Panel (Array) ventilation

[mohammedbera2]

Hi guys advice on  panel temperature   vs production

I have a north facing roof @ 30°  corrugated zinc

 And want to mount  my panels  directly   to the zinc  

Is it worth spending on rails  to lift them ?

 

 

[Guest]

Yes, but it is not an easy justification.

The cooler the panels, the better they preform. Like on a cold sunny day, they can exceed their rated specs.

So, to answer the question, maybe someone else has a better answer, the cost of lifting them off the zinc versus the additional production you can expect, it is a unknown.

Maybe is is marginal, maybe it is quite a bit, but I don't think it would be like WOW, just look at that, 30% more.

 

[SilverNodashi]

2 hours ago, The Terrible Triplett said:

Yes, but it is not an easy justification.

The cooler the panels, the better they preform. Like on a cold sunny day, they can exceed their rated specs.

So, to answer the question, maybe someone else has a better answer, the cost of lifting them off the zinc versus the additional production you can expect, it is a unknown.

Maybe is is marginal, maybe it is quite a bit, but I don't think it would be like WOW, just look at that, 30% more.

 

It shouldn't need justification. 

A client decided, 2 years ago, to justify the cost of the panel mountings. I think his roof is 30 degrees and face due North. So it's basically perfect. I saw him quite some time after that and he was upset with me for selling him **** panels (his words). Production is so bad during the day that he often still pays eskom to run his pool pump and the washing machine. I didn't see the installation, but did quote on a proper mounting system to lift the panels off the roof by about 120mm. He refused, price was too much. Today he's paying for it in another way. It took me a while to explain to him there is nothing wrong with the solar panels. They could perform as they are designed, if installed as per recommendations. 

 

@mohammedbera2 If you REALLY, really cannot afford it, don't do it, but the panels will get too hot to produce much energy. Anything beyond 25 degrees celcius will see degraded performance. My tile roof often sees temperatures upto 55 degrees, and 34 underneath the panels. That's too hot for my liking, bu I can live with it. It does mean though that I'm not getting the maximum potential from the panels. 25 degrees are optimal for any panel, though often difficult to achieve. 

 

[Chris Hobson]

@Chris-Rmounted ½ his panels 200 mm clear of his roof and the other ½ flush and there is a significant difference in production between the two strings. Unfortunately I cannot remember the exact figures.

 

[___]

Solar panels mounted far from the roof, such as mine that is tilted 35 degrees up from a flat roof, already operate well above 50 degrees Celsius in full summer sun. There is no reason to want to make this any worse.

But from another angle, I manufactured my first two frames from steel, and the third one from aluminium with proper extruded rail. Yes, the third frame was about double the cost of the first two, but I will never again use steel for this. I will in fact go back and replace one with aluminium soon.

[Guest]

Not saying it won't make a difference, it will, but what is the exact number to justify the additional expense. 

So, it boils down to: It IS better to have them well ventilated, kept as cool as possible. 

But, if you have already mounted them, does it justify the cost to change, closing the holes in the roof and all the other little bits?

Or would it be better to get another panel or two, mounted with ventilation?

My panels are on adjustable frames (no, it is not worth the risk of life and limb on our roof) and they still get damn bloody in summer.

It is a tough one.

[Chris Hobson]

My feeling is that over the lifetime of the install R1-3k extra on the install will pay for itself in the extra efficiency. 

[Guest]

6 minutes ago, Chris Hobson said:

My feeling is that over the lifetime of the install R1-3k extra on the install will pay for itself in the extra efficiency. 

YES! That I can also agree to IF the install is R3k or less.

[Chris Hobson]

5 minutes ago, The Terrible Triplett said:

YES! That I can also agree to IF the install is R3k or less.

Solarstrut roughly R55-R65/m so one adds R125 -R135/panel to the cost of the install Each panel has to produce ±100kWh extra over its lifetime.  Taking an efficiency of 3.5kWh/kW (entirely doable from PV Output data) anything over 1% increase in production for a 300W pays for itself. @PaulF007 is going to "kap" me for not including interest . Admittedly panels are not excessively hot all year round but the efficiency/temperature correlation is linear so you will see some benefit even in winter. This summer cooling my 3kW of panels with water resulted in a nearly 500W increase in production. In previous years it has been less.

[Mako]

I have two shipping containers next to each other. The tops are silver. My six panels are adjustable for tilt only and face WNW (no choice). Excellent for ventilation and maintenance as I step off a balcony which is level with the container tops. The silver top of the 'next door' container reflects onto the panels in the winter months and definitely makes a difference. Summertime reflection is wasted because of the low tilt angle.

[SilverNodashi]

10 hours ago, plonkster said:

Solar panels mounted far from the roof, such as mine that is tilted 35 degrees up from a flat roof, already operate well above 50 degrees Celsius in full summer sun. There is no reason to want to make this any worse.

But from another angle, I manufactured my first two frames from steel, and the third one from aluminium with proper extruded rail. Yes, the third frame was about double the cost of the first two, but I will never again use steel for this. I will in fact go back and replace one with aluminium soon.

 I see this "cheap mistake" all over. Aluminium is expensive. Extruded aluminium even more so. And anything solar related just takes the cake. But you need to decide whether you want to remove, and repaint the frame every year or two, and possibly replace bolts & nuts every few years, or just let the proper stuff do what it's made for. 

