Cooler roof?

[mikeypj]

Does anyone have a roof rack the sits just a few inches above the actual roof? If so, have you noticed if it has helped cool the inside of the bus? I'm kicking around an idea about helping the bus stay cooler. I've read that solar panels actually produce heat so that radiates into the bus. The roof rack keeps the direct sunlight off of the roof and with a gap it would be a cooling area between bus roof and sun.

[superdave]

ive seen them alot in mountain areas, they put rafts up there. i also saw a guy who mounted auwnings to each side of the rack so it shaded both sides of the bus also.

[mikeypj]

I'm talking about on the roof, it just needs a few inches for air to circulate.


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[Tango]

Makes a huge difference. Like the old safari model Range Rovers built for Africa, having the roof in the "shade" with some air circulation in between will greatly reduce the interior temps.

[somewhereinusa]

MCI made some buses that went to Saudi, they had a second roof with an air space.

[superdave]

Originally Posted by mikeypj

I'm talking about on the roof, it just needs a few inches for air to circulate.


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i was also, id post a pic but dont have all day. look down in tn. for a bus with the roof already installed, they put the rafts up on them to take people to the river. yes it works great.

[mikeypj]

Originally Posted by somewhereinusa

MCI made some buses that went to Saudi, they had a second roof with an air space.

That's exactly what I'm talking about, I can see the roof racks that carry the rafts working, I was talking a little more streamlined and low profile.. hmmmm how to do this.....


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[DoubleO7]

the roof-rack with awning gets me to thinking how to make the awning a rigid panel that extends and retracts like a shelf coming out of a cabinet.

[mikeypj]

Originally Posted by DoubleO7

the roof-rack with awning gets me to thinking how to make the awning a rigid panel that extends and retracts like a shelf coming out of a cabinet.

Wouldnt that be too heavy? Its a good idea but only it was made out of a strong light material.

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[Iceni John]

Between my bus's two roof hatches I built a 26'-long walkway that's about 5" above the crest of the roof, and to the sides of this walkway are hinged my eight solar panels. When they lay down against the roof for travel there's a few inches of space underneath them, enough for hot air to circulate upwards and vent out at the top. This, together with painting the roof gloss white with ceramic insulation pixie-dust added to the paint, has made the bus interior much less hot than before. I can tell inside the bus where the solar panels begin at the front merely by the difference in ceiling panel temperatures there.

And no, PV panels do not generate heat (not unless there's something seriously and dangerously wrong with them!). Their output is however affected by heat - for every degree Celsius above 25C their output drops by almost a half percent per degree C, so in other words they will produce significantly less power in very hot weather (one reason I gave them sufficient airflow underneath for convective cooling), or conversely some of the highest PV outputs are in Alaska in the winter when panels are very cold but can still get full insolation when positioned vertically.

John

[oredigger]

Iceni John,

How did you attach your solar panels and the walkway in the middle? Any details you can share?

Thanks,

[Iceni John]

Originally Posted by oredigger

Iceni John,

How did you attach your solar panels and the walkway in the middle? Any details you can share?

Thanks,

The walkway is attached with a pair of 3/8" stainless socket-head bolts through each roof rib, 38 in total; the bolts come through the ribs from underneath, leaving small holes in the ceiling that will be covered by the 1/4" cork that I will eventually glue to it. The outer edges of the solar panels have telescoping and pivoting hinged stainless struts whose lower ends slide inside aluminum T-track that is hinged to a long piece of 6061 angle that is bolted to the roof the same way as the walkway. The raised walkway is useful to cover the PV panels' two combiner boxes and panels' wiring conduits, and the three boxes for the water washdown outlets (for easily washing the panels) and for the eventual solar water heating panels that will also be hinged just like the PV panels. (The panels' downfeed cables and the PEX water lines to and from the roof are all run inside the hollow roof ribs down to the bus's interior or to the underfloor storage bays.) Some sections of the diamond-plate aluminum treadplate can be easily removed to give access to the boxes underneath. The panels are positively locked by small clamps down against the roof for travel, and everything can be easily operated by hand without any tools. The entire walkway is cross-braced to completely prevent any lateral or longitudinal movement by means of diagonal braces between every pair of supports. Everything is made from aluminum or stainless steel, with nothing to rust or need painting. So far, so good.

John

[mikeypj]

I was thinking along the lines of aluminium. Strong and light. I like your set up, but im gonna have to wrap my head around this and figure out how i would do it. Even if i dont do this my panels will be mounted at least 5" above the roof.

