg. 4. For example, n he case of he 10-hour me wndow wh bddng (bold sold lne), f capacy charges for load followng capacy are as hgh as 100$ / MW generaors can afford o charge flexble consumers f 50$ / MWh (a sgnfcan dscoun compared o he average 83.4 $/MWh) and perform as well as n he baselne scenaro. Fg. 5. Performance of proposal compared o he baselne case, for a fxed capacy prce of load followng reserve 100$ / MW. Fg. 4. Performance of couplng compared o he baselne case for a fxed capacy charge of rampng reserve 100$ / MW. hs approach s adoped n Fg. 4. he graphs n Fg. 4 plo combnaons of capacy charge and dscouned Fg. 5 s he counerpar of Fg. 4 for he case where 100$ / MWh and vares. In hs case, he ncremenal benefs from an addonal 8 hours of flexbly are greaer, and bddng n he hour-ahead marke s benefcal. Auhorzed lcensed use lmed o: Unv of Calf Berkeley. ownloaded on March 19,2010 a 18:24:49 E from IEEE Xplore. esrcons apply.

6 Agan, wh he excepon of one case he proposal s compeve o curren pracce, bu now o a greaer exen snce he couplng can be jusfed a a dscoun of f 50$ / MWh for capacy charges as low as 40$ / MW.. Oher Performance Mercs able 1 presens he dependence of some addonal performance mercs of he proposed couplng on he degree of consumer flexbly. he frs row of he able refers o he fracon of wnd power supply ha was acually used, raher han dscarded. hs power may have been allocaed eher o deferrable loads or o he marke. Ideally, hs value would be close o uny. he amoun of power whch s ulzed ncreases wh flexbly, however sgnfcan porons of power are dscarded even n he case of very flexble consumers. he second row refers o he fracon of ulzed wnd power whch was allocaed o deferrable loads, raher han o he marke. As loads offer greaer me wndows, he schedulng algorhm can ncorporae a greaer number of users (Fg. 3), resulng n an ncreased allocaon of wnd power o users raher han he marke. In conras o he case of 10-hour wndows where comparable quanes of wnd power are suppled o users and he marke n he case of 18-hour wndows he bulk of he power s suppled o users and only a small fracon s suppled o he marke when avalable wnd supply s excessvely hgh. he las row of he able refers o he fracon of deferrable consumpon whch s acually deferred, as measured n MWh. Ideally, hs fgure oo would be close o uny, snce would no be desrable o have consumers comm o a delay n her power consumpon whou he need o do so. Wh greaer me wndows more energy s deferrable, bu a he same me a relavely hgher quany of hs flexbly s ulzed. herefore, hs fgure also ncreases wh consumer flexbly bu never approaches uny. ABLE I PEFOMANCE OF HE SCHEULING ALGOIHM AS A FUNCION OF AVAILABLE POCESSING IME Processng me (hrs) Wnd power ulzaon (%) Fracon of wnd power suppled o deferrable loads (%) Fracon of deferrable consumpon whch was acually deferred (%) V. CONCLUSIONS In hs paper we propose a drec couplng beween wnd generaors and deferrable loads, n order o mgae he varably and randomness of wnd power supply. We argue ha by ulzng load flexbly and smulaneously bddng n he elecrcy marke wnd generaors can sgnfcanly mgae capacy coss resulng from he varable and random naure of wnd power supply. he proposal s compable wh exsng echnology, grd operaons and marke operaons, and s also jusfable on economc grounds. We have developed a heursc approach for achevng hs couplng whch confrms ha he economc ncenves for couplng wnd supplers wh flexble consumers exs. In fuure work we wll work on mprovng he performance of he algorhm whch we have developed and on accuraely esmang he economc savngs of he proposed couplng. VI. APPENIX A. Smulaon Assumpons and aa he smulaons were performed on a 5-day horzon. Hourahead energy prce daa were obaned from he CAISO Oass daabase (hp://oass.caso.com/) for he perod from 4/2/2007 o 4/6/2007. We used wnd speed daa whch s publcly avalable by NEL a hp://wnd.nrel.gov/publc/wwis/wnd_aa/ erms_of_use.hm. We assumed a oal of 1200 generaors dspersed n he sx locaons whn Calforna for whch he NEL daabase conans daa [11]. As prescrbed n [11], we used he power curve characerscs of Vesas V90 3 MW generaors wh a cu-n speed of 4 m/s, a cu-off speed of 25 m/s, and a speed of 15 m/s for maxmal oupu. Generaors locaed n he same se were assumed o have dencal oupus. We used daa for he me nerval from 4/2/2004 o 4/6/2004, ha s, for an dencal season as he prce daa. Unforunaely we could no fnd daa a he CAISO and NEL daabases whch overlapped. We beleve hs o be of no sgnfcance o our sudy, snce he NEL daabase s self a model oupu and n addon he mpac of wnd power generaon on Calforna marke prces n 2007 was no sgnfcan snce he negraon level n Calforna a he me was sll farly low. Incomng loads were assumed o arrve accordng o he same paern each day. A quarer of he daly loads arrved n he begnnng of he day (mdngh), half of he loads arrved n he eghh hour of he day (8 a.m.) and he remanng quarer of he loads arrved n he sxeenh hour (4 p.m.). Loads were assumed o be dencal, wh a power rang of 2 MW and an energy demand of 14 MWh. Hence, he ask of each load requres 7 hours o be compleed. I s worh nong ha he assumpon on he power rang of he loads can be relaxed o nclude smaller rangs, resulng n a beer objecve funcon value for he soluon bu a slower runnng me for he algorhm. he number of loads arrvng each day, as well as he me wndows offered by he loads, was vared n order o nvesgae he mpac of hese facors on algorhm performance. he number of daly loads vared beween 100 and 2000 loads, whle he avalable me wndow for compleng each ask vared beween 10 and 18 hours. Wnd forecass were based on a very smple forecasng model: W W W F 2 6 where F s he forecas Auhorzed lcensed use lmed o: Unv of Calf Berkeley. ownloaded on March 19,2010 a 18:24:49 E from IEEE Xplore. esrcons apply.

