Why Oversizing Solar Panel Arrays Is A Smart Move

house with lots of solar panels

Did you know you can add panels up to 133% of your inverter capacity? Read on to discover why oversizing solar is a smart move (as long as your roof is big enough – unlike this guy’s).

Installing rooftop solar systems with a total panel capacity greater than the inverter capacity is usually a very good idea.  It will certainly save you money, but it can also help get around the restrictions many Australians face on the size of inverter they can connect to the grid.

If you want to work out the total panel capacity of a rooftop solar system it is very simple.  Just multiply the number of panels by a single panel’s rated capacity in watts.

Finding the total capacity of an inverter is even easier.  It will be written on it somewhere.  On a 4,000 watt inverter you’ll find something along the lines of, “P AC norm 4000W”.  Or you could just look it up online.

It is very common in Australia for the total capacity of solar panels in an array to be the same as the capacity of the inverter.  This has the advantage that energy will never, or almost never, be lost because of the panels producing more power than the inverter can use.  But this is not much of an advantage.

Because panels rarely produce as much power as their rated capacity it is possible to add extra panels with very little power being lost.  And the extra panel capacity can help the inverter to run at a higher average efficiency which can almost entirely make up for what is lost.

When the total capacity of the solar panels is greater than that of the inverter the panels are usually said to be “oversized” or the inverter “overclocked”.  But because I think it makes a lot of sense, I tend to think of it as “right sized”.

Oversizing your solar panels can save you a modest amount of money.  But the real advantage lies in increasing your energy production when your local grid operator limits the inverter size you can install.  For example, in some locations people with single phase power are limited to installing inverters of under 5 kilowatts, many people in rural areas can only install inverters of 5 kilowatts or less unless they pay for export limiting equipment or an export limiting inverter, and in Queensland inverters larger than 3 kilowatts can only be installed if they have reactive power control.

You can ‘overclock’ your inverter by up to 133% and still receive financial assistance in the form of Small-scale Technology Certificates, or STCs, as part of the Solar Rebate. But if you go even 1 Watt over the 133% limit, your application for STCs can be refused.

The solar rebate can cover up to half the cost of your system, so it is vitally important not to go over this limit if you like money.

Your Inverter Determines The Maximum Panel Capacity

The size of the rebate (i.e. the number of STCs) received depends upon the number of solar panels you install, and that is determined by the size of the inverter.  According to section 9.4 of of the Clean Energy Council’s Grid-Connected Solar PV Systems Design Guidelines the total panel capacity cannot exceed the total inverter capacity by more than one-third.  So if you have a 3 kilowatt inverter you cannot have more than 4 kilowatts of solar panels and still receive the rebate/STCs.

This appears to be a cast-iron rule. You may quite reasonably think that if you have a system where the panels exceeded the size of the inverter by more than one-third you could claim STCs for the panels that are below the limit, but this is apparently not the case and will result in you receiving no STCs at all. I don’t know why they felt the need to stop people paying for extra solar panels out of their own pocket, but after I die I’ll be sure to find their particular circle of hell and ask them.

Your Inverter Can Handle The Extra Panel Capacity

Any inverter you can buy in Australia should be able to handle a total panel capacity one-third larger than its own without problem.   Provided the system is properly designed, they have no problems greatly exceeding this limit safely.

What inverter manufacturers care about is that the voltage and current entering the inverter never at any point exceed their specified limits.  Because it is not good when that happens.  But when properly installed an inverter attached to panels with one-third greater capacity will never exceed these limits and so inverter manufacturers are fine with it.

If you want to see what you can get away with you can go to the Sunny Design Site for SMA Inverters, click on “New Project”, and fool around with different panel configurations and inverters and see what it takes before it indicates you have created an overload.

Overclocking your Inverter Can Improve Average Inverter Efficiency

Modern inverters usually operate at a high and fairly constant efficiency level.  However, when solar panels are supplying less than around 25% of an inverter’s capacity their efficiency takes a hit.  This is demonstrated below by the SMA Sunny Boy inverter efficiency curve graph that I stole, I mean, that I am paying homage to, below:

Graph showing how inverter efficiency can fall off when solar panels aren't providing much power.

This graph shows how inverter efficiency can fall when solar panels aren’t providing much power. (Image credit SMA.)

As you can see, when panels are supplying more than 30% of an inverter’s capacity its output is fairly constant.  But when input power falls below this, and especially when it falls below 15%, an inverter’s efficiency declines.  When panels are oversized the inverter will spend less time operating at lower efficiency in weak sunlight and this improved average efficiency helps compensate for electricity lost when the panel array output exceeds the inverter’s capacity.

Warning: A “5000” Inverter May Not Be A 5,000 Watt Inverter

Some inverter manufacturers appear to have real problems counting higher than 4,000.

For example, SMA, despite making what may be the best inverters you can buy, has a real problem.  Their Sunny Boy 3000TL is a 3,000 watt inverter and their Sunny Boy 4000TL is a 4,000 watt inverter, but their Sunny Boy 5000TL is a 4,600 watt inverter. This is really quite a pity because they were doing so well matching the names of their inverters to their capacity up till then.

Growatt also has a similar problem, as the Growatt 5000MTL is also a 4,600 watt inverter. In this case they say it can be a 5,000 watts as an “option”. So I guess it all depends on if the employee who can count that high happens to be working on that particular day.

And also be aware that the “5” in Sungrow’s SG 5KTL-M inverter doesn’t stand for 5 kilowatts.  It’s a 4,600 watt inverter too.

