ELEG 620 Solar Electric Power Systems February 25, 2010
Solar Electric Power SystemsSolar Electric Power Systems
ELEG 620Electrical and Computer Engineering
University of DelawareFebruary 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 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 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
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 0
4 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 February 25, 2010
ELEG 620 Solar Electric Power Systems February 25, 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).
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.
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 February 25, 2010
Theoretical Analysis of Solar Cell
1ln
0J
J
q
kTV sc
oc
cutoff
hc
FqJ sc
1
)(
max
oc sc
PFF
V J
oc sc
in
V JEfficiency FF
P
cosh sinh cosh sinh1 1
( )sinh coshsinh cosh
g
p p emitter emitter n n base baseE
p p p p n n n nkTo c v
p p n n base baseemitter emitterd p a n
n n np p p
S L W W S L W WD D L L D D L L
J N N qeS L S L W WW WN L N L
D L LD L L
ELEG 620 Solar Electric Power Systems 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
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
At one sun
Single junction solar cell Jsc for AM1.5GSingle junction solar cell Voc for AM1.5G
ELEG 620 Solar Electric Power Systems February 25, 2010
ELEG 620 Solar Electric Power Systems February 25, 2010
Maximizing efficiency
= 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 emitterDoping and diffusion length are related