Photovoltaics
Photovoltaics (PV) literally means "light-electricity"
· direct conversion of light into electricity based on the photovoltaic effect · advanced semiconductor device: solar cells (do not confuse with solar collectors) collectors · the main energy source for the "post-fossil-era"

Photo - voltaics

Solar radiation

Solar module

Sun
A. Poruba, Solartec

Photovoltaic solar energy
Advantages:
· · · · · · · · · environmentally friendly no noise, no moving parts no emissions no use of fuels and water minimal maintenance requirements long lifetime, up to 30 years electricity is generated wherever there is light, solar or artificial PV operates even in cloudy weather conditions modular "custom-made" energy can be sized for any application from watch to a multi-megawatt power plant

Limitations:
· PV cannot operate without light · high initial costs that overshadow the low maintenance costs and lack of fuel costs · large area needed for large scale applications · PV generates direct current special DC appliances or an inverter are needed · in off-grid applications energy storage is needed

Solar cell operation
Solar cell operation is based on the photovoltaic effect:
The generation of a voltage difference at the junction of two different materials in response to visible or other radiation.

Solar cell external parameters
I-V measurement
Standard test conditions: · AM1.5 spectrum · irradiance 1000 W/m2 · temperature 25°C External parameters: · Short circuit current Isc [A] · Open circuit voltage Voc [V] · Fill factor ff · Maximum (peak) power Pmax [Wp] · Efficiency
P
Open circuit voltage Voc [V]

Peak Power Pmax [Wp]

Short circuit current Isc [A]

Pmax = Vmp I mp = ff Voc Isc

= Pmax PI = ff Voc Isc PI

Theoretical efficiency as a function of semiconductor band gap
30

GaAs Si a-Si:H Cu2S a-Si:H:F

Efficiency (%)

25 20 15 10 5

Ge

CdS

Main energy losses: · Non-absorption of low-energy photons · Thermalization of excess photon energy · Voltage factor · Fill Factor · Collection efficiency · ....
2,5

0,5

1,0

1,5

2,0

Semiconductor band gap (eV)

Three generations of solar cells
I. Wafer based Si
100 80 US$ 0.1/Wp US$ 0.2/Wp US$ 0.5/Wp Thermodynamic limit US$ 1.0/Wp Present limit I II 0 100 200 300 400 US$ 3.5/Wp 500c

II. Thin films

Efficiency [%]

60 40 20 III

III. Cheap and efficient

Cost [US$/m2]

Concepts for
· Intermediate band · Hot carriers

rd 3

generation cells
· Superlattices · Quantum dots · Nanotubes

· Up- and down conversion

Solar cell technologies
Technology c-Si
Efficiency [%]

HIT
Heterojunction with Intrinsic Thin Layer

TF Si
(stabilised)

CIS

CdTe

DSSC Polymer 11
unstable

Record cell

24.7 Mono 19.8 Multi 16.6 transfer 22.7 Mono 15.3 Multi

22.3

9.3 Single 12.4 Tandem 13.4 Triple 10.4 Triple

18.9

17.0

Record module

?

13.4

10.7

4.7

Commercial 12-17 module Cost reduction Limited

16-17

5-9

9-11

10

not available

Limited

++

++

++

++?

Bulk materials for solar cells
Bulk Crystalline Silicon

Thin-film materials for solar cells
Thin-film Silicon
Hydrogenated amorphous silicon (a-Si:H) Hydrogenated microcrystalline silicon (µc-Si:H)

PV system
Solar cell
· · semiconductor device different than collector

Solar panel (PV module) Solar array Solar system:
· · · · · solar panel battery inverters electrical components appliance

Solar cell applications
Space application
Bulk c-Si
GaAs c-Si
~12 % ~18 %

Terrestrial application
Thin Films

Mono c-Si
~ 15-17%

Multi c-Si
~ 13-15%

CIGS
lab ~ 19% ind ~ 12%

CdTe
lab ~ 16% ind ~ 9%

Poly c-Si
lab ~ 16% ind ~ 9%

TF Si
a-Si:H lab ~ 13% ind ~ 9%

Organic
lab ~ 11%

~24 %

GaAs (Gallium Arsenide) CIGS (Copper Indium Gallium Diselenide) CdTe (Cadmium Telluride) a-Si:H (Hydrogenated amorphous silicon)