So always be sure to check what the nominal AC output power is on their datasheet.  You can find the datasheet on the internet.  Or if you can’t find it that is the internet’s way of telling you to choose another inverter.

What Determines Total Panel Capacity

The total capacity of your solar panels is their nameplate capacity multiplied by how many of them you have. And when I say nameplate, their capacity in watts is usually in their name. For example, the capacity of the Phono Solar PS260P-20/U panel is 260 watts as that is what the first three digits refer to.

So if you have one dozen PS260P-20/U panels the total solar panel capacity would be 3,120 watts.  This will often be referred to as 3.12 kilowatts.

Panel Size Affects How Much You Can Oversize

You may decide you want to oversize your panels as much as you can and still receive STCs and make their total capacity exactly 133% larger than your inverter.  But in practice this will often be hard to achieve because the capacity of individual solar panels is a fixed number.  For example, if you have a 3 kilowatt inverter and you want to oversize your panels by 133% to 4 kilowatts and you are using 270 watt panels, the closest you will be able to get is 14 panels totaling 3.78 kilowatts.  You can’t get any closer as adding one more panel will take you over the 133% limit.

It is never a good idea to try to fill in a gap by using one small panel or cutting a larger panel in half.

It would be possible to get closer to the limit by using 260 watt panels and installing 15 of them.  Or the same result could be achieved by using 300 watt panels and installing 13 of them.  Or you could hit the target exactly by using 250 watt panels.

In practice you are probably far better off just selecting a high quality panel and not worrying if you can’t quite max out your panel capacity as much as you’d like.

The Pros And Cons Of Oversizing Panel Capacity

Under good conditions when the sky is clear, the sun is shining directly onto the panels, and it is not too hot, oversized solar panel arrays will produce more DC power than their inverter can turn into AC power and this results in the excess power being lost.

When this occurs it is often said the inverter output is “clipped”.  What this can look like is shown by the graphic below which I “acquired” from an SMA inverter brochure.

A graph showing the clipped output of an inverter constrained solar PV system.

The “clipped” output of a solar system with oversized panels.  (Image credit SMA)

As you can see, a 9 kilowatt inverter is unable to supply more than 9 kilowatts of AC power and the excess is “clipped” off, causing the AC output to plateau.  But this is an extreme example as the panels are 166.7% the size of the inverter.  Unless you want to pay through the nose, or possibly some other orifice, you can’t go over 133% and still receive STCs.

While it is unfortunate that some power goes to waste, oversizing the system has a number of advantages.  When conditions aren’t good the system will produce more power than it otherwise would making its output more consistent.  This can help increase self consumption of solar electricity which is an important consideration now that high feed-in tariffs are a thing of the past for most Australians.  As mentioned earlier, it can result in the inverter operating at a higher average efficiency and using a smaller inverter can potentially save money.

Inverter Lifespan

An inverter in a system with oversized panels will on average spend more time operating at its full capacity, which means it will spend more time operating at a high temperature and heat is bad for electronic devices.  On the other hand, its temperature should be more constant which will reduce expansion and contraction from thermal cycling which is also bad for electronics.  Overall I would expect inverters with oversized panels to have their average lifespan slightly reduced.  But I don’t think the loss of life would be very significant and inverter manufacturers don’t seem very worried about it.  For example I’ve never known one to base the cost of their extended warranty on whether or not the inverter is part of a system with oversized panels.

Performance Comparison Using PVwatts

I used the PVwatts site to compare the performance of solar power systems with oversized panels with systems where panel and inverter capacity are equal.  I find PVwatts gives results that are fairly accurate for Australia.  This makes it a useful tool and it is very nice of the United States to let us use it for free.  And that whole stopping Imperial Japan thing is also appreciated.

Earlier I mentioned the existence of 4.6 kilowatt inverters when I described how some inverter manufacturers have trouble counting to high numbers.  If one of these inverters has its panels oversized by 130.44% it will have 6 kilowatts of panels.  And if I assume 250 or 300 watt panels are used it can hit that amount exactly.

Pwatts told me how many kilowatt-hours the following systems would produce in a year when installed on a north facing roof in Sydney:



Overclocking your inverter loses almost no energy production over 1 year

According to PVwatts a 4.6 kilowatt inverter with 6 kilowatts of panels produces 29.9% more electricity than a 4.6 kilowatt inverter with 4.6 kilowatts of panels.  That is very good result given it only has 30.44% more solar panel capacity.

What is very impressive is a 6 kilowatt inverter with 6 kilowatts of panels will only produce around 0.4% more electricity over a year than a 4.6 kilowatt inverter with 6 kilowatts of panels.

For panels that are facing east or west in Sydney PVwatts indicates there is almost no difference in output between a 4.6 kilowatt inverter with 6 kilowatts of panels and a 6 kilowatt inverter with 6 kilowatts of panels.

The table below shows the output of solr power systems in Australian capitals with panels that are oversized by 130.44% as a percentage of the output they would produce if they were not oversized.  The results for both north facing and west facing systems are shown and are rounded to the nearest percentage point.

[wpdtable id=”7023″]

As you can see the output is almost the same in every city.

While I knew oversizing panels made sense, these results are actually better than I expected, so I checked the results with an Australian made program, PVsell, and got almost exactly the same result.

Reducing Your Inverter Size Won’t Save Too Much Money

Because systems with oversized panels perform so well with next to no loss of performance, this means households could save money by using a smaller and less expensive inverter and still produce almost the same amount of electricity.  Unfortunately, with current inverter prices, this isn’t likely to save you much money.

