1. Stress Analysis on SunSiphon Rack Design
Objective: Evaluate the SunEarth SunSiphon rack design to withstand wind loads of 30 lbf/ft2.
Modeling Assumptions and Details: A finite element analysis (FEA) model was constructed based on geometry provided by Kineo Design group. The structure was idealized as a finite element beam model.
The frame material was aluminum with a yield stress of 25,000 psi and an ultimate tensile stress of 30,000 psi (see Appendix).
Two three load cases were analyzed in this report. The first load case has the wind load lifting the frame structure away from the roof under the 30 lbf/ft2 load and the fluid storage tank is empty. The second load case is where the wind is pushing the rack downward and the SunSiphon fluid storage tank is full. The third load case is a sideways or cross-wind loading.
The SunSiphon rack is fixed at its four corners. No other roof contact is assumed between the rack and the roof.
All modeling work was done with FEMAP V9.2 and analyzed using NX Nastran V4.1.
Summary: The SunEarth SunSiphon structure is well designed to handle the 30 lbf/ft2 loading under all expected wind conditions. The uplift load case creates a maximum stress in the structure of 20,500 psi.
When the wind pushes the rack downward, the peak stress in the structure is 33,500 psi. This linear stress exceeds the aluminum’s rated ultimate stress by 10%. Since the overload margin is very small, a nonlinear analysis was performed on the structure. The nonlinear analysis results predicts a peak stress of 25,100 psi. Basically, the material yields very slightly allowing the stress concentration to dissipate within the structure. Such minor plastic damage poses no threat to the mechanical performance of the structure, and thus, the SunSiphon rack is rated to handle repeated applications of the full wind load over its lifespan of usage.
The last load case where the wind is pushing sideways on the structure creates a peak stress of 11,100 psi. This stress is well below the material’s yield stress.
In Summary, the SunSiphon system is rated to handle the 30 lbf/ft2 load case under repeated load applications. This wind load is assumed to occur perhaps a 1000 times during the lifespan of the structure. Under reduced wind loading of 20 lbf/ft2,, the SunSiphon rack has an infinite life span.

2. FEA Model Background

5. 2.0x2.0x0.1875” L-Sections:

7. Note: Cross section is rotated to the correct orientation within the SunSiphon.
Common beam sections used in the analysis.

8. Anchor Bolts: Qty 4.
The SunSiphon is pinned at the corners with bolts. The connection is assumed to be pinned and the structure can rotated around the bolted connections. The structure is assumed to have no contact with the roof except where it contacts the bolts.

9. The wind load is applied at the solar panel Z-clips
The wind load is applied at the solar panel Z-clips. The wind load was assumed to be 30 lbf/ft2. This wind loading simulates wind speeds in excess of 100 MPH. For the uplift load case, it is assumed that the storage tank empty and that the panel weight is minor.

10. Check Mass Properties
74 Element(s) Selected...
Mass =
The wind load is applied at the solar panel Z-clips. The wind load was assumed to be 30 lbf/ft2. This wind loading simulates wind speeds in excess of 100 MPH. For the down-lift load case, it is assumed that the storage tank is full. The weight of the full tank is 386*2.66 = 1,000 lbf. The panel weight is neglected.

11. Load Application:
Surface areas used for wind force calculations:
Check Sum of Forces
Summation of Forces, Moments and Pressures for Set 5 (CSys 0)
Nodal Force FX = FY = FZ =
The wind side load assumes that the rack is solid and presents a flat surface to the wind load. The wind force was 30 lbf/ft2. The total side load (FX) is 420 lbf.

12. Analysis of SunSiphon Rack with 2. 0x2. 0x0
Analysis of SunSiphon Rack with 2.0x2.0x0.1875” L-Sections under 30 lbf/ft2 Wind Loads
Analysis Notes: Results are shown for three load cases: (1) Wind load lifting the panels and the storage tank upward with the storage tank empty; (2) Wind loading pushing the panels downward with the storage tank full of fluid (a weight of about 1,000 lbf); and (3) Side wind loading with the assumption that the rack presents a solid surface normal to the wind load.
Stress results are presented in lbf/in2 and deflections is in inches. The deformation of the structure has been scaled by10x to better visualize the deflection behavior of the rack under the various wind loads.

13. (1) Wind Up-Lift
The wind load is shown applied to the model. The stress results are in psi and the deflection is in inches. The deflection of the structure has been scaled by 10x. This was done in all views.

14. (1) Wind Up-Lift

15. (1) Wind Up-Lift

16. (2) Wind Down-Push

17. (2) Wind Down-Push

18. (2) Wind Down-Push

19. (3) Wind Side-Push

20. (3) Wind Side-Push

21. (3) Wind Side-Push

22. Non Linear Analysis of SunSiphon Rack under 30 lbf/ft2 Wind Loads: Downward
Analysis Notes: With the overload conditions shown in the linear analysis, a complete nonlinear analysis was performed on the structure to investigate the stress/deformation behavior of the structure when the aluminum material is allowed to yield and plastically deform subsequent to its stated yield stress of 25,000 psi (see Appendix).

23. The peak stress on the structure is 25,100 psi with the down ward wind push load case. When the L-Section is allowed to plastically deform, the prior peak linear stress concentration of 33,500 psi dissipates quite rapidly posing no long term threat to the structure.

24. Appendix SunEarth SunSiphon Documentation Background
Aluminum Mechanical Property Certification
Executing Engineer Certification

25. SunEarth SunSiphon Documentation Background

28. Aluminum Mechanical Property Certification

30. Executing Engineer Certification

31. All work within this report was done by George Laird, Ph.D., P.E.