NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Sarah Kurtz 

Principal Scientist; 

Reliability Group 

Manager

9.9.2010

GE 2010 Electronics 

Packaging 

Symposium

NREL/PR-540-49386

Practical Issues when Selecting PV Technologies
One “winner” or many technologies?

National Renewable Energy Laboratory Innovation for Our Energy Future

Nickel cadmium

Lithium ion

Lead acid

Lithium

Alkaline Nickel metal hydride

Different technologies for different applications

Expect this for both PV and batteries

2
Outline

• Practical considerations: initial cost, efficiency, 

reliability

• Three primary approaches today

- Silicon

- Thin film

- Concentrator

• Strategies for tomorrow

- Breakthrough

- Incremental reductions in cost and improved 

efficiency

- Lifetime as a path to low cost

National Renewable Energy Laboratory 3 Innovation for Our Energy Future
Three key practical issues

National Renewable Energy Laboratory 4 Innovation for Our Energy Future

Initial Cost

Efficiency Reliability
A little history

National Renewable Energy Laboratory 5 Innovation for Our Energy Future
National Renewable Energy Laboratory Innovation for Our Energy Future

Growth of photovoltaic (PV) industry

6

Area of Si passes 

microelectronics 

Tons of Si pass 

microelectronics 

The PV industry has been doubling every ~2 years

Sources: Prometheus/Navigant
National Renewable Energy Laboratory 7 Innovation for Our Energy Future

Growth of PV industry

If we can maintain the 

current growth rate, PV 

will reach major 

milestones in < 10 yrs

1

10

100

GW of PV shipped worldwide annually

2000 2005 2010 2015 2020

Year

Annual new electricity capacity 1996-2006*

*www.eia.doe.gov/emeu/international/electricitycapacity.html (4012-2981 GW)/10 yr

Annual replacement of electricity capacity for 20 yr cycle
Ways to look at cost

Market drivers (these motivate people, but depend on 

cost of money, incentives, etc.):

• Levelized cost of electricity (cents/kWh)

• Avoided cost

Practical ways to look at cost:

• Energy payback

• $ payback

Rule of thumb: 1 kW can generate 1000-2000(+) kWh/y

(At 10 cents/kWh, value after 1 y is $100-200;

At 10% efficiency, 1 kW covers 10 sq m, so cost target 

is $10-$20/sq m if want payback in one year)

National Renewable Energy Laboratory 8 Innovation for Our Energy Future

Note: average electricity price in US in 2009 was 9.7 cents/kWh (EIA)
Three approaches to PV (and lower cost)

National Renewable Energy Laboratory 9 Innovation for Our Energy Future

Front

Solar cell

Back

2. Thin film

3. Concentrator

1. Silicon

Reduce semiconductor 

material

(historically, semiconductor was a 

primary cost driver)
Cost breakout – module cost is about half

National Renewable Energy Laboratory 10 Innovation for Our Energy Future

Source:

Cameron, et al

PVSC 2010
Higher efficiency can reduce cost

National Renewable Energy Laboratory 11 Innovation for Our Energy Future

Upfront costs:

1. Semiconductor material

2. Area-related costs (glass, installation, real estate, wiring)

3. Power-related costs (inverter, permitting, insurance)

Front Solar cell

Back

2. Thin film

3. Concentrator

1. Silicon

Reduce semiconductor 

material

Reduce area by 

increasing efficiency

Two strategies for reducing cost:

Increasing efficiency may be a key path to reduced cost
Types of PV – currently available 

• Crystalline silicon

• Mono-crystalline

• Multi-crystalline

• Ribbon

• Thin film

• CdTe (Cadmium telluride)

• CIGS (Copper Indium (Gallium) Selenide)

• Amorphous silicon – usually combined with microcrystalline 

silicon layers in a multijunction stack; may contain Ge

• Organic

• Concentrator (may be classified in many ways)

• Refractive/reflective

• Multijunction III-V or silicon

National Renewable Energy Laboratory 12 Innovation for Our Energy Future
Historic PV Technology Mix

