The solar arc--How the sun moves across the sky

East or West orientation for solar panels

by James Martin II on April 19, 2011

in Installation advice,Positioning solar PV panels

Determining the orientation and tilt angle of your solar power generation system is one of the most important considerations in designing your solar power system. As we have mentioned before, in the southern hemisphere, due North is the optimum orientation for panels. But not everyone has a perfectly oriented roof. When your two best options are East or West, which should you choose?

During the course of a day, the sun passes through the sky in a particular arc that varies throughout the year due to the earth’s orbit (see top image). The arc is always symmetrical from East to West, measuring out from the centre point, which would be midday. This means that from sunrise to midday (not counting during daylight savings time) and from midday to sunset, there is an equal number of hours of sunlight on one particular location. (You can see how this applies to your particular location using applications like SunCalc, which shows you exactly how the sun moves through the sky at different times of day.)

So, if your home or roof does not have a Northern aspect, but does have two roofs that face due East or due West, you may be asking yourself which side would be a better location for the most power generation. Making the right decision will impact on how much money you can save or possibly even make under the solar power incentive schemes available throughout Australia.

The first thing to consider is shading, of course, which can potentially have a big impact on the productivity of your system. Is either side of the roof shaded by nearby objects? If one side is shaded, choose the other side.

If you’ve determined that the shading effects are either non-existent or basically the same on both sides, then the next thing to consider is the angle of your roof–if possible, you don’t want to have to put in any mounting brackets or solar trackers. The two sides of your roof may be tilted at different angles: you will want to choose the side which is closer to being horizontal, as this will result in the most insolation (incident sunlight) throughout the day.

So, you have determined that shading is not an issue, and that both sides of your roof are symmetrically angled. What do you do now? Although Australia is well-known for its unpredictable climate, you will need to consider when you tend to have cloudy weather more often–in the morning or in the evening. This will depend on your location and climate, but for many locations (including Sydney), mornings have a greater tendency for overcast skies. Shading, even from clouds, can reduce the output of a system by up to 90%: any time it is not sunny, energy production will drop. So, in essence, the answer is that you should try to put your panels on the ‘sunnier’ side of the roof in terms of weather: if you have cloudy mornings more often, the West roof, and if you have cloudy afternoons more often, the East roof.

That being said, if you are thinking strategically about power consumption and pricing, you will want to keep in mind that in most states the price of electricity is higher around 5pm. For example, in NSW the peak electricity price at 5pm is $0.36, which is roughly twice the shoulder rate just prior to that time. If your panels are west-facing, you will be producing optimally right about this peak electricity time, potentially providing you significant savings on your bills.

For more information on west facing solar panels see our article Solar panel orientation: have we been facing the wrong way?

Written by James Martin

© 2010 Solar Choice Pty Ltd

Sources and Links:

Previous related Solar Choice Blog Entries: Orientation and tilt angle for your solar power system : Solar Power Incentive Schemes in Australia : How to install solar panels on your roof : Solar Trackers

James Martin II

James holds a master's degree in environmental management from UNSW. He has been working as analyst and online development manager for Solar Choice since 2011.

{ 35 comments }

J September 21, 2011 at 12:05 pm

I remember when reading about solar panel technology that the efficiency of mono- and poly-crystalline panels drops off with temperature increase. Is this
also a consideration when making the east vs west decision? I mean, usually the
ambient temperature will be lower in the morning and higher in the
afternoon, so the panels would be operating most efficiently in the
morning while they are cooler. Is this an argument for putting them on
the East side rather than the West (assuming all other considerations
are equal – eg, that mornings aren’t more cloudy than afternoons)?

admin September 21, 2011 at 12:06 pm

Hi Jeremy,

You’re right that temperature is an important consideration when deciding whether to place your panels on either your east- or west-facing roof. However, for the most part, it’s a bit of a coin toss in terms of efficiency loss due to overheating and the possibility of morning clouds. As a general rule, neither side will definitively have greater losses than the other.

The real deciding factor is the fact that home energy use tends to be higher in the afternoon, and therefore you’re likely to get the most out of your panels if they are west-facing–whether you’re getting paid to feed solar power into the grid, or your household is consuming it directly. This is especially so if you are on a time-of-use (TOU) billing plan with peak, shoulder, and off-peak rates. Ensuring that customers’ solar systems output optimally might be the reason that Solar Switch only installs on roofs with northerly or westerly aspects.

Hope you find this helpful!

