unit 03 solar ver 01

1839: Photovoltaic effect was first recognized by French physicistAlexandre-Edmond Becquerel. 1883: First solar cell was built by Charles Fritts, who coated thesemiconductor selenium with an extremely thin layer of gold to form thejunctions (1% efficient). 1946: Russell Ohl patented the modern solar cell 1954: Modern age of solar power technology arrives - Bell Laboratories,experimenting with semiconductors, accidentally found that silicon dopedwith certain impurities was very sensitive to light. The solar cell or photovoltaic cell fulfills two fundamental functions: Photogeneration of charge carriers (electrons and holes) in a light-absorbingmaterial Separation of the charge carriers to a conductive contact to transmit electricity

First Generation

Single crystal silicon wafers (c-Si)

• Second Generation

Amorphous silicon (a-Si)Polycrystalline silicon (poly-Si)Cadmium telluride (CdTe)Copper indium gallium diselenide (CIGS) alloy

• Third Generation

Nanocrystal solar cellsPhotoelectrochemical (PEC) cells

Polymer solar cellsDye sensitized solar cell (DSSC)

•Fourth Generation

Hybrid - inorganic crystals within a polymer matrix

Different types of solar cells and / or their semiconducting materials can be classified by generations:

•First generation solar cells are made of crystalline silicon, also called, conventional, traditional, wafer-based solar cells and include monocrystalline (mono-Si) and polycrystalline (multi-Si) semiconducting materials.

•Second generation solar cells or panels are based on thin-film technology and are of commercially significant importance. These include CdTe, CIGS and amorphous silicon.

•Third generation solar cells are often labeled as emerging technologies with little or no market significance and include a large range of substances, mostly organic, often using organo metallic compounds.

https://en.wikipedia.org/wiki/Third_generation_solar_cell

Forms of Solar Energy Gathering

• A single unit is referred to as a cell

• A collection of cells is a module

• A collection of modules is an array

Note that while they may all be made up of the same type of cell a module and an array will have different efficiencies due to the empty spaces between each cell

http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/

Cell is the fundamental single unit in PV. A module in a solar panel refers to Series and parallel arrangement of solar cells.Multiple modules for generation of large Power is called Array

Lets check How (Fundamentals)

• If a PV cell produces 0.5V, then four PV cells connected in series will produce 2.0V

• The total power across four PV cells of 0.5V connected in series when current in the cell = 1A is

2.000 W

• If a PV cell delivers a current of 0.6A and there one three PV cells in parallel there then the current flowing through the load is

1.8A

The Raw Materials Required for Solar Panels

• There are several varieties of cells today that can be used to absorb sunlight and convert those photons into electrical energy. These include:– CIS (Copper Indium Diselenide) Cells– CdTe cells (Cadmium Telluride) Cells – Organic Cells– Multi-junction Cells

• Although multi-junction cells have the highest efficiency among solar cells achieved in a laboratory setting (demonstrated by the following graph), Silicon Cells (monocrystaline, polycrystaline and amorphous) due to their low cost and decent efficiency are the most feasible for wide production and will thus be the main interest of our study.

• .In a solar panel, the metal used is Silver

In a solar panel, the metal used is ______.Answer: 3

8

CrystallineCrystalline

Non-crystallineNon-crystalline

Single crystalSingle crystal

Poly crystallinePoly crystalline

AmorphousAmorphous

Gallium Arsenide (GaAs)Gallium Arsenide (GaAs)

Conversion Efficiency of Module

Conversion Efficiency of Module

10 - 17%10 - 17%

10 - 13%10 - 13%

7 - 10%7 - 10%

18 - 30%18 - 30%

Conversion Efficiency =Electric Energy Output

Energy of Insolation on cellx 100%

Dye-sensitized TypeDye-sensitized Type

Organic Thin Layer TypeOrganic Thin Layer Type

7 - 8%7 - 8%

2 - 3%2 - 3%

Various type of PV cell• Types and Conversion Efficiency of Solar Cell

Silicon SemiconductorSilicon Semiconductor

CompoundSemiconductorCompoundSemiconductor

Solar CellSolar Cell

OrganicSemiconductorOrganicSemiconductor

• Typically the commercial efficiency of the solar cell is

about 15%

• The output power of the solar cell is of the order 1.0 W.