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[mikeypj]

Originally Posted by Iceni John

The walkway is attached with a pair of 3/8" stainless socket-head bolts through each roof rib, 38 in total; the bolts come through the ribs from underneath, leaving small holes in the ceiling that will be covered by the 1/4" cork that I will eventually glue to it. The outer edges of the solar panels have telescoping and pivoting hinged stainless struts whose lower ends slide inside aluminum T-track that is hinged to a long piece of 6061 angle that is bolted to the roof the same way as the walkway. The raised walkway is useful to cover the PV panels' two combiner boxes and panels' wiring conduits, and the three boxes for the water washdown outlets (for easily washing the panels) and for the eventual solar water heating panels that will also be hinged just like the PV panels. (The panels' downfeed cables and the PEX water lines to and from the roof are all run inside the hollow roof ribs down to the bus's interior or to the underfloor storage bays.) Some sections of the diamond-plate aluminum treadplate can be easily removed to give access to the boxes underneath. The panels are positively locked by small clamps down against the roof for travel, and everything can be easily operated by hand without any tools. The entire walkway is cross-braced to completely prevent any lateral or longitudinal movement by means of diagonal braces between every pair of supports. Everything is made from aluminum or stainless steel, with nothing to rust or need painting. So far, so good.

John

So, any problems with leakage due to the holes in the ribs? One of my concerns is vibration, its has to be bad for the solar panels. Mount them with rubber grommets..

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[superdave]

Originally Posted by DoubleO7

the roof-rack with awning gets me to thinking how to make the awning a rigid panel that extends and retracts like a shelf coming out of a cabinet.

you could do this on the drivers side, then use two awnings on the door side to use as shelter when camping.

[mikeypj]

The awnings would work great for the sides of the bus, it's the roof I'm interested in.


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[GreyCoyote]

John: That sounds like a fantastic setup. In fact, I'd sell my mother for a picture of your setup. Or give you a free dog. Come to think of it, Mom passed in 2013, but Rufus is still up for grabs!

Your roof-top picture gets his. (No deposit, no return. He comes with papers: a weeks supply! Hehehe)

[Iceni John]

Originally Posted by GreyCoyote

John: That sounds like a fantastic setup. In fact, I'd sell my mother for a picture of your setup. Or give you a free dog. Come to think of it, Mom passed in 2013, but Rufus is still up for grabs!

Your roof-top picture gets his. (No deposit, no return. He comes with papers: a weeks supply! Hehehe)

I don't have any photos of my panels in place, but the YouTube video of my bus at last year's Buses Gone Wild VII get-together shows the panels' support frames before I installed the panels themselves. My bus is the third.

John

[Iceni John]

Originally Posted by mikeypj

So, any problems with leakage due to the holes in the ribs? One of my concerns is vibration, its has to be bad for the solar panels. Mount them with rubber grommets..

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I used 1/8"-thick EPDM rubber washers as sealing grommets between the roof itself and the bottom of the walkway's support bolts, and under the nuts at the top of those bolts. I had a few slight leaks initially, but that was because I hadn't tightened all the bolts quite enough - now that they are all uniformly tight I didn't get any leaks at all during the rains here a few weeks ago. EPDM is ozone and UV resistant, so it should last a long time. I did not want to use caulk because it always seems to eventually leak and need work.

The panels themselves sit inside support frames made from 1.75" angle 6063 aluminum, and they are cushioned by closed-cell EPDM foam weatherseal in each corner of the frame. I secured each panel into its frame with four stainless bolts bearing against the top of the panel's aluminum frame. The idea behind having each panel in a support frame is to reduce the loads on the panels themselves, and to make it easier to replace panels if I needed to in the future.

John

[mikeypj]

Originally Posted by Iceni John

Between my bus's two roof hatches I built a 26'-long walkway that's about 5" above the crest of the roof, and to the sides of this walkway are hinged my eight solar panels. When they lay down against the roof for travel there's a few inches of space underneath them, enough for hot air to circulate upwards and vent out at the top. This, together with painting the roof gloss white with ceramic insulation pixie-dust added to the paint, has made the bus interior much less hot than before. I can tell inside the bus where the solar panels begin at the front merely by the difference in ceiling panel temperatures there.

And no, PV panels do not generate heat (not unless there's something seriously and dangerously wrong with them!). Their output is however affected by heat - for every degree Celsius above 25C their output drops by almost a half percent per degree C, so in other words they will produce significantly less power in very hot weather (one reason I gave them sufficient airflow underneath for convective cooling), or conversely some of the highest PV outputs are in Alaska in the winter when panels are very cold but can still get full insolation when positioned vertically.

John

Ya know i read an article about solar panels and how they get hot ( generate heat is the wrong phrase)and affect the air temp inside. Thats what got me thinking of a heat barrier for lack of a better word. Just to keep the sun from directly hitting the roof. Who knows i may just build a roof top deck.

The road goes ever on and on, down from the door where it began. Now far ahead the road has gone, and I must follow, if I can.” –J.R.R. Tolkien