From an installer’s point of view, providing a customer with a 4.6 kilowatt inverter and oversizing it with 6 kilowatts of panels takes exactly as much effort as installing a 6 kilowatt inverter and 6 kilowatts of panels. The only thing they are doing differently is installing a smaller inverter and that doesn’t save them any work at all.  Sure, it might weigh a little less and be easier to lift, but solar installers tend to be mighty so they are not going to consider that worthy of a discount.

Because the effort is the same the only money saved will be on the cost of the inverter and these days that is not likely to be much.  The difference in price between an inverter and one that is around a third larger is usually very small.  For an installer the difference between what they pay for a 3,000 watt inverter and a 4,000 watt one can be as little as $100.  That will reduce the cost of most installations by less than 1.5%.

But Oversizing Panels Does Get Around Restrictions On Inverter Size

In many places in Australia there are restrictions that effectively limit the size of solar inverters that can be installed.  Why there are so many restrictions is hard for me to understand because here in South Australia we can normally install inverters of up to 10 kilowatts without any problem.

Actually, it’s not really true that I don’t understand why there are restrictions.  I think I actually understand very well.  But because I’ve resolved to do less swearing in these articles I won’t go into the reasons why they exist.

To give just some examples, unless they want to pay extra for special inverters or equipment, many people in rural areas are limited to installing a 5 kilowatt inverter.  People with single phase power in the Ausgrid network area, such as in Sydney’s eastern suburbs, can only install inverters that are under 5 kilowatts.  And in Queensland Energex makes it difficult to install inverters that are larger than 3 kilowatts.

But by oversizing solar panels a home with a 3 kilowatt inverter can have 4 kilowatts of panels, a 4.6 kilowatt inverter can have 6.13 kilowatts of panels, and a 5 kilowatt inverter can have 6.66 kilowatts of panels, and still produce practically the same amount of electricity as if the inverter had the same capacity as the solar panels.

While potentially saving a little money on your inverter is nice, getting around restrictions on inverter size is where oversizing solar panels is really useful.


About Ronald Brakels

Joining SolarQuotes in 2015, Ronald has a knack for reading those tediously long documents put out by solar manufacturers and translating their contents into something consumers might find interesting. Master of heavily researched deep-dive blog posts, his relentless consumer advocacy has ruffled more than a few manufacturer's feathers over the years. Read Ronald's full bio.


  1. “What inverter manufacturers care about is that the voltage and current entering the inverter never at any point exceed their specified limits.”

    Am I wrong or the maximum current is not an absolute must? Some inverteres datasheets indicate a nominal input current, not a maximum input current. The current above the nominal is clipped. The voltage maximum, yes, it is a must.

    • I have read this and many comments.

      Isn’t this the real deal?

      This is my setup I am installing:

      Growatt 48v 6kw 50A AC split phase output inverter/controller offgrid.
      18 345W Trina Panels. 3 strings of 6. Each string voltage is 106 and Amps is 10. These tier 1 panels are supposed to supply at least 345W or up to 5% more when new.
      The key is the max volts and amps your charger/controller can handle. In my case, the Growatt handles up to 80A and 60-115V of solar DC input. Which means your total solar array needs to be under 80A. The key factor.
      Most dealers say that you can only add 5000w solar on the 6k Growatt offgrid. But if I only add 15 345w panels in 5 strings, that is 5,175W but only 50 amps. I still have 30 amp leeway. So if I do 6 strings, I get 6,210 solar watts and at 60amps. Which is still 20A under the 80A charge controller max. Originally I was worried about only having 5k watts solar keeping up with 6000w. But I am going with 6 strings of 18 setup and getting 6210 max solar watts. It probably could handle another string of 3.


    There are two important factors which must be considered when designing for and installing oversized PV arrays:

    1. Inverter input conditions

    The most important input characteristic which should NEVER be exceeded for any SMA inverter is the input voltage limit. Inverters and their constituent components are designed and rated for certain input voltage levels. If an input voltage were to exceed this rating, it will almost certainly result in the inverter’s immediate failure. (…)”

  3. I hope this info is correct. Ergon is against it. I was told that i must have the same voltage panels for it to work. Anybody know?

    • Finn Admin says

      Yes – you need to respect the voltage limit of the inverter, but that is very different from oversizing the kW.

  4. Again the assertion is made that distributors refuse to allow systems above a certain size. There’s no evidence for this. The link given to evidence is broken. The applicable information is given in the following PDF. The only restriction for systems above 5 kW is that they be on multiphase supply. https://www.energex.com.au/__data/assets/pdf_file/0016/340603/Connection-Standard-Small-Scale-Parallel-Inverter-STD01143.pdf

    You often have articles like this, I’ve often corrected them. You even complained in one that the distributor refused to give you the answer to the simple question, ‘what’s the maximum system size you allow’ and that you couldn’t find that info on their website.

    Surely at some point you would start to doubt your beliefs?

    • Ronald Brakels says

      Jason, thanks for pointing out that we had a broken link. I have replaced it with one that does work.

      Australians, depending on where they live, do face a number of obstacles when it comes to installing larger inverters and I have slightly altered the text of the article to make it a little clearer what they are.

      You have mentioned an important one which is homes with single phase power can be restricted to inverters of 5 kilowatts. In some places, such as Sydney, under 5 kilowatts. This is a major hurdle to overcome, as it is a big job and quite expensive to convert a house from single phase to 3 phase power. If their goal is simply to install a larger solar system I think many families would be better off economically just oversizing their panels and perhaps taking energy efficiency steps such as improving insulation, installing heat pumps, using a home energy management system, etc..

