NGHIEN C U U - T R A G D P I
XfiC DINH Tfll TRONQ TRONG THIET KE CO KHI HE THONG NfiNG LtfOfNG M^T T R O I TCT XOfiY
Nguyen Van D^\ Hoang Tiln Dat', L^ Duy Hdi^ Nguyin Hodng GiangS Van Cdng Bich' 'TrUdng Dai hpc Ky thuat Cdng nghiep, Dai hpc Thai Nguyen
^Trudng Cao ding Kinh te Ky thuat, Dai hgc Thai Nguyen, 'TrUdng Cao dang Cdng nghi?p Hue
T 6 M TAT
Bdi bdo ndy trinh bdy cdch xdc dinh tdi trgng cho bdi todn thiet keket cau cd khi cua he thong ddn ndng lUdng mat trdi tU xoay theo hUdng tia sdng. Mo men cdn thiet dexoay ddn dUdc xdc dinh de thdng sdc } qudn tinh, mo men ma sdt vd mo men cdn cua gid. Md hinh tinh todn dUdc xdy dUng nham tinh todn cong suat cdn thiet dexoay ddn tiiy thugc cong suat phdt dien yiu cau. Mo hinh co thesddun^
de tinh todn thiet kecdc he thong ndng lUdng mat trdi tU xoay khdc nhU bi'p ndu dn ndng lUdng mat trdi, dgng cd ndng lUdng mat trdi... cdn xoay theo hUdng tia sdng.
ABSTRACT
This paper presents a method to determine loads for mechanical design of solar trackers. Moment needed to operate the system following the sun is calculated from inertial, frictional moments and wind load acting on the moving parts. A calculation model was built to determine the power needed to operate the moving parts based on required output powers. The model can be used to design mechanical structures of solar systems such as solar cells, solar cookers and solar dish engines tracking the sun path.
TU khda: Ndng lUdng tdi tao, dgng lUc hgc, tdi trgng, truyen ddn cd khi.
E 9 TAP CHi CO KHi VIET NAM • Sd 4 (Thdng 4 nam 2012)
NGHIEN CUfU-TRAOeOl
1. GlCfl THifiU
Khai thac nang lugng tdi tao dang la van de dUpc quan tam nghien cdu vd ang dpng, nham dap dng yeu cau nang lUpng ngay cang cao cua con ngUdi, yeu cau giam thieu d nhi^m mdi trudng va giai quyet khd khan ve khd nang ddp ang cua nang lUpng truyen thdng. Cac nghien cUu da cho thay, chi can thu lai 10% nang lUpng mat trdi chieu tren dien tich 0,16% be mat trdi dat, da cd the cung cap 20 TW nang lUpng, gap ddi nang lUpng cd dUgc ta dot nhien li?u hda thach truyen thdng [1]. Nang lUpng mat trdi dang dUpc nghien cUu, khai thac bdng each bien ddi sang nang lUpng dien (pin mat trdi, ddng ca mat trdi), sa dung phan nhiet nang cua dnh ndng (bep nau mat trdi, binh nUdc ndng). Xoay he thdng ludn hudng ve phia mat trdi Id mdt cdch tiep can don gidn de nang cao hieu qud sa dung, thu hoi nhanh vdn dSu tu cho cac he thdng khai thac nang lugng mat trdi [ 1 -6]. Hang tram nghien cdu va ang dung da trien khai vdi muc dich xoay he thdng thu nang lugng theo hudng mat trdi [1]. Tuy vay, cho den nay, van chUa cd tdi lieu ndo trinh bdy ve tinh toan thiet ke ca khi cho he thong nang lUpng mat trdi tu xoay. Mdt vai cdng bd [2-4] da gidi thieu ket cau cd khi nhUng chi cd tinh chat nguyen ly; cac thdng so dugc chpn chUa dUa tren tinh todn theo tai trpng, do vay khd cd khd nang dp dung cho cdc trudng hpp thiet ke khdc.
Bdi bao ndy trinh bay md hinh tinh todn tdi trpng phuc vu cho thi^t ke be thdng ca khi cho ddn nang luang mat trdi tU xoay. Cdng suat xoay dan duoc xac dinh dUa tren khdi lUflng, quan tinh, ma sat cua he thdng va lUc cdn gid. Cdc thdng sd I ndy dugc tinh todn nhU cdc hdm phu thudc cdng suat mong mudn cua he thdng. Md hinh todn hpc
• dupc xdy dung cd the ap dung cho nhieu dang ket cau khdc nhau nhU ddn pin mat trdi (Solar photo- vohaic cells), Up nau (solar cooking) hay dia thu '' nhiet cho dpng cO mat trdi (Solar disc).