• The output voltage from solar cell is in the range of

0.5 V to 1.0 V. (on an average : 0.5 V).

• The current density of a photo voltaic cell ranges from

40 – 50 mA/cm2

Typical Efficiency, Voltage and current in a Solar Cell

Calculation of O/P Power

• Full sunlight is falling on a 15% efficiency solar cell of area 2 m2 at an angle of incidence of 60 degrees to the normal to the cell. What is the output power of the cell?

150 W.

Lets calculate.

Fill Factor •.A photocell has a short circuit current of 25 mA, an open

circuit voltage of 0.6 V and a maximum power output of

12 mW. What is its fill factor?

80%

Lets calculate.

PV Cells Technologies

• Characterization criterion:• Thickness:

• Conventional – thick cells (200 - 500 μm)• Thin film (1 – 10 μm). Tend to be less costly than conventional (think) cells but they also tend to be less reliable and efficient.

• Crystalline configuration:• Single crystal• Multicrystalline: cell formed by 1mm to 10cm single crystal areas.• Polycrystalline: cell formed by 1μm to 1mm single crystal areas.• Microcrystalline: cell formed by areas of less than 1μm across.• Amorphous: No single crystal areas.

• p and n region materials:• Same material: homojunction (Si)• Different material: heterojunction (CdS and CuInSe2)

PV Technology Classification

Silicon Crystalline Technology Thin Film Technology

Mono Crystalline PV Cells Amorphous Silicon PV Cells

Multi Crystalline PV Cells Poly Crystalline

PV Cells ( Non-Silicon

based)

PH 0101 Unit-5 Lecture-2 14

Based on the types of crystal used, solar cells can be classified as,1. Mono crystalline silicon cells2. Polycrystalline silicon cells3. Amorphous silicon cells

1. The Monocrystalline silicon cell is produced from pure silicon (single crystal). Since the Monocrystalline silicon is pure and defect free, the efficiency of cell will be higher.

2. In polycrystalline solar cell, liquid silicon is used as raw material and polycrystalline silicon was obtained followed by solidification process. The materials contain various crystalline sizes. Hence, the efficiency of this type of cell is less than Monocrystalline cell.

5. Types of Solar cell


3. Amorphous silicon was obtained by depositing silicon film on the substrate like glass plate.

• The layer thickness amounts to less than 1µm – the thickness of a human hair for comparison is 50-100 µm.

• The efficiency of amorphous cells is much lower than that of the other two cell types.

• As a result, they are used mainly in low power equipment, such as watches and pocket calculators, or as facade elements.

Silicon Crystalline Technology

Currently makes up 86% of PV market Very stable with module efficiencies 10-16%

Mono crystalline PV Cells

•Made using saw-cut from single cylindrical crystal of Si

•Operating efficiency up to 15%

Multi Crystalline PV Cells

•Caste from ingot of melted and recrystallised silicon

•Cell efficiency ~12%

•Accounts for 90% of crystalline Si market

CdTe/CdS Solar Cell

• CdTe : Bandgap 1.5 eV; Absorption coefficient 10 times that of Si

• CdS : Bandgap 2.5 eV; Acts as window layerLimitation : Poor contact quality with p-CdTe (~ 0.1 cm2)

Thin Film Technology

Silicon deposited in a continuous on a base material such as glass, metal or polymers

Thin-film crystalline solar cell consists of layers about 10μm thick compared with 200-300μm layers for crystalline silicon cells

PROS• Low cost substrate and fabrication process

CONS• Not very stable

Amorphous Silicon PV Cells The most advanced of thin film technologies

Operating efficiency ~6%

Makes up about 13% of PV market

PROS• Mature manufacturing technologies available

CONS• Initial 20-40% loss in efficiency

Poly Crystalline PV Cells

Copper Indium Diselinide

CIS with band gap 1eV, high absorption coefficient 105cm-1

High efficiency levels

PROS• 18% laboratory efficiency• >11% module efficiencyCONS• Immature manufacturing process• Slow vacuum process

Non – Silicon Based Technology

Poly Crystalline PV Cells

Cadmium Telluride ( CdTe) Unlike most other II/IV

material CdTe exhibits direct band gap of 1.4eV and high absorption coefficient

PROS• 16% laboratory efficiency• 6-9% module efficiency CONS• Immature manufacturing

process

Non – Silicon Based Technology

• The solar cell is the basic building block of solar photovoltaics.

