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Roof structure


SolarNoob
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Has anyone had any issues with their roof structure from the weight of the PV panels over time?

My roof is a pitched tiled roof and I'd rather be aware of possible issues now rather than later.

Has anyone reinforced their roof trusses? Is is necessary?

I want to put up 18 170W thin film panels which weigh 20KG's each, split across two adjacent roof pitches so 180KG on each roof surface but a total of 360KG for the lot.

Any advice would be appreciated.

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It has been noted in regulations that if in doubt, it is best to get a engineer in to check the trusses.

Problem is not the weight of the panels, but the pressures caused by wind via the panels onto the structure.

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39 minutes ago, The Terrible Triplett said:

It has been noted in regulations that if in doubt, it is best to get a engineer in to check the trusses.

Problem is not the weight of the panels, but the pressures caused by wind via the panels onto the structure.

Thanks TTT. The panels are flush with the roof structure and the tiles so I assume the wind loading shouldnt be much of a factor as it is a solid plane as is the tiles. My assumption would then be that only the weight would be a determining factor?

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6 hours ago, SolarNoob said:

My assumption would then be that only the weight would be a determining factor?

I would just check with a specialist. It costs nothing and you then know all is save.

From what I have heard it is all about the profile of the roof sheet differing that could cause issues in storm winds.

In Cpt and places like PE etc. it is a very definite consideration to keep in mind.


EDIT: Example. I have a Kliplock profile roof. After contacting the supplier asking them about mounting panels, they very quickly responded, having done tests, to not use certain parts. I must for example drill into the beams, cannot use the fancy clips you get nowadays.

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Something to keep in mind is the height of the panels ( Distance between the roof and the panels ) It has a major effect on the production of the panels. I have two strings, one 100mm above the sink roof and the other 200mm. At 12 noon when the sun is pretty much at the same angle to both, I still have a huge difference in production. I am busy testing, but at this stage I have to guess it is the temp difference at the two different strings!

 

Just something to keep in mind

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18 hours ago, Mark said:

I use these and they allow for some height adjustment if the roof has some undulations.  Pre-drill a hole though the sheet and into the beam and use a spanner or drill driver to screw them in.  Work perfectly on a wooden beam roof.  Stainless Steel as well!

 

 

2017-01-31 18.59.00.jpg

Where did you buy those?

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On this topic: Where do I get an affordable aluminium frame (or material to make one) for a flat chromadeck-type roof? Might seem like an odd question, but my present panels were all installed on steel frames I welded together myself, and though I didn't do too bad a job, this time the installation will be visible from the road/front of the house so I'm willing to throw a bit of money at something that looks nice. What's available in Cape Town?

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On 1/31/2017 at 4:49 PM, Chris-R said:

Something to keep in mind is the height of the panels ( Distance between the roof and the panels ) It has a major effect on the production of the panels. I have two strings, one 100mm above the sink roof and the other 200mm. At 12 noon when the sun is pretty much at the same angle to both, I still have a huge difference in production. I am busy testing, but at this stage I have to guess it is the temp difference at the two different strings!

 

Just something to keep in mind

Yup. PV production goes down as temps rise above 25 degrees Celsius (generally). The cooler, during mid day, you can get them, the better. 

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On 2/2/2017 at 7:57 PM, plonkster said:

On this topic: Where do I get an affordable aluminium frame (or material to make one) for a flat chromadeck-type roof? Might seem like an odd question, but my present panels were all installed on steel frames I welded together myself, and though I didn't do too bad a job, this time the installation will be visible from the road/front of the house so I'm willing to throw a bit of money at something that looks nice. What's available in Cape Town?

I can supply you with TUV & SABS rated mounting structures, if you tell me how many panels, and what size you need?

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Yesterday the temp in Bloem were about 21C and at 12h00 I got in excess of 5100w per string consisting of 19 260W panels. It was partly cloudy and cool. I panicked, but checking the voltages it was about 630v per string. I was concerned that the Imeon would blow up.!!! Temp has a very big influence on the amount oggenerated power !

I am very sure that the distance of my panels from the roof, has a major role to play in this. I need to test the theory, but it is major work to reduce the height of the one string, just for testing purposes.

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16 hours ago, SilverNodashi said:

I can supply you with TUV & SABS rated mounting structures, if you tell me how many panels, and what size you need?

I have three 320W panels, they are 1954mmx982mm according to the spec sheet, ie 2m by 1m for all practical purposes. My plan is to point two of them North West, so I will need a frame that can take two (or maybe three), depending on price that I can mount on a flat roof (Chromadeck). The existing frames are steel, I simply welded three triangles at roughly 35 degrees with some straight angle-iron running across for rails, and hold-down brackets to hold the modules down, all hand made. So what I envisioned is making three similar triangles out of angle-aluminium, throwing slotted rails across that. So I could just go down to the local aluminium people and see what I can get... or get something ready made if it's not too expensive :-)

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  • 2 weeks later...
On 2/17/2017 at 11:18 AM, plonkster said:

Okay, I just ordered a whole lot of angle-aluminium to make that frame. My hande is mossie rond nie.

Gaan jy dit sweis of hoe gaan jy dit aanmekaarsit? Jy kan nie regtig stainless, galv of mild steel boute en moere gebruik nie a.g.v. galvanic corrosion, veral omdat jy naby die see is met baie vogtige souterige seelug.

 

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Okay, so I already know steel is a problem. It is good for maybe 5 years if you use the right coating.

So because I know that the standard solar rails uses a stainless hanger bolt with a stainless angle and another stainless bolt to hold on the aluminium profile, and then you have the hold-downs which is very often also stainless, I did not think stainless steel bolts would be a problem.

The tiny bit of research I did just now (because you awoke my worried nature) suggests that the aluminium will suffer the corrosion in this case BUT... that it isn't that simple, because the aluminium has a natural layer of corrosion (aka it's anodised) and the stainless steel bolt has the same layer, so the reaction is between these two oxide compounds (aluminium oxide and chromium oxide) rather than the metals themselves. This is a less severe combo, but in the presence of salt water still a problem.

How much salt water though? Some articles suggest you can use a stainless steel bolt on the aluminium mast of your boat as long as you throw in some "tef gel".

The other option, of course, is aluminium rivets. I have no idea how I feel about that though.

WWSD? (What Would SuperDIY do?)

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