Nishioka, K; Takamoto, T; Agui, T; K Author(s) Uraoka, Y; Fuyuki, T. Solar Energy Materials and Solar Cel 57-67

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1 JAIST Rposi ttps://dspac.j Titl Annual output stimation of concntr potovoltaic systms using ig-ffi InGaP/InGaAs/G tripl-junction sola on xprimntal solar cll's caract fild-tst mtorological data Nisioka, K; Takamoto, T; Agui, T; K Autor(s) Uraoka, Y; Fuyuki, T Citation Solar Enrgy Matrials and Solar Cl Issu Dat Typ Journal Articl Txt vrsion autor URL Rigts ttp://dl.andl.nt/10119/3391 Elsvir B.V., Knsuk Nisioka, Tat Takamoto, Takaaki Agui, Minoru Kani Uraoka and Takasi Fuyuki, Solar En and Solar Clls, 90(1), 2006, ttp:// Dscription Japan Advancd Institut of Scinc and

2 For corrspondnc Nam: Knsuk Nisioka Addrss: Japan Advancd Institut of Scinc and Tcnology, Asaidai 1-1, Tatsunokuci, Isikawa, , JAPAN Tl/Fax/ / / nisioka@jaist.ac.jp Annual Output Estimation of Concntrator Potovoltaic Systms Using Hig-Efficincy InGaP/InGaAs/G Tripl-Junction Solar Clls Basd on Exprimntal Solar Cll s Caractristics and Fild-Tst Mtorological Data Knsuk Nisioka 1, Tatsuya Takamoto 2, Takaaki Agui 2, Minoru Kaniwa 2, Yukiaru Uraoka 1 and Takasi Fuyuki 1 1 Graduat Scool of Matrials Scinc, Nara Institut of Scinc and Tcnology Takayama, Ikoma, Nara , Japan 2 SHARP Corporation Hajikami, Sinjo-co, Kitakatsuragi-gun, Nara , Japan ABSTRACT T tmpratur dpndncs of t lctrical caractristics of InGaP/InGaAs/G tripl-junction solar clls undr concntration wr valuatd. For ts solar clls, convrsion fficincy ( ) dcrasd wit incrasing tmpratur, and incrasd wit incrasing concntration ratio owing to an incras in opn-circuit voltag. T dcras in wit incrasing tmpratur dcrass wit incrasing concntration ratio. Morovr, t annual output of a concntrator systm wit a ig-fficincy tripl-junction cll is stimatd utilizing t xprimntal solar cll s caractristics obtaind in tis study and fild-tst mtorological data collctd for on yar at t Nara Institut of Scinc and Tcnology, and compard wit tat of a nonconcntration flat-plat systm. KEYWORDS: multijunction solar cll, tmpratur cofficint, concntration, annual output 1

3 1. INTRODUCTION Multijunction solar clls consisting of InGaP, (In)GaAs and G ar known as supr-ig fficincy and ar now usd for spac applications. Multijunction clls lattic-matcd to G substrats av bn improvd and tir convrsion fficincy as racd 31% (AM1.5G) owing to tir lattic-matcd configuration [1, 2]. Trfor, concntrator potovoltaic systms using ig-fficincy solar clls ar on of t important issus in t dvlopmnt of an advancd PV systm. T production cost of multijunction solar clls composd of III-V matrials is igr tan tat of Si solar clls. Howvr, t ncssary cll siz dcrass wit incrasing concntration ratio, tus rducing t total cost of concntrator systms will dcras. Hig-fficincy multijunction clls undr ig concntrations av bn invstigatd for trrstrial applications [3, 4]. Also, for low-concntration opration, multijunction clls av bn invstigatd for spac satllit us [5-7]. It is considrd tat t tmpratur of solar clls incrass undr ligt-concntrating oprations. Suc clls, if insulatd, ar potntially atd to 1400 o C at 500 suns concntration [8]. Tir convrsion fficincy dcrass wn tir tmpratur incrass [9, 10]. Toug passiv cooling mtods wit a at sink [11] or a at spradr [12] av bn favord for cost and rliability purposs, ty could not compltly supprss tis incras in tmpratur. Howvr, t tmpratur caractristics of InGaP/InGaAs/G tripl-junction solar clls undr concntration av not bn valuatd in dtail. In tis study, w av valuatd suc tmpratur caractristics undr concntration conditions. T annual output of a concntrator systm wit a ig-fficincy tripl-junction cll is stimatd utilizing fild-tst mtorological data collctd for on yar at t Nara Institut of Scinc and Tcnology (NAIST, Japan) and xprimntal cll caractristics 2