2. BAI TOAN THIET KE 2.1. Cac nguy&n tac xoay dan
True tu xoay cua trai dat nghieng 23^27' so vdi
mat phang chda quy dao quay cua nd quanh mat trdi. Thdi gian chieu sang vd sU hinh thdnh cac mda trong nam Id ket qua chuyen ddng tU xoay vd chuyen dpng quay cua trdi dat quanh mat trdi (Hinh 1).
] linh 1: (~litivOii JOIIL; CLia Irai dat va cac miia Iroiig nam
,iii\ ili'iiii,ilt|Mi ; i 1
Hinh 2: Chuyen dpng tUOng ddi cua mat trdi so vdi 1 diem tren mat dat
Trong khodng thdi gian chieu sdng mdi ngdy, mat trdi chuyen ddng tUOng ddi so vdi diem dat he thdng thu nang lUpng theo mpt quy dao ta Ddng sang Tdy (chuyin ddng quay theo gid). Mat phang chda quy dao chuyen ddng ndy caa mat trdi cung dich chuyen tUOng doi giCa cdc ngdy trong nam (chuyin ddng theo ngdy - xem minh hpa tren hinh 2).
Cac he thdng bam theo quy dao mat trdi (Solar tracking) thUdng dUOc thiet ke dUa tren nguyen tac phdi hpp giCa hai trong sd 3 chuyen ddng quay quanh 3 true X, Y va Z nhU minh hpa tren hinh 3.
TAP CHi CO KHi VI£T NAM V Sd 4 (Thang 4 nam 2012)
NGHIEN CUfU-TRAODOl
2.2. Bdi toan c^n gidi quy^t
Bdi toan dat ra Id ta cdc thdng sd kich thudc vd khdi lUpng bp phan thu ndng lUpng (da xdc djnh theo yeu cau cdng suat cua h^ thdng, ching ban, dien tich cdc tdm pin, kich thUdc gUpng pa-ra-bdn thu nhi?t...), can xdc dinh tdi trpng dat Ien h? thdng. Xdc djnh dUgc tdi trgng se la ca sd de tinh todn chgn d^ng cO di^n vd cdc thdng s6 kit cdu ca khi de ddm bdo ddn boat ddng dn dinh vd dd ben.
Md men cdn khi xoay ddn cd the xdc djnh ta 3 thdnh phan:
M^^=M^+M„ +M^_^ (1) Trong dd, M , M va M Ian lupt Id md
D ' e ' ms glo T
men cdn do dan dat lech tam so vdi trpc xoay (hinh 4), md men can do ma sdt tren true xoay vd md men can cua gid tac ddng Ien he thdng khi xoay.
F i f - • ^ ^
Hinh 4: Momen l^ch tam Nhu minh hpa tren hinh 4, ngay ca kh ddn cd khdi lUpng dugc phan bd deu hai ben trui xoay (Fj=F2=F), nhUng khi trpng tam dan led so vdi tdm xoay mdt khoang e, van gay nen mO momen l^ch tam .\t^ = /^(Z, -A) = F.e.sma Momen nay cd gia tri Idn nhat khi a = ± 90", nghii Id, khi ddn vudng gdc vdi phuang nam ngang.T?i thdi diem khdi dpng, md men khd ddng cdn can thdng sac i (qudn tinh) cua cac do;
tupng xoay, tac la:
A^™ :M+M, +M, +M„, (2)
3. CAC CO Sd TiNH TOAN
Cac thanh phan momen can khi xoay dan dugc tinh toan nhU dUdi day.
