Solar Photovoltaics in Severe Weather: Cost Considerations for Storm Hardening PV Systems for Resilience

James Elsworth and Otto Van Geet

National Renewable Energy Laboratory

NOTICE

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Federal Energy Management Program. The views expressed herein do not necessarily represent the views of the DOE or the U.S. Government.

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

U.S. Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents are available free via www.OSTI.gov.

Table of Contents

1 Introduction…………………………………………………………………………………………………………………………. 1 2 Baseline Assumptions …………………………………………………………………………………………………………. 4 2.1 Labor …………………………………………………………………………………………………………………………… 4

2.2 Modules……………………………………………………………………………………………………………………….. 4

2.3 Hardware ……………………………………………………………………………………………………………………… 4

2.4 Other Considerations……………………………………………………………………………………………………… 5 

3 Storm Hardening Measure Costs ………………………………………………………………………………………….. 6

 3.1 Measure 1: Properly Torque Fasteners and Perform a Torque Audit…………………………………….. 6

3.2 Measure 2: Fasteners ……………………………………………………………………………………………………… 8 3.2.1 Wedge-Lock Washers ………………………………………………………………………………………… 9

Other Locking Systems ………………………………………………………………………………………………… 11

3.2.2 Belville Washers ……………………………………………………………………………………………… 11

3.2.3 Rivet Lock Bolts………………………………………………………………………………………………. 13

3.2.4 Pre-Applied Thread Lock………………………………………………………………………………….. 15

3.2.5 Bolted Joint Standards………………………………………………………………………………………. 17

3.3 Measure 3: Through Bolt Modules ………………………………………………………………………………… 17

3.4 Measure 4: Use Marine-Grade Steel Fasteners ………………………………………………………………… 21

3.5 Measure 5: Select Panels With Appropriate Resistance to Design Wind Loading ………………… 22

3.6 Measure 6: Use a Three-Framed Rail System………………………………………………………………….. 24

3.7 Measure 7: Use Two Driven Steel Pile Supports ……………………………………………………………… 26

3.8 Measure 8: Use Closed Form Frame Elements ………………………………………………………………… 29

3.9 Measure 9: Use a Wind Calming Fence ………………………………………………………………………….. 32

3.10 Measure 10: Use Enclosures With Integrated and Contiguous Rubber Door Seals and Compression Latches on All Sides…………………………………………………………………………………. 35

3.11 Measure 11: Install Equipment on Elevated Pads …………………………………………………………….. 36 3.12 Measure12:EnsureSiteHasWell-DesignedandMaintainedDrainageSystems………………….37

3.13 Measure 13: Take Pre- and Post-Storm Measures ……………………………………………………………. 38 

4 Cost Comparison of Measures……………………………………………………………………………………………. 39

5 Costs of System Including All Measures …………………………………………………………………………….. 41

6 Other Considerations …………………………………………………………………………………………………………. 42 6.1 Modules……………………………………………………………………………………………………………………… 42

6.2 Through Bolt Pull-Out …………………………………………………………………………………………………. 42

6.3 Wire Management ……………………………………………………………………………………………………….. 42

6.4 Insurance ……………………………………………………………………………………………………………………. 43

6.5 Risk Acceptance ………………………………………………………………………………………………………….. 43

6.6 O&M …………………………………………………………………………………………………………………………. 43

6.7 Warranty and Liability …………………………………………………………………………………………………. 43

6.8 Alternate Clamping and Bolting Methods……………………………………………………………………….. 44 

7 Conclusion ………………………………………………………………………………………………………………………… 45

References ………………………………………………………………………………………………………………………….. 46

List of Figures

Figure 1. Wedge-lock washers…………………………………………………………………………………………………… 9

Figure 2. Belleville washer ……………………………………………………………………………………………………… 11 Figure 3. Excerpt from a module installation manual. Depending on the attachment design, the module has drastically different push (Front) and pull (Rear) load tolerance………………………………. 23

Figure 4. A solar installation in hurricane-prone Florida using a three-framed rail system to support the solar modules. ………………………………………………………………………………………………………… 25