4 obtaind in tis study, and compard wit tat of a nonconcntration flat-plat systm. Tn, t possibilitis of concntrator systms ar discussd. 2. InGaP/InGaAs/G TRIPLE-JUNCTION SOLAR CELL Figur 1 sows a scmatic illustration of t InGaP/InGaAs/G tripl-junction cll valuatd in tis study. T subclls (InGaP junction, InGaAs junction and G junction of tis cll) wr grown on a p-typ G substrat using mtal-organic cmical vapor dposition. T In 0.49 Ga 0.51 P top subcll, In 0.01 Ga 0.99 As middl subcll, and G bottom subcll wr all lattic-matcd. T InGaP subcll was connctd to t InGaAs cll by a p-algaas/n-ingap tunnl junction. T InGaAs subcll was connctd to t G cll by a p-gaas/n-gaas tunnl junction. T lctrods wr fabricatd by vaporation. T lctrod consistd of a 5- m-tick Ag. T widt and pitc of t grid lctrods wr 7 m and 120 m (optimizd for ig-concntration oprations), rspctivly. 3. TEMPERATURE CHARACTERISTICS OF TRIPLE-JUNCTION SOLAR CELL UNDER CONCENTRATED LIGHT Ligt from t solar simulator (Ligt sourc: X lamp) was adjustd to 1 sun (AM 1.5G, 100 mw/cm 2 ), and focusd by a Frsnl lns. Concntration ratio was dtrmind by dividing sort-circuit currnt (I sc ) undr concntratd ligt by I sc undr 1 sun illumination. It was varid from 1 sun to 200 suns. T cll was attacd to a trmostat stag by a soldr wit ig at conductivity. T tmpratur dpndncs of t solar cll s caractristics wr invstigatd in t tmpratur rang from 30 C to 120 C. Tabl 1 sows t caractristics of t solar cll at 25 C for various concntration ratios (1 sun, 17 suns and 200 suns). Figurs 2(a)-(d) sow t tmpratur dpndncs of t caractristics ((a) opn-circuit voltag: V oc, (b) sort-circuit currnt: I sc, (c) fill factor: 3

5 FF and (d) convrsion fficincy: ) of t InGaP/InGaAs/G tripl-junction solar cll. Tabl 2 sows t tmpratur cofficints of ts caractristics (dx/: X mans V oc, I sc, FF and ) and t tmpratur cofficints normalizd by t sam paramtr at 25 C ((dx/)/x (25 C) 100). Figur 2(a) sows t tmpratur dpndnc of V oc. For all concntration ratios, V oc dcrasd wit incrasing tmpratur. T I-V caractristics of t solar cll ar xprssd by qv I = I xp 1 nkt 0 I sc, (1) wr I 0, q, n, k and T ar t saturation currnt, lmntary carg, diod idality factor, Boltzmann constant and absolut tmpratur, rspctivly. From q. (1), V oc (I=0) is givn by nkt I sc V = ln + 1 oc. (2) q I 0 From q. (2), it is considrd tat t tmpratur caractristic of saturation currnt (I 0 ) markdly influncs t tmpratur caractristic of V oc. T saturation currnt dnsity (J 0 ) is givn by J 0 D = q τ 1/ 2 n N 2 i A S S ( τ / D ) ( τ / D ) 1/ 2 1/ 2 cos( x sin( x p p / / D τ ) + sin( x D τ ) + cos( x p p / / D τ ) Dτ ) D + q τ 1/ 2 n N 2 i D S S ( τ / D ( τ / D ) 1/ 2 ) 1/ 2 cos( x sin( x n n / / D τ ) + sin( x D τ ) + cos( x n n / / D τ ), (3) Dτ ) wr n i is t intrinsic carrir concntration, N A and N D ar t accptor and donor concntrations, S and S ar t surfac-rcombination vlocitis in t n- and p-typ matrials, x p and x n ar t ticknsss of t p- and n-typ layrs, D and D ar t diffusion constants of lctrons and ols, and and ar t liftims of lctrons and 4

