Solar Electric Power Systems

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Solar Electric Power Systems. ELEG 620 Electrical and Computer Engineering University of Delaware March 4, 2010. ELEG 620 Outcomes. Understanding the nature of Solar Radiation 2 . Design of a solar cell from first principles 3. Design of a top contact system

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Solar Electric Power Systems

ELEG 620

Electrical and Computer Engineering

University of Delaware

March 4, 2010

ELEG 620 Solar Electric Power Systems March 4, 2010

ELEG 620 Outcomes
• 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:

Light generated current at short circuit

Open circuit voltage

Maximum power (show voltage and current at maximum power)

Efficiency

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

ELEG 620 Solar Electric Power Systems March 4, 2010

I-V Curve of a Well Behaved Solar Cell

I

+

ILight

60

Current (mA)

IDiode

V

40

20

_

Voc

-1

-0.5

0.5

1

Voltage(V)

-20

-40

Isc

-60

(Vmp,Imp)

I-V curve of a well behaved solar cell

ELEG 620 Solar Electric Power Systems March 4, 2010

Solar Cell Design

ELEG 620 Solar Electric Power Systems March 4, 2010

Dp ni2

Xj

Dn ni2

Xj

q

+

tanh

tanh

Lp Nd

Lp

Ln Na

Ln

Jo = q

ELEG 620 Solar Electric Power Systems March 4, 2010

Dp ni2

Dn ni2

q

+

Lp Nd

Ln Na

Jo = q

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).

ELEG 620 Solar Electric Power Systems March 4, 2010

I

Front contact

Emitter

Voc

Pmax

Base

0

V

Back contact

Isc

Structure, Equivalent circuit and IV curve of solar cell

+

Ilight

V

I-V Characteristic of Solar Cell

Equivalent circuit of solar cell

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

ELEG 620 Solar Electric Power Systems March 4, 2010

dn

dp

+

qDn

Jn = qun n E

dx

dx

-

qDp

Jp = qup p E

ELEG 620 Solar Electric Power Systems March 4, 2010