      People with single phase power could request permission to install a larger inverter, but even if they could be confident of receiving permission, the need to apply and then wait for approval is still an obstacle.

      If you look at page 8 of the PDF you kindly provided a link to, you can see where Energex requires Reactive Power Control for all export inverters of over 3 kilowatts.

      Thanks for the help!

  5. This has worked very well for me. I doubled the number of panels, putting them on the side of the roof to get afternoon sun. Now in Credit from the power company! That’s why Ergon would be against it.

  6. Brian Aylmore says

    Hi I have 14 x 240 q cell north facing in Perth and can only get about 2800wTts per hour max,the inverter is 3kw sunny boy , how many more panels can I attach to bring it up to the 133%
    Cheers Brian

    • Greg McILWAIN says

      Well I have known about extra panels for several years now about strings of panels, total ohms and voltage
      Ergon restricted me to 3.2kw inverter so I’ve picked a company from the Sunshine Coast to install 235W Qcells x11 with a SMC Sunny Boy it come 2.54kw total.
      But that installer Company supposedly Australian wide went Bankrupt even though they contracted a Cairns Electrician to come down to Townsville to install it.
      For 9 mths after Ergon put my new Electronic uboot Metre in I no solar electicity was feed into the Grid, zilch no rebate so I rang Ergon as soon as I received the 3rd bill and complained and tgey sent out a man and he fixed it and said it wasnt even connected, but wouldn’t say whose fault it was.
      So I ended up with 150-200+kw per 90days but only reduce my anual bill by about $1500.00.
      So apart from moving Mt Stuart who hides the morning sun really well I found out after much investigations and an honest Electrician from Cairns whim installed my split systems that I could install another STRING of 16x250kw panels and increase my original 11 Qcells to the same, as long as the ohms of each panel wouldn’t go over the max SMC allowed in their Sunnyboy 3.2kw Inverter which was underrated in specs to what it could in reality handle.
      I think thats the 133% margine you are talking about in oversizing and to make their Inverter safer for idiots that will try to put too much voltage current and ohms in. Though I think that even too much current would only be wasted and given off in heat from the Inverter or simply prevented electronically from entering this over feed into the Grid.
      So we added 5 more a year ago and he just told me he applied to Ergon 1 year ago and got permission to add the other 14 to to SMC string and in his kindness I can pay him when I no longer have NO electricity bill.
      Oh the added 5 panels a year ago lifted production by a small amount but the Qcells decreased through lines of corrosion under the glass too.
      So my electrician is going to make a Warrenty claim and tells me he will use SAPPIRES in the 2nd string which he has been using for years with most excellent back up service and reliability from the Company for many years.
      He experimented with this max number on each string and Ergon alowing it in Cairns now several years ago.
      My turn soon I hope.

      Sorry for rsving on.
      Hope this will help someone,

  7. Brian Aylmore says

    Thanks Ronald,,have got SunnyBoy 3000T Lbut not sure how manyMPPTs are connected,will check,done all the other suggestions,tree in neighbours backyard is shading 1/4 of panels from 2pm onwards in winter months and it’s still growing

  8. Jack Wallace says

    …..er. Please explain.
    Does the information above (source??) make the point that solar panels rated (x) kw can actually produce 100% of (x) in each pf the caitals if (y) ,,,,,, another 30% of panels —— are added????

    Did’ja ever hear the fable about the Stone Soup?? 😉

  9. I am installing 14x 310 watt Risen panels with and ABB Aurora 4.2 Inverter. Could I add an extra 2 panels (or more) down the track if needed and comply?

    • Ronald Brakels says

      Hi Di. With a 4.2 kilowatt inverter you could add up to 4 extra panels for a total of 18. As long as you don’t go over 5.6 kilowatts of panels you should be fine. An exception to this would be if you have single phase power (most people do) and are in the Endeavour network area, which includes western Sydney. They will normally limit both inverter and total panel capacity to under 5 kilowatts.

      But if your system isn’t installed yet, the easiest time to add extra panels will be now. It will almost certainly be a lot cheaper than getting it done later.

  10. What is the maximum size inverter allowed in Melbourne?

  11. Stephen Hull says

    I currently have a 3 kw system. I wish to upgrade my inverter to 5 KW and panels to the max. I live in W.A. and connected to Synergy, will they allow this without me loosing my lousy 7.1350 cents REB. I cannot seem to find anything in print on the SYNERGY web site. I am making preparations for battery power sometime in the future.
    Cheers have a nice day ….

    • Ronald Brakels says

      Hi Stephen. Fortunately your 7.135 feed-in tariff will be retained if you increase the size of your solar system.

  12. Hi all i have a plan to make a battery bank of around 240volts dc and have a change over switch to make the inverter think its still sunny when the sun goes down so i can still run at night…my question is will this damage the inverter? Maximum voltage input is 600volts dc so im safe there..but it says max input current is 20 amps. My battery bank will be capable of delivery hundreds of amps…..will the inverter only draw the current it needs too ?

    • Ronald Brakels says

      Hello Steven.

      Unless you have the proper qualifications to do this work I really don’t recommend it as it may kill you if something goes wrong. And it could potentially kill line workers if the house isn’t properly islanded from the grid.

      Because you are asking this question it makes me think you don’t have the proper background in this area to do this safely.

