Thin-Film Photovoltaics · PDF fileThin-Film Photovoltaics ... Mechanical Pressure Precursors...

HelioVolt Confidential and Proprietary

Thin-Film Photovoltaics

Bert Haskell – Director of Product Development


Outline

• Overview of HelioVolt

• Thin Film CIGS technology

• Thin Film device structure and packaging

• Distributed energy in urban environments

• Rooftop PV

• Building Integrated PV


About HelioVoltFounded: 2001Location: Austin, TXEmployees: 100+Technology: Revolutionary method for manufacturing high-efficiency

CIGS PV circuits

o Completed $101M Private Equity Financing Round late 2007o Launching 20 MW commercial production facility in Austino Seeking strategic partners for product collaboration


MissionTo develop and commercialize a new generation of efficient, safe,

reliable, and attractive thin-film photovoltaic solar power

products that are the first to enable energy production at cost

parity with conventional sources of electricity.

Cost

Durability

Efficiency

Lowest cost thin film circuits, less than half that of

silicon PV and one fourth that of current Building

Integrated PV (“BIPV”) products

Warranted Lifetime of 25 years for first products

Comparable conversion efficiencies to multicrystalline

silicon


Solar Product Availability• Crystalline Silicon ~ 18% conversion efficiency

• Multi-crystalline Silicon ~ 14%

• Amorphous Silicon ~ 6-8%– Flexible and rigid

• Cadmium Telluride ~ 9-10%– First Solar capturing significant market share for

central power applications

• CIS/CIGS ~10-12%– New commercial availability entering the market in

2008

90% of

current market

10% of

current market

but fastest

growing segment

http://i.treehugger.com/files/Solar panel 5.jpg


Inefficiencies in Today’s Value Chain

15 – 20 + % margins at each step in the value chain

$0.00

$1.00

$2.00

$3.00

$4.00

$5.00

$6.00

$7.00

$8.00

Raw silicon Wafer mfg Cell Module assembly

Inverters System Eng Installation

$

$

$

$

$

$

2nd Generation

Thin Film

Advantage

System

Integration

Advantage

US PV System

Price $/w ~ $7.50



Thin Film Manufacturing Challenges

HelioVolt’s technology addresses most significant PV challenges:

CIGS thin-film technology is the most promising candidate to replace

expensive silicon-based technologies

FASST™ process technology will produce high quality CIGS

photovoltaics in minutes, an 80-98% reduction over other CIGS thin-

film manufacturing processes

$1.00

$0.03

x-Si CIGS

Semiconductor Materials Cost ($/Wp) Time (minutes)

3

30

360

Metal Selenization Coevaporation HelioVolt FASST™

360


CIGS Thin-Film Products

substrate

Moly

CIS

ZnO buffer P2

P1

P3

Alloy of Copper, Indium, Gallium and Selenium

CIGS is one of three known intrinsically stable PV materials (with Silicon and Gallium Arsenide)

• Intrinsic stability required for building integrated products

More efficient absorber of light than any other known semiconductor

Requires 1/100th of the material compared to silicon for comparable light absorption



PVIC Manufacturing Process Flow

Glass CleanMetal

Deposition

Metal

Pattern (P1)

Precursor

DepositionFASST™

Synthesis

Buffer

Deposition

Absorber

Pattern (P2)TCO

DepositionTCO

Pattern (P3)

Product

Packaging Test & Ship

1.

Front End

2. CIGS

Synthesis

3.

Buffer

4. Device

Processing

5.

Back End

PVICs


Proprietary FASST™Manufacturing Process

FASST™ - Field Assisted Simultaneous Synthesis and Transfer

HelioVolt’s two step process enables

high throughput low cost manufacturing of CIGS PVICs.