•When charged by the sun, this basic unit generates a dc photovoltage of 0.5 to 1.0V and, in short circuit, a photocurrent of some tens of mA/cm2.

•Since the voltage is too small for most applications, to produce a useful voltage, the cells are connected in series into modules, typically containing about 28 to 36 cells in series to generate a dc output of 12 V.

•To avoid the complete loss of power when one of the cells in the series fails, a blocking diode is integrated into the module.

•Modules within arrays are similarly protected to form a photovoltaic generator that is designed to generate power at a certain current and a voltage which is a multiple of 12 V.


Materials for Solar cell

Solar cells are composed of various semiconducting materials

1. Crystalline silicon2. Cadmium telluride3. Copper indium diselenide4. Gallium arsenide5. Indium phosphide6. Zinc sulphide

Note: Semiconductors are materials, which become electrically conductive when supplied with light or heat, but which operate as insulators at low temperatures


6. Principle, construction and working of Solar cellPrinciple: The solar cells are based on the principles of photovoltaic effect.The photovoltaic effect is the photogeneration of charge carriers in a light absorbing materials as a result of absorption of light radiation.

Construction

• Solar cell (crystalline Silicon) consists of a n-type semiconductor (emitter) layer and p-type semiconductor layer (base). The two layers are sandwiched and hence there is formation of p-n junction.

• The surface is coated with anti-refection coating to avoid the loss of incident light energy due to reflection.


The mechanism of electricity production- Different stages

Conduction band High density

Valence band Low density

E

The above diagram shows the formation of p-n junction in a solar cell. The valence band is a low-density band and conduction band is high-density band.


Stage-1

Therefore, the hole (vacancy position left by the electron in the valence band) is generates. Hence, there is a formation of electron-hole pair on the sides of p-n junction.

When light falls on the semiconductor surface, the electron from valence band promoted to conduction band.



E


Stage-2

In the stage 2, the electron and holes are diffuse across the p-n junction and there is a formation of electron-hole pair.



Ejunction


Stage-3

In the stage 3, As electron continuous to diffuse, the negative charge build on emitter side and positive charge build on the base side.



Ejunction


Stage-4When the PN junction is connected with external circuit, the current flows.



Ejunction

Power


• Over 95% of all the solar cells produced worldwide are composed of the semiconductor material Silicon (Si). As the second most abundant element in earth`s crust, silicon has the advantage, of being available in sufficient quantities.

• To produce a solar cell, the semiconductor is contaminated or "doped".

• "Doping" is the intentional introduction of chemical elements into the semiconductor.

• By doing this, depending upon the type of dopant, one can obtain a surplus of either positive charge carriers (called p-conducting semiconductor layer) or negative charge carriers (called n-conducting semiconductor layer).


• If two differently contaminated semiconductor layers are combined, then a so-called p-n-junction results on the boundary of the layers.

• By doping trivalent element, we get p-type semiconductor. (with excess amount of hole)

• By doping pentavalent element, we get n-type semiconductor ( with excess amount of electron)

n-type semiconductor

p- type semiconductor

p-n junction layer


2. Photovoltaic effect

Definition:The generation of

voltage across the PN junction in a semiconductor due to the absorption of light radiation is called photovoltaic effect. The Devices based on this effect is called photovoltaic device.

Light energy

n-type semiconductor

p- type semiconductor

Electrical Power

p-n junction


3. electron-hole formation• Photovoltaic energy conversion relies on the number of photons strikes on the earth. (photon is a flux of light particles)

• On a clear day, about 4.4 x 1017 photons strike a square centimeter of the Earth's surface every second.

• Only some of these photons - those with energy in excess of the band gap - can be converted into electricity by the solar cell.

• When such photon enters the semiconductor, it may be absorbed and promote an electron from the valence band to the conduction band.


• Therefore, a vacant is created in the valence band and it is called hole.

• Now, the electron in the conduction band and hole in valence band combine together and forms electron-hole pairs.

holeValence band

Conduction band

electron

Photons

35

Mechanism of generation• Voltage and Current of PV cell ( I-V Curve )

(V)

(A)

Voltage(V)

Cu

rre

nt(I

)

P

N

A

Short Circuit

Open Circuit

P

N

V

about 0.5V (Silicon)

High insolation

•Voltage on normal operation point0.5V (in case of Silicon PV)

•Current depend on- Intensity of insolation- Size of cell

•Voltage on normal operation point0.5V (in case of Silicon PV)

•Current depend on- Intensity of insolation- Size of cell

Low insolation

Normal operation point(Maximum Power point)

I x V = W

Fill Factor The ratio of Maximum obtainable power to the product of the open ckt voltage and s/c current.

