Tubular towers and PV mounting [RE-wrenches]

[Jeff Clearwater, Village Power Design]

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Hi Ian and all,

We've considered adding what amounts to side loads to our Rohn 45G 
guyed tower (radio antennae, PV) and determined it can work IF you 
look closely not only at side loading issues but also resonance 
issues.   Our Whisper 3.2KW pretty much maxes out a 45G.   You really 
need to have a structural engineer look at your proposed design 
closely.  Yes it can be done, but you'll probably find that the 
towers available (both the Rohn series and the pipe/pole kits) are 
engineered for one lateral load at top.   They'll probably work with 
some degree of mid pole lateral loading but someone really needs to 
crunch the full set of engineering loading calcs to make sure it will 
work.  With one lateral top load you have some simple resonance calcs 
(usually making sure that the length from the rotor shaft to the top 
set of guys isn't mirrored by an integral multiple in the guy wire 
spacing below.)  With two loads pushing from the side you can get 
some complicated resonance action.  Bridge engineers deal with this 
all the time and as I understand it. (remember the Tacoma Narrows 
bridge -  it was broght down by resonance)

This is especially true with the sizes you are talking about.  2-3 KW 
worth of PV is a big sail - think about the strength of the top of 
pole mounts - 2-3 KW of PV require an 8" Schedule 40 pole that can't 
be more than about 16' tall without needing guys.  So think of that 
kind of strength at the middle of a tall tower.  And the lateral 
loading of a 15' diameter wind turbine is no small load. Together - 
imagine one getting hit with a gust of wind and then the other just 
as the "wave" created by the first is passing up or down the tower. 
The two loads can be additive at the middle and you can get some 
scarry things happening.

Long winded for - don't guess - hire a structural engineer to stamp this one!

Or put the PV on a separate pole mount engineered for that purpose 
and the Wind genny on a dedicated tower engineered for it.   It may 
turn out a lot simpler and safer.

Hope that helps!

Jeff C.
Village Power Design

>Greetings Wrenches,
>
>Kelly Keilwitz of Whidbey Sun & Wind and I are planning for a 
>project that will be the installations for both the SEI PV and wind 
>workshops here next October. We're looking at a 140 to 160 foot 
>tower with a 12-15 foot diameter wind turbine and 2 to 3 KW of PV 
>mounted at 60 to 90 feet up the tower.
>
>The customer is interested in a tubular tower for aesthetic reasons. 
>I have no experience with these, and prefer the idea of a 
>three-legged freestanding tower like the Rohn SSV, both for mounting 
>PVs on and for climbing. On the other hand, I'm always up for a new 
>adventure, so I need to find out if a tubular tower is practical for 
>this project.
>
>Do any of you have experience with:
>* Tall tubular towers
>* Putting PVs on tubular towers
>
>Please share your experience, recommendations, warnings, hopes, and 
>dreams. ;-)
>
>Thanks,
>
>Ian

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jeff Clearwater
Village Power Design Associates
http://www.villagepower.com
Sustainable Energy & Water Solutions for Home & Village

Office:  (413) 256-6777,  Cell: (720)480-8455 
Fax:  (413) 825-0372
61 Baker Road
Shutesbury, MA 01072;
PO Box 115
Boonville, CA  95415
(707) 895-9015
Fax: (707) 897-0224

Council Member - Ecovillage Network of the Americas - http://www.ecovillage.org
Advisory Board - Living Routes - Ecovillage Education - 
http://www.livingroutes.org
Founder:  Ecovillage Research, Development, and Demonstration Program:
http://www.home.earthlink.net/~clrwater/RDD/rdd.html
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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