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ELEG 620 Solar Electric Power Systems March 4, 2010
Solar Electric Power Systems
ELEG 620Electrical and Computer Engineering
University of DelawareMarch 4, 2010
ELEG 620 Solar Electric Power Systems March 4, 2010
ELEG 620 Solar Electric Power Systems March 4, 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 March 4, 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 circuit2. Open circuit voltage3. Maximum power (show voltage and current at maximum
power)4. Efficiency5. Thickness and doping of each layer Show key equations
ELEG 620 Solar Electric Power Systems March 4, 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
I-V Curve of a Well Behaved Solar Cell
I-V curve of a well behaved solar cell
Voltage(V)C
urr
en
t (m
A)
0.5-0.5-1 12
04
06
0-2
0-4
0-6
0
(Vmp,Imp)
Voc
Isc
)1(exp0
kT
VqIIDiode
IDiode
_
+
VILight
I
LightIkT
VqII
)1(exp0
in
mpmp
Power
IVEfficiency
ELEG 620 Solar Electric Power Systems March 4, 2010
ELEG 620 Solar Electric Power Systems March 4, 2010
ELEG 620 Solar Electric Power Systems March 4, 2010
ELEG 620 Solar Electric Power Systems March 4, 2010
ELEG 620 Solar Electric Power Systems March 4, 2010
Solar Cell Design
Jo = q tanh tanhDp ni
2
Lp Nd Xj
Lp+
Dn ni2
Ln Na Xj
Ln
q
ELEG 620 Solar Electric Power Systems March 4, 2010
Jo = q Dp ni2
Lp Nd +Dn ni
2
Ln Na q
ELEG 620 Solar Electric Power Systems March 4, 2010
1ln
0J
J
q
kTVoc L
Lifetime Voltage (mV)
1 ms 561
100us 506
10us 467
Wn(um)
Wp(um)
S(cm/s)
De(cm2/s)
Dh(cm2/s)
ND
(cm-3)NA
(cm-3)Jsc
(mA/cm2)
10 500 0 35 12 1e15 1e14 43.6
ELEG 620 Solar Electric Power Systems March 4, 2010
1ln
0J
J
q
kTVoc L
Wn(um)
Wp(um)
S(cm/s)
De(cm2/s)
Dh(cm2/s)
ND
(cm-3)NA
(cm-3)Jsc(mA/cm2)
10um 500 0 35 12 1e15 1e14 43.6
1 500 0 35 12 1e16 1e15 43.6
Lifetime Voltage (mV)
1 ms 561 620
100us 506 565
10us 467 526
ELEG 620 Solar Electric Power Systems March 4, 2010
ELEG 620 Solar Electric Power Systems March 4, 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 March 4, 2010
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).
Structure, Equivalent circuit and IV curve of solar cell
Ilight
Equivalent circuit of solar cell
I-V Characteristic of Solar Cell
+
V
Base
Emitter
Back contact
Front contact
( 1)qV
kTD oI I e
I
V0
Isc
Voc
Pmax
0 (exp( ) 1)qV
J JkT
0 (exp( ) 1) sc
qVJ J J
kT
ELEG 620 Solar Electric Power Systems March 4, 2010
ELEG 620 Solar Electric Power Systems March 4, 2010
Maximizing efficiency
h = Isc Voc FF
Pin
Isc
• EG
• Reflection• Surface• Metal
• Ln, Lp
• Sr
• xj optimum
Voc
• EG
• doping• Ln, Lp
• Sr
FF• Series R
• Metal• Emitter
• doping• Thick emitter
Doping and diffusion length are related
Jn = qun n E qDndn
dx
+
Jp = qup p E qDpdp
dx
-
ELEG 620 Solar Electric Power Systems March 4, 2010