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Best roof direction for solar panels?

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Started 2 years ago by SJ2571
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SJ2571
Member

Hi all, I was wondering about the best roof position for solar panels for my house. See the pic in this link:

http://img819.imageshack.us/img819/1769/solarr.jpg

I was planning on having the panels put where the black circle is. See how the sunshine in the afternoon comes from the northwest? That way, the sun (sort of) shines on the circled section from about 11am onwards. The only thing is, maybe the sun won't be shining directly on the panels? Any advice you can give, based on the photo?

The alternative is to put the panels on the other side of the roof, which would catch the morning sun but stop getting it from about 2pm onwards. That section of roof faces northeast.

Which section of roof would you recommend? Thanks.

Posted Wednesday 21 Jul 2010 @ 6:46:40 am from IP #
matas
Member

I have little experience in these things, but your roof is fairly flat.
Couldn't you run a tilt frame, obliquely, from along an east west line. So the panels are facing perfectly north ?
Or the row perpendicular to the main roof ridge, so the panels point NWN (again with a tilt frame) ?
Do you get any other shading from trees etc ?

Posted Wednesday 21 Jul 2010 @ 7:16:50 am from IP #
SJ2571
Member

I'm a solar newbie and won't be installing anything myself. It's up to Origin Energy.

So what you're saying is that it's probably a bad spot for them?

Posted Wednesday 21 Jul 2010 @ 7:44:20 am from IP #
matas
Member

Is the roof shaded significantly by trees or anything ?
If not, then I would say its a good spot.

Posted Wednesday 21 Jul 2010 @ 8:12:12 am from IP #
matas
Member

But I think, it would definitely be a long way short of ideal, if you mounted the panels flush on the roof, on either side.
You should measure the slope angle of the roof, and the azimuth (eg NNW).
Then go to this excellent solar calculator, to see how much less than ideal, different locations would be.
http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/
It really is a fantastic tool.

Posted Wednesday 21 Jul 2010 @ 8:31:39 am from IP #
SJ2571
Member

I have no idea (or the tools) to measure angles or azimuth. Total newbie, remember. Assume you're talking to Mr Bean. Anyway, I took 2 photos this afternoon at 3:30pm showing the state of the roof. See here:

http://img843.imageshack.us/img843/7825/roof.jpg

Okay, in the first little image you can see the direction that each roof side faces (one slightly NE, one slightly SW). The sun rises in the morning at the bottom-right side of the little image, and sets in the top-left side of it.

If you look at the NE roof pic, you can see that by the afternoon, a lot of it is shaded, but in the morning it will totally lit by the sun. My only worry about this side, is that in summer, the other side will get more light due to daylight savings.

If you look at the SW roof pic, you can see that by the afternoon, a tree will be covering about half of the roof. But the panels could be installed at the very far side of it which is never covered.

So, I don't know, but I'm thinking the NE side would probably be best, to soak up the morning rays till about 2pm-ish? I just wonder if that will generate enough power to be financially viable.

Would the Origin Energy installers decide the best spot anyway, on the day of installation?

Oh, and I don't think I need lifters or anything, the panels will be flush on.

Posted Wednesday 21 Jul 2010 @ 1:30:55 pm from IP #
dave lawrence
Member

as matas said
"Couldn't you run a tilt frame, obliquely, from along an east west line. So the panels are facing perfectly north ?"
if you want your panels to operate as efficiently as possible ,then this is what you must do .
I am aware of how little interest many installers have in the "inconvenience " of organizing tilt frames , however it is your money and potentially your system . If they cant be bothered helping you out , go to somebody who will .
Or alternatively , preorganise the frames design and installation and then get the panels erected .
by the way, daylight saving makes zero difference to the path of the sun. the suns apparent path does change dramatically from winter solstice (shortest day ) to summer solstice (longest day )... it rises south of east in summer then sets south of west .
In winter it rises north of east, north of west . IT ONLY ever rises due east and sets due WEST on the spring and autumn equinox.
The fact that most solar installers are not aware of this is a worry.

Posted Wednesday 21 Jul 2010 @ 8:07:40 pm from IP #
Russell Moore
Member

It is a bit hard to tell from the photos, but I would agree with the others that you need step frames to lift and point the panels to the north.