Precursors

Substrate

Stage 1:Precursor Deposition

Stage 2:Rapid Thermal

Anneal and Separation

Heat

Electrostatic &

Mechanical

Pressure

Precursors

Substrate

CIGS Layer

Printing Plate

Printing Plate


Initial Standard Module Product Specifications• HelioVolt CIGS Photovoltaic Module

– Residential or commercial applications

– BIPV products in development

• Nominal Power at STS = 75 – 85 W

• Voltage at Max Power = 67v

• Connectors: Tyco Micro Solar Lock

• Approximate physical dimensions:

– 620 mm x 1200 mm x 7 mm (unframed)

– Glass-glass laminate construction

– Approximate weight - 12 kg

• Certifications (at launch): UL (ULC) , IEC

• Warranty: 25 years


Planned

Efficiencies 11% 12% 13% 14%

Conversion

Product Roadmap

2009 2010 2011 2012

Rigid modules for commercial

and residential applications

AC modules for traditional

applications

Modules adapted for BIPV

applications:

Facades, sunshades, roof tiles

AC BIPV components

Flexible substrate product

development


Advantages of thin film PV• Efficient and high performing materials

– Direct bandgap semiconductors– Better energy output – kWh/KW – CIGS record at 19%+ conversion efficiency

• Significantly reduced costs– Less material usage

• Not affected by silicon supply shortages

– Potential for improving costs throughout value chain

• Advanced manufacturing techniques– Fewer processing steps– Monolithic integration of circuits– Automation

• Better aesthetics


Device structure and design

• Thin Film PV Devices

– Equivalent Circuit

– Key Electrical Parameters

– Cell Structure

– Isolation and Interconnect

• Thin Film Cell Design

– Module requirements

– Cell Optimization


Equivalent CircuitSource: Wikipedia


Key Electrical Parameters

• Standard Test Conditions (STC): 1,000 W/m² , 1.5 AM, 25ºC

• Inverter should adjust load to achieve Pmax

I-V curve for a solar cell

efficiency

fill-factor

Source: Wikipedia

http://upload.wikimedia.org/wikipedia/commons/8/8d/SolarCell-IVgraph3-E.PNG


Cell Structure(typical CIGS solar cell cross section)

• Source: Handbook of Photovoltaic Science and Engineering, Luque & Hegedus, Wiley 2003.

Soda lime glass (3mm – substrate)

Mo (0.5µm – back contact)

Cu(InGa)Se2 (2 µm – absorber-layer p-type)

CdS (0.05µm – buffer layer n-type)

ZnO (0.5µm – doped conductive front contact)

High Resistance ZnO

-

+

TCO layer(Transparent Conductive Oxide)

CIGS layer


Isolation and Interconnect(typical CIGS solar cell)

Soda lime glass

Mo


Isolation and Interconnect (typical CIGS solar cell)

Soda lime glass

Mo P1



Soda lime glass

Mo

Cu(InGa)Se2

CdS

High Resistance ZnO

P1



Soda lime glass

Mo

Cu(InGa)Se2

CdS

High Resistance ZnO

P1

P2



Soda lime glass

Mo

Cu(InGa)Se2

CdS

ZnO

High Resistance ZnO

P1

P2



Soda lime glass

Mo

Cu(InGa)Se2

CdS

ZnO

High Resistance ZnO

P1

P2 P3



Soda lime glass

Mo

Cu(InGa)Se2

CdS

ZnO

High Resistance ZnO

-

+ P1

P2 P3

-

+


Thin Film Cell Design

Drivers

Module Constraints

Cell Optimization

Module

Scribe zone

Cell length

Cell width

+ -

Bus Bar


Module requirementsVoltage

Vmodule = Vcell x Ncell

Application dependent

24 V for battery charging

String inverters limited to 600V or 1000V strings

PVAC requires higher voltages (~250V) for optimum efficiency

CurrentImodule = Icell

Power Output/ EfficiencyEfficiency = Power output/{Module Area * Solar

Incident}

Maximize to achieve best $/watt


Cell Optimization

1. Determine acceptable module voltage range

2. Select cell length that maximizes module efficiency within the acceptable module voltage range

Trade-off between dead area from scribing and I²R losses through TCO. (Shorter cells have less resistive loss, but more dead area from scribing)

TCO properties are critical (resistance vs. transmissivity)

Vcell is a characteristic of the material bandgap

Icell depends on the cell area

Cell length (mm)

η%

3 4 5 6 7

Curve not based on actual data; Illustrative purposes only


Device Packaging and Reliability• Packaging

– Bus bars

– Encapsulation

– Junction box

– Framing

• Reliability

– Common Failure Modes

– Stress Testing

– Certification Testing

– Certification Failure Modes


Bus bars

Bus bar is required to avoid resistive losses associated with current collection

Tinned copper ribbon is typical bus bar material

Bus bar requires sacrificial cells on each end of module

Bus bar must conduct power outside of encapsulated module and into junction box.