6 ols, rspctivly. J 0 strongly dpnds on T troug its proportionality to t squar of n i. n i is xprssd by n 2 i = 4M c M v ( E kt ) (2π kt / ) ( m m ) 3 / xp, (4) g wr M c and M v ar t numbrs of quivalnt minima in t conduction and valnc bands, is Planck s constant, and m * and m * ar t ffctiv masss of lctrons and ols, rspctivly. From qs. (2)-(4), it is found tat t dcras in V oc wit incrasing tmpratur ariss mainly from t cang in n i. J 0 incrass xponntially wit dcrasing 1/T, and V oc dcrass almost linarly wit incrasing T. D, D, and ar all tmpratur-dpndnt, and t tmpratur dpndnc of J 0 is sligtly influncd by tir tmpratur dpndncs. Morovr, V oc incrass wit incrasing concntration ratio. From q. (2), V oc incrass logaritmically wit radiation intnsity [13-16]. It is found tat t dcras in V oc wit incrasing tmpratur (dv oc /) gts smallr wit incrasing concntration ratio, as sown in Tabl 2. For t n + /p junction, J 0 is approximatd as J D q 0 τ 1/ 2 n N 2 i A. (5) D and in q. (5) ar all tmpratur-dpndnt. If D / is proportional to T, wr is a constant, tn from qs. (4) and (5) J 0 T (3+ γ / 2) E ( T xp kt g ), (6) wr E g (T) is t band-gap nrgy at T and t tmpratur dpndnc xponnt (3+ /2) is from t tird-ordr dpndnc of n i 2 and -ordr dpndnc of D /. 5

7 T variation in bandgap wit absolut tmpratur is xprssd as [17] wr and ar constants. 2 αt Eg ( T) = Eg (0), (7) T + β T diffrntiation of q. (2) wit rspct to T and t substitution of band-gap voltag (V g (T)) for E g (T)/q rsult in dv Vg ( T) Voc + (3 + γ / 2) V = T + V 1 I dv ( T oc T disc 1 g ) T + sc VT, (8) wr V T, t trmal voltag, is substitutd for kt/q. T scond trm in q. (8) can b nglctd compard wit t first trm. Trfor, t tmpratur dpndnc of V oc is approximatd as [10] dv Vg ( T) Voc + (3 + γ / 2 V = T oc ) T. (9) T dominant part of tis quation is (V g (T)- V oc ), and w can s tat t tmpratur dpndnc of V oc is smallr for solar clls wit a larg V oc. Trfor, t dcras in V oc wit incrasing tmpratur dcrasd bcaus of t incras in V oc wit incrasing concntration ratio. Figur 2(b) sows t tmpratur dpndnc of I sc. T incras in minority-carrir diffusion lngt and t sift in optical absorption dg nrgy wit incrasing tmpratur produc a small incras in I sc. An incras in I sc wit incrasing tmpratur rsults from t cang in absorption cofficint wit tmpratur. Figur 2(c) sows t tmpratur dpndnc of FF. FF dcrasd wit incrasing tmpratur, and incrasd wit incrasing concntration ratio. FF at 200 suns is smallr tan tat at 17 suns bcaus of t influnc of sris rsistanc. T tmpratur dpndnc of FF is mainly drivd from t tmpratur dpndnc of V oc. 6