Steve December 28, 2011 at 5:55 pm

For those of you in the tropics (Brisbane included) keep in mind that its not uncommon to have an afternoon thunderstorm (summer) on a regular basis. If not a thunderstorm then certainly a build up of clouds. Therfore, a North East facing system is always better.
I speak from experience in my own system, plus the observation of many others on pvoutput.org.

Hope this is useful.

Chris March 4, 2012 at 12:28 am

Dear Sir/Madam,

We live in Townsville North Queensland and our house sits South North on the block, best roof position will be East or West both 25 degrees, we are looking at a 4Kw system no shading or trees at all so which side would be best. (East West is 90 / 270 degrees with a compass)

admin March 19, 2012 at 12:33 pm

Hi Chris,

West is generally the next best option after north. For further advice, please get in touch with one of our brokers directly by calling us on 1300 78 72 73 or by filling out a Solar Quote Comparison request form. Our service is 100% free to our customers.

Chris March 4, 2012 at 12:30 am

Love the amount of unbiased info on your site.

Steve May 20, 2012 at 12:29 pm

Hi,
I live in Melbourne and only have NE or SW orientation that would be suitable for 8 panels,could you tell me what direction would you recommend.

admin May 28, 2012 at 3:02 pm

Hi Steve,

Thanks for the enquiry. NE would definitely be the preferred option over SW. South-facing roofs don’t get much sunlight in Australia. The above article is basically just trying to say that if you don’t have the option to put your panels on a north-facing roof, the next best option between east and west is generally west. South would not be considered a viable option by most installers.

Teresa June 4, 2012 at 3:42 pm

We are looking at upgrading our solar from 1Kw to 5Kw system but would need to split the pannels as we only have enough room for 1.5Kw on our Northern roof next to the solar hot water. Does having Western facing pannels running through the same inverter at the Northern facing pannels decrease the efficiency of the Northern Pannels or does the system work as every pannell for himself to do the best that he can when he can?

admin September 6, 2012 at 3:40 pm

Hi Teresa,

Sorry for the delay in replying. While it is possible to add extra capacity to your existing solar system keep in mind that it may forfeit your eligibility for the states feed-in tariff, you’re best to check with the government website for more information. To our knowledge you will be able to receive the current feed-in tariff in your area for the new sized system.

If you do decide to proceed you will need to purchase an extra inverter for the Western panels as they cannot run off the same inverter.

Barbara Bennett June 27, 2012 at 8:03 pm

I’ve had 2 quotes for my 3KW system, one company suggested N-W side, the other N-E side. I don’t have straight N facing roof space. I live in Perth.

To me N-W seems more sunny even in winter. I do prefer the company suggesting N-E, should I ask them to redesign to N-W? :)

admin June 29, 2012 at 5:35 pm

Hi Barbara,

You live in an area with no government-sponsored Solar Feed-in Tariff, so the important thing for you is to ensure that you are using all the power that your solar system produces while it is being produced. It is worth more to you if you do this than if you allow it to be fed into the grid.

So the main question is whether you are at home and using more power in the mornings or the afternoon. If you plan on using lots of electricity during the mornings, having an east-facing system will help you offset your bill. If you plan on being home in the afternoons, a west-facing array would be better. A west-facing array would also be good because it would enable you to avoid paying peak electricity rates, which are higher than off-peak morning rates.

Hope this has been helpful.

Barbara Bennett July 7, 2012 at 12:52 am

Thank you very much. All things considered, it wil be NW :)
Regards

tim June 28, 2012 at 4:54 pm

G’day & great feedback on your website. I am getting a 5.5kw system with 30 panels installed on my house. i am getting 18 on the west facing roof and 12 on the east side. The west side has 5 degrees of north. Is this the best configuration or should I put all the panels on the west side? (yes I am getting an inverter with dual input). 2e are in maryborough qld.

admin June 29, 2012 at 5:16 pm

Hi Tim.

Thanks for the comment. As long as your inverter is dual MPPT-capable (which it should be for a system of that size), it’s perfectly fine to split the array as you have indicated, but depending on what time of day you expect to use power most (and if there is a Solar Feed-in Tariff available where your house is located) it would probably be best to install more panels on the west side of the roof. There are 2 reasons for this: It does have a slightly more favourable aspect (slightly northwest if I understand you correctly), plus the above-mentioned advantage of more power production during peak times.

Hope this has cleared things up for you a bit. Feel free to comment again if you have more questions.

