OWSJ? "Roof" for Solar Panels

[MAPeirano]

This is basically a MIN - MAX equation question relative to project-design-cost-efficiency.
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Project is to design a basic structure onto which solar panels (1900 of them) can be attached, with cost being the primary focus. The footprint of the structure is 265' X 110'. The Solar Panels, Mounts, Wiring, etc. weigh in at just under 50lbs each. The minimum height for the 'solar lattice' is 12'.
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Since there is no limitation on how often I can put vertical supports to hold this lattice in place...and since shorter span OWSJs are less costly, I wonder how often is just too often to have vertical pillars for the OWSJs? At what point is the cost of more 12' vertical supports outweighed by the reduction in OWSJ costs/span? At what point does this become shameless for a SE?
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Any rules of thumb?

 

[SteelPE]

Most of the solar frames I have seen are made from galvanized steel angles and channels. Never seen one done out of OWSJ. I would guess that you are familiar with how OWSJ are designed and what the bracing requirements are.

Is the system going to be supported on one big structure, or is it going to be broken up into smaller structures? What are the access requirements for servicing/cleaning of the panels?

 

[MAPeirano]

Ultimately, we're charged to reccommend a design idea, and then we'll be told to design it.
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The area where the panels are meant to be is currently a rather boring courtyard, and the idea was to build a "something" that could hold them off the ground high enough that residents "could" still have access to the courtyard.
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The project calls to hold so many (almost 1900)panels (WestinghouseSolar 230/235DC Landscape 65.5"X39.2") that we're kicking around all sorts of ideas to keep the cost down. The clients "hope" is to be able to have humans still be able to wander around beneath this structure(s)..(perhaps a frolic beneath the solar panels, dear sir?). The panels require little maintainence after installation so access is not a major concern. The structure wouldn't have to shed water, so we could even access the panels from beneath...
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Your suggestion of 'several' structures is possible as well... but costs are the focus for us.
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We're decent engineers...we can even be a bit 'artsy' on rare unplanned occassions, but we are not the best cost accountants, I hoped someone had some experience with a "cheap and deep" solution.

 

[paulyshore]

I recently had the opportunity to do a similar analysis and ended up recommending 44" deep trusses spanning 50' and spaced at 8' c/c across 40' wide bays (40'x50' column grid). The bay geometry was also sized for repetition of a number of panels compatible with the downstream electrical devices.

You have known vertical loads (panel weight, wind, snow). Estimate a psf for the joists (a joist supplier's rep suggested 2-4 psf - we ended up at 3 psf). Cost out a few column/footing sizes then plug in different bay widths and span lengths to refine the joist and girder weights and find where the sweet spots are. Least weight of steel is probably the least installed cost, but the number of members to erect and amount of connections become a factor in the labor estimate. There are members other than the joists to consider: the joist bracing and members connecting the panels to the joists added 30% to the 'roof' steel in our case.

Our preliminary cost estimate was $18/ft^2 for foundation and superstructure materials and construction, including panels in position. Site complications were a factor that slightly increased the construction estimate.

 

[hokie66]

Whatever you decide for the platform framing, don't forget lateral loading. The panels make good sails, and a bunch of them 12' in the air will require a lot of bracing.

 

[SteelPE]

Well it can be done with OWSJ you just either have to indicate to the MFR where the bracing for the TC is or design bracing to be a maximum 3'-0" o.c. That is the base SJI requirement.

I have seen some "artsy" solar panel arrays for courtyards and open spaces before. They were very "artsy" and look was the main concern with holding panels being the second concern. In this instance large holes were placed so that trees could grow up in-between the arrays.

I would be prepared to allow for access to the panels from the top (someone walking around on the structure).

 

[azcats]

This one is near me.

http://www.fireflyliving.com/uncategorized/powerparasol-creates-solar-energy-and-shades-asus-lot-59/

Might be some ideas in the photos.

 

[SteelPE]

Well, now that you know the name of one here are some great photos:

http://www.flickr.com/photos/powerparasol/page1/

 

[msquared48]

You might think about putting a roof over the panels so they don't get wet.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[azcats]

Why SteelPE, I get the idea you may have been involved in that project?

Was it completely bolt together in the field? Sure looked like it with everything being galvanized. If you don't mind telling, who was the fabricator?

 

[SteelPE]

I can tell you for a fact that I was not involved with the project. What I can tell you is that Google is amazing.

 

[racookpe1978]

OK. Well, I hate the inefficiency and general a waste of solar panels in general, but since you've got a contract to provide "shade" for people, you might as well cover the roof with solar as with anything else. 8<)

But, you do have solar panels to use, so you might as well try to set them up to be as productive as reasonable.
To avoid shading their fellow panels, you need to avoid dips or valleys.
To generate as much self-cleaning as possible from gravity and rain, you need as steep an angle on each panel as possible to knock off debris when it does rain, WITHOUT creating any troughs where debris accumulates and cannot naturally fall out onto the ground. (You also don't want the debris to fall off the roof panel into your patio/fellowship area and cause a mess on the floor or clobber up your water drains.)
To generate solar power (heat or electrical) you need each panel to be perpendicular to the sun at every day of the year. Moveable panels (trackable by time-of-day (east-to-west as the sun rotates)and up-and-down by day-of-year are a non-starter because they are wayyyyy tooooo expensive for this application, so you are needing to set your panels "up" angle from the ground at the latitude of your installation. I am also assuming you will not manually go back to the building every day/week/month and move the panels - which is done by the most enthusiastic of solar users. regardless, a fixed panel at the latitude of the building will give you an "average" yearly reception as large as theoretically possible at the least expense.

OK. That said, you can get a little bit of attractiveness - and some utility and efficiency as well - by setting the whole panel array at that latitude's angle, THEN adding a curved (convex) surface to that angle with your OWSJ's. Then, as your solar angle at noon each day changes through the year (from a low angle of latitude - 22.5 in the sky at Dec 22 to the latitude angle at Mar 22, then to a higher angle (latitude + 22.5) at June 22, then back to latitude angle at Sept 22, some significant part of the whole array is receiving more near-perpendicular rays every day.
Plus, in the 3 critical hours before local solar noon, and the 3 critical hours immediately after local solar noon, the "lower" part of the convex array WILL be still getting even more rays than the upper part will be loosing.
Net? A prettier, more efficient mounting to generate power.

110 feet across is not a long span for 50 lb panels. Consider them an expensive sun-shade for your patio/tennis court/basketball court/vollyball court.

Can't grow anything though. can't get a suntan. 8<( No sunshine.

 

[MAPeirano]

Apparently it is the clients hope to tilt the entire 'solar lattice' toward the south as much as possible...

The 'Lattice' is 110' wide ....and 265' long... Unfortunately, the 265' is where the tilting should occur.... 10 Foot at the south end.....and about 1,000,000 feet tall at the north end or the 265' run....

Oy Vey....

How tall can one end be and still be affordable?

 

[racookpe1978]

What latitude?

 

[MAPeirano]

~ 38 DEGREES North (ZIP 65084)