8 Figur 2(d) sows t tmpratur dpndnc of. T tmpratur dpndnc of is mostly affctd by t tmpratur dpndnc of V oc. For all concntration ratios, dcrasd wit incrasing tmpratur, and incrasd wit incrasing concntration ratio bcaus of t incras in V oc. T normalizd tmpratur cofficint of t convrsion fficincy of t InGaP/InGaAs/G tripl-junction solar cll ((d /)/ (25 C) 100) is %/ o C at 1 sun, as sown in Tabl 2. On t otr and, t normalizd tmpratur cofficint of t convrsion fficincy of a crystallin-silicon solar cll is -0.4 or -0.5%/ o C undr 1 sun opration. Tis indicats tat InGaP/InGaAs/G tripl-junction solar clls av an advantag ovr crystallin-silicon solar clls undr ig-tmpratur conditions. Morovr, t dcras in wit incrasing tmpratur dcrass wit incrasing concntration ratio. Ts rsults indicat tat concntration oprations av bnficial ffcts on ig-tmpratur oprations. 4. ESTIMATION OF ANNUAL OUTPUT A nonconcntration flat-plat 50-kW PV systm was installd at NAIST. Tis systm automatically masurd mtorological data and oprating condition data in 200 cannls at an intrval of 6 sc, and t data wr stord in a databas. A pyrliomtr, a pyranomtr, a spctroradiomtr, a rain gaug, a wind spd mtr, and a trmomtr wr usd to masur mtorological data. In tis study, t annual data from August 1999 to July 2000 wr adoptd. Figur 3 sows t diffus irradiation and dirct irradiation for ac mont. T dirct irradiation was approximatly alf of t global irradiation (t sum of diffus irradiation and dirct irradiation). Nonconcntration flat-plat systms can utiliz bot diffus and dirct irradiations, wil concntrator systms can utiliz only dirct irradiation. Tus, it is important to compar t annual output of concntrator systms composd of suprigly 7

9 fficint InGaP/InGaAs/G tripl-junction solar clls wit tat of t nonconcntration systms composd of Si solar clls. In tis study, t annual output nrgis of a 17 sun concntrator systm and a 200 sun concntrator systm pr 1 m 2 irradiation ara wr stimatd basd on t xprimntal cll caractristics (dscribd in t prvious sction) and fild-tst mtorological data (obsrvd at NAIST). For comparison wit tat of a flat-plat systm, t annual output nrgy of a nonconcntration flat-plat systm composd of singl-crystallin Si solar clls pr 1 m 2 irradiation ara was stimatd. T output nrgy of a flat-plat PV systm is xprssd by [18] P out K T K f P g s, (10) wr P out is t output nrgy, P g is t global irradiation (diffus irradiation + dirct irradiation), s is t undr t standard tst conditions (100-mW/cm 2 irradiation, 25 o C modul tmpratur, and AM1.5 global spctrum), and K f is t corrction cofficint for all factors xcpt tmpratur. In tis brif stimation, K f was assumd to b 1. Wn t standard tmpratur is st to 25 o C, t corrction cofficint for tmpratur K T is K T =1 + a (T m - 25), (11) wr T m [ o C] is t modul tmpratur and a is t normalizd tmpratur cofficint ((d /)/ (25 C) 100). W obtaind P g and T m from fild-tst data. A normalizd tmpratur cofficint of -0.4%/ o C and a of 17.4% (world-rcord modul fficincy for Si solar clls) at 25 o C wr usd for s in qs. (10) and (11). T output nrgy of a concntrator PV systm is xprssd by P out K T K f P d s, (12) wr P d is t dirct irradiation. Wn t standard tmpratur is st to 25 o C, t corrction cofficint for tmpratur K T is K T = 1 + a (T m(con.) - 25), (13) 8

