Mounting solar thermal panels on the roof in high wind environment

[Sunking]

i live about 9 miles from the continental divide at about 3900 feet.

Is that a typo? Sounds l little low in altitude.

[ChuckD]

Still here...

Thanks for the feedback, all. Monday's the day we get them put up.
mtmtntop, you bring up my biggest concern at this point. The panels and racks are rated to 130mph winds, so I'm told. But I'm more concerned abut my roof.

Since this is over a vaulted ceiling with no attic underneath (and no stomach right now for repair work to the ceiling and the required rigging to reach it's ~20' height), I'm hoping ample lag bolting will suffice. To allay that concern I'd like to possibly mitigate the lift a strong wind would cause with some kind of deflector. That's why I posted that link earlier. They refer to this idea but that was just a summary with no details.

Thanks again.

C.

[mtmtntop]

just to complete the thread, no typo. i live in helena, mt. and it is at 3900' and very close to the divide. the divide here is not that high in elevation.

[russ]

just to complete the thread, no typo. i live in helena, mt. and it is at 3900' and very close to the divide. the divide here is not that high in elevation.

Been through Helena quite a few times (40 years back) - that place can get cold! Most perennial ornamental plants are considered annuals there.

[djl02]

I used struts and leg bolts to go through rafters.

Tried to post pics but they didnt show up.

[johnnybrown786]

Using Solar panel is a good way to save electricity bills and reduce pollution which is spreading cause of gases and redemption of energy sources used in producing energy to meet the general requirements. I think that we all should encourage people by adverting or slogan that uses green products or solar panels for small work.

[russ]

Using Solar panel is a good way to save electricity bills and reduce pollution which is spreading cause of gases and redemption of energy sources used in producing energy to meet the general requirements. I think that we all should encourage people by adverting or slogan that uses green products or solar panels for small work.

Really! That statement was basically green blather. To be 'green' only requires someone with no thought process of their own.

What one may want is to be 'sustainable' - an entirely different concept.

[Martshmoo]

Hi all,
First post here. Thanks to all who provide and support this forum, lots of great information.

We're installing a solar thermal system on our roof to supplement a new geothermal system, and to provide DHW. We're committed to an installer, who we like, who at first was going to install some Schuco panels flat. I've talked him out of this and we're going to install them on ezFlatroof racks, also from Schuco. So here's some vitals:

We're at about 43 degrees N lat.
The roof is sloped directly south and has a 4.5/12 pitch (roughly 20 degrees).
The lowest solar max. altitude occurs around December 21 and is roughly 23 degrees.

So my reasoning for not flat mounting them is that at the time of year when I need them the most, the best sun angle on them would be roughly 45 degrees, which means roughly half the available energy would be harvested. This seems elemental to me but I'll take a sanity check on that theory. There's no dispute involved, and he's very willing to mount them on the racks for an acceptably small extra charge.

The issue though is that we're pretty exposed at 1000' elevation and in a fairly high wind area, high enough that I can seriously consider a wind turbine at some point. But the other side of that is we get gusts on occasion that really rattle our 2x6 walled house. My installer is aware of this too and it was one of his reasons cited for flat mounting.

So, I don't think we're the first to have this scenario, and I was hoping someone out there might offer some practical advise for how these should be mounted. My first thought is there should be some kind of fairing involved to divert the wind. It's pretty predictable from the WNW, but we do occasionally get it from other angles. I'm also thinking the racks should get extra lags, but what good would that be if the panels are in the next field over?

Also, if anyone can shed some more light on this presentation I'd like to hear it:

"Analysis of Wind Forces on Roof-Top Solar Panel"

http://adsabs.harvard.edu/abs/2011APS..MARV31015P

This would've been interesting to hear, especially as they apparently allude to solutions at the end:

'The present study concluded to reduce the strong wind uplift by designing a guide plate or a deflector before the panel. '
Details please!

Thanks for reading

Chuck

Chuck,

Check this out (Attachment) about how angles mathematically affect Panel Outputs:

Now from this you can see you are 100% right with a steeper Angle needed.

I Have mine on top of a flat roof at 60 Degrees (41 degrees N) now (adjustable from 0 to 70 degrees) and with a standard racking Kit with additional "L" brackets holding the panels in place.

I survived 4 or more 80 k/h winter storms, and shoveled (or better stated brushed with my pool sweeper) over 50cm of snow off them.

Now, 45 Degrees, with Snow adds some stress to the middle, so the steeper the angle the better... so the snow falls off.

just a point..

Hope this helped...

[mtmtntop]

snow load and angles

we just had 14" of snow. my panels are 65-70 degrees (evacuated tubes) , but i have my power backup pv panel at 45 degrees. guess what it looked like after the snowstorm? 14" on the pv panel, none on the tubes. not even at the bottom of the rack, since they are mounted about a foot above the roof. if you live in high northern (or southern) lats, like above 40 degrees, and like most of us, need the heat in the winter, mount the panels 20 degrees more than your latitude. that is what worked for me.

[ChuckD]

Thanks again for the feedback.
As I said a while back, I'll post a couple pictures and here they are.

Again, these are Schuco Advanced panels, something less than 3'x7' facing directly south. They're warming a Schuco 115gal. storage tank that feeds our El Cheapo 40 gal electric tank heater (Kenmore, IIRC). As I took those pictures the outside air was 26F. The fluid entering the tank hit 130F and the tank got up to 90F in spite of a midday shower taken.

We're at 42.8 N lat., 1000' elevation. The roof slope is 4.5 on 12 (20.6 deg.) and the racks tilt up 30 deg. giving the panels a 50.6 deg total tilt. At our latitude the lowest midday sun elevation comes around December 21 at 23.8 deg. elevation giving the angle of incidence of ~105deg. The date of direct 90deg. insolation will be Feb 23 (hope it's sunny!).

This is my first experience with solar (and geo which was installed at the same time) so I'm not sure what to expect. I do know not to expect too much at this time of year so I'm happy for the boost we're getting to the dhw.

Lastly, prevailing winds are from the WNW and we've already had a few 'trials' and, well, they're still there. Aesthetically, if I'd been there the day they set them up I'd have asked they be brought down from the ridge a bit (I'm certain we have the same solar exposure), but it's not that big a deal and as I said earlier, we're about 400' off the road so it's not like it stands out or anything.

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[Mike90250]

You have a house, not a sailboat. Get the panels down below the ridge.

Do you get snow ? got to be sure you leave a way for the panels to not be a snow fence.