PV industry
PV industry: the fastest growing industry in the world
MW
3000

Solar cell production 1999-2006 2006: 90% wafer-type c-Si technology
2536 1815
40%

Market Jobs Predictions

2500 2000 1500 1000 500 0

1256
45%

202
1999

287
42%

401
40%

560

750
68% 34%
Estimation market:

39%

2005 ~ 9 000x106

2000

2001

2002

2003

2004

2005

2006

Photon International, March 2007

~ 70 000 jobs

PV applications
1. Off-grid (stand alone) residential power systems
(solar home systems for individual household)

2. Grid connected PV systems
(roofs and outer walls of buildings, noise barriers along the motorways)

3. Off-grid industrial power systems
(water management, lighting, and telecommunication)

4. Consumer products
(watches, calculators, and lanterns)

5. Space applications

PV module market
Market sector [MWp]
Consumer products US off-grid residential World off-grid rural Communications/signal PV/diesel commercial Grid connected Central power Total Average price (US$/Wp)

1993
18 5 8 18 10 2 2 63 4.25

1996
22 8 15 23 12 7 2 89 4.00

1999
35 13 31 35 25 60 2 201 3.50

2001
45 19 45 46 36 199 5 395 3.50

2003
65 30 70 70 50 365 8 658 3.00

P.D. Maycock, Renewable Energy World, Vol. 7, No. 4, 2004

Primary challenge for PV
Cost reduction of factor 5
to become competitive with conventional electricity

Today PV module price: 3.5-5.0 /Wp
Integral approach:

(Wp = Watt peak)

Reducing module costs raw materials & labor, investments efficiency, lifetime Optimizing systems integration area and power related costs Note: overall optimum highest efficiency

Learning curve
The combined effect of technology development and manufacturing experience

Cost reduction of PV systems
Requirements: · low cost solar energy material · high efficiency and good stability · low manufacturing cost with good yield · environmental safety and short energy pay back time

Energy pay back time: the time required for an energy conversion system or device to produce as much energy as is consumed for its production

PV electricity price
Wim Sinke (ECN,
Leader of WG 3 : Science, technology & applications of EU PV Technology Platform

)

2005

PV electricity price ( / kWh) 0.50

consumer electricity price ( / kWh) 0.22 0.14

0.16 0.16

PV electricity prices*) compared with typical consumer electricity prices

0.42 0.11 0.36

0.31

0.20 0.12 0.10

*) depreciation 25 yrs, real interest rate 4%, O&M cost 1%/yr, PR 0.75 (example)

0.28

"grid parity"

PV electricity price
2010
PV electricity price ( / kWh) 0.35 0.23 0.15 consumer electricity price ( / kWh)

0.17 0.17

PV electricity prices compared with expected consumer electricity prices (+ 1%/yr)

0.29 0.11 0.25

0.22 0.13 0.11

0.21

0.19

PV electricity price
2015
PV electricity price ( / kWh) 0.25 0.24 0.16 consumer electricity price ( / kWh)

0.18 0.18

PV electricity prices compared with expected consumer electricity prices (+ 1%/yr)

0.21 0.12 0.18

0.16 0.13 0.11

0.22

0.14

PV electricity price
2020
PV electricity price ( / kWh) 0.20 0.26 0.16 consumer electricity price ( / kWh)

0.19 0.19

PV electricity prices compared with expected consumer electricity prices (+ 1%/yr)

0.17 0.12 0.14

0.13 0.14 0.12

0.23

0.11

PV electricity price
2030
PV electricity price ( / kWh) 0.10 0.28 0.18 consumer electricity price ( / kWh)

0.20 0.20

PV electricity prices compared with expected consumer electricity prices (+ 1%/yr)

0.08 0.14 0.07

0.063 0.15 0.13

0.26

0.055