7 wnd power supply made n nerval for wo hours ahead. he forecas s smply a lnear exrapolaon of an hourly sample of wnd power generaon. he forecas s 12% (sandard devaon as a fracon of oal nsalled wnd capacy), whch s no sgnfcanly worse han he expeced forecasng error of 7-9% n he CAISO large scale negraon sudy [4]. B. Schedulng and Bddng Algorhm he problem posed n (1)-(8) can be nerpreed as an opmal nvenory conrol problem and varous echnques can be used o solve ncludng dynamc programmng, model predcve conrol or varous schedulng heurscs. In he smulaons, we have aaned a subopmal soluon o he problem by breakng n wo componens, load schedulng, and opmal bddng, whch are solved sequenally. he schedulng sub-problem s solved frs by use of he earles deadlne algorhm. Subsequenly, bddng n he marke s deermned by a very smple heursc: a each perod, he bd quany s 20% of he excess forecas supply: B ). F( 6( 1) 1) s he 0.2( F6( 1) 1 c6( 1) 1, I wnd forecas n he frs nerval of he I c ( 1) 1, - h hour and 6 s he aggregae supply of power o deferrable loads n he frs nerval of he - h hour. he amoun of wnd power suppled o he marke n nerval s hen he mnmum of he marke commmen and he acually avalable wnd r mn( W, B 2 ). ACKNOWLEGMENS he auhors graefully acknowledge he conrbuons of avd Hawkns, John Goodn and Waler Johnson from he Calforna ISO, as well as anel Greene from XEOX PAC for her helpful commens. [8] B. J. Krby, "Spnnng eserve from esponsve Loads", Oak dge Naonal Laboraory, N, ech. ep. ONL/M-2003/19, Mar [9] B. J. Krby, "emand esponse for Power Sysem elably: FAQ", Oak dge Naonal Laboraory, N, ech. ep. ONL/M-2006/565, ec [10]. Soshans, and W. Shor "Evaluang he Impacs of eal-me Prcng on he Usage of Wnd Generaon", he Economcs of Energy Markes, June 20-21, 2008, oulouse, France. [11] C. W. Poer,. Lew, J. McCaa, S. Cheng, S. Echelberger, and E. Grm "Creang he aase for he Wesern Wnd and Solar Inegraon Sudy (U.S.A.)", n Proc h Inernaonal Workshop on Large Scale Inegraon of Wnd Power and on ransmsson Neworks for Offshore Wnd Farms, pp VII. BIOGAPHIES Anhony Papavaslou s a hrd year Ph suden n he deparmen of Indusral Engneerng and Operaons esearch a UC Berkeley. He has receved a Bachelor s degree n Elecrcal Engneerng and Compuer Scence from he Naonal echncal Unversy of Ahens, Greece. Hs employmen experence ncludes nernshps a he Xerox Palo Alo esearch Cener and he Energy Economcs and Envronmenal Modelng Laboraory a he Naonal echncal Unversy of Ahens. Anhony has receved an honorable menon from he Lnk Foundaon Energy Fellowshp program and wo UC Berkeley suden awards for hs work on wnd power negraon. Shmuel Oren s Professor of Indusral Engneerng and Operaons esearch a he Unversy of Calforna, Berkeley. He s he Berkeley se drecor of PSEC. He has publshed numerous arcles on aspecs of elecrcy marke desgn and has been a consulan o varous prvae and governmen organzaons ncludng he Brazlan regulaory commsson, he Albera Uly Board, he Publc Uly Commsson, he Polsh sysem operaor and he Publc Uly Commsson of exas. He holds a Bachelor s and Maser s degree n Mechancal Engneerng and Maeral Engneerng from he echnon n Israel and he receved a Maser s and Ph degree n Engneerng Economc Sysems n 1972 from Sanford. r. Oren s a fellow of INFOMS, and a fellow of he IEEE EFEENCES [1]. Ackermann, Wnd Power n Power Sysems. Chcheser: John Wley and Sons, [2] E. Hrs and J. Hld, "Inegrang Large Amouns of Wnd Energy wh a Small Elecrc-Power Sysem", Bellngham, WA, and Xcel Energy, enver, CO, Apr [Onlne] Avalable: hp:// edu/ hepg/papers/hrs_hld_wndinegraonepor.pdf. [3] F. van Hulle, "Large Scale Inegraon of Wnd Energy n he European Power Supply: Analyss, ecommendaons and Issues", European Wnd Energy Assocaon, Brussels, [4] C. Louan, and. Hawkns, "Inegraon of enewable esources", Calforna Independen Sysem Operaor, CA, Nov [5] S. Borensen, M. Jaske, and A. osenfeld, "ynamc Prcng, Advanced Meerng and emand esponse n Elecrcy Markes", Cener for he Sudy of Energy Markes, CA, ech. ep. CSEMWP 105, [6] H. Chao, and. Wlson, "Prory Servce: Prcng, Invesmen and Marke Organzaon", he Amercan Economc evew, vol.77, No. 5, pp , ec [7]. Gedra, and P. Varaya, "Markes and Prcng for Inerrupble Conracs," IEEE rans. on Power Sysems, vol. 8, No.1, pp , Feb Auhorzed lcensed use lmed o: Unv of Calf Berkeley. ownloaded on March 19,2010 a 18:24:49 E from IEEE Xplore. esrcons apply.