An Objective Measure of Interconnection Usage for High Levels of Wind Integration

Transcription

1 An Objectve Measure of Interconnecton Usage for Hgh Levels of Wnd Integraton Yoh Yasuda Kansa Unversty Osaka, Japan Ana Estanquero LNEG Lsbon, Portugal Ncolaos Antono Cutululs DTU Lyngby, Denmark Emlo Gómez Lázaro Unversdad de Castlla-La Mancha Albacete, Span Junj Kondoh Tokyo Unversty of Scence Tokyo, Japan Mchael Mllgan NREL Colorado, USA Hannele Holttnen VTT Espoo, Fnland Antje Orths Energnet.dk Frederca, Denmark J. Charles Smth UVIG Vrgna, USA Abstract Ths paper analyzes selected nterconnectors n Europe usng several evaluaton factors; capacty factor, congested tme, and congeston rato. In a quanttatve and objectve evaluaton, the authors propose to use publcally avalable data on maxmum net transmsson capacty (NTC) levels durng a sngle year to study congeston rates, realzng that the capacty factor depends upon the chosen capacty of the selected nterconnector. Ths value wll be referred to as "the annual maxmum transmsson capacty (AMTC)", whch gves a transparent and objectve evaluaton of nterconnector usage based on the publshed grd data. Whle the method s general, ts ntal applcaton s motvated by transfer of renewable energy. Keywords- wnd power; grd ntegraton; flexblty; nterconnector; congeston tme; duraton curve ABBREVIATIONS AND SYMBOLS A. Abbrevatons and Acronyms AMTC Annual Maxmum Transmsson Capacty ENTSO-E European Network of Transmsson System Operators for Electrcty EU European Unon EWIS European Wnd Integraton Study IEC Internatonal Energy Agency NTC Net Transmsson Capacty TBCF Transmsson B-lateral Capacty Factor TCF Transmsson Capacty Factor TEBR Transferred Energy Balance Rato TRM Transmsson Relablty Margn TSO Transmsson System Operator TTC Total Transmsson Capacty B. Abbrevatons (Name of Natons and Areas) DE Germany DKE Denmark East DKW Denmark West ES Span FR France GB Great Brtan IT Italy NL The Netherlands SE Sweden NO Norway C. Symbols CF + [%] TCF (n export drecton) CF [%] TCF (n mport drecton) CF BL [%] TBCF C + AMTC [MW] AMTC (n export drecton) C AMTC [MW] AMTC (n mport drecton) C + NTC [MW] NTC (n export drecton) C NTC [MW] NTC (n mport drecton) P + [MWh/h] exported physcal energy flow per hour P [MWh/h] mported physcal energy flow per hour R balance [%] TEBR R C [%] congeston rato T C [h] congested tme I. INTRODUCTION For hgh levels of grd ntegraton of varable renewable energy ncludng wnd power, the flexblty of the grd wll become ncreasngly mportant. Four mportant components of grd flexblty are () dspatchable generaton, () energy storage, () nterconnectors and (v) demand sde management [1]. In ths paper, the authors wll