The best place appears to be towards the SW corner of the NE facing roof, assuming that you are using 9 panels, I would put 4 at the back and 5 at the front, in 2 rows.

The frames can point them north, and angle them about 6 degrees less than your latitude. For example if you were in Sydney, the lat' is 34 degrees, and the best angle (tilt) is 28 degrees.

Azimuth is longtitude degrees, ie north is 0, east 90, south 180, west 270, etc. Tilt or angles is the angle above horizontal. The best way to check for approx' solar north is to see which way the shadow from a vertical object is pointing at noon, and that shadow will be pointing south, so of cause the opposite direction is north.

One of the problems with frames is that you need to space the rows so as the front row doesn't shade the back row when the sun is low on winter mornings/afternoons.

Posted Wednesday 21 Jul 2010 @ 10:38:04 pm from IP #
dave lawrence
Member

to find true north (AKA solar north ) , out you need to first know when solar NOON is. DO NOT assume it is 12AM.
that is easy ... on any given day find out what time is sunrise and what time is sunset .
work out the exact middle of the day according to those times ... that time is solar noon.

Posted Wednesday 21 Jul 2010 @ 11:01:10 pm from IP #
matas
Member

Another way to check a bearing easily, using a Google maps based tool.
Goto to the tool
http://www.acscdg.com/
Type in your address and zoom in maximum, and use satellite photo view.
Then just click at one point on your roof, then click at a second point.
The bearing (azimuth) will show in the table.

I am fairly sure that map grid north, is almost identical to polar (solar) north.

Posted Thursday 22 Jul 2010 @ 2:44:43 am from IP #
SJ2571
Member

Okay, I tried the azimuth thing that matas mentioned and it says 77 if I go from the west roof side to the east, or 165 from the north roof side to the south.

I've got photos of the roof at solar noon, as calculated by what Dave said, and will put a link later. But I definitely think I will need pitching frames. Can they go shorter at one end and longer at the other?

Posted Thursday 22 Jul 2010 @ 2:51:12 am from IP #
living sustainably
Member

Using my good old image processing tools, it appears to me that the azimuth of your Western roof is 257 degrees and of your Eastern roof just the opposite, 77 degrees. Your roof has a 10 degree slope.

Posted Thursday 22 Jul 2010 @ 3:03:09 am from IP #
matas
Member

It seems your roof ridge runs pretty close to north south
Here is a picture of what you probably need.
Look at the "fin mount" picture for east roofs (at the page bottom).
http://www.vibrantsolar.com/solarbasics4.htm

Posted Thursday 22 Jul 2010 @ 3:13:39 am from IP #
matas
Member

And I think you would just use a stock standard tilt frame.
It just means the panels would slope down the roof, a bit.
So they tilt a bit sideways, as well as tilting back (optimally at 28°, as Russell said, for Sydney)
It shouldn't be a problem, because the slope of your roof is so shallow.
The only small possible issue, is shading from the roof ridge, in the late afternoon of the east side panels, and shading in the early morning of west side panels. But again, because your of your shallow roof slope, this should not be significant.

Posted Thursday 22 Jul 2010 @ 5:02:40 am from IP #
Russell Moore
Member

The 'fin mount' that matas's link has is a perfect example of what is needed for your install SJ2571, just in your case they will face north of cause, and be twisted the other direction to the example.

If you go for the 1.5kW system that will be 9 panels, again I would suggest putting them in the SW corner of the NE roof, 4 panels at the back and 5 panels at the front, well spaced to avoid shading each other.

Posted Thursday 22 Jul 2010 @ 7:34:24 am from IP #
SJ2571
Member

Thanks again for all the responses. Your advice and tips have been great!

After checking my roof out for the last few days, I am certain that a fin mount will be necessary, otherwise the panels just won't get enough sun as they will be facing more east-west than north-south. I only hope Origin doesn't charge a lot to add those!

As for the best position, see my new pic here (retouched):

http://img205.imageshack.us/img205/7953/roofb.jpg

I've observed over the last few days that the best spot would be along the upper-right corner of the house in that pic, ie. along the rectangle of grass. Reason being is that spot gets sun all day, and also keeps it from being visible from the street, which is what my council requires. Anywhere else on the roof, like in that position but on the other half, gets too much shade from summer trees.