 

P.S. Not aiming this at you, @plonkster

[SilverNodashi]

7 hours ago, The Terrible Triplett said:

Not saying it won't make a difference, it will, but what is the exact number to justify the additional expense. 

So, it boils down to: It IS better to have them well ventilated, kept as cool as possible. 

But, if you have already mounted them, does it justify the cost to change, closing the holes in the roof and all the other little bits?

Or would it be better to get another panel or two, mounted with ventilation?

My panels are on adjustable frames (no, it is not worth the risk of life and limb on our roof) and they still get damn bloody in summer.

It is a tough one.

Not saying it would be too expensive, but would you risk burning some panels which got too hot? It has happened before. Those diodes, the soldering and even the silicone wafers can only handle a certain temperature. Normal electronic components normally have an upper operating limit of 80 degrees celsius. 

[Guest]

28 minutes ago, SilverNodashi said:

... would you risk burning some panels which got too hot?

Been there done that.  Panels is however working again. 

But yes, you are right, it is a point to consider.

[SilverNodashi]

3 minutes ago, The Terrible Triplett said:

Been there done that.  Panels is however working again. 

But yes, you are right, it is a point to consider.

That alone is a no-brainer to me. Proper mounting structure is expensive (as have been discussed many times on this forum in the past, by many people) but it has a very valuable purpose in your expensive investment. 

[___]

3 hours ago, SilverNodashi said:

I see this "cheap mistake" all over. Aluminium is expensive.

Well.... about that. I made two steel frames. One of them is doing very well. No problems. The other one is not doing well. It comes down to the products used on the steel. Even with good products, steel will need attention every few years, but it also depends on where you live. My father had steel frames up... 15 years... not a single problem. Cause we hardly get any rain you see :-) And in my defence, using steel was a calculated move. It bought me time. And I can weld (I'm not a boiler maker, but good enough), and it did save me money at a time when I wanted to spend the money on better equipment. The saying goes that you should build a structure that will last the lifetime of the panels, and frankly, those old 150W Tenesols have to make space for larger panels soon. So I could argue that worked out just fine :-)

Now about the cost. The aluminium frame probably costs about 3 times more than the steel one... BUT... it is much faster to manufacture. With steel, you have to cut it, line it up, make sure it is level, tack-weld, then weld, clean off the slag, then paint that thing 3 layers or more. It is amazing how long it takes just to cut everything to size and at the right angles. With aluminium, no painting, cutting with a Mitre saw is super quick. I probably did in two days what took me a week with steel. And it looks way better.

How much is your time worth to you? I'm not using steel for this again, just for that reason :-)

[mohammedbera2]

Thanks 4 all the info - 

correct me if im wrong  : 

i have 12 x255w already mounted flat on roof and ordered 9x320w (should get them in a week )

from all this info I  feel it's better to put (aluminum ) rails and brackets  for the new panels - will pay itself off  over time 

( Not worth it to remove and reinstall the old one's on rails )

 Dose anyone  know what is the minimum  distance  it should be between the  roof -panel  ?

 

[Mark]

On 1/26/2018 at 6:38 AM, Chris Hobson said:

 

Edited January 28, 2018 by Mark
Deleted - new Thread

[Guest]

11 hours ago, mohammedbera2 said:

Dose anyone  know what is the minimum  distance  it should be between the  roof -panel  ?

The angle towards the sun, winter and summer average, for where you are, is what should drive the installation.

Then, the bigger the space underneath the panels, the more ventilation, and on wind still days, less heat buildup.

 

[Chris Hobson]

I think in some Canadian Solar documentation they mention a figure of 200mm. I am not home at the moment and cannot confirm this.

 

[mohammedbera2]

 

I found  this on the internet -

( Roof mounting clearance

Solar panels you want to mount on a roof must have at least 3 inches but 4 to 6 inches is better, distance between the roof and solar panels frame. The reason for this clearance is that it allows air flow under the solar panels for cooling them. You must never mount panels in a way there isn't any air flow under them because they can become very hot in that way. )

[SilverNodashi]

4 hours ago, Chris Hobson said:

I think in some Canadian Solar documentation they mention a figure of 200mm. I am not home at the moment and cannot confirm this.

 

Yes Chris. Many manufacturers recommend 200mm minimum. 

[PaulF007]

On 1/26/2018 at 12:05 PM, Chris Hobson said:

is going to "kap" me for not including interest .

Oh well that depends on if you are borrowing the using your own cash 

[mohammedbera2]

10 hours ago, The Terrible Triplett said:

The angle towards the sun, winter and summer average, for where you are, is what should drive the installation.

 In south Africa  what's  the best angle  is 30°  OK  

Being  in nylstroom / modimolle  ?

Please  advise 

[SilverNodashi]

34 minutes ago, mohammedbera2 said:

 In south Africa  what's  the best angle  is 30°  OK  

Being  in nylstroom / modimolle  ?

Please  advise 

If it's fixed, try and get as close to your latitude as possible. Otherwise stick with the 30 degrees if you have to. You might loose about 5% efficiency in winter. In summer you would probably loose some efficiency due to too much heat in that area. 

[Mark]

Try this tool (bottom of page)

http://www.pveducation.org/pvcdrom/properties-sunlight/solar-radiation-tilted-surface

You adjust the location and it tells you your options.