David June 29, 2012 at 8:24 pm

Hi recently moved 6 x180w panels from west to due north and left 6x180w panels on the west side to try and maximise production.
I have a 2kw orion system have i down the right thing?
Thanks
David

admin July 4, 2012 at 4:34 pm

Hi David,

Generally speaking it makes more sense to keep all panels facing due north, as doing so results in greater overal solar power yield throughout the day. The only reasons you might put the panels on the west are 1) if you had no option to install on a north-facing roof, 2) if you had shading on your north-facing roof, or 3) if you were really keen on taking advantage of the sun as it goes down (some people might do this to insulate themselves against paying peak rates for electricity, but for the most part the efficiency losses mean that it’s not worthwhile). Do any of these options describe your motivations for the change?

Whether you did the right thing also depends on whether your inverter has dual inputs for separate strings. I’ve conducted a quick search but have been unable to confirm this. If you have only one input, your system will suffer significant output losses through the day due to the fact that panels will not receiving an equivalent amount of solar irradiation–the output of the entire array is limited by the ‘weakest link’.

Shane July 1, 2012 at 9:48 pm

I have an existing 3kw system,installed 14months ago. If I want to install a new 2kw system to reach the maximum 5kw will i need to register again before July 9 to receive the 44c or am I covered by the existing contract. (Brisbane)

admin July 4, 2012 at 2:42 pm

Hi Shane,

Thanks for the comment. Applications for the 44c/kWh Queensland Solar Bonus Feed-in Tariff are on per premise–a second system will not be eligible for the 44c rate if it is on the same property as the first system. Hope this helps.

Paul August 12, 2012 at 1:04 pm

Hi, we live in Brisbane and we are looking at getting a 5kw system with 27 panels (price $11500) on a due WEST facing roof. At this time of year, the roof starts to get sun at around 9.30 (on an acute angle of course) and the roof is in shade by about 4.20pm (we live on the eastern side of a hill). We did qualify for the 44c tariff and I am wondering, considering the info above, if you think it is a worthwhile investment and what do you think the return would be per quarter, just having trouble deciding if it is the right way to go or not. Cheers for your help, Paul

admin August 13, 2012 at 5:12 pm

Hi Paul,

What capacity are the panels when totalled up? I presume they’re around 5kW?

Also, do the times you’ve mentioned apply to both summer and winter?

Give us a ring on 1300 78 72 73 if you’d like to speak with us further

Paul August 14, 2012 at 5:50 am

I think total capacity would be around 4.1kw because the “salesman” said you could add another 6 panels to the system later.

The times I mentioned just apply to August, in Summer we would benefit from longer days.

admin September 6, 2012 at 2:59 pm

Hi Paul,

You might want to consider looking into another installer. I don’t know what quality components they’re offering, but you can easily find a decent quality system for around that price–with panel capacity that roughly matches inverter capacity! We generally don’t recommend going with an ‘upgradable’ system (i.e. inverter bigger than panel array capacity), as they’re sometimes called, because when you eventually add on the extra panels you need to make sure you use the same exact products to make sure you’re getting the best out of the whole array. Additionally, it’s not good to mix older and newer panels–panels degrade slowly with time (perfectly normal) but you won’t get the best out of the new ones because their output will be ‘dragged down’ by the older ones.

You can get a free comparison of quotes from installers in your area by filling out our Quote Comparison Request form and checking your inbox. We also provide advice if you get in touch with us (1300 78 72 73), and our services are 100% free to our customers.

Mathew August 22, 2012 at 12:01 pm

I am at Mango Hill-north of Brisbane. I ordered Origin 4.7Kw system. When they came to install, without a site inspection, 22 Sharp 215W Panels with Clenrgy SP50 Inverter, only 18 would fit on my Northside & I did not know that the panels could not be split between North & West without a Dual Tracking Inverter. When I called Origin, they said they do not install a Dual feed Inverter. So I was left to make a decision on the spot – “Should I put only 18 Panels on the Northside or put all 22 Panels on the West side?” I decided on all 22 on Westside. Did I make the right decision? What is the loss calculation between the 2 choices?
Also I am not happy with the Clenergy Inverter display – it does not have a date entry & doesnot re-set daily to show peak Output/day. Is there anyway to improve output info?
After a few years, if I decide to install panels on the Northside, is it possible to have 2 inverters connected to the grid?

admin September 6, 2012 at 3:34 pm

Hi Mathew,

Thanks for the comments.