National Renewable Energy Laboratory 13 Innovation for Our Energy Future

• Early markets were dominated by consumer electronics

• Historically, crystalline silicon has dominated the market

• Technology mix is becoming more diverse

• CdTe is primary new entrant; CIS may be 5-7 yr behind; CPV ~ 10 yr

Source: 

PHOTON 

International

Calculators
0.001 0.01 0.1 1 10 100 1000

Installation size (MW)

A key factor affecting technology mix: Distributed vs Central

National Renewable Energy Laboratory 14 Innovation for Our Energy Future

PV

Solar Thermal

Modern Wind

Residential Commercial Utility

200

150

100

50

Maximum PV Plant Size (MW)

0

2004 2006 2008 2010 2012

Year

Planned

Recently PV has seen increases in:

• Maximum system size

• Average system size

• Ground mount (in addition to roof mount)

• Connection at transmission instead of 

at distribution voltages

• Utility ownership

These changes may affect the technology mix
Within US, predictions are for large utility growth

National Renewable Energy Laboratory 15 Innovation for Our Energy Future

8

6

4

2

0

GW

2009 2010 2011 2012 2013

Year

Rogol

Lorenz

Projected Installed US Utility-Scale Capacity

All US installations in 2009

Source: PHOTON International

If utility growth is this large, it will change the technology mix
Three approaches to PV – 1. Silicon

National Renewable Energy Laboratory 16 Innovation for Our Energy Future

Front

Solar cell

Back

2. Thin film

3. Concentrator

1. Silicon

•Mono-crystalline

•Multi-crystalline

•Ribbon
Silicon modules

SiliconS

Glass

.Backsheet .

Silicon cell Tab

Common packaging materials

EVA - Ethylene vinyl acetate

PET - Polyethylene terephthalate

PVF - Poly vinyl fluoride

ETFE – Ethylene tetrafluoroethylene 

Si module cross section 

(not to scale)

Construction of silicon modules is simple in concept

EVA
Crystalline Silicon - history 

• Predictions of the demise of silicon PV have been 

voiced for decades:

• Silicon cells must be fairly thick, increasing material cost

• Shortage of silicon feedstock – in 2007, 2008 we saw this 

(fast-growing industries tend to develop shortages)

National Renewable Energy Laboratory 18 Innovation for Our Energy Future

Area of Si passes 

microelectronics 

Tons of Si pass 

microelectronics 

Despite the predictions, silicon PV is alive and well
Crystalline silicon

Advantages:

• Builds on strong industry

• Silicon is abundant and non toxic

• Efficiencies of 15%-20% are achievable

• Demonstrated > 20 years performance in field

• Warranties typically < 1% degradation/y

• Potential for further cost reduction

Disadvantages:

• Costs are higher than desired

National Renewable Energy Laboratory 19 Innovation for Our Energy Future
Three approaches to PV – 2. Thin film

National Renewable Energy Laboratory 20 Innovation for Our Energy Future

Front

Solar cell

Back

3. Concentrator

1. Silicon

2. Thin film

•CdTe

•CIGS 

•Amorphous Si 

•Organic

Reduce semiconductor 

material
Thin-film approaches on the market

National Renewable Energy Laboratory Innovation for Our Energy Future

CuIn(Ga)Se CdTe Amorphous silicon

21
Monolithic module integration

National Renewable Energy Laboratory Innovation for Our Energy Future

+

Contact

Cell

(Inactive)

Contact

Cell

(Inactive)

Active Cell

Glass

5 x 120 μm

Conductor

Device

Conductor

– w

22

Thin-film modules have a different construction than Si modules
Thin film products vary in their construction, 

but many use glass-glass construction

National Renewable Energy Laboratory Innovation for Our Energy Future

Glass

ITO or TCO

CdS

CdTe

Metal

Glass for strength

CdTe uses superstrate

Glass for protection

ZnO or TCO

CdS

CuInGaSe

Molybdenum

Glass

CuInGaSe uses substrate

Not to 

scale

23

EVA

EVA
Is glass/glass construction required?

