Photovoltaics Cells

7/27/2019 Photovoltaics Cells

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PV Cell Working Principleand Applications

1/Dec/2008Ir Dr Edward LO

Associate Professor Department of Electrical Engineering

The Hong Kong Polytechnic University2

How Powerful is Solar Power? Solar power intensity just outside the

atmosphere of the Earth: 1.353 kW/m 2.This value is also called solar constant .

With the known radius of Earth ~=6380km, solar power falling on The Earth~=173000TW

While the current global power consumption average over a year is only ~16TW as in 2005

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Solar power intensity ~ 1kW/m 2 atsea level in sunny day

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First application of PV cells

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How PV generates


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Common Types of PV cells

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Different PV technology

mono-crystalline (m-Si)typical efficiency: 15%+

poly-crystalline /multi-crystalline (p-Si)

typical efficiency: 10-15%

Copper Indium Diselenide(CIS)typical efficiency: 9-12%

Amorphous Silicon (a-Si)typical efficiency: 4-7%

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crystalline PV cells

m-Si14.46%

p-Si12.62%

p-Si8.29%

p-Si12.68% p-Si

13.66%

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Semi-transparent PV cells

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Cell,Module, Array

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Typical I-V & P-V Curve of a PVCell at a given solar irradianceI

V

1000W/m2

Power


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Typical I-V Curve of a PV Cell atdifferent values of solar irradiance

I

V

1000W/m2

800 W/m2

600 W/m2

400 W/m2

200 W/m2

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Electrical properties, I-V curveI

V

Load curve of maximum power point

resistive load 1000 W/m2

800 W/m2

600 W/m2

400 W/m2

200 W/m2

STC MPP

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Effect of cell temperature on the V-ICurve (at given solar irradiation)

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Name Plate Rating of a PV Panel

It is themaximumpower outputat STC(Standard TestCondition)

Usually STC =1000 W/m 2,25 C PanelTemperature

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efficiency characteristics

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Effect of partial shading onperformance of PV array

100% irradiance

10% irradiance

Very low output fromthe PV system,althoughOnly of themodules are shaded


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100% irradiance

10% irradiance

Must maintain 3/4full output from thePV system, when of the modules areshaded

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BlockingDiodes

BypassDiodes

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BIPV Building IntegratedPhotovoltaic System

Act as other building functions other thangenerating electricity

No harmful side effects No moving parts silent, solid state device No (low) maintenance

Modular format /non-intrusive Versatile

Locations Rural/Urban Applications for stand alone applications

Water pump, Lighting, Desalination plants

The Plus Points:

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Barriers to BIPV application

Relatively high capital cost of the PV panels. Module efficiency is still relatively low

Little understanding of PV system design Less real experience of installations Incentives (in HK) not yet in place

The HK scenario:

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Why BIPV? (1) Replace conventional building materials

concept of avoided cost Does not require any extra land area Does not require any additional support or

infrastructure installation

The above three points smallincremental cost for BIPV systems

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Why BIPV? (2) May cover part of the electricity consumption of

the building. Can provide electricity during peak demand time

times and thus reduce the utility's speak deliveryrequirements.

May reduce transmission and distribution loss.

These points reduce the electricity bills of thebuilding and delay the need for construction of new power plants.


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Time of day N oo n

kW

Po we r co ns um pti on by a bu ild in g

Po w er ge ne ra tio n by PV pa ne ls

Consumption Curve and Generation Curve

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Why BIPV ? (3) Can provide an improved aesthetic

appearance in an innovative way. Can integrated with maintenance, control

and operation of the other installations andsystems in the building.

Can provide reduced planning costs.

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With grid connection, the system cantotally eliminate the storage batteries andits associated problems.

Hence lower capital, replacement andmaintenance cost.

Why BIPV ? (4)

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PV system: stand-alone vs.grid-connected

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Grid-connected systems(G-BIPV) PVs connected to the public grid via an

inverter. Eliminate the expensive and bulky

batteries. Involve local regulatory issues. Must compete against the cost of the

conventional energy source used to supplythe grid.

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Block diagram of G-BIPV Loc al l oads

Power conditioning subsystemco-ordinated with the electromechanical

safety disconnect subsystem

from utility grid

electromachanical sa fetydisconnect

manual disconnect sw itch / electromachanical safe ty disconnect

PV arra ys DC

AC


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Grid-connecting inverter

2kW2kW

convert DC to AC

capacity ranges from 100W to 500kW

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New generation inverters (stringinverter)

100W

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Characteristics of an inverter

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inverter selection

high efficiency (of course) selection of inverter nominal P in with array's

rated kW p (e.g. vertical facade array) read the data-sheet carefully

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BIPV system at Wan Chai Tower

Three systems: Rack type at the roof Sun shading type at mid-floors Skylight type at the lift lobby of ground floor

The site: 22 16 50 N and 114 10 30 EOrientation: south facing about 5 degree off

south toward east

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Wanchai Tower of HKGovernment Building

3 BIPV Systems


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Wan Chai Tower Roof Rack BIPV SystemLocation Roof

Orientation 10 degree to horizontal,facing south

Type of panels Polycrystalline

No. of panels per string 18

No. of strings 7 strings per group, 2 groups

Total no. of panels 252

Total PV panel area 164.70 m 2

System rated power 20.16 kW

No. of inverters 1 inverter per group

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WanChai Tower: Roof Polycrystalline 20 kWpeak

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Wan Chai Tower Sun Shade BIPV System

Location Middle section of the building

Orientation Vertically facing south

Type of panels Monocrystalline


No. of strings 8 strings per group, 2 groups





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WanChai Tower: Sun ShadingBIPV system

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Wan Chai Tower Skylight BIPV System

Location Ground floor lobby

Orientation Vertically facing south

Type of panels Monocrystalline


No. of strings 7 strings





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WanChai Tower: Skylight BIPVsystem


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Science Park 1 BIPV System

Type:PV /grid-connectedPVtechnology:m-SiPV nos/area:1380 / 3019.8m2kWp= 198kW

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The End For This Part Thanks for your attention

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Possible Talks from PolyU EE Dept: Electricity generation, transmission & distribution Renewable Energies Energy Efficiency Intelligent Buildings Electric Vehicles LED Lighting and other new lighting systems Power electronics & drives Railway and its signaling systems Application of photonic devices in engineering Etc..

Photovoltaics Cells

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