      If you make a battery bank that can supply 240 volts at hundreds of amps, then you will have created a monster. At 240 volts and 200 amps it will supply 48 kilowatts of power. That’s equal to the power output of about 10 Powerwall 2s and enough to run about 1,000 modern television sets.

      I really suggest scaling back.

  13. Neville Sutherland says

    Hi Ronald,
    It seems that here in SA the ability to overclock inverters is capped at 10kW per phase of power (so for single phase installations, a 10kW array is the maximum allowable size of a PV system). This situation seems ridiculous to me, as a 10kW inverter (or in my case, 2 X 5kW inverters) is also allowed… but because the array size is limited to 10kW, I cannot have my inverters operating as efficiently (nor my solar self-consumption being as efficient) as I would like them to be if they had an extra 1.5kW of PV panels each to feed them at low sunlit times of the day.
    Can you comment on this situation, or provide information that may point me to a way around this situation without having to provide SAPN with a power limiting device if I wish to increase my PV array to more than 10kW?
    Kind regards,

  14. Peter Wilson says

    Hi Ronald.

    I have a system with microinvertors, one per panel. They have also been undersized with respect to the panel size and I am struggling to see how this can be seen as a benefit.

    I have 3 phase power so I’m not limited to 5 kW and could use all of the 7.2kW of panel capacity available from the 25 x 290W panels that I have, but the microinvertors are only 230W each, despite the fact that (unbeknown to me at the time of ordering) there is also a 270W choice available from the same manufacturer. Can you comment please.


    • Ronald Brakels says

      Hi Peter

      There should be no real difference in output between a 290 watt solar panel with a 230 watt microinverter and one with a 270 watt microinverter. This is because panels rarely operate at their full rated output. Heat is a major reason why, but other factors such as dirt also play a role. Because of this very little energy would be lost from having a 230 watt microinverter and it may spend more time at its most efficient point which can make up for energy that is lost. So all else equal their output should be basically the same.

  15. Kevin Kersten says

    working on a 16.9 KW panel set up for victoria BC, calculating with the calculator below, going 1.1 on the inverter gives me best resold,so I wonder where the 130% range comes from.

    I thought I did something wrong so checked the Sidney, Australia location from the article, same 6 KW panels, yet the ratio it gives me to be best is 1.2
    where 1.2 means an inverter of 5KW, am i missing something ?

    I want the right size for my set up, the supplier offers me 1.3, yet seems less efficient then 1.1 this meant I can reduce my panel size from 325W to 285W.
    in other words saving myself 2 KW in panels that are not giving me more.

    i just dont understand the calculations based on http://pvwatts.nrel.gov/pvwatts.php and then advice going almost 130%

    any input

    • Ronald Brakels says

      Hello Kevin

      In Australia having an inverter that is 75% of panel capacity will only result in around 1% less generation than if the inverter capacity was 100% of panel capacity. Since the loss is so small, it make economic sense to go with a smaller inverter that costs less. So you can loose a little bit of generation, but it is possible to save a significant amount of money.

      This is more important in Australia because the subsidy for rooftop solar is based on panel capacity and not inverter capacity — with the limitation that panel capacity can’t be more than one third greater than inverter capacity.

      • Karina Kersten says

        ahh, ok,

        it was just that when I read it all, it talked about 130%, while when I did the test, I could not get to that number, and remain efficient.

        so in my situation, I was offered 325W panels, on AP YC500C inverters

        when going to the PVwat site, and fill our Victoria BC, the actual wattage generated is up at a ratio of 1 to 1.1, yet will go down at 1 to 1.2

        so I wonder if I should not go with 285 W panels (save on the cost per watt on the panel, while at 285W, im still 15% over.

        re-invest the savings in more panels and inverters.

        see, with the 325 panels, I’m 30% over the rating of the inverter, yet the PV watt, site tells me that this is not gaining me any more yield.

        I’m not saying the sales guy douse not know what he is talking about, yet I have a hard time spending a fair mound of $ on something I dont understand,

        asking you for advise, is not influenced by a sale over here.

        looking forward to your input

        I’m bang on south facing, and will be ground mounted on a open field. later on (not now) I want to make my frame to pivot on 1 axle, and then go 30 degree to the east following to the south and then west, yet this is something for later on.


        I’m just trying to figgure out what is right and what is wrong, the dollar is quickly spend, but I want to spend it wisely

        • Ronald Brakels says

          Assuming that microinverter has 500 watts capacity (it is probably a little less than this) and is designed to have two panels attached to it, So with two 285 watt panels per microinverter the panel capacity will be 114% of inverter capacity and with two 325 watt panels it will be 130%. On Australian roofs there would be very little difference in total output per watt of panel capacity between the two. But I strongly suspect loses in Canada will be greater with the 130% system due to lower temperatures and because you can mount them at an optimal angel. So if the 285 watt panels are cheaper per watt — for the entire system including ground mounts, as you will need more of them, then they make sense.

          • Karina Kersten says

            I got pricing based on $ per watt, be it 325 W or 285W, so at $0.75/W the 325 is 243,75 CND and the 285w $213,75

            mounting is not a problem be it 325 or 285

            what it is for me, is, it douse not seem logick to pay $30 more for the 325W units over 285W once, while these added 40 W are not going to yield more once passed the inverter

            unless the PV watt site is off, however at this time it seems the cap of yield is at around 1 to 1.1

          • Ronald Brakels says

            You can use the advanced settings on PVWatts to adjust the inverter ratio. But with solar panel capacity at 133% of inverter capacity less than 1% of electricity generated is typically lost in Australia. This is because solar panels very rarely operate at their full capacity. For example the sun often isn’t directly over the panels, there can be clouds, there can be dirt on panels, and they can get hot which reduces their efficiency.