But my question now is: would Origin Energy put it there at my request, or do they themselves choose the position?

And lastly: the panels will needing pitching frames, but do the panels need to be raised at one end from the roof, so that they're 100% level and horizontal? Or can they be flush with the roof and thus running in a line to match the roof's slope?

Oh yeah, I've been meaning to ask: is it the actual sun LIGHT that generates the power, or the sun HEAT?

Thanks!

Posted Friday 23 Jul 2010 @ 1:25:42 am from IP #
termite
Member

It's the photons, of which visible light comprises a subset. Infra-red photons (lower wavelength than visible light) are perceived by us as heat. I don't know what wavelength range that typical silicon PV cells are sensitive to, though I see there is some research to cells that are sensitive to different spectral ranges, in particular infra-red.

Most solar water heaters absorb heat directly, from infra-red photons directly received from the sun or re-emitted from nearby objects. They are cheaper (more efficient?) at achieving the same performance than using PV cells - but they aren't as flexible in their use.

Posted Friday 23 Jul 2010 @ 2:01:40 am from IP #
matas
Member

You are paying the money.
I am fairly sure Origin Energy would place the panels where ever you want (especially if it gets a lot of sun, like you say).
There should be no problem for them, to install a standard tilt frame, in the "fin mount" style, on a shallow metal roof, like yours.
I didn't realise that councils want to limit the view of PV panels.
I didn't even ask my council.

Posted Friday 23 Jul 2010 @ 2:41:56 am from IP #
Russell Moore
Member

Before my panels were installed, I agonised for months over where I would put them,I probably had 7 or 8 different layouts before I settled on the final one.

I have shade problems with one of my own trees, and it is too large for me to trim myself, and would cost a bomb to get in tree loppers, although if I ever extend my system it will have to go.

Most positions are a compromise, as few of us have a completely shade free site.

I was lucky enough to have a huge north facing roof (5 deg's east of true north)that is large enough to have over 10kWs of panels if I want to, (I currently have 5kWs)

No, you don't need to have the panels horizontal on frames, they can follow the roof slope, as per matas's link. I have seen a set of tilt frames on Todae Solars site and they hold 2 panels each and cost $225 each. Remember they are replacing the normal flush roof mount anyway, and shouldn't be that more expensive.

It is your money, and your house, YOU can tell them to install it where YOU want to!

Posted Friday 23 Jul 2010 @ 2:54:28 am from IP #
matas
Member

Russell, I also had a huge tree, in my yard, shading my panels, in the morning.
When I started comparing my system output, to others, it was well down.
My tree would also have cost a fortune to get pruned, and was much too high for me to climb (30metres).
So I bought one of these rope saws.
http://cgi.ebay.com.au/Hand-Chain-Saw-Chainsaw-WEB-TEX-Survival-Kit-Bushcraft-/140286272623?cmd=ViewItem&pt=LH_DefaultDomain_3&hash=item20a9b6a46f
and used a slingshot to get a nylon fishing line over each branch, then pulled a larger rope over, with the rope saw finally attached.
It was a long slow awkward process, and I came close to failing with every branch.
But I eventually removed about 10 very large branches, working from the ground, so the panels are no longer shaded.
I hated doing it to the tree, but half the branches were dying anyway, and there were termites thoughout.
As a big bonus, I now, for the first time, get winter sun, in a row of my largest windows
And I don't use artificial heating, so it makes a big difference to my comfort level.
Also I can now grow some vegetables and fruit trees, in the spot I really wanted to, because the sun gets to it.
So I am really extra glad I got the PV panels, because I wouldn't never, ever, have attempted the pruning otherwise.

Posted Friday 23 Jul 2010 @ 5:02:13 am from IP #
SJ2571
Member

Well I just had the inspection for our panels and the company said our roof is unsuitable for panels without both bridging beams AND tilt frames. They said it needs bridging beams because the existing roof struts are too thin to anchor the panels and/or tilt frames on. So, about $300 for those and Origin Energy said another $700 for tilt frames. Great.

So I rang Origin and cancelled the installation. They are refunding my deposit of $299 and first payment of $112 in about two weeks. TWO WEEKS! They took it overnight so I don't know why they can't refund in at least 48 hours.

