Transcript Slide 1

Solar Electric Power Systems
ELEG 620
Electrical and Computer Engineering
University of Delaware
February 25, 2010
ELEG 620 Solar Electric Power Systems
February 25, 2010
ELEG 620 Outcomes
1. Understanding the nature of Solar Radiation
2. Design of a solar cell from first principles
3. Design of a top contact system
4. Design, construction and test of a solar
power system
ELEG 620 Solar Electric Power Systems
February 25, 2010
ELEG 620 Solar Electric Power Systems
February 25, 2010
ELEG 620 Outcomes
1. Understanding the nature of Solar Radiation
2. Design of a solar cell from first principles
3. Design of a top contact system
4. Design, construction and test of a solar
power system
ELEG 620 Solar Electric Power Systems
February 25, 2010
Solar Cell Design
Silicon Solar Cell Design Homework
Due: March 9, 2010
Design a silicon solar cell. Calculate the following:
1. Light generated current at short circuit
2. Open circuit voltage
3. Maximum power (show voltage and current at maximum
power)
4. Efficiency
5. Thickness and doping of each layer
Show key equations
ELEG 620 Solar Electric Power Systems
February 25, 2010
Solar Cell Design
Silicon Solar Cell Design Homework
Due: March 9, 2010
Design a silicon solar cell.
Following assumptions can be used
•Structure is N on P
•There is no surface recombination
•There is no surface reflection
•Series resistance = 0 ohms
•Shunt resistance is infinite (shunt conductance = 0)
•Sunlight = AM 1.5 global
ELEG 620 Solar Electric Power Systems
February 25, 2010
I-V Curve of a Well Behaved Solar Cell
IDiode
V
-0.5
q V q V
II Diode
I 0 (exp
I 0  (exp  1) I1Light
)
kT kT
Voltage(V)
1
-20
0.5
-40
-1
Voc
20
_
40
60
+
Current (mA)
ILight
I
-60
(Vmp,Imp)
Isc
Efficiency 
I-V curve of a well behaved solar cell
ELEG 620 Solar Electric Power Systems
February 25, 2010
Vmp  I mp
Powerin
Solar Cell Operation
Key aim is to generate power by:
(1) Generating a large short circuit current,
Isc
(2) Generate a large open-circuit voltage,
Voc
(3) Minimise parasitic power loss
mechanisms (particularly series and
shunt resistance).
ELEG 620 Solar Electric Power Systems
February 25, 2010
Design rules for high performance
For a high solar cell efficiency,
simultaneously need high absorption,
collection, open circuit voltage and fill
factor.
Absorption and collection are typically
achievable by “clever” engineering &
innovation.
Voltage is controlled by worst, localized
region, NOT the same region which
absorbs the light – this is fundamentally
why single crystal solar cells are highest
efficiency.
Predictive models and design rules for all
characteristics are necessary for the
device parameters.
ELEG 620 Solar Electric Power Systems
February 25, 2010
Structure, Equivalent circuit and IV curve of solar cell
I
Front contact
Emitter
Base
Back contact
Ilight
I D  I o (e
0
qV
kT
 1)
Voc
+
V
Isc
Pmax
I-V Characteristic of Solar Cell
Equivalent circuit of solar cell
qVqV
J
(exp(
 1)
J  JJ 
(exp(
) ) 1)
 J sc
0
0
kTkT
ELEG 620 Solar Electric Power Systems
February 25, 2010
V
Theoretical Analysis of Solar Cell
J sc  q
Theoretical Isc
Voc 
Calculate Voc
J o  N c N v qe
Fill Factor (FF)
Efficiency
 Eg
kT
cutoff

F (  ) 
hc  1
 J sc
kT
ln 
 J
q
0


 1


S p Lp
W
W
S n Ln
W
W
cosh emitter  sinh emitter
cosh base  sinh base
Dp
Lp
Lp
Ln
Ln
1 Dp
1 Dn Dn
(

)
Wemitter
Wemitter
N d Lp S p Lp
N a Ln S n Ln sinh Wbase  cosh Wbase
sinh
 cosh
Dn
Ln
Ln
Dp
Lp
Lp
FF 
Pmax
Voc J sc
Efficiency 
ELEG 620 Solar Electric Power Systems
Voc J sc
FF
Pin
February 25, 2010
The maximum theoretical limit of single junction solar cell depends on the incident spectrum.
It is 29.2% for AM1.5G
Spectrum Irradiance AM1.5G
Single junction solar cell efficiency for AM1.5G
ELEG 620 Solar Electric Power Systems
February 25, 2010
Single junction solar cell Voc for AM1.5G
At one sun
Single junction solar cell Jsc for AM1.5G
Material
Voc(mV)
Isc(mA)
FF(%)
Efficiency(%)
Ge
280
60.9
70.9
12.1
Si
732
43.7
85.1
27.2
InP
946
35.0
87.7
29.0
GaAs
1024
32.0
88.4
29.0
GaP
1833
9.6
92.7
16.4
ELEG 620 Solar Electric Power Systems
February 25, 2010
Maximizing efficiency
h=
Isc Voc FF
Pin
 Isc
•  EG
•  Reflection
• Surface
• Metal
•  L n, L p
•  Sr
• xj optimum
 Voc
•  EG
•  doping
•  Ln, Lp
•  Sr
 FF
•  Series R
• Metal
• Emitter
•  doping
• Thick emitter
Doping and diffusion
length are related
ELEG 620 Solar Electric Power Systems
February 25, 2010