FF = (Imp x Vmp) / (IL x Voc).

Cells with high Fill Factor have a low equivalent series resistance and a high equivalent shunt resistance, so less of the current produced by the cell is dissipated in internal losses.

What’s in a Polycrystalline Si Solar Cell?

-Polycrystalline cells are slightly less efficient thanmonocrystallinesolar cells, but are cheaper to manufacture in wafer form.-The diagram below from How Stuff Works illustrates the order of the raw ingredients needed to create a generic polycrystalline silicon cell. They include:A.A layer of glass for protectionB.Antireflective coatingC.Contact gridD.Highly purified N-Type SiliconE.P-Type SiliconF.Back Contact.

Emerging Technologies

Electrochemical solar cells have their active component in liquid phase

Dye sensitizers are used to absorb light and create electron-hole pairs in nanocrystalline titanium dioxide semiconductor layer

Cell efficiency ~ 7%

‘ Discovering new realms of Photovoltaic Technologies ‘

Electrochemical solar cells

Emerging Technologies

Ultra Thin Wafer Solar Cells

Thickness ~ 45μm Cell Efficiency as high as

20.3%

Anti- Reflection Coating

Low cost deposition techniques use a metalorganic titanium or tantanum mixed with suitable organic additives

Open circuit voltage (VOC) Short circuit current (ISC) Maximum power Efficiency

Solar Cell Properties

Factors affecting Solar Cell PerformanceLight intensity (type of light)Light wavelength (color of light)Angle of incident lightSurface condition of solar cells (cleanness)Temperature on solar cells

Peak Power Point (Maximum Power)• A solar cell may operate over a wide range of

voltages (V) and currents (I). By increasing the resistive load on an irradiated cell continuously from zero (a short circuit) to a very high value (an open circuit) one can determine the maximum-power point, the point that maximizes V×I, that is, the load for which the cell can deliver maximum electrical power at that level of irradiation.

• Dynamically adjust the load so the maximum power is always transferred, regardless of the variation in lighting.

The Band Gap• A property of the

atoms of the semiconductor

• This is the energy gap between two “bands” of energy between tow electron states in a solid

• Only photon energy which matches the band gap energy of the material can free an electron from that state. Energy of a photon

http://mousely.com/encyclopedia/Band_gap/

Solar Cell Efficiency

• Considers how much energy available and compares it to how much energy is used

productively

Solar cell efficiency ( ) depends on

- The total power light power density (JV) on the cell

- The actual potential difference of the system

- The actual current density of the system

- The “fill factor” constant which is the ratio between the actual values and the maximum values

Conventional Silicon Solar cellsSingle and Polycrystalline SiliconCommercial Efficiency ~ 16 %Laboratory ~ 26%

Thin Film Solar Cellsa Si , CdTe, CIGS and thin film crystalline SiCommercial Efficiency ~ 10 %Efficiency at Laboratory scale ~ 16 %

Three Generations of solar cell technology:1.Single-crystal silicon based photovoltaic devices

• Good efficiency• High Cost

Higher than traditionally-produced electricity

2.CuInGaSe2 (CIGS) polycrystalline semiconductor thin films

• Low Cost• Less Efficiency

3.Nanotechnology-enhanced solar cells• Low Cost• Medium Efficiency

46

Various type of PV cell•Roughly size of PV Power Station.

How much PV can we install in this conference room?

1 kw PV need 10 m21 kw PV need 10 m2 Please remember

10m(33feet)

20m

(66f

eet)

ConferenceRoom

(We are now)

Our room has about 200 m2

We can install about20 kW PV in this room

(108 feet2)

(2,178 feet2)

• Loads/sources wired in parallel:

– VOLTAGE REMAINS CONSTANT– CURRENTS ARE ADDITIVE – Two interconnection wires are used between two components

(positive to positive and negative to negative)– Leave off of either terminal – Modules exiting to next component can happen at any parallel terminal

Parallel Connections

unit 03 solar ver 01

Documents

generation solar cells

pv cells

modern solar cell

collection of cells

solar panelsthere

varieties of cells

silicon cells monocrystaline

photovoltaic cell