Should you point your solar panels North so that you get the maximum power from them?
Not necessarily…let me explain:
And here’s the transcript if you prefer reading:
Hi! I’m Finn Peacock, which direction should your solar panels face? Well, in an ideal world to maximize the power output of your panels, your solar panel direction should be north. But not everyone has a north facing roof or has a north facing roof that’s big enough for a decent sized solar system. So a very common question I get is:
“I’ve only got an east or a west facing roof area, which side should I put my solar panels on?”
Well in terms of power output, in theory, because the sun rises in the east and sets in the west, you should get exactly the same amount of power whether you put them on the east or the west.
But it’s almost always the case that you’re better off put them on the west. Why is that? Because if your panels are on the west, you will generate your solar electricity later in the day.
Now why is that a good thing? Because generally most Australian homes use more electricity in the afternoon, generally there’s more people in the house and you’ll use more electricity later in the day than you’ll use in mid-morning morning. Why is that a good thing?
Well in most parts of Australia, you want to minimize the amount of solar electricity you are exporting. Why? Because generally solar power is worth less if you export it because the feed in tariffs these days are pretty miserly and the other point is, you can’t predict what they’re going to be more than a few years in the future.
But if you use the the solar electricity yourself, you know that you’re offsetting the current electricity tariff which is going up every year and your solar energy is going to be more valuable if you generate it later in the day. Hence, if you’ve got a choice between east and west, your solar panel direction should be west.
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I have an east/west roof facing house on which an installer has decided that the west facing roof would be best suited – with north tilted panels – for a 2.5 kwt array. Your statement above agrees with him However, I am a retired person who does most electrical activity (house cleaning, washing etc.) in the mornings and very little in the afternoons. I also have a reverse cycle air cond which in summer – which in my location is hot – I use most of the day for cooling and in winter from very early until late in the mornings and then late afternoon until late in the evenings for heating. I am therefor wondering if the panels could be as effective if they were divided and placed on either side of the house or would this reduce the intake?.
It would be good to actually measure your usage on a hour-by-hour basis – a good installer knows how to do this.
If your panels are tilted north then it is irrelevant which roof face they are on – as they will be pointing North.
If you only have east/west facing roof areas and you are not using tilt frames then you can put half of the panels East and half West as long as you use an inverter with 2 MPPTs as explained here:
http://www.solarquotes.com.au/blog/solar-panels-on-roofs-facing-different-directions-then-you-need-to-do-this/
That will extend the amount of time you are generating electricity.
Try thinking outside the box ~ both of you.
It’s often ( ALWAYS on a stand-alone system) by far the best idea to run the short-term energy-hungry equipment off a small generator. A few hundred dollars will buy you a hi-tech, quiet-running, pure-sinewave generator that (typically) runs on less that a litre of petrol an hour.
Save your solar panels for the longer-use things:- lights, TV, etc., and adjust your usage to minimise power-use even then.
For example, since I live alone I have the tv going almost all day for noise/company in the background. So I bought a 6″ tv (ebay ~ $54) that runs on 8 watts ac/dc. When I want to watch something in particular I switch on a 25″ set (AWA, also ebay ~ $89) which runs at 60w.
And because my FIT makes it worthwhile I bought a couple of 170w panels compatible with my grid-connect array (ebay, 95c per watt) which runs my computer (and/or sometimes a 260lt chest freezer) all day (most days), while every watt the grid-connect system collects magically turns into money in my wallet.
I also run my large fridge/freezer on a timer:- off all day, and full-on during the off-peak hours.
Works well (except during days-long heatwaves) and earns me some cash-back from Origin.
Me & my neighbor installed an exactly the same 1kw system back in 2009 one on the west facing roof & the other other facing north. For a period of 79 days the two systems generated north facing 297.4kw, the west system 181.2kw. I moved the panels to the garage facing north roof by sharing cost with original system supplier.
Hi Jack,
If you had left them for 1 year, I’ll bet my bottom dollar that you would have only seen a 15% difference.
What pitch/angle was your roof and their roof?
What part of Australia?
And what were the months that you did the comparison?
Let me know and I can let you know exact numbers.
Finn
I’ve been using solar panels since the early ’80s and worked on lots of others’ systems ~ all sorts of set-ups, brands and sizes ~ and would be pleased to take your bottom dollar any time you want to bring it along! Ambient light only goes so far even with the best of panels; I’LL bet my bottom dollar you can even generate some power if you face your panels SOUTH!
But back in the old days solar panels were so expensive it was worthwhile buying or building a ‘tracker’, and the pioneer users went to a lot of trouble to record every watt in their efforts
at efficiency. Though geography, minute-to-minute light fluctuations, temperature, altitude, etc. all make a difference to production there’s NO substitute for direct sunlight.
To suggest otherwise is a nonsense!
