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A solar photovoltaic system with ideal efficiency close to the theoretical limit

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Abstract

In order to overcome some physical limits, a solar system consisting of five single-junction photocells with four optical filters is studied. The four filters divide the solar spectrum into five spectral regions. Each single-junction photocell with the highest photovoltaic efficiency in a narrower spectral region is chosen to optimally fit into the bandwidth of that spectral region. Under the condition of solar radiation ranging from 2.4 SUN to 3.8 SUN (AM1.5G), the measured peak efficiency under 2.8 SUN radiation reaches about 35.6%, corresponding to an ideal efficiency of about 42.7%, achieved for the photocell system with a perfect diode structure. Based on the detailed-balance model, the calculated theoretical efficiency limit for the system consisting of 5 single-junction photocells can be about 52.9% under 2.8 SUN (AM1.5G) radiation, implying that the ratio of the highest photovoltaic conversion efficiency for the ideal photodiode structure to the theoretical efficiency limit can reach about 80.7%. The results of this work will provide a way to further enhance the photovoltaic conversion efficiency for solar cell systems in future applications.

©2011 Optical Society of America

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Figures (7)

Fig. 1
Fig. 1 Equivalent circuit diagram of an ideal single-junction solar cell.
Fig. 2
Fig. 2 Schematic diagram of the optical path with five photocells and four filters used in the spectrum-splitting solar photovoltaic conversion system.
Fig. 3
Fig. 3 To match the spectral response of each photocell, four optical film filters have spectral transmission windows of 300-480nm, 400-630 nm, 600-730 nm and 700-870 nm, respectively, as measured by spectroscopic ellipsometry, and are used to divide the solar spectrum into five sub-spectral regions of (I) 300-480 nm, (II) 480-630 nm, (III) 630-730 nm, (IV) 730-870 nm, and (V) 870-1800 nm, respectively.
Fig. 4
Fig. 4 The I-V curves of five single-junction photocells are measured under the 2.8SUN solar irradiation intensity condition.
Fig. 5
Fig. 5 The measured photovoltaic conversion efficiency changes with the solar irradiation intensity.
Fig. 6
Fig. 6 Schematic diagram to show that the output power will be reduced by the internal shunt and series resistances as the powers Psh and Ps, respectively in the practical application of a solar cell.
Fig. 7
Fig. 7 Photovoltaic conversion efficiency of the spectrally divided system designed in this work to have an optimal efficiency of 42.7% obtained under ideal condition in which Ris = 0 and Rish = ∞.

Tables (2)

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Table 1 Parameters extracted from the I-V curves of 5 five single-junction photocells measured under the 2.8SUN solar irradiation intensity condition

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Table 2 Measured photovoltaic conversion efficiencies of five photocells in the sub-spectral regions with comparisons to the ideal efficiency under the perfect photo diode structure condition and the efficiency limit calculated by the detailed balance model

Equations (31)

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I i ( V i )= I ph i I 0 i [exp( q V i k T C )1],
I ph i =q( F ph F 0 ), I 0 i =q F 0 ,
F ph =A λ n λ n+1 N ph i (λ)dλ, F 0 =2A E g /h N 0 i (ν)dν ,
N ph i (λ)= C e Eλ hc , N 0 i (ν, T C )= 2π c 2 ν 2 exp(hν/k T C )1 ,
I i ( V i )=qA λ n λ n+1 C e Eλ hc dλ 4πqA c 2 exp( q V i k T C ) E g /h ν 2 exp( hν / k T C )1 dν .
P i = I i V i .
P i V i =0.
[1+ q V m i k T C ]exp( q V m i k T C )= h 2 c 4π k 3 T C 3 λ n λ n+1 C e Eλ dλ m=1 1 m 3 [y e 2 y +2y e y +2 e y ] y=m E g /k T C
P m i =qA V m i λ n λ n+1 C e Eλ hc dλ 4πqA c 2 k 3 T C 3 h 3 V m i exp( q V m i k T C ) m=1 1 m 3 [y e 2 y +2y e y +2 e y ] y=m E g /k T C .
η model = i=1 N P m i P in ×100%,
P in =A 0 C e Edλ
η exp = i=1 5 I m i V m i P in ×100%,
P out i = P in i ( P dio i + P s i + P sh i ).
P ideal i = P out i + P s i + P sh i ,
P out i = I i V i , P s i = ( I i ) 2 R s i , P sh i = ( V i + I i R s i ) 2 / R sh i .
{ 1 R sh = 1 R sh0 I 0 V T exp( I sc R s V T ) R s = R s0 V T I 0 exp( V oc V T ) I 0 = I sc exp( V oc V T )exp( I sc R s V T ) ,
η ideal = i=1 5 P ideal i P in ×100%,
I i ( V i )=qA λ n λ n+1 C e Eλ hc dλ 4πqA c 2 exp( q V i k T C ) E g /h ν 2 exp( hν k T C )1 dν .
a x 2 e x 1 dx= m=1 1 m 3 [y e 2 y +2y e y +2 e y ] y=ma ,
I i ( V i )=qA λ n λ n+1 C e Eλ hc dλ 4πq c 2 k 3 T C 3 h 3 Aexp( q V i k T C ) m=1 1 m 3 [y e 2 y +2y e y +2 e y ] y=m E g /k T C .
P i =q V i A λ n λ n+1 C e Eλ hc dλ 4πq c 2 k 3 T C 3 h 3 V i Aexp( q V i k T C ) m=1 1 m 3 [y e 2 y +2y e y +2 e y ] y=m E g /k T C .
P i V i =Aq λ n λ n+1 C e Eλ hc dλ 4πq c 2 k 3 T C 3 h 3 A[ 1+ q V i k T C ]exp( q V i k T C ) m=1 1 m 3 [y e 2 y +2y e y +2 e y ] y=m E g /k T C =0
I= I ph I 0 [exp( V+I R s V T )1] V+I R s R sh .
I sc = I ph I 0 [exp( I sc R s V T )1] I sc R s R sh .
0= I ph I 0 [exp( V oc V T )1] V oc R sh .
I 0 [exp( V oc V T )exp( I sc R s V T )]+ V oc R sh I sc (1+ R s R sh )=0.
I 0 = I sc exp( V oc V T )exp( I sc R s V T ) ,
I= I 0 exp( V oc V T ) I 0 exp( V+I R s V T )+ V oc VI R s R sh .
( R s dV dI )[ I 0 V T exp( V+I R s V T )+ 1 R sh ]=1.
1 R sh = 1 R sh0 I 0 V T exp( I sc R s V T ).
R s = R s0 V T I 0 exp( V oc V T ).
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