3.1. Momen can do Ifch tam
Hinh 3: Cac true xoay dan vd cac thdnh phSn tai trgng [8]
Cdc he thdng thu nang lUpng mat trdi thudng cd khdi lUpng kha Idn. Khdi lUpng naf neu l?ch tam xoay se gay md men cdn xoay rat dang ke. Gpi khoi lU<?ng lech tam Id m, khoang l^ch tam Id e, momen can xoay do 16ch tdmUu TAP CHi CO KHi V I £ T NA M •!• SA 4 ^Thdne 4 nam 2012)
NGHIEN CUTU-TRAO 961
dan dang d vi tri hgp vdi phuong nam ngang 1 gdc a (xem minh hpa tren hinh 4), dupc tinh theo cdng thdc (2) vd cd dang:
M^ = m - g - e - s i n a (3) De thay, momen can do lech tam dat gid
tri Idn nhdt khi a bang a= ± 90 dp, tac Id khi ddn xoay v^' hudng can Ddng hoac can Tay. NhU vdy, trong trUdng hgp dan quay 2 true, neu phdi bd tri mdt true xoay nao dd lech tam so vdi trpng tdm cua dan, can bd tri true xoay theo gid l^ch tdm it hpn. Tdt nhat nen bo tri tam xoay di qua trpng tam cua dan.
3.2. Momen ma sat tren d Ian
Thdnh phan ma sdt tren 6 Ian thudng cd gid tri rat nhd - chiem khodng 0,01 den 0,015 tong cdc gia tri momen can va cd the bd qua khi xdc dinh cdng suat xoay dan.
Trong dd:
• Cj^ , Q^^, Cp^ va Cp^ Id cac he sd tinh todn, php thupc vi tri ddn so vdi chieu gid thdng qua cdc gdc a, ^. Gid tri Idn nhat cua cdc h^ sd ndy dUpc cho trong bdng 1;
H$ sd Cmyo dupc tinh theo cdng thac;
c,,, = c^, + c,,.(/..';,;
• A la di?n tich be mat dan (m^);
• Q Id dp lUc cua gid Ien ddn (N/m^);
• h Id kich thudc be rdng cda ddn (m);
Bdng 1: Cac gia tri h§ s6 tinh toan khi tdi gid co tac dyng Idn nhdt [8]
3.3. Momen can cua gio
Cd the dp dpng ket qua nghien cau cda Peterka [8] de tinh todn momen xoay vd lUc tdc dung ngang Ien ddn nhU sau (Cdc thdnh phan lUc vd momen xoay dUpc minh hpa tren hinh 3):
- Momen Idn nhat khi xoay theo phUPng ngang:
M ^ .A.O.I
- Momen xoay theo phUPng dang;
M^ =C^..A.O.w
- Momen Idt theo phUOng ngang:
- LUc tac dung ngang:
F^=C^^.A.Q - LUc keo/nen dpc true:
F,=C,.A.Q
(7)
(8) - Cac thanh phan F^ M, co gia trj rat nhd nen co the bo qua.
Goc a (do) Goc p (do) Cft CFZ CMV Cih
Fx. Mvo max 90
0 4.0 1.0 0.25 0,29
Fz: Mv max 30
0 2.1 2.8 0^
0,06 Mzmax
90 65 3.7 0,5 0.15 0.7
(4)
(5)
(6)
Trong tinh todn co khi, momen xoay M^, va M se dUpc sa dung de xdc dinh cdng suat can thiet de xoay ddn; cdc lUc F^, F^ vd momen M^^
M se dupc sii dung de tinh ben cho cdc ket cau khung dd he thdng.
3.4. Momen qudn tinh khi khdi d^ng Trong trudng hpp he thdng quay gidn doan, qua trinh khdi ddng dUpc lap lai nhieu Ian, cdn ke d^n momen can do quan tinh cua ddn.
Momen ndy dUpc tinh theo cdng thac :
T,< = ^ 'd
(9)Trong do, 3 d la gia toe goc cua hi khi bat dau khdi dong (m/s^); J^^ la mo men quan tinh ciia he th6ng xoay quanh true quay (Kg.m^).
4. KET QUA VA THAO LUAN
Trong phan nay, m o hinh tinh toan dUoc
TAP CHl CO KHf V l f T NAM V 86 4 (Thing 4 nam 2012)
NGHIEN cUU-TRAOePi
phat trien cho cae dan phSng mang eac tam pin mat trdi co cong suat phat dien khac nhau. Cae thanh phan momen do l?ch tam, sOlc i cua h^
thdng (quan tinh) dUdc tinh todn theo c4e cdng thiic CO bdn trong cdc giao trinh nen khdng c5n dien giai chi tiet d day Difdi ddy trinh bdy md hinh tinh todn cho momen cdn trong dit?u ki^n cd gid.
Gpi van tdc gid Id v (m/s), cd th^ tinh ap lue gid theo cdng thiic:
(5 = 0,613.1'' (N/m') (10) Thay (11) vdo cdc cdng thiic tinh momen cdn theo phuong ngang vd diing (5) vd (6), thu
dupe:
M = ( „ .O.en.v'.A.h M, = r „ .0,613.v^/l./!
