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Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia

Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of

Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Assessment of Photovoltaic

Surface Texturing on

Transmittance Effects and

Glint/Glare Impacts (PowerEnergy2015-49481)

ASME 2015 Power and Energy Conversion Conference

San Diego, CA, June 28 – July 02, 2015

Julius Yellowhair

Clifford K. Ho

Sandia National Laboratories

Concentrating Solar

Technologies

Albuquerque, NM 87185-1127

jeyello@sandia.gov

SAND2015-5177C

Background

Motivation for this work

Approach

Results and Discussion

Conclusion & future work

Outline

2

Background – PV Module Construction

3

www.solarquotes.com.au

Background (2/2) – Reflections

4

http://www.iala-aism.org/wiki/dictionary/index.php?title=Mixed_Reflection

1. Solar glint/glare from PV modules is caused by

reflections off PV glass covers – minimize this.

2. Maximizing transmittance through cover glass to

solar cells can increase energy production.

Motivation

5

www.pagerpower.com www.freerepublic.com

Surface Roughness Measurements Process

6

Prepare & clean the PV panel to be replicated

Replicate the PV panel surface with a 2-part

rubber compound

Measure the small replica with

an optical profilometer

Analyze the measured surface data to get the

surface statistics

Mountain Digital Surf Matlab

1.

2.

3.

4.

Surface Roughness Measurement Data

7

Reflectance Measurements

8

Reflected Solar Beam Spread Measurements

9

Smooth (float) glass, Lightly textured glass, Deeply textured glass

Samples courtesy of Canadian Solar, Inc.

Beam Spread Calculations

10

0 0.2 0.4 0.6 0.8 1 1.2 1.40

200

400

600

800

x (m)Frame #212

500 1000 1500 2000 2500 3000 3500 4000

500

1000

1500

2000

2500

Beam spread at 1 = 27.3 mrad

00.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0

200

400

600

800

y (m

)

Beam spread at 1 = 27.8 mrad

Results on Surface Roughness & Beam Spread

11

Ocular Hazards Study

12

𝐸𝑟 =𝜌𝐸𝐷𝑁𝐼𝛽2

𝑑𝑝2𝜏

𝑓2

𝐸𝑟,𝑓𝑙𝑎𝑠ℎ =3.59 × 10−5

𝜔1.77

Irradiance on the retina:

Irradiance threshold for

after-image potential:

Ocular Impacts From PV Surface Texturing

13

𝐸𝑟 < 𝐸𝑟,𝑓𝑙𝑎𝑠ℎ

𝛽 𝜌 >𝜌𝐸𝐷𝑁𝐼𝑑𝑝

2𝜏

𝑓23.59 × 10−5

10.23

Low potential

for after-image

Potential for

after-image

Low potential

for after-image

Potential for

after-image

Example of PV Cover Glass Design

14

Measured reflectance, surface roughness, and solar beam spread from several PV modules

We attempted to correlate the beam spread to the surface roughness

Developed a design method to minimize glint/glare from PV modules and maximize transmittance

Results were incorporated in the SGHAT code

Would like to study soiling effects on textured surfaces

Build engineered surface texturing for PV and evaluate

Conclusions & Future Work

15

Extra Slides

16

Replication Accuracy & Verification

17

Slope Error Calculation From Glare Measurements

• The angular beam spread after reflection is defined as:

– where the Sun subtended angle (𝜎Sun) is about 9 mrad

• The ‘Total Slope Error’ quantity is a combination of the panel surface slope error and specularity due to surface texturing; it’s typically defined as:

– where 𝜎SEis from the surface slope errors, and 𝜎Spis the specularity

from the surface texturing (i.e. surface roughness); the factor of 4 is because the surface slope errors are measured at the surface, whereas the specularity is measured at the reflected beam – note that with a single glare measurement, these two quantities are difficult to decouple

18

𝜎BeamSpread = 𝜎Sun + 𝜎Total_SlopeError

𝜎Total_SlopeError = 4𝜎SE2 + 𝜎Sp

2

Note that can be one-sided or two-sided. In this analysis,

a two-sided is used, which gives the full beam spread.