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Exzerpt aus:. Photovoltaics. Clemson Summer School 6.5. – 8.5.06 Dr. Karl Molter FH Trier www.fh-trier.de/~molter [email protected] Technology Components and Systems Applications. Zum Original : http://www0.fh-trier.de/~molter/clemson/PV-en.ppt.

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Photovoltaics

Exzerpt aus:

Photovoltaics

Clemson Summer School

6.5. – 8.5.06

Dr. Karl Molter

FH Trier

www.fh-trier.de/~molter

[email protected]

Technology

Components and Systems

Applications

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


Content

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

Content

  • Solar Cell Physics

  • Solar Cell Technologies

  • PV Systems and Components

  • PV Integration into buildings

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Photovoltaics

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:

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

.

Clemson Summer School


1 solar cell physics

1. Solar Cell Physics

  • Solar Cell and Photoelectric Effect

  • The p/n-Junction

  • Solar Cell Characteristics

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


History

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 %)

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Solar cell and photoelectric effect

h

  • Light absorption

  • Generation of „free“ charges

+

  • effective separation of the charges

-

Solar Cell and Photoelectric Effect

Result: wearless generation of electrical Power

by light absorption

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Energy states in solids band pattern

energy-states in solids:Band-Pattern

Atom

Molecule/Solid

energy-states

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Energy states in solids insulator

energy-states in solids:Insulator

electron-energy

conduction-band

bandgap EG

(> 5 eV)

Fermi-

level EF

valence-band

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Terms

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, the

electrons 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 and

conduction band

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Energy states in solids metal conductor

energy-states in solids :metal / conductor

electron-energy

Fermi-

level EF

conduction-band

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Energy states in solids semiconductor

energy-states in solids:semiconductor

electron-energy

conduction-band

bandgap EG

( 0,5 – 2 eV)

Fermi-

level EF

valence-band

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Electron energy

Electron-Energy

At 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:

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Energy states in solids energy absorption and emission

x

h

h

x

Generation

Recombination

+

+

-

-

energy-states in solids:energy absorption and emission

electron-energy

conduction-band

EF

valence-band

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Energy states in semiconductors physical properties

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)

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Doping of semiconductors

IIIB

IVB

VB

Si

B

P

14

5

15

doping of semiconductors

In 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:

„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:

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


N doping

energy-band view

conduction-band

majority carriers

P+

P+

P+

P+

P+

P+

EF

Si

Si

Si

Si

Si

Si

Si

Si

Si

Donator level

valence-band

-

-

-

-

-

-

-

N - Doping

crystal view

n-conducting Silicon

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


P doping

energy-band view

conduction band

B-

Si

Si

Si

Si

Si

Si

Si

Si

Si

EF

Acceptor level

B-

B-

B-

B-

B-

majority carriers

+

+

+

+

+

+

+

valence-band

P - Doping

crystal

p-conducting Silicon

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


P n junction without light

depletion-zone

Diffusion

Ud

EF

P+

P+

P+

P+

P+

B-

B-

B-

B-

B-

+

+

+

+

+

+

Diffusion

p – type region

Ed

-

+

n – type region

internal electrical field

-

-

-

-

-

-

p/n-junction without light

Band pattern view

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Irradiated p n junction

E = h

photocurrent

+

+

+

+

+

+

-

irradiated p/n-junction

band pattern view (absorption p-zone)

depletion-zone

-

-

-

-

-

Ud

EF

P+

P+

P+

P+

P+

B-

B-

B-

B-

B-

Ed

p–type region

-

+

n–type region

Internal electrical field

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


P n junction with irradiation crystal view

h

+

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

p-Silizium

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

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

+

+

+

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

+

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

diffusion

E

electrical field

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

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

-

-

-

-

-

-

n-Silizium

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

depletion zone

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

-

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

p/n–junction with irradiationcrystal view

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


The real silicon solar cell

Front-contact

-

hn

Antireflection-

coating

n-region

p-region

~0,2µm

+ + + + + + + + + +

+

- - - - - - - - - -

~300µm

depletion zone

Backside contact

The real Silicon Solar-cell

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Equivalent circuit of a solar cell

ISG

IL

IPH

RS

ID

current

source

RP

RL

USG

UL

UD

Equivalent circuit of a solar cell

IPH: photocurrent of the solar-cell

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

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

RS:serial resistor due to resistance of the silicon-bulk and contact material

ISG/USG: Solar-cell current and voltage

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

ISG = IL,USG = UL

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Solar cell characteristics

ID

diode-

characteristic

ID

ISG

UD=USG

UD

RL

RL= 

RL=0

MPP

ISG / PSG

Load resistance

ISG = I0 = IK

solar-cell

characteristics

ID

IMPP

Power

MPP = Maximum Power Point

USG

UMPP

U0

Solar-Cell characteristics

simplified circuit

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Solar cell characteristics1

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

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Solar cell characteristics2

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).

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Solar cell characteristics3

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

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Solar cell characteristics csi

P = 0,88W, (0,18)

P = 1,05W, (0,26)

P = 0,98W, (0,29)

Solar-cell characteristics (cSi)

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Solar cell characteristics4

Solar-cell characteristics

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Photovoltaics

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

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

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


Photovoltaics

This Powerpoint Presentation can be downloaded

from:

www.fh-trier.de/~molter

www.fh-trier.de/~molter

Clemson Summer School

Dr. Karl Molter / FH Trier / [email protected]


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