2 focus on the thrd component; nterconnectors, comparng and analyzng several European nterconnectors. In the European and US grd, some reports have ponted out that there are bottlenecks n selected nterconnectors used to transfer varable renewable energy; ths s one barrer to ncreasng wnd penetraton levels. Ths paper analyzes selected nterconnectors n Europe, usng several evaluaton factors; capacty factor, congested tme, and congeston rato. In a quanttatve and objectve evaluaton, the authors propose several new defntons for the capacty factor of nterconnectors, whch are based on transparent publshed data of net transmsson capacty (NTC). Ths s because the capacty factor depends upon the capacty of the chosen nterconnector. Although the nstalled transmsson capacty looks lke the most mpartal ndcator, t s not always easy to get the latest data from TSOs. NTC s the most transparent parameter n Europe, because t s publshed by every TSO and ENTSO-E. However, t s not a constant value but a varable across the year. Also, thermal capacty s not always transparent because not all TSOs release the latest value. Therefore, a new factor, "the annual maxmum transmsson capacty (AMTC)", based on the annual net transmsson capacty, s defned n ths paper. Ths factor s transparent and objectve based on the publshed grd data. Defntons of congested tme and congeston rato are also prepared usng the AMTC, as further descrbed n Secton II. Usng the analyss as descrbed below, the potental usage of the exstng nterconnectors can be nvestgated to examne the opportunty for mproved flexblty. Synchronous wnd plant output tme seres data wll be requred for a detaled analyss. II. DEFINITION OF EVALUATION METHOD FOR INTERCONNECTION USAGE To evaluate how to measure the usage of nterconnectors quanttatvely and objectvely, the authors propose the followng ndcators; (1) annual maxmum transmsson capacty, (2) capacty factor, (3) congeston tme and (4) congeston rato. In ths secton, defntons of each ndcator wll be ntroduced. A. Annual Maxmum Tranmsson Capacty What s transmsson capacty? It s not easy to concsely answer the queston. There are numerous sources of uncertanty regardng the determnaton of the transmsson capacty [2]. Some TSOs do not publsh nstalled capacty (thermal capacty) of ther nterconnectors. ENTSO-E had publshed an annual Statstcal Yearbook [3] n the past, but no updated verson has been publshed snce 211. Fortunately, net transmsson capactes (NTCs) for all nternatonal nterconnectors n Europe are publshed on the ENTSO-E Transparence Platform [4]. For each border or set of borders, the NTC s determned ndvdually by all adjacent countres through negotaton between the nvolved TSOs. As the NTC vares dynamcally from the grd relablty vewpont, sets of NTCs are publshed as hourly (day-ahead), monthly and annual values by every TSO and ENTSO-E. On the ENTSO-E s web ste Transparency Platform, sets of day-ahead hourly NTCs on every nternatonal nterconnector on the borders between member countres can be found [4]. The calculaton method of the NTC s not unversal and s not fully clarfed by many TSOs. Normally, the total transmsson capacty (TTC), whch means the maxmum capacty to satsfy grd relablty, s determned by a certan method. Then, the NTC s calculated by subtracton of the transmsson relablty margn (TRM) from the TTC to provde a margn of safety. However, the TTC and TRM are not generally publcly avalable. In ths report, the authors defne a new ndcator annual maxmum transmsson capacty (AMTC) to evaluate nterconnector usage quanttatvely and objectvely from transparent NTC data. Usng a set of the publshed NTC data, the AMTC, or maxmum avalable NTC n each drecton over the course of the year, s defned as follows; The calculated AMTC can be consdered nearly the same as the thermal capacty of the selected nterconnector. The mportant pont s that an objectve ndcator can be obtaned from transparent publshed data. In ths way, t s possble to determne capacty factor and congested tme quanttatvely and objectvely. B. Transmsson B-lateral Capacty Factor The capacty factor s normally an ndcator that evaluates the performance of a generator. In ths paper, the authors try to gve a smlar defnton for an nterconnector. Whle the capacty factor of a generator s calculated on the bass of rated (nomnal) power, transmsson capacty factor (TCF) of an nterconnector s determned on the bass of the above dscussed AMTC n each drecton: 876 () P + CF + 1 (3) C + AMTC () P CF 1 (4) C AMTC 876 The transmsson b-lateral capacty factor (TBCF), s smply defned as the sum of the transmsson capacty factors n the export and mport drectons: CF BL CF + + CF (5) Here, the TBCF of the gven nterconnector s calculated as the sum of the TCBs n both export/mport drectons. However, t never exceeds 1% because only one of the capacty factor parameters can have a non-zero value at any gven tme. The metrc calculates the hourly avalable capacty and normalzes the average. The newly defned TBCF of an nterconnector can be consdered as a useful ndcator to evaluate how much the selected nterconnector s used n a gven year and how much room there s to accept more renewables. (1) (2)