Figure 5. Standard two-rail racking frame …………………………………………………………………………………. 25 Figure 6. Solar PV racking with a single support pile. ……………………………………………………………….. 27 Figure 7. A ground-mount solar array using a dual pier support system ……………………………………….. 27 Figure 8. C, Z, and U purlins for solar racking …………………………………………………………………………… 30 Figure 9. Cold rolled steel support structures are lightweight but can be weak along certain axes……… 30 Figure 10. Tubular steel could provide more strength to PV racking systems. ……………………………….. 31 Figure 11. Highway snow fence ………………………………………………………………………………………………. 32 Figure 12. Porous wind-calming fence ……………………………………………………………………………………… 32 Figure 13. Wind-calming fences are porous and let some of the incoming wind pass through, so as not to create a low-pressure region downwind of the fence. Overall, this deflects more wind above

the protected area. …………………………………………………………………………………………………… 33 Figure 14. Wind and dust fences surrounding solar installations ……………………………………………………… 33 Figure 15. Flow visualization for wind loading a PV array. Perimeter rows are 2.25 times more heavily

loaded than inner rows of the array……………………………………………………………………………. 34 Figure 16. Post-hurricane flooding. ……………………………………………………………………………………………… 38 Figure 17. A comparison of the per-Watt premiums for each of the measures estimated in this report….. 39 Figure 18. An older PV module featuring thicker frames and cross supports. This design on today’s

modules would add strength……………………………………………………………………………………… 42 Figure 19. Module installation manual showing different approved attachment methods and rated loads

for each………………………………………………………………………………………………………………….. 44

List of Tables

Table 1. Storm Hardening Measures for PV Systems and Their Added Cost ………………………………………. 2 Table 2. Ground-Mount Baseline System Assumptions ……………………………………………………………………. 4 Table 3. Roof-Mount Baseline System Assumptions ……………………………………………………………………….. 5 Table 4. Ground-Mount Cost Calculation for Measure 1: System Torque Audit………………………………….. 7 Table 5. Roof Mount Cost Calculation for Measure 1: System Torque Audit ……………………………………… 8 Table 6. Ground-Mount Cost Calculation for Measure 2.1: Wedge-Lock Washers…………………………….. 10 Table 7. Roof-Mount Cost Calculation for Measure 2.1: Wedge-Lock Washers………………………………… 11 Table 8. Ground-Mount Cost Calculation for Measure 2.3: Belville Washers……………………………………. 12 Table 9. Roof-Mount Cost Calculation for Measure 2.3: Belville Washers ……………………………………….. 13 Table 10. Ground-Mount Cost Calculation for Measure 2.4: Rivet Lock Bolts ………………………………….. 14 Table 11. Roof-Mount Cost Calculation for Measure 2.4: Rivet Lock Bolts ……………………………………… 15 Table 12. Ground-Mount Cost Calculation for Measure 2.5: Pre-Applied Thread Lock ……………………… 16 Table 13. Roof-Mount Cost Calculation for Measure 2.5: Pre-Applied Thread Lock …………………………. 16 Table 14. Ground-Mount Cost Calculation for Measure 3: Through Bolting …………………………………….. 19 Table 15. Roof-Mount Cost Calculation for Measure 3: Through Bolting…………………………………………. 20 Table 16. Ground-Mount Cost Calculation for Measure 4: Use Marine-Grade Steel Fasteners ……………. 21 Table 17. Roof-Mount Cost Calculation for Measure 4: Use Marine-Grade Steel Fasteners………………… 22 Table 18. Ground-Mount Cost Calculation for Measure 5: Module Selection ……………………………………. 24 Table 19. Ground-Mount Cost Calculation for Measure 6: Use a Three-Framed Rail System ……………… 26

Table 20. Roof-Mount Cost Calculation for Measure 6: Use a Three-Framed Rail System …………………. 26 Table 21. Ground-Mount Cost Calculation for Measure 6: Use Two Driven Steel Pile Supports …………. 29 Table 22. Cost Calculation for Measure 8: Use Closed Form Frame Elements ………………………………….. 31 Table 23. Cost Calculation for Measure 9: Use a Wind-Calming Fence……………………………………………. 35 Table 24. Cost Calculation for Measure 11: Install Equipment on Elevated Pads ………………………………. 37 Table 25. Cost Premium of a PV System Containing All of the Recommended Measures Individually … 41