(u;
(12) D^ minh hga sd li^u tinh toan cu thi cho nhi^u cd cdng sudt khdc nhau, cd the lay gid tri trung binh cua cdng sudt phat cho moi watt di^n Id 0,009 mVWe d^ tinh gdn dung dien tich can t\nit cua ddn. Gid tri trung binh cua cdng suit phdt cho mdi watt di?n dUpc lay trung binh th6ng ke qua khdo sat mpt sd tam pin mat trdi thong dpng (xem bdng 2).
Bang 2- Thong s6 mdt s6 tam pin thong dpng
Model Cong suit 0\'e) Dien tich (m-) Khoi li?ong (kg) He so dien tich cong suit (m- We)
He so khoi lupng cong suit ft? ^Ve)
CIC- lOW- MONG
10 0.09S
1.15 0,0085
0.115 CTC- 50W- MONO
50 0.391
5 0,0098
0.1 CTC-
• 5 \ \ - MONG
"5 0,632
8.2 0.0078
0.109 CTC- lOOfl'- POLV 100 0S5O 10 0.0084
0.1 BP Solar
120 1.025 12.3 0,0085 0.1025
CTC- 200fl"
MONO 200 163"
19.3 O.O0S2
0.09'
De don gidn cho tinh todn so sdnh mdt sd ddn cd cdng suat khdc nhau, gid thiet rdng cac ddn pin cd kich thUde ddi va rdng nhu nhau; cho phep ddn lam viec binh thudng khi cd gid cap 6 (van tdc gid khoang 12 m/s). Stt dung cae he sd trong bang 1 cho cac phuang trinh (11) vd (12), de dang tinh dupe cac thdnh phan Idn nhat cua lile va momen can cua gid. Cac thdnh phan momen qudn tinh vd momen lech tam dupc tinh theo cdc cdng thiic da neu d tren theo eac sd lieu ket cau chpn theo dieu kien ben. Bdng 3 tdm tat mpt sd
ket qud tinh todn chinh. Momen quan tinh diioc tinh vdi gia thiet gia tdc gdc Id 1 rad/s2 (thdi gian de ddn khdi dpng tit 0 den tdc dp 1 vong/phdtlJ 0,05 giay). Trong thUc te, ede ddn cd cdng suitIfln hon thudng cd thdi gian khdi ddng lau hon va do vay, gid tri momen quan tinh se nhd hdn so vdi ket qua trong bdng. CQng ed the tham khao nhanh gid tri momen quan tinh thiic te bang cadi nhan ket qud tinh mpmen qudn tinh trong bang vdi gid tri gia tdc gdc thiic te.
T ^ P CHi CO KHi V I E T N A M • S6 4 (Thang4 nam 2012)
NGHIEN cUU - TRAO 0 6 l
Bang 3; Ket qua tinh toan cho mpt so ddn pin mat trdi Cong sua! phat dieD (\Ve)
Dien tich dan pin (m-) Momen quan tinh (Nmi
Momen lech torn fNm), do iecn tdm s = 100 mm
Momen can cita gto (tntc ngang}, Xm Momen can cua gio (tntc dierigl. Xn.
Cong suit can gio, xoav quanh true ngajig (W) Cdng suit can gid, xoav quanh true dung (W)
100 0.9 2,26 12,61
41,S 4S,9 4.4 5.12
300 2.7 16,01 4S,39 2SS.3 274.6 24.6 2S.75
1.000 9 .'2.0,75' 140,63 1.551.6 1.S10.3 162.5 189.56
2.000 18 459,2}
2S1.59 4.257,7 4.967,4 445.8 520.15
3.000 27 1.013,89
422,21 S.0S0,6 9.427,3 846.1 987.15
Qua bdng 2, cd the nhan thay, momen can cua gid cd gid tri rat Idn so vdi momen qudn tinh hay momen lech tam (Td 8 den 20 Ian). Cung lUu y rang, neu dan dUoc thiet ke vd che tao hpp ly, momen lech tdm cd the bang 0. Trong hai thanh phan momen can cua gid, momen cdn khi xoay ddn quanh true ddng cd gia tri Idn hon. Day cung cd the la ly do md cdc dan xoay mpt hoac hai true trong thUc te thudng it khi xoay quanh true dang.
