Final check before fixing my solar panel to the roof (1 Viewer)

[Lizbiebrowne]

I've read through a lot of posts on here about how to fix a solar panel to the roof and I'm now ready to do the job. But I wanted a sanity check first.

I have a 20 kg solar panel, 1700 mm x 1100 mm, to which I'll fix 4 x 500 mm pieces of 50 x 50 x 3 aluminium alloy, 2 on each of the longer sides with rivnuts. The van is a Hymer with a painted aluminium roof

The plan: Abrade the roof where the alloy angle will sit (do I need to go down to the metal?), drill holes in the alloy angle to allow the sealant to push through, use 4mm tile spacers to get the correct thickness of sealant, use Sikaflex 522 as the adhesive (do I need to use a primer?), put plenty of adhesive in place and lower the panel onto it and use the weight of panel to allow it to settle on the adhesive bed.

Any thoughts and advice gratefully received.

 

[Carpmart]

Sounds like you have a good plan!

It’s a key on the paint you’re afternoon, don’t take down to bare metal.

 

[dunnah01]

How long will the 50x50 angles be? if it's just 4 No. 50mm long contact patches then that sounds a bit lightweight tbh. I'd be working with at least 10 No. 100mm angle sections. 4 No. along each long edge and 1 No. in the middle of each shorter edge. It's a big panel you're fitting.

 

[Jimbohorlicks]

More of the angle pieces at least 3 down each side and one in the middle of the ends plus decide if the angles will be turned in under your panels or sticking out?.how long were you thinking of cutting the angle.?

 

[Gellyneck]

Personally, and it may be over-cautious, but I would be putting an angle across the full front edge to ensure wind doesn't get under it and potentially create a lift factor.

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[Lizbiebrowne]

How long will the 50x50 angles be? if it's just 4 No. 50mm long contact patches then that sounds a bit lightweight tbh. I'd be working with at least 10 No. 100mm angle sections. 4 No. along each long edge and 1 No. in the middle of each shorter edge. It's a big panel you're fitting.

More of the angle pieces at least 3 down each side and one in the middle of the ends plus decide if the angles will be turned in under your panels or sticking out?.how long were you thinking of cutting the angle.?

Personally, and it may be over-cautious, but I would be putting an angle across the full front edge to ensure wind doesn't get under it and potentially create a lift factor.

Sorry, my mistake. The angle prices I have are 500 mm lengths of 50x50x3, so 1 m of angle down each of the long length. Post edited.

 

[Gellyneck]

Sorry, my mistake. The angle prices I have are 500 mm lengths of 50x50x3, so 1 m of angle down each of the long length. Post edited.

Are you fitting the 1700mm across or lengthwise on the roof?

 

[Guigsy]

Personally, and it may be over-cautious, but I would be putting an angle across the full front edge to ensure wind doesn't get under it and potentially create a lift factor.

The wind doesn't have to get under it to feel lift. If there's negative pressure over that bit of the van at speed, it'll get aerodynamic lift forces regardless. You might get a bit less turbulence forces with the end blocked off. But personally I'd care more about supporting the long sides of the panel.

 

[Gellyneck]

The wind doesn't have to get under it to feel lift. If there's negative pressure over that bit of the van at speed, it'll get aerodynamic lift forces regardless. You might get a bit less turbulence forces with the end blocked off. But personally I'd care more about supporting the long sides of the panel.

Agreed, you can get negative pressure lift but I believe that to be less than an open front edge.

That's the reason I asked which direction was it being fitted as if lengthwise it could have an airflow diverter across the front.

 

[Tombola]

and also dont forget to sand/abrade the angle too

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[BouncyBoatFolk]

Yes, abrade the angles footprint area back to metal, otherwise the bond is with the pigment,you can allow a couple of mm around the outside to preserve the finished look. Paint does breakdown and ultimately fail and flake off.
a 200mm ally section midway along the short edges in conjunction with 6 along longer sections on the long edges will be fine.
Some acetone cleaner to all the surfaces to be bonded will make it squeaky clean. NO ADDITIONAL WEIGHT IS NEEDED. Why did I shout that? Because I got it wrong, but got lucky with it, you may not be so lucky.
Mike.

 

[VXman]

I've read through a lot of posts on here about how to fix a solar panel to the roof and I'm now ready to do the job. But I wanted a sanity check first.