3 Fgure 1. Defntonn of congested tme. [5] C. Congested Tme There s another ndcator that evaluates nterconnector usage; congested tme, as can be seen n the European Wnd Integraton Study (EWIS) report [5]. In the EWIS report, the congested tme s calculated as shown n Fgure 1. However, there s no descrpton about a base transfer capacty n the report. In our paper, usng the proposed AMTC, a congested tme can be clearly defned as; C T [h]= countf P + () C AMTC D. Congeston Rato It s not dffcult to calculate a congeston rato f the congested tme can be determned objectvely. The defntons based on the AMTC are respectvely gven as followng; R C T C ( ( +countf ( P + ) () C AMTC )) (6)) (7)) Regardng the congestonn rato, an earler study done n the Western US n 23 used a dfferent congeston metrc. It s based on the percentagee of tme that a gven nterface s wthn 1% of ts maxmum rated capacty [6], [7]. E. Transferred Energy Balance Rato Whle some nterconnectors are operated wth a balance between exported and mported energy, others seems to be domnated by export or mport only. Ths usage off the nterconnector may gve some ndcaton of future potental to accept more renewables. To evaluate these stuatons, we proposed a new ndcator; transferred energy balance rato (TEBR) R balance as follows: III. COMPARISON C ANALYSIS ON MAJOR M INTERCONNECTORS IN EUROPEE In ths chapter, comparson analyss on several major nterconnectors nn Europe are e performed usng the above defned ndcators. A. Selected Interconnectors Here, we evaluate the followng ndcators; () AMTC, () capacty factor, () congested tme, (v) congeston rato, and (v) TEBR, aganst the followng selected nternatonal nterconnectors nn Europe as shown s n Fgure DKWW > NO (DC)) 2. DKWW > SW (DC)) 3. DKWW > DE (AC)) 4. DKE > SE (AC)) 5. DKE > DE (DC)) 6. FR > DE (AC)) 7. FR > GB (DC)) 8. FR > IT (AC)) 9. FR > ES (AC)) 1. NO > NL (DC)) 11. NL > GB (DC)) The drecton (>) ndcates the export (postve) drecton of the energy transfer n each nterconnector. All the dataa on the selected nterconnectors were obtaned from thee ENTSO-E Transparency Platform [4]. In the current analyss, we downloaded a set of hourly cross- border physcal flows f P + () [MWh/h] and P () [MWh/h] and day-ahead hourly NTC C N NTC [MW] durng 1st January 213 to 31st December 213 (876 hourly data per data set). B. Qualtatve Analyss usng Duraton Curves Fgure 3 shows varous duraton curves of physcal flows n the selected nterconnectors.. A quck comparson clearly shows the varety of usage of ndvdual nterconnectors. For example, some nterconnectorss (lke DKW > NO, FR > GB and NO > NL) have flat horzontal lnes at the left-top and/ /or rght-bottom corners on ther duraton curves. It denotes that the nterconnector s fully used n some degree. Another group (e.g. DKW > DE, FR > DE and IE > GB) shows steep peaks at the left-top and/or rght-bottom corners, whch means the nterconnector s not fully used. R balance 876 P P + () ()+ 876 P 876 P () 1 If export and mport are balanced, Rbalance b become zero accordng to the above equaton, whereass t becomes 1% f ether export or mport domnates. () (8) Fgure 2. Selected S man nterconnectors n Europe.

4 1, DKW>NO DKW>SE -1, (1) DKW > NO (2) DKW > SE 1,8 1,7 9-9 DKW>DE DKE>SE -1,8-1, (3) DKW > DE (4) DKE > SE 6 4,5 3-3 DKE>DE 3, 1,5-1,5-3, FR>DE -6-4, (5) DKE > DE (6) FR > DE 2, 3, 1, -1, FR>GB 2, 1, -1, -2, FR>IT -2, -3, (7) FR > GB (8) FR > IT Moreover, some graphs show clearly unbalanced curves between the upper quadrant (export) and lower quadrant (mport). From the qualtatve observaton of the above characterstcs of the duraton curves, four groups as shown n Table I can be categorzed. The groups by row are classfed by whether the shape of the curve s convex (facng upwards) or concave (facng downwards), whereas those n column are classfed by whether they are symmetrc or not. Fgure 3. Duraton curve of physcal flows n the selected nterconnectors. A convex characterstc n the duraton curve ndcates that the gven nterconnector s heavly loaded, whch means there s lttle ablty to accept more renewables. In contrast, a concave curve denotes a less heavy use of the nterconnector, ndcatng t has sgnfcant potental to accept more renewable energy and enhance flexblty.

