Parabolic Trough VS

Optical Characterizat

2005-2006

Tim Wendelin

NREL/PR-550-40024Presented at the 2006 Parabolic Trough Technology Workshop held on February 14-16
Disclaimer and Government License

This work has been authored by Midwest Research Institute (MRI) under Contract No. DE-AC36Department of Energy (the “DOE”). The United States Government (the “Government”) retains athe work for publication, acknowledges that the Government retains a non-exclusive, paid-up, irrepublish or reproduce the published form of this work, or allow others to do so, for Government puNeither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employeeor implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulnesproduct, or process disclosed, or represents that its use would not infringe any privately owned ri

specific commercial product, process, or service by trade name, trademark, manufacturer, or othimply its endorsement, recommendation, or favoring by the Government or any agency thereof. authors and/or presenters expressed herein do not necessarily state or reflect those of MRI, the agency thereof. 
Trough Deployment/Operation 

• Development

– R&D directed at maximizing performance/cost ra– Requires testing tool(s) that provide detailed dat

mirror panel positioning

• Manufacture/Installation

– QC testing of mirror panels (statistical sampling)– Module assembly– Requires fast, relatively simple optical character

problems & fix

• Maintenance/Operation

– Many contributors to optical performance (e.g. sp

distortion, dirt, receiver shape/position)

– Large fields require simple, fast, effective tools to 

problems & maximize performance
Optical Characterization 

• Mirror Optical Accuracy

– Mirror contour– Mirror specularity

• Mirror Panel Alignment

– Tilt– Position

• Receiver Positioning

Each issue is uniquely present in e
Trough Optical Characterizat

• Single biggest challenge to fast, e

characterization:

– Lower concentration, line focus optic

area and subsequent spatial test zon

• Development

– Less of an issue

• Manufacturing/Installation

– Somewhat of an issue

• Operation/Maintenance

– BIG issue

• Point: Different tools needed for d
2005 Activities

• Focused on development and manufacturing/in

– Solargenix Advanced Parabolic Pilot Project– Industrial Solar Technology (IST) Parabolic Trou

Development Project

• Improve/Modify/Update VSHOT for Parabolic T

Measurements

• Use VSHOT to quantify for both Solargenix and 

Technology designs

– Mirror Optical Accuracy

• Mirror contour• Mirror specularity

– Mirror Panel Alignment

• Tilt• Position
Field Ready VSHO

• Laptop controlled• Updated development environ• National Instruments Image A

and Processing libraries

• Firewire camera implementat• Equipment organization and s

container

• Fixed camera supports/target 
VSHOT

• Originally 

designed for pointfocus concentrators

• Adapted for linefocus optics 

(samples one vertical slice at a time)

• Measures bidirectional surface 

slope, fits data to user defined shape, reports errors relative to that shape

T

FireWire Camera

Test Article

Camera Support Arms

Laser “Spot”
Solargenix Advanc

Parabolic Trough Pilot 

• Leveraged off of the Nevada S

West Energy Partnership

• Focuses on Manufacturing an

Installation Phase
Primary Objective

Full-Scale Testing....

.... Prior to 50 M

Deployment
History and Linkage to Natio

• 4-yr USA-Trough development (• Major advances, but need full-sc

– New lightweight structure– New drive– New controls– New concrete piers and support pe– New ball joint assemblies
Project Hardware

• Advanced low-cost bearings installe• Construction completed (All 24 space • Controllers and drives installed
VSHOT Test Objec

• Provide Solargenix with data 

optical errors

• Validate the “new and improv

ready VSHOT system

• Lessons learned and identific

improvements to assist future 
First Round of Tests

Starnet SpaceframeFebruary ‘05





Initial Test Results (Fe

• Only tested 3 columns 

of glass mirrors

• Not enough data to 

come to any conclusions regarding mirror optical accuracy.

• Validated outdoor 

testing
2nd Round of Tests (J

• Fully populated SCA (6 Starnet m

each side of drive)

• Randomly select two mirror colum

(24 VSHOT profiles total)

• Use data to quantify SCA twist an

optical slope error

• Identify specific contributors to slo

(i.e. mirror panel distortion and/or 
.

• Average 

r.m.s. slope error = 4.4 mrad

• Average best 

fit focal length = 58.73”compared to design of 58.66”

Best Fit Focal Lengt

57.657.8

58

58.258.458.658.8

59

59.259.4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 

R.M.S. Slope Erro

0123456789

10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 
Conclusions (StarNet Spac

• Misalignment and distortion contri

optical error

• 4.4 mrad r.m.s. slope error not un

but improvements could be madein mirror panel misalignment

• Cannot say much about SCA twis

drive drift during during test periodtests necessary.
Gossamer Spacefra

• Solargenix sought out new su

spaceframe

• Potential for lower assembly c

better performance

• Tests on new modules perfom

September, October ‘05
Gossamer

Spaceframe
VSHOT Improveme

• Camera integrated 

into target

• Leveling tools built 

into tripod

• Much faster data 

acquisition now possible

FireWire Camera

Test Article

Camera Arms
Gossamer Result

• R.M.S. Slope Error approachi• Based partly on these results 

has decided to use Gossamespaceframes in their 64 MW E

Valley plant.
Industrial Solar Techn

Parabolic Trough Devel

Project

• IST scaling up their unique st

concentrator design to LS-2 tydimensions

• Requires optical characterizat

baseline of their existing prod

• VSHOT used to provide data
• Current IST design is continuous 

reflector (no individual mirror pane

• Concentrator module itself provide

stiffness along module length (no structure required)

• 10 VSHOT profiles taken along le

baseline IST module (using polymreflector) to characterize optical p

Industrial Solar Techn

Parabolic Trough Devel

Project
Initial Module Res

• Average r.m.s. 

slope error = 4.46 mrads

• Average best fit 

focal length = 29.92” compared to design of 30.06”

• Very consistent 

along module 

length

R.M.S. Slope Err

0123456

Profile

#1

Repeat

of

Profile

#1

Profile

#2

Profile

#3

Profile

#4

Profile

#5

P

Best Fit Focal Len

20222426283032

Profile

#1

Repeat

of

Profile

#1

Profile

#2

Profile

#3

Profile

#4

Profile

#5
• Consistent profile 

along module length

• Exhibits a 

flattening or parabolic curve at rims

• Better machining 

tolerances could improve this considerably

Results

dZ/dY Error Relative to 

-50-40-30-20-10

0

1020304050

-50 -40 -30 -20 -10 0 

Y (inch

dZ/dY Error (milliradi
Recent results

• Two new improved 

modules assembled and tested

• Significant 

improvement in slope error ~ 3.4 mrad r.m.s.

• Closer to design focal 

length of 30.35”

Not including re-tensio

012345678

1 2 3 4 5 6 

Profile #

R.M.S. Slope Error (mrads) 

Not including re-tensio

101520253035

1 2 3 4 5 6 

Profile #

Best Fit Focal Length (inches)