I think you made the right decision to go with the 22 panels on the west side–generally you only lose up to 20% of the output of the system by going from north to west (depending on the angle of the roof). This is especially so if installing the system means you were able to meet the deadline for the 44c/kWh feed-in tariff, which is now closed to new applicants!

For a rough comparison:

a) Assuming an average 10% output loss due to undersized inverter and fewer panels:

18 panels x 215W x 4 hours sun/day x 90% = 13.9kWh/day

b) Assuming 20% output loss due to west-facing panels, but with the full array of panels:

22 panels x 215W x 4 hours sun/day x 80% = 15kWh/day

So option b) seems to be the better one, especially when you consider that the most expensive electricity rates are charged during late afternoon if you are on a ‘time of use’ electricity metre.

About putting more inverters on the northern aspect of your house: If you’re currently receiving a Feed-in Tariff, adding a second inverter might result in the forfeiture of the eligibility for the FiT on the original system, so consider carefully.

Best of luck with your system!

Peter October 12, 2012 at 1:54 pm

Hi
Live in a duplex on the Gold Coast so we have no choice as the postion of the panels-the roof faces predominately east and just a little south
One company suggested racks to ensure they face north but this not our preferred option ($900 extra)
Will it be okay if they face as is.
Cheers

Solar Choice October 15, 2012 at 10:36 am

Hi Peter,

Without seeing the building I wouldn’t be able to comment, what we normally advise is that panels are faced north for maximum exposure and if that isn’t available on a west facing roof space. You may still get some light and generate some power if you have them installed ‘as is’, but the $900 extra cost for the racks to get them to face north may be worth the extra investment because of the extra energy you’ll generate and, therefore, extra money you’ll save on your energy bills.

It doesn’t look like you went through ourselves in order to get a FREE Solar Quote Comparison. I’d recommend you fill this is in as in addition to getting a quote fr up to 7 installers who operate in your local area, you’ll be allocated your own personal Solar Broker who’ll be able to take you through the quote and help you deal with any issues you have up to, during and after installation. All our installers are Clean Energy Council accredited so you know you’re getting the job done properly. If you’d rather speak to one of our Brokers direct call 1300 78 72 73.

We hope this helps.

Tony Austin October 12, 2012 at 3:06 pm

I live in Cleveland just south of Brisbane. I have had a 4.7kw system installed but haven’t got exactly what I was quoted on. On my house there is no northern roof to install the panels, therefore, the quote was for all 24 panels to go on the western roof which is where all of the companies I got quotes from recommended. During installation, they found that all panels would not fit on the western roof and I would need to put some on the east. I was not very happy but I agreed verbally only to find that they actually installed half of the system on the eastern side. It is a split system so yes, it will work but from my research it won’t be as affective. I wasn’t happy with the whole outcome because at the end of the day, I haven’t received what was quoted on and I asked for a slight discount. The contractor then came up with electrical jargon saying it was actually better that the panels were on the east side. I disagree. What is your opinion? At this stage I haven’t paid the total balance which means I haven’t signed the paperwork which will ensure me the 44c tariff. Please advise.

Solar Choice October 15, 2012 at 11:13 am

Hi Tony,

I had a look on the system and it looks like you didn’t go through ourselves to get your solar quotes. If you did go through ourselves and used one of our installers please let us know and we may be able to speak to the installer on your behalf regarding the situation.

It sounds like you are going to have a few issues, the first is that the 44¢ tariff ended in July, we don’t know of any way that you would be able to receive this if you didn’t submit the paperwork before the closing date. The second issue very much depends on your energy usage, what we recommended to our customers is that they install a system that closely matches their energy needs, as the State solar incentives (or feed-in tariffs) are so low there isn’t much incentive to feed back the grid. When the premium feed-in tariffs were still available, or we could ensure that customers would have the system installed and the paper work completed before the cut-off date, we recommended a larger system that would feed into the grid as the money the system made helped to pay it off much quicker.

In either instance we would look at your roof space and work out what size of system you could accomodate, if the East side of your roof would generate an acceptable volume of energy we would advise installing there, but only if it would be an economically viable option. In the first instance we always look for the north facing roof, or, generally speaking, west in the second. If the East side of your roof faces due East and there is little to no shade it shouldn’t make a huge difference, your installer should have a ‘Performance Guarantee’ which means if your panels are significantly under performing they should come out and move them at no extra cost. It will be part of your contract.