5 1,5 1, , -1, , , (9) FR > ES (1) NL > NO (11) NL > GB FR>ES NO > NL NL > GB Fgure 3. Duraton curve of physcal flow n the selected nterconnectors. (cont.) TABLE I. QULALITATIVE CLASSIFICATION OF DURATION CURVES OF SELECTED INTERCONNECTORS (a) Symmetrc (b) Asymmetrc (I) Concave (1) DKW>NO (2) DKW>SE (5) DKE>DE (7) FR>GB (1) NO>NL (11) NL>GB (II) Convex (3) DKW>DE (4) DKE>SE (9) FR>ES (6) FR>DE (8) FR>IT C. Quanttatve Analyss usng the proposed Indcators To confrm these characterstcs dentfed vsually from the duraton curves, we employ the quanttatve ndcators defned n Secton II. Table II shows the calculated results of ATMC, TBCF, congested tme, congeston rato, and TEBR of the selected nterconnectors as determned from Equatons (1) - (8). Fgure 4 llustrates bar graphs that summarze the nformaton gven by Table II, where TBCF and congeston ratos based on AMTC are compared. Fgure 5 plots the congeston rato aganst the TBCF for the selected nterconnectors. The data can be dvded nto two groups. These two groups correspond to the classfcaton Groups I and II accordng to the qualtatve characterstcs n the duraton curve dscussed n Table 1 above. Another comparson can be made by plottng the TBCF aganst the TEBR. From Fgure 6, four groups clearly can be recognzed n the graphs. These groups correspond to Groups Ia, Ib, IIa and IIb, as dscussed n Table I. There s one excepton, the nterconnector between France and Germany (FR >DE), whch cannot be categorzed from the duraton curve because the ATMCs n both drectons are orgnally asymmetrcal. Although t s dffcult to dstngush nto whch group the gven nterconnector should be categorzed, t s easy to classfy usng the quanttatve ndcators proposed n ths paper. TABLE II. EVALUATION ON INTERCONNECTOR USAGE USING PROPOSED INDICATORS (213) AMTC CAPACITY FACTOR Congested Congeston TEBR Interconnector lnk Tme Rato R balanced C + AMTC C AMTC CF T C [h] R C [%] [%] [MW] [MW] [%] CF [%] CF BL [%] equatons (1) (2) (3) (4) (5) (6) (7) (8) DKW > NO DC 1, 1, DKW > SE DC DKW > DE AC 1,78 1, DKE > SE AC 1,7 1, DKE > DE DC , FR > DE AC 1,8 3, , FR > GB DC 2, 2, , FR > IT AC 2,75 1, FR > ES AC 1,3 1, NO > NL DC , NL > GB DC 1,16 1, ,

6 Ths paper proposed a novel ndcator, annual maxmum transmsson capacty (AMTC), for quanttatve and objectve evaluaton of nterconnector usage for hgh penetraton of renewables. Usng a very transparent parameter,.e. a set of day-ahead hourly NTCs, the AMTC can be calculated n an objectve fashon. The authors also propose defntons for transmsson b-lateral capacty factor (TBCF), congested tme, congeston rato and transferred energy balance rato (TEBR) usng the abovementoned AMTC. Usng these objectve and quanttatve ndcators, the usage of the selected nterconnectors n Europe was evaluated. From the correlaton of the TBCF, congeston rato and TEBR, t s clear that the selected nterconnectors can be categorzed nto several groups that correspond to the qualtatve characterstcs of the duraton curves gven from the physcal energy flow data. It s hoped that the proposed ndcators wll help to evaluate any nterconnector to determne f addtonal capacty s avalable to enhance grd flexblty and enable transfer of addtonal renewable energy. Congeston rato [%] Fgure 4. TBCF and congeston rato n the selected nterconnectors. IV. CONCLUDING REMARKS 1 8 Group (I) Group (II) TBCF [%] REFERENCES [1] IEA: "Harnessng Varable Renewables - A Gude to the Balancng Challenge", OECD/IEA (211) ng_varable_renewables211.pdf [2] J. Matevosyan: Wnd Power n Areas wth Lmted Transmsson Capacty, Chapt. 2 n WIND POWER IN POWRE SYSTEMS, 2 ND EDITION ed. by T. Ackermann, Wley 212. [3] ENTSO-E: Statstcal Year Book 211 (212) [4] ENSTO-E web ste: Transparency Platform [5] European Wnd Integraton Study (EWIS), Fnal report (21) [6] The Seams Steerng Group Western Interconnecton (SSG-WI): Framework for Expanson of the Western Interconnecton Transmsson System (23) [7] M. Mlgan and D. P. Berger: A Prelmnary Analyss and Case Study of Transmsson Constrants and Wnd Energy n the West, NREL Conference Paper NREL/CP (25) Fgure 5. Correlaton between TBCF and congeston rato. 1 8 Group (I) TBCF [%] 6 4 Group (II) 2 Group (a) Group (b) tranferred energy balance rato [%] Fgure 6. Correlaton between TEBR and TBCF.