I have a 20 kg solar panel, 1700 mm x 1100 mm, to which I'll fix 4 x 500 mm pieces of 50 x 50 x 3 aluminium alloy, 2 on each of the longer sides with rivnuts. The van is a Hymer with a painted aluminium roof

The plan: Abrade the roof where the alloy angle will sit (do I need to go down to the metal?), drill holes in the alloy angle to allow the sealant to push through, use 4mm tile spacers to get the correct thickness of sealant, use Sikaflex 522 as the adhesive (do I need to use a primer?), put plenty of adhesive in place and lower the panel onto it and use the weight of panel to allow it to settle on the adhesive bed.

Any thoughts and advice gratefully received.

I used primer too

 

[Lizbiebrowne]

Are you fitting the 1700mm across or lengthwise on the roof?

Across the roof.

 

[Lizbiebrowne]

I used primer too

Which primer did you use - there appear to be several Sikafkex ones available?

 

[Jon Stewart]

The wind doesn't have to get under it to feel lift. If there's negative pressure over that bit of the van at speed, it'll get aerodynamic lift forces regardless. You might get a bit less turbulence forces with the end blocked off. But personally I'd care more about supporting the long sides of the panel.

Yes, sealing off an end between the panel and the roof will only increase the pressure difference.

There will be higher pressure underneath the panel and lower pressure above, with faster moving air, so a nett upward pressure.

Driving into gusting wind would be the worst situation, where you get a 'pull relax' up-down motion which might.

I'd be more inclined to allow 'some' air under the front, and out the back.

Of course, if the connection between the panel and the roof is strong enough, it's probably that none of the above matters!

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[Jon Stewart]

Personally, and it may be over-cautious, but I would be putting an angle across the full front edge to ensure wind doesn't get under it and potentially create a lift factor.

That's actually the wrong way around.

If the van is in motion, still (or slower moving) air under the panel (at high pressure), and faster moving air over the top (low pressure), creates an upward nett force.

This is the same principle of how the wing on a plane, or a sail on a yacht works, and why people who got their polytunnels wrecked by winds often had the doors closed!

 

[pat100]

The aerofoil therories here are irrelevant. A solar panel doesn’t have an aerofoil section. In forward motion, a lifting effect will mostly occur due to wind force on the front and on partially trapped air on the underside of the panel. (Some of this would be drag on an aerofoil) So, streamlining the front edge is important. As with air dams at the front of fast cars. Most commercially fitted solar panels are streamlined down to the roof. Your umbrella doesn’t break due to aerofoil lift but because of the air getting under it. So, you use common sense and tilt it down to prevent this. If you have ever carried a sheet of wood on a windy day you know all this!

 

[Gellyneck]

That's actually the wrong way around.

If the van is in motion, still (or slower moving) air under the panel (at high pressure), and faster moving air over the top (low pressure), creates an upward nett force.

This is the same principle of how the wing on a plane, or a sail on a yacht works, and why people who got their polytunnels wrecked by winds often had the doors closed!

Can't add anything to what pat100 says below.

 

[Jon Stewart]

Most commercially fitted solar panels are streamlined down to the roof.

...and if that's true, with the panels being flush to the roof, then the pressure effect is irrelevant. However, I've seen plenty that were most definitely not flush with the roof.

Your other analogies are false comparisons, as panels are never mounted with the front of them higher than the rear. You'd have to be really dumb to do that.

 

[Jon Stewart]

Can't add anything to what pat100 says below.

I didn't expect that you would.

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[DerryW]

That's actually the wrong way around.

If the van is in motion, still (or slower moving) air under the panel (at high pressure), and faster moving air over the top (low pressure), creates an upward nett force.

This is the same principle of how the wing on a plane, or a sail on a yacht works, and why people who got their polytunnels wrecked by winds often had the doors closed!

Every days a school day.

 

[VXman]

Which primer did you use - there appear to be several Sikafkex ones available?

Actually - thinking back I'm not sure it was primer - actuator? I know I used 2 things when the guide I was reading suggested 3. I think views vary a lot on what's really necessary.

This is what I used , seems to be a primer\activator.

United Industrial: Supplier of Engineering and Automotive Products

United Industrial Ltd. supplies engineering and automotive products, hand and power tools, janitorial, PPE and workshop consumables throughout the UK.

www.unitedindustrial.co.uk

 

[Gellyneck]

...and if that's true, with the panels being flush to the roof, then the pressure effect is irrelevant. However, I've seen plenty that were most definitely not flush with the roof.

Your other analogies are false comparisons, as panels are never mounted with the front of them higher than the rear. You'd have to be really dumb to do that.