  16. Peter Wilson says

    Hi Kevin. I have recently had my system installed in Canberra, Australia, and despite the fact that it is our summertime, after one month with a brand new system I am now a convert to the point of view that oversizing the panels is worth it. It does not take much in the way of cloud cover or a bit of haze in the air to knock the panels down in their output. I have 290W panels with 230W invertors and I expected the invertors to be running at full power for most of the time, but they don’t. I’m lucky if they make it for as much as 50% of the day on a clear sunny day. I don’t have any trees or other shading affecting my system.
    If I had increased the invertor power to the next model (270W) to better match the panels I would be getting no more than about 5% in total kWh on a good day for an additional outlay of 10% to 15% in cost.
    My recommendation to you is spend the money on more panels instead.
    Hope this helps
    Regards Peter

    • Kevin Kersten says

      Thanks all,

      so we cut to cord and they broth 56 panels, 325W each, 28 AP YC500A inverts.

      We got 40 cm of snow the last few days, and more to come next week, meaning, I got some time to plan my framing (on ground) and start in early spring.

      I have in mind to track on 1 axis, as we got the space, hoping to harvest up to 24,000 Kwh annually

      will keep you updated

  17. Chris Treadwell says

    Hi Ronald,
    Seems to be a common line here “to get around the input restriction”, which isn’t really the correct way to think about it. To oversize panels simply means you will come closer to the 4600 W export restriction. You can’t “get around it” you can only work within the rules. Not trying to be pedantic. Most people know the reason networks limit this is due to phase in-balance, your local transformer & a host of other excuses that probably don’t mean much but it is the reality that we can’t argue with.
    A lot of 5kW inverters are rated at 4600W refers to their export limit which seems to be mostly limited by the local network authorities in Australia. I also notice that we are probably referring here to Australian versions & international versions can be 5000W export, depends of course on each individual unit? When you view the spec sheets you will see different versions with different outputs.

    The 1.33 rule also only applies to systems without batteries. A system with batteries are allowed to go bigger again on oversizing panels as they can then split the output not only to premises use then export but also to recharging the batteries. My system has 5kW inverter limited to 4600W export with 6.62kW of panels & 13 kWhr of lithium batteries. With a 90% DOD that takes a minimum of 4.7 hours to recharge at 2500W which is the chargers limit as it’s a 50A charger. So as my premises averages 500W + 2500W, I need a minimum of 3000W to charge the battery for around 5 hours & that’s without exporting anything or running any aircons or dishwashers etc. So, to get close to my export limit I’d need 7600W? That of course isn’t going to happen so my next step will be to fit another 5 x 265W panels. This will increase my panels to 7.95kW on 2 strings & still be under the inverter manufacturers max input voltage. However once again this is all in theory & I’m sure I won’t get near the output of 7600W? Probably closer to 6500W. Just as a rule of thumb, I regularly see 5500W generated but only once or twice noticed 4600W being exported. To much other stuff going on. Average of 25 kWhrs generated per day.
    Next step after the 5 extra panels will be another 6.5 kWhr battery if they get down in pricing this year? My battery brand can daisy-chain up to 10 x 6.5 kWhr batteries so I reckon 19.5 kWhr will do us.Sure it will need another 2.4 hours of charging but if it’s not used it won’t need recharging.

    Chris T

  18. Hi Ronald,

    I was proposed a solar system with 3 strings of solar panels, with 2 strings connected in parallels (i.e. 7 panels per string), 1 string facing north, and the other facing east. I understand that when connected in parallel, the current from 2 parallel strings add up. In the evening, when the east string don’t get the sun, will that also affect (i.e. degrade the performance) the north string that is still getting sun?

    Also does the parallel strings have to be equal length?

    Thank you

    • Ronald Brakels says

      Hello Yong

      The north facing panels and the east facing panels would be attached to separate Multiple Power Point Trackers (MPPTs) on the inverter. This will allow the two arrays to operate independently of each other so one won’t interfere with the output of the other. This would be necessary to meet Australian standards where a single inveter is used. It is now pretty much standard for all but the smallest inverter sizes to have two MPPTs.

      Parallel strings should be matched as closely as possible and so have the same number of panels.

      • Hi Ronald,

        Thank for the reply.

        In my case, due to my roof situation, 3 strings are proposed, with 1 east-facing string and 1 north-facing string connected in parallel on 1 MPPT, and another 1-north facing string (on separate roof) on the other MPPT.

        I am not clear when the east-facing string does not get the sun in the afternoon, whether it would hinder the north-facing string (that is connected in parallel) from producing power? Any disadvantage of connecting in parallel with this configuration.

        If the panels are Trinal maxim panel, would it be better (for max power production) to connect all the panels in one strings instead of 2 strings in parallel?

        I could not find any info on this. Thank you.

        • Ronald Brakels says

          While it is possible for inverters to have restrictions on the size and orientation of panels connected to separate MPPTs this is unlikely to be the case. (You would have to check the inverter installation manual to be certain.) Because the east and north facing panels are connected to separate MPPTs when the east facing panels aren’t getting sunshine they won’t interfere with the output of the north facing panels.

          This article gives a good example:


          Exactly how the panels connected to one MPPT are wired up will depend upon what best meets both the inverter manufacturer’s instructions and Australian standards.