dd thi quan he gifla 2 loai cdng suat nay nhU minh hpa tren hinh 5. Qua do thi, cd the thay, vdi cdc dan pin mat trdi cd cdng suat phat dien dUdi 30 KWe, cdng suat cdn cua gid ludn nhd b a n cdng suat phdt dien. NhU vay, viec sfl dung ket cau ddn xoay cho cdc ddn ndy la cd hieu qua. Cung can lUu y rang, hau bet cac ddn nang lugng mat trdi deu quay gian doan. Tong thdi gian xoay dan trong mdi ngdy la rat nhd so vdi thdi gian thu nang lupng cua ddn.
. /
Hinh 5: Quan he giiia cong suat xoay dan (thing siSc can ciia gid) va cong sudt phat dien
Gid trj cdng suat can khi xoay ddn da tinh todn dupc sii dung de chpn ddng co truyen dan cho chuyen ddng xoay dan. Khi tinh ben cho he thdng, ngpai momen, cdn can xdc dinh lUc tdc dpng cua gid (cdc cdng thiic 8,9); ddng thdi ke den thdnh phan momen khdi dpng nham thang siic 1 ciia he thdng. Ciing can het siie tranh bd tri true quay lech tam. Cd the tranh lech tdm bang cdch sii dung ddi trpng can bang trong trudng hpp can thiet.
Cae ddn xoay theo hudng mat trdi cd tdc dp xoay rat nhd (thudng khoang 1-3 vdng/phiit);
T i & hanh tinh todn cdng suat xoay ddn thdi gian khdi dpng ed the dai hon 0,05 giay nhu tdi thie'u di t h i n g siie cdn cua gid (cSp 6) vdi cae da gid thift. Do vdy, momen qudn tinh thudng dan cd cdng sudt phdt dien khdc nhau, thu dupc nhd hon nhieu so vdi momen cdn cua gid
TAP CHl CO KHi VIETNAM • Sd 4 (Thdng 4 nam 2012) ^ ^
NGHIEN CUU - TRAO DPi
5. KET LUAN
Md hinh tinh todn cdng suat cdn khi xoay ddn nang lilpng mat trdi trong dieu ki$n cd gid da dupe phdt trifo cho cdc gid tri cdng sudt phdt di?n khdc nhau. Kft qud tinh todn cho thiy, cdng suat cdn ciia gid Id thdnh phdn tdi trpng chinh y^u vd ddng k^ h d n hdn sp vdi cac thanh phan khdc. Md hinh tinh tpdn cd th? dUpe sii dyng d l tinh todn chpn dpng cP vd tinh ben cho cdc dan nang Idpng mat trdi tU xpay K^t qud tinh todn sau khi dUpe ki^m chiing thiic nghifjn se cho dp tin e^y vd khd nang ling dyng cao. •
Tai lieu tham khao:
[1]. H. Mousazadeh et al.; A review of principle and sun-tracking methods for maximizing solar systems output; Renewable and Sustainable Energy Reviews 13 (2009) 1800-1818.
[2]. R, Abu-Malouh et al.; Design, construction and operation of spherical solar cooker with automatic sun tracking system; Energy Conversion and Management 52 (2011) 615-620.
[3]. RM. Al-Naima, N.A. Yaghobian; Design and construction of a solar tracking system; Solar & Wind Technology Vol. 7, No. 5 (1990), pp. 611-617.
[4]. 1. Sefa et al.; Application of one-axis sun tracking system; Energy Conversion and Management 50 (2009)2709-2718.
[5]. P Baltas, M. Tortoreli And P. E. Russell, Evaluation of power output for fixed and step tracking photovoltaic arrays. Solar Energy Vol. 37, No. 2. (1986) pp. 147-163
[6]. K.K. Chong, C.W. Wong; General formula for on-axis sun-tracking system and its appUcationfii improving tracking accuracy of solar collector; Solar Energy 83 (2009) 298-305.
[7].S. Roy Chowdhury, H. Saha; Maximum power point tracking of partially shaded solar photovoltaic arrays; Solar Energy Materials Si Solar Cells 94 (2010) 1441-1447.
[8]. ).A. Peterka and R.G. Derickson, Wind load design methods for ground-based heliostats and para- bolic dish collectors, SAND92-70D9, 1992.
^ TAiP CHf CO KHi VIETNAM • Sd 4 (Thdng 4 nam 2012)