To me flush means fitted directly to the roof without any space between the back of the panel and the roof therefore the panel will follow the profile of the roof and as there is no open lower surface there would be no aerofoil effect.

If you mean off the level with the roof that is a different matter. To achieve an aerofoil effect the top face would normally have a greater curve than the lower face thereby creating a Bernoulli effect (eg an aircraft wing profile).

I, personally have never seen a solar panel shaped similar to an aircraft wing but if you have so be it.

If you mean a drag effect that is different to an aerofoil effect. This is the effect you seek to eliminate by fitting an air deflector.

I didn't expect that you would.

?????

 

[Gellyneck]

Lizbiebrowne

Your thread has digressed into a potential difference of opinion which will add no real value to your question. Apologies from me for this.

I will only add this is how our manufacturer installed solar panel is fitted -

Longer length down the roof to minimise drag, both front and rear edges with full width brackets and both long sides open.

 

[Jon Stewart]

To me flush means fitted directly to the roof without any space between the back of the panel and the roof therefore the panel will follow the profile of the roof and as there is no open lower surface there would be no aerofoil effect.

If you mean off the level with the roof that is a different matter. To achieve an aerofoil effect the top face would normally have a greater curve than the lower face thereby creating a Bernoulli effect (eg an aircraft wing profile).

I, personally have never seen a solar panel shaped similar to an aircraft wing but if you have so be it.

If you mean a drag effect that is different to an aerofoil effect. This is the effect you seek to eliminate by fitting an air deflector.


?????

I think we're mostly in agreement, and I took your original post to imply the panel wasn't flush mounted (I saw a panel mounted well above the roof rather than flush in a post somewhere here not to long after!)

I completely agree with having a sloped deflector to reduce air turbulence, thus parasite drag on the front if flush mounted.

The solar panel doesn't need to be the shape of an aerofoil. You just need still (or slower moving) air below, and faster moving air above to create a positive upward force.

Apologies for the apparent incorrect inference on my part. I guess I've seen it so many times before in other contexts!

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[Lizbiebrowne]

Actually - thinking back I'm not sure it was primer - actuator? I know I used 2 things when the guide I was reading suggested 3. I think views vary a lot on what's really necessary.

This is what I used , seems to be a primer\activator.

United Industrial: Supplier of Engineering and Automotive Products

United Industrial Ltd. supplies engineering and automotive products, hand and power tools, janitorial, PPE and workshop consumables throughout the UK.

www.unitedindustrial.co.uk

Thank you - that's useful. Reading the product literature it says it has a flash off time of 10 minutes - I'm not sure what that means, did you leave it more than 10 minutes before you applied the adhesive?

 

[bigtwin]

I will only add this is how our manufacturer installed solar panel is fitted

I wonder if the manufacturer employed any aerodynamicists.

Ian

 

[Gellyneck]

I wonder if the manufacturer employed any aerodynamicists.

Ian

Funnily enough when we were considering fitting a second panel I spoke with them and, after advising speak to their dealer for retro fit, they did say it would be fitted with full width brackets at front and rear edges to mitigate potential lift from air flow underneath. And, no there is no air dam fitted to front so there is drag created by it.

As it turned out we went with a Snipe satellite dish instead and the strong recommendation was to fit it with hinged side to the front (the mounting panel is actually marked as such) to ensure the lift created was pulling against the hinge and not the retaining pin.

 

[Lizbiebrowne]

I think we're mostly in agreement, and I took your original post to imply the panel wasn't flush mounted (I saw a panel mounted well above the roof rather than flush in a post somewhere here not to long after!)

I completely agree with having a sloped deflector to reduce air turbulence, thus parasite drag on the front if flush mounted.

The solar panel doesn't need to be the shape of an aerofoil. You just need still (or slower moving) air below, and faster moving air above to create a positive upward force.

Apologies for the apparent incorrect inference on my part. I guess I've seen it so many times before in other contexts!

Couldn’t someone develop a solar panel in the shape of an inverted aerofoil so that the faster you go the more it’s forced onto the roof of the van? I wouldn’t have to bother with the glue them.

 

[Gellyneck]

Couldn’t someone develop a solar panel in the shape of an inverted aerofoil so that the faster you go the more it’s forced onto the roof of the van? I wouldn’t have to bother with the glue them.

However, you'd also need them to fit a rudder on top of it to counteract the centrifugal force when cornering!

OK, I'll shut up now and bu**er off!

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