Without knowing what installer you used I can’t confirm, but all of our installers are Clean Energy Council accredited which gives our customers the knowledge that the job is being done to a certain standard. There are guidelines on the Clean Energy Councils website for consumers which may help you further.

We hope you get this sorted out soon and can start enjoying the benefits of solar PV.

Graeme January 16, 2013 at 8:42 pm

Hi, my current usage per day is approx 40kw and I have had 18 x 200w panels installed on the west side of the roof with a 5kw inverter , the installer asked were I wanted the panels , and I said that you are the installers and should tell me, the installer went on the roof and came back and said he could either do the west or east, he suggested the east as there was only 1 % difference between the west and east on his “meter” and said that we would loose that 1 % due to the extra wiring needed to get to the inverter.Can you advise wether this is right. My east roof is 98 degrees east and 296 degrees west on my compass,hope that makes sense and look forward to your reply

Solar Choice January 17, 2013 at 9:38 am

Hi Graeme,

The preference is a north facing roof but there arguments about the benefits of placing panels on a west facing roof. If you’re roof runs directly through the east/west orientation there would be no real difference in the energy generated by the panels and the installer is correct about the energy loss through the additional wiring although it should be minimal.

I am slightly concerned that they asked where you wanted them as opposed to doing the site survey and talking you through the best options, I would monitor the outage of your system and if it’s not performing ask the installer to come back and move the panels. Have a look at your contract, some installers have a clause that means they will move the panels free of charge if they are not producing to the optimum level because of their position.

If you’ve not had the panels installed and want a second opinion you can complete our FREE Solar Quote Comparison, you’ll get quotes from up to 7 installers in your area.

We look forward to hearing from you.

Nicholas January 21, 2013 at 10:32 pm

Hi,
I am in the process of getting Solar Panels installed on my roof. The front of my house faces north. The sales person suggested I install a 2.2kW system with 12 panels . The techs rocked up on my door step and informed me that they will not be able to fit 12 panels on the front roof (lack of roof space) and suggested that I split the panels- 6 facing west and 6 facing east. They have offered me a Dual tracking inverter.
I am now a bit worried about the efficiency and have read on multiple sites that it is ideal to install the panels facing the north. The techs have assured that they done similar setups(east and west panels) for other customers and the result was good.
I have been searching the web for reviews on a similar setup but have not been able to get a decent review
Does anyone have any suggestion?
I have clearly informed the installers that if the setup is not efficient in terms of power generation then I will not make the full payment and that they will need to relocate the panels.
Any suggestions would be highly appreciated.
Thank You

Note: Not sure if I am posting this in the right area.

Solar Choice January 22, 2013 at 9:26 am

Hi Nicholas,

What the installer has proposed sounds like a good solution, what is concerning me is the number of panels they are selling you. If you are getting 2.2kW from 12 panels the panels would be around 180-190 watts each, which will cost you less but isn’t as efficient as some of the newer panels on the market which are between 220-250 watts.

Some installers do have a clause within their contract that states they will relocate panels for free if they are not operating to their optimum capacity. If you would like a second opinion and a review of the market you can complete our FREE Solar Quote Comparison located to the right of the page. That way you’ll be able to ensure you got a good deal, have been advised correctly about the size of system best suited to your needs and, if not, have a selection of locally operating installers to choose from.

Hope that helped and we look forward to assisting you in the future.

George Laws February 4, 2013 at 4:40 pm

I live in Cairns and have had solar panels (8 giving 1.5Kw output placed in a 3,3,2 config.) since Feb 2010. My house is E/W facing with no obstructions or overhangs. I had complained many times that my panels seemed to be set too steep. I had them reduced end of last
year by about 50% (guessing) but the output is no different. I produce on an optimum day ( i.e. sun all day) 6 kw hrs total and export an average 2 kw per day.
Our latitude is 17 deg S. Am I getting the right value??
Thanking you, George Laws

Solar Choice February 19, 2013 at 12:44 pm

Hi George,

With regard to the tilt and orientation of your panels, in an ideal world all panels would face due north and be tilted to a degree a little less than the line of latitude. In Cairns the optimum tilt for north facing panels is 16 degrees. If you’re panels are either the East or West facing (or both) you can expect the production to drop to around 85%.

The other reason you’re panels may not be producing what you expect may be a fault with the inverter or an issue with the wiring, the installer should be able to check both of these for you.

Hope this helps

Comments on this entry are closed.

Previous post:

Next post: