A LOOK AT

PHOTOVOLTAICS Rui Castro, rcastro@ist.utl.pt

IST – Technical University of Lisbon, Power Systems Group

1

The sun

Passive heat This is heat which we receive from the sun naturally; this can be

taken into account in the design of buildings so that less additional heating is required

Solar thermal Uses the sun’s heat to provide hot water for buildings

Photovoltaic (PV) energy Converts energy from the sun into electricity

2

Some figures

Renewables 3

Some figures

Wind 4

Some figures

PV 5

Some figures

PV annual increase

Source: IEA Trends in Photovoltaic Applications

6

Europe: Global PV market leader

Source: Global Market Outlook for PV until 2013

7

How does PV work

Photovoltaic effect

Phenomenon that certain materials produce electric current when they are exposed to light

Discovered in 1839 by 19 year old Alexandre Edmond Becquerel French physicist

1873: Willoughby Smith discovered the photoconductivity of selenium

1923: Albert Einstein received the Nobel Prize for his theories explaining the photoelectric effect

1954: The PV effect in Cadmium was reported; primary work was performed by Rappaport, Loferski and Jenny

8

How does PV work

PN Junction and Semiconductors

One pure silicon crystal is doped with two

different dopants (e.g. arsenic, gallium,

aluminum, phosphorus)

One half of the crystal is left electron

deficient: p-type layer and the other half has

an excess of electrons: n-type layer

There is an electric field across the junction

between the two halves

Electrons in the crystal can only travel in one

direction - from the electron rich half to the

electron poor half

Where the two halves of the crystal meet is

called a PN junction, and this doped crystal

is a semiconductor

9

How does PV work

Energy from sunlight

The light from the sun is made up of

packets of energy called Photons

When a visible light photon strikes a

solar cell it can pass straight through, be

reflected, or be absorbed

If the photon is absorbed its energy is

absorbed by an electron enabling it to

cross the junction and fill a hole

Electrons are physically moving across

the PN junction and the holes are

moving in the opposite direction

DC current is established around the

load circuit

10

PV power

The power that a PV produces depends on

The amount of incident sunlight (irradiance)

The efficiency of the PV at converting this light to

electricity

Peak power (Wp)

Output power at Standard Test Conditions (STC)

STC: teta=25ºC; G=1000W/m2

11

PV electricity potential in Europe 12

Annual frequency of hourly irradiation

Lisboa

4170

1093

598 568484 523

322 332 275 235159

0

1000

2000

3000

4000

5000

0 0-100 100-200 200-300 300-400 400-500 500-600 600-700 700-800 800-900 900-1000

Radiação (W/m2)

Fre

qu

ên

cia

de o

co

rrên

cia

(h

)13

Average monthly irradiation

77,0

111,9

177,2

217,2

262,9

300,2307,0

273,9

209,6

135,5

87,8

63,6

0

100

200

300

400

Jan Fev Mar Abr Mai Jun Jul Ago Set Out Nov Dez

Rad

iação

so

lar

incid

en

te G

(W

/m2)

14

Some simple technical calculations

Global yearly irradiation @ Lisbon: H=1600kWh/m2

Sample PV module: Pp=200Wp, A=1,5m2

Average efficiency: Ef=12%

Yearly PV energy production: Ea=12%*1600*1,5=288kWh

Yearly utilization factor (equivalent hours @ peak power) ha=Ea/Pp=1440h

15

Renewables utilization factor

Large Hydro

Wind

PV

Portugal

16

PV technologies

Crystalline silicon technology

Efficiency ranges between 12% and 17%

This is the most common technology representing

about 90% of the market today

Types of crystalline cells

Monocrystalline (Mono c-Si)

Polycrystalline (or Multicrystalline) (multi c-Si)

Ribbon sheets (ribbon-sheet c-Si)

17

PV technologies

Thin film technology

Depositing extremely thin layers of photosensitive materials onto a low-cost backing such as glass, stainless steel or plastic

Lower production costs compared to the more material-intensive crystalline technology

Price advantage is currently counterbalanced by lower efficiency (5% to 13%)

Types of thin film modules depend on the active material Amorphous silicon (a-Si)

Cadmium telluride (CdTe)

Copper Indium/gallium Diselenide/disulphide (CIS, CIGS)

Multi junction cells (a-Si/m-Si)

18

Thin films 19

PV technologies

Other cell types

Concentrated photovoltaic (CPV) Designed to operate with concentrated sunlight

Built into concentrating collectors that use a lens to focus the sunlight onto the cells

Use very little of the expensive semiconducting PV material while collecting as much sunlight as possible

Efficiencies are in the range of 20 to 30%

Flexible cells Based on a similar production process to thin film cells, when

the active material is deposited in a thin plastic, the cell can be flexible

This opens the range of applications, especially for Building integration (roofs-tiles)

20

MST Ltd. (Israel) is developing a novel concentrating PV (CPV) technology.

The basic unit is the solar tracker, with an output power of about 50 kWp.

The system's lenses concentrate sunlight to 500 suns on multi-junction highly-efficient (37 %) solar

cells.

CPV 21

Flexible cells 22

PV applications

Grid-connected domestic systems

Most popular type for

homes and businesses

in developed areas

Connection to the local

electricity network

An inverter is used to

convert the DC power

to AC

23

London City Hall, 67 kWp PV system 24

Woking Station (UK), 73 kWp PV 25

Chicken farm, 160 kWp solar tiles,

Switzerland 26

PV housing community, Malaysia 27

PV applications

Grid-Connected power plants

Production of a large

quantity of

photovoltaic electricity

in a single point

The size ranges from

several hundred

kilowatts to several

megawatts

28

Solar farm, 23 MW PV, Spain 29

Solar farm, 20 MW PV, Spain 30

PV applications

Off-grid for rural electrification

Where no mains electricity is available

The system is connected to a battery via a charge controller

An inverter can be used to provide AC power

Use of normal electrical appliances

31

PV applications

Off-grid industrial applications

Repeater stations for

mobile telephones

Traffic signals

Marine navigation aids

Security phones

Remote lighting

Highway signs

Waste water treatment

plants

32

PV in Portugal

Source: IEA Report 2008 - Portugal

33

Moura PV Power Plant

One of the world largest centralized PV plants, with 45,6 MWp installed power

Located @ Amareleja, east Alentejo and owned and operated by Acciona Energy

Built in about 13 months

262 080 PV modules

2520 solar trackers (azimuthal)

Area occupied 250 ha

The estimated annual output is 93 GWh

Final yield slightly over 2000 kWh/kWp

34

Source: IEA Report 2008 - Portugal

Moura power plant

Aerial view 35

Moura power plant

Sun tracking system 36

WS Energia developed and patented the DoubleSun® Technology which duplicates the annual

energy yield of commercial PV modules by combining extremely light flat mirrors with easy-to-

mount, quick-to-install tracking systems.

Double sun (Portugal) 37

Costs

Feed-in tariff vs market prices

Market price

Renewables feed-in tariff

38

Source: Energy Services Regulatory Authority

Costs

Renewables feed-in tariff

PV

Wind

39

Source: Energy Services Regulatory Authority

Some simple economic calculations 40

PV

• Investment=5€/Wp

• Utilization =1500h

• Cost=370€/MWh

Wind

• Investment=1€/W

• Utilization=2200h

• Cost=70€/MWh

Energy cost

Investment

Energy cost

Utilization