10 wr T m(con.) [ o C] is t modul tmpratur for t concntrator systm. W obtaind P d from fild-tst data. For concntrator PV systms, K f is mainly dtrmind by optical loss. K f for t 400 sun concntrator systm using a Frsnl lns is [19]. Trfor, w usd tis valu as K f. T tmpratur of t concntrator modul (T m(con.) ) is xprimntally givn by [20] T m(con.) = T m + 17 P d. (14) A tmpratur cofficint of %/ o C and a s of 34.4% masurd xprimntally (obtaind in tis study) wr usd for t stimation of t 17 sun concntrator systm. A tmpratur cofficint of %/ o C and a s of 36.7% masurd xprimntally (obtaind in tis study) wr usd for t stimation of t 200 sun concntrator systm. T tmpratur cofficint and s dscribd in tis study ar t data for 100 mw/cm 2 dirct irradiation. In an actual nvironmnt, t dirct irradiation is almost always lss tan 100 mw/cm 2. It is considrd tat, in most cass, t tripl-junction clls of 17 sun and 200 sun concntrator systms oprat at lss tan 17 sun and 200 sun concntration ratios. Trfor, t tmpratur cofficint and s wr corrctd dpnding on dirct irradiation by intrpolating t data in Tabl 1 and 2. Using ts mtods, t annual output of t flat-plat and concntrator PV systms wr stimatd as sown in Fig. 4. T stimatd annual output of t concntrator systms is igr tan tat of t nonconcntration systm. T annual output of t 200 sun concntrator systm is igr tan tat of t 17 sun concntrator systm. Altoug t systm bcoms incrasingly mor complx, concntrator systms wit a igr concntration ratio will attain xcllnt prformanc bcaus of its incrasing cll fficincy and suprior tmpratur cofficint. Morovr, a igr output nrgy can b xpctd in ig dirct-irradiation aras suc as Miami (USA) or t Grat Sandy Dsrt (Australia) [21]. 9

11 5. CONCLUSIONS T tmpratur dpndncs of t lctrical caractristics of InGaP/InGaAs/G tripl-junction solar clls undr concntration wr valuatd. T tmpratur dpndnc of is mostly affctd by t tmpratur dpndnc of V oc. dcrasd wit incrasing tmpratur, and incrasd wit incrasing concntration ratio bcaus of t incras in V oc. T normalizd tmpratur cofficints of t convrsion fficincy ((d /)/ (25 C) 100) of t InGaP/InGaAs/G tripl-junction solar cll is %/ o C at 1 sun and %/ o C at 200 suns. T dcras in wit incrasing tmpratur dcrass wit incrasing concntration ratio. Ts rsults indicat tat concntration oprations av bnficial ffcts on ig-tmpratur oprations. Morovr, t annual output of a concntrator systm wit a ig-fficincy tripl-junction cll is stimatd using t xprimntal caractristics of solar cll obtaind in tis study and fild-tst mtorological data collctd for on yar at NAIST, and compard wit tat of a nonconcntration flat-plat systm. W found tat t annual output of concntrator systms composd of ig-fficincy InGaP/InGaAs/G tripl-junction solar clls was igr tan tat of flat-plat systms composd of Si solar clls, bcaus of t ig fficincy and suprior tmpratur cofficint of t formr systms. ACKNOWLEDGMENTS Tis work was partially supportd by t Nw Enrgy and Industrial Tcnology Dvlopmnt Organization undr t Ministry of Economy, Trad and Industry, Japan. 10