• Strategies to avoid glass/glass construction:

• Reduce moisture sensitivity (change cell design)

• Develop flexible moisture barrier

• If successful, opens many markets:

• Awnings

• Shingles

• Car roofs, etc.

National Renewable Energy Laboratory 24 Innovation for Our Energy Future

If moisture problem is solved, flexible packages can open new markets
Thin film vision – looking to the future

National Renewable Energy Laboratory 25 Innovation for Our Energy Future

Vision (advantages)

• ~1-μm-thick film on inexpensive substrate

• Materials requirement is small: reduced cost

• Organic PV Vision: a PV plastic wrap

• Dye-sensitized Vision: PV spray-on paint

• Low CapEx enables easy ramp up

• Can be integrated into building façade

Challenges (disadvantages)

• Growth on inexpensive substrates limits efficiency

• Sensitivity to moisture leads to glass/glass laminate

• Infrastructure is not as well developed as for silicon 

• Building integration increases operating temperature
First Solar demonstrated thin-film concept

National Renewable Energy Laboratory 26 Innovation for Our Energy Future

2000

1500

1000

500

0

Capacity (MW/y)

2005 2006 2007 2008 2009 2010 2011

Year

Projected

First Solar Production Capacity

#1 in world

First Solar grew to be #1 in world in just four years, demonstrating 

the benefit of using less semiconductor material 
Historic PV Technology Mix

National Renewable Energy Laboratory 27 Innovation for Our Energy Future

• First Solar has put CdTe on the map 

• Dozens of other thin-film companies hope to be the next “First Solar”

Source: 

PHOTON 

International

First 

Solar
Comparison of efficiencies

National Renewable Energy Laboratory 28 Innovation for Our Energy Future

In general, silicon outperforms thin film in terms of efficiency

Thin film is catching up!

Source: DOE EERE 2008 Solar 

Technologies Market Report

Si

Thin Film

Miasole just 

announced
Comparison of degradation rates

National Renewable Energy Laboratory 29 Innovation for Our Energy Future

Statistically, observed 

degradation rates are about 

0.5%/y

Degradation rates of recent 

thin-film products are smaller 

than for pre-2000 products

Source: Jordan, et al. PVSC 2010
Three approaches to PV

National Renewable Energy Laboratory 30 Innovation for Our Energy Future

Front

Solar cell

Back

2. Thin film

3. Concentrator

1. Silicon

Reduce semiconductor 

material
National Renewable Energy Laboratory Innovation for Our Energy Future

Two primary concentrator approaches

High concentration

• 35% - 40% III-V cells

• 400X – 1500 X

Low concentration

• 15% - 25% Silicon cells

• 2X – 100 X

Amonix JX Crystals

31
Concentrator technology

Maturity is 

similar to that 

of airplanes 

100 years ago

National Renewable Energy Laboratory 32 Innovation for Our Energy Future
CPV

Advantages:

• CapEx is typically smaller than for silicon

• Reduces use of semiconductor material, potentially 

enabling low cost

• Allows use of very high efficiency solar cells

• Module efficiency up to ~ 30% (verified)

• Is mostly an engineering project

Disadvantages:

• Only uses direct beam (no output on cloudy days)

• Not yet well established

• Difficult to integrate into buildings (was rejected in ‘90s)

National Renewable Energy Laboratory 33 Innovation for Our Energy Future
CPV

Current status

• Dozens of companies exploring CPV

• A handful of companies are setting up automated 

production

• These companies are likely to each install > 1 MW in 

2010

• Amonix just announced 30 MW project in Colorado

• Once bugs are worked out, could ramp quickly

• Not yet clear whether applications will be limited to 

utility-scale

National Renewable Energy Laboratory 34 Innovation for Our Energy Future
Returning to the question of cost 

Practical ways to look at (real) cost:

• Energy payback

• $ payback

Rule of thumb: 1 kW can generate 1000-2000+ kWh/y

(At 10 cents/kWh, that’s $100-200 in first year;

At 10% efficiency, 1 kW covers 10 sq m)

For payback in one year: cost target is $10-$20/sq m

Note: installation and permitting costs can exceed this 

budget

National Renewable Energy Laboratory 35 Innovation for Our Energy Future
Strategies for tomorrow’s PV

• Breakthrough

• Higher efficiency

• Lower cost

• Cost avoidance

• Incremental reductions in cost and improved 

efficiency

• Lifetime as a path to low cost

National Renewable Energy Laboratory 36 Innovation for Our Energy Future
‘Breakthrough’ or ‘Revolution through Evolution’?