          If the panels are all Trina Maxim panels, then they technically could all be connected to one MPPT even if facing in different directions without affecting output, but there is no advantage.

  19. “However, when solar panels are supplying less than around 25% of an inverter’s capacity their efficiency takes a hit.”

    We are getting a 3 kW system with a 5 kW inverter, with plans to add more solar panels in future. I understand it costs us a bit more now for extra inverter capacity that we won’t be using yet, but do expect to use it eventually.

    However, in the meantime, we’ll have a 3 kW system with a 5 kW inverter. When the panels are producing less than 1.25 kW in the mid afternoon (NE facing panels, <25% inverter capacity) does this mean the inverter will be supplying even less power than that to us?

    • Ronald Brakels says

      The 1.25 kilowatts your inverter is producing in the mid afternoon would be its AC output after any inverter losses, so you are getting that much power.

  20. Currently, I have a system installed in April 2016:
    1 x 4.6kW Bosch Inverter Single Phase
    17 x 260W Hanwha Solar Panel (Poly) a total of 4.42kW.

    Can I add more panels to oversize to 133% of Inverter capacity? Is it a good idea? Will it be expensive? Any legal complications?

    • Ronald Brakels says

      Hi Thomas

      You can install extra panels to increase your solar system’s capacity. With a 4.6 kilowatt inverter you can add up to an additional 1.7 kilowatts for a maximum of 6.13 kilowatts.

      It is best to use the exact same type of panels. You can get away with using different panels but they should be the same 260 watts capacity as the current panels. That size is still available at the moment.

      Your inverter will have to meet current standards. If your inverter is a Bosch Power Tec GmbH BPT-S 4.6 I believe that is okay.

      Unfortunately, it is likely to be expensive to expand your system like this. One reason is installers generally don’t like to touch other people’s work and so you may either be stuck with the original installer or have to search around for one who’s willing to do it. But you can start with your original installer, if they’re still around, and see what kind of quote they offer.

      There are a couple of other options you could consider for expanding your solar capacity. If you have 3 phase power you could just add a completely new and separate solar system and leave the old one as it is. If you have single phase power you can still do the same — provided you aren’t in WA — by getting a second solar system and export limiting it so it never sends more than 0.4 kilowatts of power into the grid at any one time. Because solar panels’ output rarely reaches their rating this works better than many people expect. You could also consider a solar hot water system although that may not be as cost effective as a second PV system.

  21. Just for the interested analytical types out there-
    After using PVWatts the other day, I found the reason for Ronald’s observation:
    >What is very impressive is a 6 kilowatt inverter with 6 kilowatts of panels will only produce around 0.4% more electricity over a year than a 4.6 kilowatt inverter with 6 kilowatts of panels. While I knew oversizing panels made sense, these results are actually better than I expected

    Unfortunately the PVWatts program appears to calculate the inverter clipping incorrectly because of the way they use solar insolation data. They appear to calculate the solar panel output (on a given day of the year) as the average of several years of data. Which is fine for calculating average panel output, but gives the wrong value for inverter-clipped output.
    So for example, let’s say the 15 of January 2019 had the following solar panel outputs (based on weather station insolation readings) for the last three years
    15 Jan 2016: 6 kW; 15 Jan 2017: 6 kW; 15 Jan 2018: 3 kW (cloudy day)
    If you have a 5 kW inverter, on each of these days you would have got
    2016: 5 kW; 2016: 5 kW; 2018: 3kW. So your average clipped power loss was (1 + 1 + 0) / 3 = 0.67 kW
    But PVWatts calculates the average power over three years (6 + 6 + 3) / 3 = 5 kW and clips that, i.e. no loss at all.
    So in this case it predicts no power loss due to clipping when actually you are losing 0.67 kW = 10% power.

    I used the data to try and figure out how much is actually being lost, and the number is a few percent – more than 0.4% but still not much. When you calculate the incremental power generated for the incremental cost of the extra panels, the payback is still ridiculously short, mostly because the extra RECs cover most of the panel cost.

    • Laurie Kane says

      Yes, PV Watts is not equiped for this modelling. You need a proper modelling platform like SolarPlus (yes I’m biased) to accurately simulate the effect of clipping. Using typical year solar radiation data that is local (10 km2 grid) and generated to maintain hourly variability it can simulate current and power clipping at both the input and output stage of the inverter.

  22. Hi
    I recently got solar and a battery system installed on my property. 9 kw of panels with 5kw solaredge inverter with a DC coupled LG Resu 10HV Battery was installed. I am unhappy with the setup as the system is getting clipped everyday even in winter. When I was sold the system I was not told about this clipping that would happen. The battery can take 5kw per hour in addition to the inverters 5kw but the battery is usually full by 11.30am each day and then the solar array is getting clipped out at 5kw for the rest of the day. I am currently logging a compliant with the company, I wanted to check is the systems compliant with the CEC Guidelines? Is the dc coupled battery treated as an addition inverter for the system to be compliant with the 133% inverter over sizing for the a STC?

    • Laurie Kane says

      So you lost some free clean energy – what a terrible problem. The extra panels don’t cost much and you get more charge into your battery on cloudy days. Maintaining good battery charge probably mean more savings (esp. if you are on TOU tariff) and helps to maintain a healthy battery for longer life. I would be very surprised if there was no discussion of this setup before you bought it. The 133% rule is pretty dumb over-regulation, I would be happy with clipping and the benefits that come with it.

