Get the best value from your solar power

Electricity bills are set to skyrocket for the 146,000 households that have been part of the NSW Government’s Solar Bonus Scheme (SBS). The generous subsidised tariffs for exporting all of their rooftop solar power into the grid will stop at the end of this year. If you’re one of these customers, or if you’re a solar PV owner anywhere in Australia, we’ve put together some tips to keep your bills to a minimum and make the most of your solar power.

Read Alison Potter’s article.

I’m pleased to see that experts are now agreeing with what I’ve been telling people for many years!


Maybe. If you have the same use pattern as the test data you will get a saving of own use shortfall of about 4 percent in comparison to the standard north outlook for a typical sized array. If you go overboard and make your orientation too far to the east and west you will be worse off not better.

It would take some clever modelling (the method of which is not provided) of your situation, knowing your daily use pattern and the insolation in your area to work out the optimum orientation for your array. Since you would not know your daily use pattern before installation I wonder if this any value at all. You could take a guess and put a few panels on the NE and NW (if your roof allows) but how would you ever know if you guessed right?

If we orient our houses to the sun how many designs have roofs that face NE or NW? There may not have been any houses used to gather the base data that had such orientation, it isn’t stated. This study does not measure the outcome of orienting panels but calculates it under various assumptions and all the houses included are lumped together.

It is unlikely that anybody is going to do the modelling required before installing panels even if they had the base data to do it. Is there a simple rule of thumb that will suffice to give you a hand instead? No.

This system is more in the category of an academic curiosity and will not go far to stabilise the grid nor save large amounts of money as I see it.

It should be part of the expertise and advice a CEC accredited designer brings to a customer as part of each quote.

Our experience was each business providing a quote stated their assumptions re self consumption and usage. The discussion prior illuminated the preference of several to a heavy bias on daytime self consumption. IE bias to a shorter payback period.

We’ve put solar on two properties with very different roof layouts. What else does experience show?

Firstly maximise the size of the system and number of panels. Why? Because the system performance is an average. Averaged output is much lower in winter than summer. By a factor of 2 times typical. And daily output peak days vs cloudy/storm days can vary by a factor of 10 times.

Secondly your roof configuration and shading may limit your options to one or none. Which is why the previous point wins every time. If you do have a surplus of roof options there will be an average solution, one solution slightly better and one slightly worse. With extra PV panels after credits costing $100-150 each max out in panels. If you do know or think you know prioritise to when your peak power use may be. Winter or Summer, morning or afternoon. A suspicion is the answers are different for Cairns vs Hobart, Canberra vs Darwin.

If nothing else the study highlights the need for users to establish their usage patterns in advance of getting solar PV. Firstly to get a more honest appraisal of the payback. Secondly if there is an option in rooftop orientations, to make the more optimal choice, (+/- 10%)?

If there is a rule of thumb. Hot and in the north of Australia, east and west is best. While in the south with clouds about I have my doubts, try north abouts? :wink:

No science has been applied or harmed in the making of these assumptions.


The higher your Southern latitude the more time the sun spends behind north facing panels in summer, so E/NE and W/NW facing is still a good idea IMO.
It does help the grid too, by reducing the duck curve.
If it is heavily overcast much of the time, then facing them near straight up gives the most output.


Every once in a while I receive phone calls from dubious people saying that I have qualified for a government solar rebate or something, and they need to confirm a few details. Noting that it could be a SPAM caller the usual response is “I am not saying” to their questions and soon they get the hint and hangup. Another number to block. If I want to buy solar panels then I will go to a reputable supplier in my local area rather than a fly by night outfit that happens to call me out of the blue.

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Indeed. Reputable installers have subscriptions (?) to systems that know everything there is to usefully know about a potential installation from aspect to azimuth, but seem short on understanding nearby hills or buildings that will shade earlier in the day as well as ‘outlying’ trees.

They make reasonable forecasts through the day, throughout the year, based on climatic information that appears to even include some adjustment for average cloud cover!

My installer provided my usage report from my data, obtained from Ausnet, and explicitly demonstrated when I use most electricity; on awakening (coffee and kettle) and when making dinner (oven). Minor events such as turning on the entertainment systems also show up, as does the routine fridge defrosting cycle.

The system was designed to produce as much electricity as possible when I use it without adding more than minor incremental installation costs, not the most possible over a day, on the longer term there was also the presumption the FiT will approach or even go to zero before the system needs replacing.

That attention to detail was the selling point; I found the installer from solarquotes.



  • There is no algorithm provided.
  • In general there will not be any specific use data to run such an algorithm.
  • Very few houses have NE or NW roof sections so even if you know the theoretical layout you are unlikely to be able to use it unless you install rather expensive additional framing.

The study did not set out to provide a practical system for panel optimisation it did some mathematical modelling that showed under some conditions, that may or may not be met at any given location, a small performance gain could be found. It did not verify this by measurement.

It does not need to. Any reliable and competent solar PV designer has the necessary tools. The value of the study for me has been to demonstrate that where there are options, (existing or new properties) there may be a best choice.

The study does challenge some of the misconceptions that are common. Enough to encourage future purchasers to at least be better informed. As @PhilT has responded,


Did it need to? From first hand experience I can compare two systems with very different roof configurations, and site constraints. Both within the same climate influence hence solar irradiation. I’ll simply suggest what I said previously.


Do you have anything to say about the limitations mentioned in my three dot points? Given that a bad guess about placing panels can make performance worse not better this idea has a long way to go before it would of any practical value in the domestic context. There may be a better choice than due north for any given house but this study doesn’t give a usable procedure for finding out what it is nor assessing if implementing that outcome will be cost effective.

For the examples given it does and describes the methodology. It’s also possible to use tools such as PVWatts to determine the relative difference between systems for different roof configurations. Although a reputable installer’s solar designer will be able to provide comparative assessments, and a recommendation.

Yes, in that I suspect we are not on the same page. I didn’t interpret the core article or referenced report as delivering a universal formula. It does however challenge soundly the north is best paradigm. That is the point I took away. Nothing more or less.

In considering whether the average home owner can use the suggested knowledge. For one of our PV installs we’d agree. There was only one option. The gabled roof faced east and west. For the other the roof had 5 different facets not counting south to work with. The final choice made two years previously reflected without prior knowledge the observations of the report we have been discussing.


I can see why these orientations (we have NW facing panels) have benefits. If a household uses more power (when their consumption peaks) in the morning or afternoon, different orientation makes sense. Morning peaks could be from washing (clothes or dishwasher), showers, hot breakfast etc) and afternoon when getting home for the day, turning on heating/aircon and cooking evening meal).

We are happy with NW in Tasmania as consumption increases substantially from about 10am until about 8.00pm (peak depends on how busy the business is and when we use power domestically…but could be mid to late afternoon). With daylight saving this shifts the production earlier and best matches our anticipated peak use of mid to late afternoon.

North facing panels don’t make sense unless one has peak use in the middle of the day or there is little consumption during the day and FIT is greater than import tariffs.

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Exactly, and it would be a very rare household that has a load profile that matches output from north facing panels.

The increasingly duck-like curve that is the NEM load graph shows that peak loads are 8 - 8:30am and ~6pm


There are those who would content that some of the more efficient arrays actually track the sun and are heavily guarded by ‘Camelus Dromedarius’ …