Two camps predicting future of PV:

- Need revolutionary breakthrough

- Achieve revolution through evolution

Potentially high-efficiency breakthrough 

approaches have been explored for 

decades:

• Intermediate band, 

• Hot carrier, 

• Multiple exciton.

National Renewable Energy Laboratory 37 Innovation for Our Energy Future
National Renewable Energy Laboratory Innovation for Our Energy Future

Efficiency differentiates technologies

38
Kurtz, Prog. In PV, 2008.

Three ways to achieve higher efficiencies: 

1.more junctions, 2. excellent material quality, 3. use concentration

Efficiency can give incremental improvement

80

60

40

20

0

Maximum Efficiency (%)

1 2 3 4 5 6

Number of junctions

Theoretical

(detailed balance)

Amorphous 

Single-crystal

Polycrystalline

One sun

80

60

40

20

0

Maximum Efficiency (%)

1 2 3 4 5 6

Number of junctions

Theoretical

(max. conc.)

Single-crystal

Polycrystalline

Concentrated sunlight

1000 kW/m 2

500 kW/m 2

(232X)

(180-

1000X)

(360X)

(14X)

Efficiency opportunities
Reduce cost of PV modules

Strategies avoiding glass:

• PV plastic wrap

• PV spray-on paint

(must solve moisture problem and improve efficiency)

Avoid cost by incorporating into building material

• Shingles, etc. replaces building material, so now 

compete with cost of that building material.

(in most cases higher operating temperature means 

lower efficiency: can be 10% to 15% relative effect)

National Renewable Energy Laboratory 40 Innovation for Our Energy Future
Reduce cost through longer lifetime

Rule of thumb: 1 kW can generate 1000-2000 kWh/y

(At 10 cents/kWh, that’s $100-200 – fundamental rub;

At 10% efficiency, 1 kW covers 10 sq m)

Payback of 1 yr @10% efficiency requires <$10-20/sq m

Payback of 1 yr @20% efficiency requires <$20-40/sq m

Payback of 50 yr @20% efficiency requires <$1000-

2000/sq m (assuming no maintenance costs)

Current costs demonstrated at ~ $3000 / sq m

Are 100 year lifetimes possible? If so, we’re ‘there’!

National Renewable Energy Laboratory 41 Innovation for Our Energy Future

Long lifetime may be practical way to reach cost-effective PV
PV prices have decreased

National Renewable Energy Laboratory 42 Innovation for Our Energy Future

Source: PHOTON International

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Module price ($/Watt) 

February June October

2009 2010 

February

Crystalline silicon

Cadmium Telluride (First Solar)

Prices have been coming down; how much more?
Moving cost target?

National Renewable Energy Laboratory 43 Innovation for Our Energy Future

6

5

4

3

2

1

0

Initial cost ($/W)

Old coal New coal Clean coal PV

*Fortnightly’s SPARK, p. 10, May 2008

Assumption of 10 cents/kWh 

may or may not represent 

electricity costs of the future.

New coal plants are more 

expensive than older plants
Summary

• Three practical approaches:

• Lower cost

• Higher efficiency

• Longer lifetime

• Silicon, thin-film, and concentrator 

approaches are all making progress

• In the future, practical strategies could 

include:

• Dramatically reduce cost by removing glass

• Replace other materials (e.g. shingles)

• Lots of incremental improvements

• Long lifetime

National Renewable Energy Laboratory 44 Innovation for Our Energy Future
National Renewable Energy Laboratory 45 Innovation for Our Energy Future

The world can change 

a lot in 100 years.

What will our world be like 

100 years from now?