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

urre

nt (m

A)

0.5-0.5-1 120

4060

-20

-40

-60

(Vmp,Imp)

Voc

Isc

)1(exp0

kTVqIIDiode

IDiode

_

+

VILight

I

LightIkTVqII

)1(exp0

in

mpmp

PowerIV

Efficiency

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

0JJ

qkTVoc 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

0JJ

qkTVoc 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 performanceFor 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)qVkT

D oI I e

I

V0

Isc

Voc

Pmax

0 (exp( ) 1)qVJ JkT

0 (exp( ) 1) scqVJ J JkT

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