ASCE 7-05 Wind Loads - Solar array on monopole

[RHTPE]

I would be interested in everyone's thoughts on the following.

I am attemping to establish the proper methodology for analyzing wind loads on a solar array mounted on a single pole. The array design and its supporting structure will evolve to provide for full tracking of the sun, both seasonal and daily movement. The array angle at this latitude would vary from 18 degrees (Summer solstice) to 66 degrees (Winter solstice) from horizontal.

ASCE 7-05's procedure for an open structure monoslope roof would apply for slopes up to 45 degrees from horizontal (Figure 6-18a or 6-19a).

ASCE 7-05's procedure for solid signs applies for the array when it is in a vertical position (for maintenance) (Figure 6-20).

For an array slope over 45 degrees from horizontal, should one simply use methodology of Figure 6-20 using the array's projection onto a vertical plane?

Ralph
Structures Consulting
Northeast USA

 

[a2mfk]

Interesting project.

I'd treat it like a sign like you said, taking the vertical projection for lateral loading...

 

[Den32]

I have recently done this, except it was a fixed 45 degree tilt solar panel.

I ran both wind loads using ASCE 7-05 for 'Open Monosloped Roof' and 'Solid Sign'. From there, I compared loads of two methods and made a reasonable assumption. In my case, the Monosloped Roof loads governed, so I used them.

 

[RHTPE]

The array supplier is working on a controller for his array that will monitor wind speed. When the wind speed exceeds a yet-to-be-determined value, the controller will automatically reduce the slope of the array to about 5-7.5 degrees from horizontal to help minimize the loads on the mast & foundation, thereby helping to keep the costs down by not having to build to extreme events. The controller will be equipped with a battery back-up to ensure that the functionality is maintained. But then there's Mr. Murphy ....

Ralph
Structures Consulting
Northeast USA

 

[Den32]

how big is this solar array? And how expensive is it?

These should be considerations for pole base design. excessive deflection during a design wind event is one thing, but complete failure is another.

what is the 'wind speed monitor' does not work or gets damaged/broken at some point? I would still think you would want to design for worst case wind speed.

Question to the owner would be - would an extra $500 in foundation & pol structure costs be worth saving $10,000 in solar equipment?

 

[RHTPE]

Den32 - I agree with all of your points. However, there are client considerations that factor into the whole picture. The solar PV industry is slowly shaking out here in the Northeast, and right now things are a bit competitive. There a few PV installers who actually involve a structural engineer for their installations.

My original question has to do with the appropriate application of ASCE 7-05's procedure.

Ralph
Structures Consulting
Northeast USA

 

[Den32]

Okay, well I gave you my opinion on ASCE 7-05 and what I have done in the past.

I don't know your specific situation, was just trying to help with further insight.