….as is the acceptance of “only” a 15% difference in productivity/efficiency, due to the stupidity/carelessness of some rip-off-merchant installer. I’LL bet MY bottom dollar the mongrel wouldn’t have accepted “only” a 15% reduction of the price he was charging.
In any case, I’d challenge your 15% estimate, and point out that no amount of academic qualification (or statistics/averaging) will be more accurate or reliable than long-term hands-on experience.
(That’s why they offer no Uni degrees in chicken-sexing or chain-saw sharpening 😉 )
I’m surprised you’re defending that sort of rort, Finn, instead of directing defrauded customers to the ACCC or a lawyer.
Solar power is worth less if you export its products because the feed in tariffs these days are pretty miserly and you can’t predict what they’re going to be more than a few years in the future.
We have two rooves one facing south-east and one south-west both with approx 30dg pitch. During the winter months in Tasmania the south-east roof gets little if any sun at all. In your opinion would we be wasting our time and money installing a solar panel system.
Hi Tony,
According to my calcs 30 degree pitch SE or SW panels in Tasmania will generate about 60% of the power compared to the same panels on a North Facing roof.
So probably not worth it!
Hope That Helps,
Finn
See my note below.
Build a cheap pergola, garden-shed, carport, whatever and orientate it for the best possible result.
And if you’re prepared to go to that extent, perhaps go a stp further and build it so that the angle of the roof is adjustable.
For example, the posts used for the back (south) wall could be ‘Acrow props’ (hinges bolted/welded on as required.)
Cheers
Dear Finn
We have 12 x 250w panels on a 38 degree pitch, due east facing roof
Even during the season/s when the sun is precisely perpendicular in mid to late morning, the inverter has never shown an input wattage of more than just over 1100w
When asked about this, the supplier stated that as the system was delivering the very conservative minumum daily output that they had contracted to provide (based on guaranteeing an end to power bills and it does that) they weren’t interested in finding out why the panels weren’t delivering anything close to their rated output.
The difference of the sun position/strength of ~1-2 hours earlier than the sun’s peak elevation doesn’t seem to account for a 30% difference in the rated output of the panels and the actual output at the inverter (I assume that readout is pre-inverter)
That ~1100w max output has been constant for the last 6 months that the panels have been on the roof
In fact, during summer the output hit 1100w not long after 9am and stayed at that plateau until very late morning, like it was governed at the inverter… I say that because it never seems to appreciably scale back due to the heat effect
I’s also add that a sunny morning and an afternoon of light cloud cover produces the maximum daily output for an east facing system. An afternoon of blue sky is hard pressed to raise triple figures on the watt meter
FYI, we currently generate 230% of our consumption
I’d be very interested to here your expert opinion
Philip
Oh dear! A brain gremlin substituted 1100w for 2100w in my post above…
If a choice has to be made, preference for East or West pretty much comes down to your own estimate of usage and how much it saves, and your feed-in tariff and how much that is worth. But this is all based on the assumption that we can’t store electricity (at least, not economically). One option not mentioned above is battery-electric cars. I expect that within my lifetime (and the lifetime of my solar panels) I will be plugging my car in to house power for shopping or trips later in the day. Just a thought.
Shouldn’t systems in Canberra or inland areas and anyone with a Gross FIT agreement place their panels where the generation was maximised in the morning. When panels are cooler their efficiency goes up. By late afternoon a combination of higher ambient temps and heat soak would reduce the efficiency. My 2c.
Worth noting that later in the day (when the West facing panels get all the sun) it is usually significantly hotter so the cells will be less efficient.
Half right.
Speaking as someone who put up his first solar-system in 1981 (or before Finn was born?), and has since installed or helped install a few hundred (non-commercial) solar-systems for friends and strangers since: then mostly in rough forested areas ~ including one array we hung 80 foot (25 metres) up a tree because the owner couldn’t afford a bulldozer to clear access to the sun ~ I have few bits of advice.
1….. Forget brand-names: such things ceased to matter 30 years ago. Pay ONLY for ~ and READ carefully the fine-print of! ~ a solid warranty (avoiding such crap as ‘replace solely at out discretion’, etc. ) As far as possible determine that the party liable for warranty matters will still be around to service it in coming years, and make sure that any work/replacement carries a NEW warranty for the same period as did the original ~ NOT a ‘pro-rata’ period.
2…. Keep in mind that any commercial ‘expert view’ has the purpose of selling you something to the expert’s benefit.. That’s not necessarily a bad thing, but the warning-signals shouldn’t be ignored.
I had my grid-connect system installed early in the piece ( due to the FIT of 66cents per KWH), which has long since paid for the system) and, having done my homework, decided upon an Aero-Sharp inverter…at a time when all the ‘experts’ were shitcanning them as being cheap Chinese crap. But they were solid (old-fashioned copper-transformer technology), cheap, and had a 10-year unconditional warranty when most of the others were offering 2 years’ (conditional on all sorts of bullshit) and the most expensive brands were offering 5 years ‘conditional’.
