Download ppt - Photovoltaics Technology Components and Systems Applications Clemson Summer School 6.5. – 8.5.06 Dr. Karl Molter FH Trier molter [email protected]

Photovoltaics

Technology Components and Systems

Applications

Clemson Summer School

6.5. – 8.5.06

Dr. Karl Molter

FH Trier

www.fh-trier.de/~molter

[email protected]

Exzerpt aus:

Zum Original: http://www0.fh-trier.de/~molter/clemson/PV-en.ppt

http://www.fh-trier.de/~molter

mailto:[email protected]

http://www0.fh-trier.de/~molter/clemson/PV-en.ppt


6.6.06 - 8.6.06 Clemson Summer SchoolDr. Karl Molter / FH Trier / [email protected]

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Content

1. Solar Cell Physics

2. Solar Cell Technologies

3. PV Systems and Components

4. PV Integration into buildings




6.6.06 - 8.6.06 Clemson Summer School 3.

Ich benutze nur das Kaptel 1 „Solar Cells Physics“ und einige Folien aus Kapitel 2 (Materials).

Ich empfehle aber den gesamten Vortrag von Dr. Molter:





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1. Solar Cell Physics

• Solar Cell and Photoelectric Effect

• The p/n-Junction

• Solar Cell Characteristics


5

History

• 1839: Discovery of the photoelectric effect by Bequerel

• 1873: Discovery of the photoelectric effect of Selen (change of electrical resistance)

• 1954: First Silicon Solar Cell as a result of the upcoming semiconductor technology ( = 5 %)


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Solar Cell and Photoelectric Effect

1. Light absorptionh

-

+2. Generation of „free“

charges

3. effective separation of the charges

Result: wearless generation of electrical Power by light absorption


7

energy-states in solids:Band-Pattern

Atom Molecule/Solid

ener

gy-s

tate

s

• • • • • • • •


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energy-states in solids:Insulator

electron-energyconduction-band

valence-band

Fermi-level EF

bandgap EG

(> 5 eV)


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Terms:

Fermilevel EF: limit between occupied and non occupied energy-states at T = 0 K (absolute zero)

valence-band: completely occupied energy-band just be-

low the Ferminiveau at T = 0 K, theelectrons are „fixed“ inside the atomic structure

conduction-band:energy-band just above the valence-band, the electrons can move „freely“

bandgap EG: distance between valance-band andconduction band


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energy-states in solids :metal / conductor

electron-energy

conduction-band

Fermi-level EF


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energy-states in solids:semiconductor

electron-energy

conduction-band

valence-band

Fermi-level EF

bandgap EG

( 0,5 – 2 eV)


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Electron-EnergyAt T=0 (absolute zero of temperature) the electrons occupy the

lowest possible energy-states. They can now gain energy in two ways:

• Thermal Energy: kT (k = Boltzmanns Constant, 1.381x10-23 J/K, T = absolute temperature in Kelvin)

• Light quantum absorption: h (h = Plancks Constant, h = 6.626x10-34 Js, = frequency of the light quantum in s-1).

If the energy absorbed by the electron exceeds that of the bandgap, they can leave the valence-band and enter the conduction-band:


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energy-states in solids:energy absorption and emission

electron-energy

conduction-band

valence-band

EF

+

-

h

Generation

+

-

h

Recombination

x

x


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energy-states in semiconductorsphysical properties:

thermal viewpoint: The larger the bandgap the lower is the conductivity. Increasing temperature reduces the electrical resistance (NTC, negative temperature coefficient resistor)

optical viewpoint: the larger the bandgap the lower is the absorption of light quantums. Increasing light irradiation decreases the electrical resistance (Photoresistor)


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doping of semiconductorsIn order to avoid recombination of photo-induced charges and to „extract“ their energy to an electric-device we need a kind of internal barrier. This can be achieved by doping of semiconductors:

IIIB IVB VB

Si14

B 5

P15

„Doping“ means in this case the replacement of original atoms of the semiconductor by different ones (with slightly different electron configuration). Semiconductors like Silicon have four covalent electrons, doping is done e.g. with Boron or Phosphorus:


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N - Doping

Si Si

Si

Si

Si

Si

Si

Si

Si

P+

-

n-conducting Silicon

-

crystal view

conduction-band

valence-band

EF

- - - - -P+ P+ P+ P+ P+

majority carriers

Donator level

energy-band view


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P - Doping

Si Si

Si

Si

Si

Si

Si

Si

Si

p-conducting Silicon

B- +

+

crystal

conduction band

valence-band

EF B- B- B- B- B-

majority carriersAcceptor level

+ + + + +

energy-band view


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p – type region

EFB- B- B- B- B-

+ + + +

n – type region

- - - -P+ P+ P+ P+ P+

p/n-junction without lightBand pattern view

+

--Diffusion

+

Diffusion

internal electrical field

+ -Ed

Ud

depletion-zone


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p–type region

EFB- B- B- B- B-

+ + + +

n–type region

- - - -P+ P+ P+ P+ P+

irradiated p/n-junctionband pattern view (absorption p-zone)

+

-

+

photocurrent

Internal electrical field

+ -Ed

Ud

depletion-zoneE = h

-


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p/n–junction with irradiationcrystal view

n-Silizium

- - - - - - - - - - - -

- - - - - - - - - - - -

- - - - - - - - - - - -

- - - - - - - - - - - -

p-Silizium

+ + + + + + + + + + + +

+ + + + + + + + + + + +

+ + + + + + + + + + + +

+ + + + + + + + + + + +

+

-diffusion

-

+

electrical fieldE- - - - - - - - - - - -+ + + + + + + + + + + +

+-

h

-

+

-

-

-

+

depletion zone


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Antireflection-coating

The real Silicon Solar-cell

~0,2µm

~300µm

Front-contact

Backside contact

n-region

p-region

-

+

h

depletion zone

- - - - - - - - - -+ + + + + + + + + +


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Equivalent circuit of a solar cell

RP

USG

RSISG

RL

UL

ILID

UD

currentsource

IPH

IPH: photocurrent of the solar-cell

ID /UD: current and voltage of the internal p-n diode

RP: shunt resistor due to inhomogeneity of the surface and loss-current at the solar-cell edges

RS: serial resistor due to resistance of the silicon-bulk and contact materialISG/USG: Solar-cell current and voltage

RL/IL/UL: Load-Resistance, current and voltage

ISG = IL, USG = UL


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Solar-Cell characteristics

ID ISG

RLUD=USG

ID

ISG / PSG

USG

solar-cellcharacteristics

ISG = I0 = IK

RL=0 RL=

Power

UD

diode-characteristic

ID

U0

Load resistance

UMPP

MPP

IMPP

MPP = Maximum Power Point

simplified circuit


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Solar-cell characteristics

• Short-current ISC, I0 or IK:• mostly proportional to irradiation• Increases by 0,07% per Kelvin

• Open-voltage U0, UOC or VOC:• This is the voltage along the internal diode• Increases rapidly with initial irradiation• Typical for Silicon: 0,5...0,9V• decreases by 0,4% per Kelvin


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Solar cell characteristics

• Power (MPP, Maximum Power Point)• UMPP (0,75 ... 0,9) UOC

• IMPP (0,85 ... 0,95) ISC

• Power decreases by 0,4% per Kelvin

• The nominal power of a cell is measured at international defined test conditions(G0 = 1000 W/m2, Tcell = 25°C, AM 1,5) in WP (Watt peak).


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Solar cell characteristics

• The fillfactor (FF) of a solar-cell is the relation of electrical power generated (PMPP) and the product of short current IK and open-circuit voltage U0

FF = PMPP / U0 IK

• The solar-cell efficiency is the relation of the electrical power generated (PMPP) and the light irradiance (AGG,g) impinging on the solar-cell :

= PMPP / AGG,g


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Solar-cell characteristics (cSi)P = 0,88W, (0,18) P = 1,05W, (0,26)

P = 0,98W, (0,29)


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Solar-cell characteristics


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Zu den weiteren Folien bitte Dr. Molter‘s homepage besuchen:





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This Powerpoint Presentation can be downloadedfrom:



http://www.fh-trier.de/~molter