solar and snow drift

[acolakoglu]

Do you know about a paper or any other reference regarding snow drift under tilted solar panels?

Thanks,
ahmet

 

[ishvaaag]

Except the structure being quite critical to the concentration of snow load, one can imagine solar panels 6x8 ft in plan at most can only cause moderate concentrations of snow. For reinforced concrete floors as those here made for dwellings for most cases the effects of the average loads and the actual loads would be quite similar.

Anyway, all the snow on the corresponding plan of the panel can be dumped before it, and this become critical to some purlin or deck, maybe. That would be a conservative assumption for the dump point. For the panel zone, assume then a uniform distribution and you have both extremes covered.

However if you think that what above does not lead to a safe situation you need still look for some more accurate statements. Not to forget concentration of snow from wind as with any obstacle, and concentrations on valley and retention points of the roof, the same. Or the cases where a huge amount of solar panels are the roof itself, then one must look at where it dumps.

 

[acolakoglu]

I am looking for a reference for such loading. 6'x8' panels cover the entire 1000 ft 2000 ft roof.

Thanks,
ahmet

 

[ishvaaag]

Since when practicing this here we have overly heavy bases, plus (the solar panels use to be water-heating) the significan loads of the panels, AND snow loads use to be small, it is not unusual to have here just uniform distributions of the load retouched by whatever it is necessary, or per area. The reinforced concrete structures, maybe half the times lately plates, allow for that without further comment.

On the case the roof was of steel I might be in your ploy more than anything to battle excessive cost. Will keep looking.

 

[ishvaaag]

ASCE 7.05 in commentary C7.4 seems to concurr.

This may result in the elimination of snow loads on upper portions of the roof and their concentration on lower portions.

Also, what the

http://www.suntreksolar.com/solarElectricity/files/FIRE DEPT REQUIREMENTS.pdf

California Department of General Services . Division of the State Architect . Interpretation of Regulations Document
DSA (SS) IR 16-8 Solar Photovoltaic and Thermal
(iss 08-15-08) Systems Acceptance Requirements Page 1 of 5
SOLAR PHOTOVOLTAIC AND THERMAL
SYSTEMS ACCEPTANCE REQUIREMENTS
References: 2007 California Building Code (CBC), Sections 1609A and 1613A Issued 08-15-08
IR 16-8

has to say is

6.1.5 Roof Live Loads on Panels. It is not necessary to include roof live load (20 psf) in the area(s) covered by the panels when these area(s) are inaccessible, or
fenced off with posted signs prohibiting storage under the panels.
When applicable, include snow loads and loads from snow drift.

It interestingly resolves -their way- the question on if keeping the live load on the solar panels plan.

For Wisconsin...

http://commerce.wi.gov/sb/docs/sb-UDCCommentary21A.pdf

"The UDC does not set lower snow live load values for roofs with glass or other slippery surfaces unless per s. Comm 21.27(1)(b), the slope is 7 in 12 or greater just as for other roof types. Otherwise, attached greenhouses, solar spaces, solar panels and other similar roof construction should be designed to withstand 40 or 30 PSF for zone 1 or 2 respectively."

http://www.tdpud.org/pdf/SB1-solar-leadership report.pdf

 

[cvg]

try this link

http://www.kaldtklima.net/node/234