Anyway, there you go. Thanks to all who replied to my questions in these forums, it was VERY informative and helpful. But I guess I won't be visiting here much anymore, LOL. Thanks guys.

Posted Friday 20 Aug 2010 @ 3:21:55 am from IP #
peta
Member

AWWW - Can't you add the extra bucks to about 9 months payback time ? (without really knowing your circumstances but.. have alook?)

I need an entire new roof and battens at 17K to make it worthwile. It will take me about 4.5yrs for 2.8/3KW system to payback, and the next 8 yrs after that to pay for my new roof with the savings !!!
... ?

Posted Friday 20 Aug 2010 @ 6:56:59 am from IP #
SJ2571
Member

Hi Peta, I did ask Origin about that possibility but they said no because it's not part of the finance deal. So they'd want $700 up-front. Oh well. It's always the rich who get what they want in life.

Posted Friday 20 Aug 2010 @ 8:23:45 am from IP #
peta
Member

Not always the rich SJ2571 - sorry if I offended you. We're not doing the 17K roof, 'cause were not rich. but we're looking at the panels to save 2K/Yr to go towards it.

Posted Friday 20 Aug 2010 @ 8:43:25 am from IP #
SJ2571
Member

Peta, I wasn't offended. The rich comment was (partly) just a joke. (See the wink after it?). Anyway, yes it's a shame that I can't have it installed, as I was looking forward to cheaper bills. It's my first home and I never knew why a north aspect was so important. Now I know. Live and learn.

Posted Friday 20 Aug 2010 @ 10:17:26 am from IP #
matas
Member

SJ2571 I would approach some other companies, for quotes.
Just explain the setup you want.
Different companies may use differenet tilt frames, that do not require bridging beams.
Sunsavers has some very good prices
http://www.sunsavers.com.au/
or Laddertech, a Sydney installer
http://www.laddertech.com.au/

Posted Friday 20 Aug 2010 @ 11:06:54 am from IP #
thatmosis
Member

The panels should be fixed facing North and the angle of attack will be determined by the Latitude you are on. Its not complicated but it would be an idea to get some professional help from a reputable Solar expert first as its crucial that your panels get the most use of the sun. My Solar man is one of the best in Australia and is responsible for telling the Government what to do and how to do it regarding Solar. Would be happy to pass his name on if you are interested.

Posted Friday 20 Aug 2010 @ 10:41:44 pm from IP #
termite
Member

FYI, the latitude of some major Australian locations:
Sydney -33.8 Melbourne -37.8 Brisbane -27.5
Adelaide -34.9 Perth -32.0 Canberra -35.3
Darwin -12.5 Hobart -42.9 Alice Springs -23.7
Cairns -16.9 Launceston -41.4

"A ratchet system can also be used on the solar panel angle mount to seasonally shift position from winter to summer settings."

The tilt of Earth's axis is about 23.5 degrees.

To calculate the best solar panel angle (from horizontal) when the sun is at zenith on:
1. The equinox = latitude (eg about 33.8 degrees to the north for Sydney)
2. The summer solstice = latitude + axial tilt (eg about 10.3 degrees to the north for Sydney)
3. The winter solstice = latitude - axial tilt (eg about 57.3 degrees to the north for Sydney)

Please someone tell me if that's wrong... of course the sign of the numbers dictates that a negative result means tilting to the north, a positive result means tilting to the south.

Posted Friday 27 Aug 2010 @ 2:08:57 am from IP #
thatmosis
Member

The obvious and best idea is to have a sun tracker unit that follows the sun during the day and at night returns to catch the first rays in the morning. There are various methods of doing this and some can be done by a competant DIYer using simple bits and pieces like a photo electric cell, a simple electronic board that can be made from readily available items from a store like Dick Smith, a car electric window winder and a bit of welding and cutting. This method means that the panels receive the top amount of sunlight for the full 8 hours or so.

Posted Friday 27 Aug 2010 @ 2:16:42 am from IP #
SJ2571
Member

Just an update: my full refund from Origin Energy came into my bank account today. So it's now well and truly over. Anyway, it was a great learning experience, and if/when I buy another house I'll be better prepared!

Posted Tuesday 14 Sep 2010 @ 9:51:18 pm from IP #

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