+ -

Bus Bar


Encapsulation

Glass-glass construction is typical for thin film modules

Encapsulant (EVA, PVB,..) adheres cover glass and keeps out moisture

Encapsulant must be very transparent and must not degrade with environmental/UV exposure

Top glass

Bottom glassEncapsulant sheet

Laminate

Solar module lamination system


Junction box

J-Box typically integrated with connectors for creating module strings

Must capture and seal bus bar exit zone

Often integrates bypass diode to protect string from partial shading losses


Framing

Thin-film modules are available in framed and un-framed configurations

Framing is usually extruded aluminum and must be grounded

Residential modules must be framed (UL); Commercial/PPA (inaccessible to public) can be unframed

Framing can provide additional edge seal protection.

Framed Un-framed


Stress Testing

1. Temperature

2. Voltage

3. Current

4. Moisture

5. Thermal cycling

6. UV-Vis

7. Mechanical

-40ºC to +90ºC - 6 hour cycle –

200 cycles(per UL/IEC test requirements) 85ºC / 85% RH – 1000

hours(per UL/IEC test requirements)


Certification Testing Test Name Test Description (Per UL/IEC

test requirements)

Performance +/- 10% of specified electrical parameters

Outdoor Exposure 60kWh/m^2 , Maintainperformance,Maintain leakage

Thermal Cycling • -40C to +90C (UL)

Damp Heat Humidity Freeze

•85/85• -40C to +90C w/condensation

Mechanical Robustness

•Shading hot-spot •Connectors /J-boxes pull test•400 pound weight loading•Steel ball impact (51 inch, 1.18lb)

Shock Hazard •No leakage current after environmental exposure.


Certification failure modes


Growth of Distributed Energy

Office building

and school

roof top

examples

(MW) 2009E 2010E 2011E 2012E

Global Rooftop PV

Demand 4,437 6,860 9,506 13,061

Commercial Rooftop Systems Building Integrated Photovoltaic Systems

Residential

roof tile and

façade

examples



PV Solutions for Urban Solar Applications



Commercial flat roof (attached & ballasted)



Pitched roof (tiles & rack mount)



Covered parking



Covered areas (walkways, outdoor Cafés, etc..)



Sunshades



Curtain Wall (Spandrel or renovative façade)



B

O

S

Balance of Systems(Mounting, wiring, inverters, etc.)



B

O

S

PV Solutions for Urban Solar Applications


PV Mounting Systems for Commercial Rooftop

• Flat Roof

– Attached

– Ballasted

– Hybrid

– BIPV

• Standing Seam Metal Pitched Roof

– Attached

– BIPV

• Tile/Shingle Pitched Roof – Attached

– BIPV


Flat Roof – Attached• Description

– Typically very low slope (1/4 :12)

– Built-up Roof (BUR) or Membrane construction

– Attaches to building framing

• Benefits/Issues – Requires roof penetration

– Reduced dead load to roof structure

– Engineered live loading of structure

– Less constrained tilt angles due to higher tolerable wind loads

– Improved drainage management

• Module Requirements– Compatible clamping hardware

– Potential weight limitations

• Leading Hardware Vendors– Schletter (world leader)

– Unirac

– DPW solar

– ProSolar

– RoofScreen

Schletter - attached system



Flat Roof – Ballasted• Description



– Relies on dead weight to maintain position on roof

• Benefits/Issues – Requires no roof penetration

– Less involvement from building roofer

– Less impact on roof warranty

– Limited pitch options due to wind loads

– Applied to roofs where weight is not a big concern


– Good off-angle harvest


– Unirac

– DPW solar

– SunLink

– Schuco

DPW - ballasted system



Flat Roof – Hybrid• Description



– Relies on weight plus minimal frame attachment

• Benefits/Issues – Requires some roof penetration

– More pitch options than ballasted

– Can be used to reduce ballast in weight constrained situations



– Unirac

– DPW solar

– SunLink

– Schuco

Schletter - hybrid system



Flat Roof – BIPV (BAPV)• Description



– PV Integrated into roofing materials

• Benefits/Issues – Integral to roofing solution

– Less clutter and obstruction on rooftop

– Most solutions deploy horizontal PV (non-optimal)

– Roof warranty may be too short for ROI

– Potentially less expensive PV installation

• Module Requirements– Involved design integration with

mounting system vendor

– Flexible PV currently preferred

• Leading Hardware Vendors– Solar Integrated

– UniSolar

– Lumeta

– Solar Frameworks

Solar Integrated- Flat Roof BIPV



Standing Seam Metal Roof – Attached

• Description– Pitched roof for commercial applications

– Standing seam provides convenient attachment point for module mounting

• Benefits/Issues – Simple solution from S5 is widely

deployed

– Reportedly the lowest installation cost for commercial rooftops

– Metal roof does not need to be replaced for life of building

– Weight may be a concern on some metal buildings

– Peel and stick Unisolar solutions also available


• Leading Hardware Vendors– S5 (module clamp)

– Unisolar (peel and stick)

S5 – standing seam mounting system



Standing Seam Metal Roof – BIPV• Description

– Pitched roof for commercial applications

– BIPV is pre-mounted to metal roof panels

• Benefits/Issues – Low profile integration creates desirable

appearance on pitched roofs

– Metal roof does not need to be replaced for life of building

– Potentially less expensive PV installation

• Module Requirements– Involved design integration with

mounting system vendor

– Flexible PV currently preferred

• Leading Hardware Vendors– Centria and other Unisolar partners



Tile/Shingle Pitched Roof – Attached

• Description– Pitched roof for commercial applications

– Utilizes tiles or shingles like residential construction

– PV modules are retrofitted to roof using racking system

• Benefits/Issues – Residential pitched roof racking systems

are applicable


• Leading Hardware Vendors– Residential mounting system vendors



Tile /Shingle Pitched Roof - BIPV• Description

– Pitched roof for commercial applications

– Utilizes tiles or shingles like residential construction

– PV is integrated into roofing tiles or shingles

• Benefits/Issues – Residential PV roof-tile products are

applicable

– Potential cost reduction through PV integration has yet to be realized

• Module Requirements– Modified PVIC required

– Certification as roofing material

required

• Leading Hardware Vendors– Suntech

– Q-Cell

– Sharp


BIPV Product Requirements• Aesthetics:

– Visual attention – may or may not “blend into building”

– Uniform patterns and colors

– Must complement building design

• Efficiency:

– Highest conversion efficiency per application

• Physical properties:

– Flexibility in size

– Flexible and rigid

• When glass = High quality flat glass

– Thermally or acoustically insulating

• Cost:

– Smart integration


BIPV Applications Roofing

– Most common BIPV application today

Sunshades

– Energy conservation and reduced building operating costs

– Cooling load mitigation and glare control

– Easiest retrofit for PV

Overhead glazing (canopies, skylights, atriums)

Curtain wall / Facades

HelioVolt platformfits all formats


Standard Product Platform Applied to our Expanded Product Portfolio

High Efficiency PVIC Platform

Commercial Roof Top

Systems

BIPV – spandrels

BIPV – sunshades Parking Structures


Thin-film Roof PV


Amorphous silicon PV facade


SolarIntegrated – flexible aSi


Other Topics

• Color and Transparency/Translucency

• Flexibility

• Spray on

• AC modules

• Balance of Systems (BOS) costs


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Balance of Systems Costs

Established solar manufacturers are realizing cost reductions across the value

chain and will reduce installed system cost by approximately 50% by 2015

• Note the high level of indirect and labor costs - these are driven by regulatory,

educational and financing hurdles (non-R&D).

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“Innovative Urban Solar Solutions”

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