Progress Toward Roll Processing 

Reflective Material

Russell Smilgys and Steve Walla

Science Applications International Cor

McLean, VA

Cheryl Kennedy

National Renewable Energy Laborat

Golden, CO

Presented at Solar Forum 2001 

April 23, 2001

NREL/PR-550-40031Presented at the 2001 Solar Energy Forum: The Power to Choose held on April 21-25, 2001, in Washington, D.C.
Disclaimer and Government License

This work has been authored by Midwest Research Institute (MRI) under Contract No. DE-AC36-9Department of Energy (the “DOE”). The United States Government (the “Government”) retains anthe work for publication, acknowledges that the Government retains a non-exclusive, paid-up, irrevpublish or reproduce the published form of this work, or allow others to do so, for Government purNeither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employeesor implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulness product, or process disclosed, or represents that its use would not infringe any privately owned rig

specific commercial product, process, or service by trade name, trademark, manufacturer, or otheimply its endorsement, recommendation, or favoring by the Government or any agency thereof. Tauthors and/or presenters expressed herein do not necessarily state or reflect those of MRI, the Dagency thereof. 
Goal:

Demonstrate that it is possible to cost-effectively 

performance solar reflective material using vatechniques.

high performance:

Specular reflectance above 90% for at lea

cost effective:

$10.8 per square meter ($1 per sq ft.)

Approach:

Develop roll coating process for a first surface s

mirror with a protective alumina coating.

Focus on increasing durability and lowering pro
First Surface Mirror under Devel

Replace Thin Glass

• Vacuum evaporate metal layers

• Deposit alumina coating by EB-PVD techniq

ion beam assisted deposition

• Process compatible with roll coating for effic

Top Protective Layer (0.5 - 4 

μm Al

2

Reflective Layer (100 nm Ag)

Metal Back Layer (optional)

PET Substrate

o

r (Chrome Pl
Possible Application for Mate

Dish/Engine System

Mirrors arrayed on a dish concentrate sunlight onto 

Pictured system was designed and built 

by SAIC (Golden, CO)

Concentrator:

- stretched-membrane faceted dish- 90 square meters- 1 mm thick silvered thin glass- 90% reflectivity 

Issues:- Individual panes of glass are cut and glued to stainless 

very labor intensive

-Reduction in cost of complete system possible if steel 

be supplied with mirror finish
Outline of Program

1994 First sample of solar reflector material prod

World Industries.

1995 Start of funding by NREL to make samples 

coating 0.5 to 5.6 microns thick using sma

Prepare analysis of cost to produce material 

1997 Build large coating system at SAIC.1998 Increase alumina deposition rate from 1 nm1999 Increase alumina deposition rate to 20 nm/2000 Build web-handling machine and integrate 

system.

2001 Produce solar reflector material on 12 foot lo

chrome-plated steel web (underway).
First Test Samples Produced in S

Coater

• 66 cm wide box coater• Electron beam evaporator • Cold cathode ion source• 8 kW power supply• Quartz crystal rate 

monitor/ controller

• No direct cooling of 

substrates

Box coater located at Armstrong World IndustriesPenn State University
Typical Deposition Proced

1. 6”x6” PET sheets stretched over shim stock ho

rotating planetary holders. 

2. Sputter clean PET with argon ion beam for 5 m3. Evaporate copper, 50 nm thick @ 1 nm/s4. Evaporate silver, 100 nm thick @ 1 nm/s5. Evaporate alumina, 0.5-4 

μm thick @ 1 nm/s
Solar Simulator Data of First Surf

with Alumina Coating (1nm/s dep

Longest durability in solar simulator of any fir

9092949698

100

0 500 1000 1500 2000 2500 3000 

Solar Simulator Exposure Time (Hours)

% Hemispherical Reflectance 0
Outdoor Colorado Exposure Da

Surface Mirrors with Alumina 

(1 nm/s deposition rate

Sample with 4 micron coating lasts 4 yea

707580859095

100

0 6 12 18 24 30 36 

OD-CO Exposure Time (Months)

% Hemispherical Reflectance 0.

 
Cost Model to Produce Solar R

Material in Roll Coater (circa 

Geometry

Web length 2400 ftWeb width 3.5 ftWeb diameter 12 inches

Evap Process

Capital Equipment $1MWeb line speed 80 ft/hrCycle time/web 30 minWorkers 1 @ 100%

IBAD Process

Capital Equipment $1.19MCycle time/web 83.4 hr @ 32 nm/sWorkers 2 @ 100%

Plan

300 days/3 shifts/d8 hr/shift15% capi5% capita$35 wage $0.10 ele

Ma

Alumina Silver Copper PET 
Result of Cost Model to Produ

Reflective Material in Roll C

When alumina coating is 4 micron thick, need 

$1/sq.ft.. (Assumes production volume one million s

per year.)

$1/sq.ft.

60 nm/s
Build Bigger Coating System at 

Increase the Deposition R

• Vacuum system walk-in sized

- cylinder 7 ft diameter, 12 ft long- Stokes 412 roughing pump- three CTI-10 cryopumps

• Evaporators

- rod fed source (2” OD) - 4 pocket source (each 60 cc)- 14 kW Temescal power supply

• Ion source

- 16 cm CSC gridded, high output 

1.25 A @ 1000 V
Increase Alumina Deposition Rate + 

Cooled A

Cooled Al plate mounts sheets 7”x25”

Evaporators and ion source located

at bottom of chamber
WOM Data of First Surface Mir

Alumina Coating (higher depos

Samples with 10x increase in deposition rat

707580859095

100

0 2 4 6 8 10 12 

 WOM Exposure Time (Months)

% Hemispherical Reflectance 3 nm/s 5 nm/s 7 nm/s 10 nm/s 

11.5 nm/s 
Roll Coater Design

Specifications

Web width 30.5 cmWeb speed 1-89 cm/minWeb tension 1-189 NReel ID 30.5 cmDrum temperature > 77 K

Intended web is chrome-plated steel strip, 12” w
Roll Coater at SAIC (McLean

Rear view showing chain drive

Front view sh

advanced ove
Roll Coater at SAIC 

(McLean, VA)
Development Path to Commercial 

of Solar Mirror

Current Work: 

• Transition coating process from PET t

chrome-plated steel web (12” wide).

• Produce solar reflective material on 12

strips of chrome-plated steel. 

Future Work: 

• Produce 280 lineal feet of solar materi

field trials.

• Increase the alumina deposition rate be

20 nm/s. 
Acknowledgments

Northeastern University

Dr. Jackie Isaacs

Armstrong World Industries

Dr. J. S. Ross

Penn State University:

Prof. Singh 

Tom Medill

Dale Donner