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