The warranty was backed up by the Chinese government which owned half the factory ~ and had a large import/workshop facility in Melbourne.
Six months in a problem arose (voltage suppressors collapsed). Rang the installer who offered to come up that day to repair or replace (from 2 and a half hours away), but I said I could fit a replacement if he’d arrange for one to be sent up. It arrived early next morning by courier. Right inverter, different fittings. I rang the company, got profuse apologies and the right model delivered the following morning ~ with a brand new 10-year warranty.
No questions asked, no demands for transport-costs or that the other two be sent back first, no ifs, ands or maybes. How much is that worth?
It’s hummed along since at around 97% efficiency. Same story with fairly cheap ‘Perlight’ panels, though they’ve never skipped a beat.
It’s true that ambient heat can make a huge difference: up to about 15% in my system. I’ve also found that all else being equal (brand/technology/etc.) more smaller panels are much more productive ona very hot day than fewer bigger ones, and can only conclude that’s due to less-massive panels shedding heat more readily.
3…. The East/West argument is bullshit! Would you buy a new car and accept square wheels on it?? If your roof REALLY can’t accommodate a northerly orientation get a few pine poles and build a pergola or garden shed to suit. A coupla hundred dollars well-spent, and insist that the installer deduct it from his price ~ and be willing to go elsewhere if he won’t. It’s YOUR money, Ralph!
4….I sized my system to run my whole house (with occasional generator backup) on the incontrovertible basis that government/industry promises are NOT to be relied upon. That’s proven to be the case with subsidies/FITs, etc being dismantled. And athough I have a ‘Premium’ contract until 2024, I’m not counting on it. (but have been clearing a nett profit of $1600 pa.)
The minute they ever send me another bill I’ll disconnect from the grid and convert my 2.5kw system into a stand-alone unit. (I’m already using a battery-bank for assorted reasons).
It’s an easy conversion ~ but y’need to do the arithmetic carefully ~ and an alternative I’d recommend to anyone, given the very cheap prices of components these days.
All the best.
Jason
[email protected]
An old blog but still relevant.
I’m in Brisbane, and I had a not so young 5kW system upgraded last year – new 5kW Huawei inverters (2) and more panels to give ~6.6kW per inverter.
Panels are split 50/50 so both inverters have identical old and new panels across two strings each. (Mostly so I can simply compare if any panels are sus).
My house roof is exactly on a North/South axis so roof faces are East or West at ~20 pitch. I left the old panels facing West (rewired for the 50/50 split to give approx 2.5kW per string), and all the new panels are facing East (approx 4.1kW per string).
East is slightly better from a shading point of view, and I think East will prove to be better overall as cloud tends to form through the day and so afternoons (West facing panels) will suffer some “cloud” loss, but it is one fact that is somewhat hard to measure.
IF batteries ever become cost effective, the space exists to increase the panel numbers to the 10kW per inverter, I understand I can have with a battery system.
Firstly I’m now wondering if the split is approaching what I would get if panels faced North?
Second and following on from the first query – in light of your recent article about “how big”, I am thinking of adding another inverter and 6.6kW of panels, and would like a review of my options.
I could squeeze additional 6.6kW of panels on the East/West house roof faces, or I have an option of the carport roof which is about 23degrees West of North.
The first option may preclude the 10kW upgrade later, unless I replace the original 20 panels. (Of course they may be end of life by the time batteries happen).
The second option on the carport has disadvantages too. First it is only 2 degrees slope to the North/North/West, and probably needs the panels tilted to the ~25 degree angle); second, the 42m2 of roof is a tight squeeze and higher output panels may be required (more expensive I think?). Also no scope for the possible 10kW upgrade later.
Third, maybe allowing for three batteries (bloody expensive at whatever price) and associated panel space is crazy, but my thought here is that VPP will happen and allow a decent payback on the investment. Crystal ball gazing required please – will it take off?
Keep up the great work!!
Roy
Hi Roy
I’ll just mention you can use the PVWatts site:
https://pvwatts.nrel.gov/
To compare the difference in expected output between east (90 degrees) and west (270 degrees) facing panels.
As for VPPs taking off, the type of offers we are seeing from them may improve, but I am pinning my hope on the price of good quality batteries falling at some point and making them a worthwhile investment.
Thanks Ronald, with that great site I can test out all the scenarios!
Regards
Hi,
for the person looking for panel lift system to make the zig-zag E-W system, I found the economical panel lift info that I saw at Energynext:
It is a Clenergy system called PV-ezRACK ComT 2.0. It is engineered for a lift angle (15 deg & other avail) where the lifts attach to a rail with a single connection. Should be economical due to simplicity.
regards, Doug