12 REFERENCES 1) J. M. Olson, S. R. Kurtz and A. E. Kibblr: Appl. Pys. Ltt. 56 (1990) ) T. Takamoto, T. Agui, E. Ikda and H. Kurita: Proc. t 28t IEEE Potovoltaic Spcialists Conf., Ancorag, (2000) ) H. L. Cotal, D. R. Lillington, J. H. Ermr, R. R. King and N. H. Karam: Proc. 28t IEEE Potovoltaic Spcialists Conf., Ancorag, (2000) ) A. W. Btt, F. Dimrot, G. Lang, M. Musl, R. Bckrt, M. Hin, S. V. Risn and U. Scubrt: Proc. 28t IEEE Potovoltaic Spcialists Conf., Ancorag, (2000) ) C. J. Gldrloos, C. Assad, P. T. Balcwicz, A. V. Mason, J. S. Pow, T. J. Prist and J. A. Scwartz: Proc. 28t IEEE Potovoltaic Spcialists Conf., Ancorag, (2000) ) M. J O Nill, A. J. McDanal, M. F. Piszczor, M. I. Esknazi, P. A. Jons, C. Carrington, D. L. Edwards and H. W. Brandorst: Proc. 28t IEEE Potovoltaic Spcialists Conf., Ancorag, (2000) ) D. D. Krut, G. S. Glnn, B. Bailor, M. Takaasi, R. A. Srif, D. R. Lillington and N. H. Karam: Proc. 28t IEEE Potovoltaic Spcialists Conf., Ancorag, (2000) ) K. Araki, H. Uozumi and M. Yamaguci, Proc. t 29 t IEEE Potovoltaic Spcialists Conf., Nw Orlans, (2002) ) S. M. Sz, Pysics of Smiconductor Dvics, (Wily-Intrscinc Publication), (1981) ) A. L. Farnbruc and R. H. Bub, Fundamntals of Solar Clls, (Acadmic Prss, Inc.), (1983) ) M. J. O`Nill t al., Proc. 28t IEEE Potovoltaic Spcialists Conf., Ancorag, (2000) ) V. D. Rumyantsv t al., Proc. 28t IEEE Potovoltaic Spcialists Conf., Ancorag, 11

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14 Fig. 1. Scmatic illustration of InGaP/InGaAs/G tripl-junction solar cll. Fig. 2. Tmpratur dpndnc of caractristics ((a) V oc, (b) I sc, (c) FF and (d) convrsion fficincy) of InGaP/InGaAs/G tripl-junction solar cll. Fig. 3. Diffus irradiation and dirct irradiation for ac mont monitord at NAIST. Fig. 4. Estimatd annual output nrgis of concntrator PV systm wit tripl-junction cll and flat-plat PV systm wit Si cll. 13

15 Tabl 1 Cll caractristics at 25 C for various concntration ratios. V oc (V) J sc (ma) FF (%) 1sun suns suns

16 Tabl 2 Tmpratur cofficints of InGaP/InGaAs/G tripl-junction cll s caractristics (dx/: X mans V oc, I sc, FF and ) and tmpratur cofficints normalizd by t sam paramtr at 25 C ((dx/)/x (25 C) 100). V dv oc [V/ o C] 1 o oc(25 C) dv oc sun 17 suns 200 suns I [%/ o C] di sc [ma/ o C] 1 o sc(25 C) 1 FF di sc 100 [%/ o C] dff [/ o C] o (25 C ) dff 100 [%/ o C] dη [%/ o C] 1 η o (25 C) dη x x x x x x [%/ o C] 15

17 Fig. 1 K. Nisioka 16

18 (a) sun 17 suns 200 suns V oc (V) Tmpratur ( o C) 1600 (b) 1400 I sc (ma) sun 17 suns 200 suns Tmpratur ( o C) Fig. 2. K. Nisioka 17

19 (c) sun 17 suns 200 suns FF Tmpratur ( o C) 38 (d) Convrsion Efficincy, η (%) sun suns 200 suns Tmpratur ( o C) Fig. 2. K. Nisioka 18

20 Ammout of Irradiation (kw/m 2 ) Jan Fb Mar Apr May Jun Diffus irradiation Dirct irradiation Jul Aug Sp Oct Nov Dc Fig. 3 K. Nisioka 19

21 Annual Output Enrgy (kw/m 2 ) Flat-plat systm wit Si cll 17 sun Concntrator systm wit tripljunction cll 200 sun Concntrator systm wit tripljunction cll Fig. 4 K. Nisioka 20