  23. Guy Harrison says

    I am looking at installing an upgrade to my existing 5kw solar, and adding an additional 18.5kw of solar on a Huawei 17Kw inverter to offset the big drop I will receive in my feed in tariff from 60c down to around 11c.
    With regards to overclocking to maintain inverter efficiency and help maximise my return, and given that i will be running 6 strings in total (on both the East and West sides of the house) how will efficiency be effected if half of the system faces 180 degrees off of another string,
    The 18.5Kw system is already slightly overclocked, but would have capacity to go up to 22.6 (and I think we have enough roof space) should we add further panels, and will the East/West facing arrays diminish the efficiency? (ie does this model assume all panels face the same direction and produce equal power?)

    • Ronald Brakels says

      If you have panels facing east and west then then a panel capacity of 133% of inverter capacity is likely to have an insignificant effect on output. This is because the peak production of east and west panels happens at different times. On a roof with a low 15 degree slope on average they will be around 2 hours apart. The steeper the roof, the longer the time between peak generation.

      The best way to arrange the panels to get the very best efficiency will depend on the inverter characteristics and the panel characteristics. There are companies that make this information available on the internet, but you are unlikely to find it for most brands. Your installer will be able to design the system and maximise efficiency. What cannot be done in normal circumstances is to have panels on the same string facing different directions.

  24. I’ve got 19 Enphase microinverters built up to a 4.6kw system. The max in my area (Latrobe Valley Victoria) was 5kw, or so I was told when I signed up for this one. Is there any latitude to maximize my system? Can I “overclock” my system, considering it has microinverters? Is adding a battery cost effective yet? Do you have suggestions for a type/brand of battery, if it’s a good idea to add one? – do I need to use the Enphase battery? Thanks! And sorry for all the questions ?

    • Ronald Brakels says

      Hi Michael

      If you have Enphase microinverters that are rated as 240 watts of continuous output each then you will have a total of 4.560 kilowatts of inverter capacity at the moment. This means you could add only one more modern panel with a modern microinverter to stay within the 5 kilowatt inverter limit. It’s not going to be worthwhile to pay someone to install a single panel but you do have a couple of options. One thing you could do is keep your current microinverters but replace the panels with larger ones of up to 315 watts. With 19 panels of 315 watts you would have 5.985 kilowatts. Add one more panel and that will come to 6.3 kilowatts. Another option would be to replace your current system with a larger new one that is close to 6.66 kilowatts in panel capacity. Keeping your current system and adding a second new system is an option, but that will involve export limiting which adds some complexity and cost. If export limiting interests you it is possible you could be better off replacing your current system with one large export limited one in the long run.

      While 6.6 kilowatts is considerably larger than 4.6 kilowatts, if your budget is an issue, you’d want to be sure that expanding it will pay for itself in a time frame that’s acceptable to you.

      Batteries are not cost effective yet and if and when you decide to get one it won’t need to be Enphase. A battery system like a Powerwall 2 can be used no matter what type of solar inverter or inverters you have.

  25. Aamir Mushtaq says

    Hi… i am working on a 20kW system that is installed in public building and only resistive load is connected to the system. My question is, during winter season when fans are off, when building requires few kilowatts then we have surplus power and our inverters run on under rated capacity. is this underrated operation of inverters effect their performance or life span…

    • Ronald Brakels says

      Running solar inverters at under their rated capacity should have little or no effect on their overall performance or lifespan. Because their average temperature should be lower the effect is likely to be beneficial.

  26. Hi Fin,

    I really hope you are able to definitively answer my question.

    I have heard from a couple of sources that the ability to get STCs with a design upto 33% max over-sizing of PV arrays to inverter ONLY applies to on-grid connections and that for complete off-grid power systems you are able to over-size your PV array greater than 33% and still be eligable for STCs.

    Unfortunately i am unable to find any information to back this up. I though may-be in your extensive travels of the solar industry you may know or if not know who would know?

    I’m keen to max. my PV array to its warrantied limit of 1.5



    • Ronald Brakels says

      Hi Lain, Ronald here.

      If a solar system is off-grid you can install panel capacity up to the inverter manufacturer’s recommended maximum and receive STCs for them, even if this results in the panel capacity being greater than 133% of the inverter capacity. Unfortunately, off the top of my head, I can’t recall where you’d find that written down.

  27. Hi Ron,

    I am not sure what the price difference between solar panel and inverter in 2016. I am currently looking to install a 6.6kw solar panel on my roof. From your article, i am under impression the following combination should output similar electricity (6.6kw panel + 5kw inverter vs 6kw panel + 6kw inverter).
    I suspect having the panel down from 6.6kw to 6kw and pay for 6kw inverter in place of 5kw inverter will be cheaper than going with 6.6kw panel and 5kw inverter? I think the price difference of 5kw inverter and 6kw inverter is less than the additonal 600watt of panel (say 2 x 300watt panel). Am i correct here?


    • Ronald Brakels says

      Hi Jackson

      A system with 6.6 kilowatts of panels and a 5 kilowatt inverter and a system with 6.6 kilowatts of panels and a 6 kilowatt inverter will have almost the same total output. The difference may be only 1-2% with the exact amount depending on the orientation of the panels. A system with 6.6 kilowatts of panels and a 5 kilowatt inverter will definitely produce more energy than a system with 6 kilowatts of panels and a 6 kilowatt inverter.

      In Australia the subsidy for home solar, often called the “solar rebate”, depends on the how many kilowatts of solar panels you have and not the size of the inverter, so it normally makes sense to get the panel capacity as close as possible to the permitted maximum of one-third larger than the inverter size.

      • Thanks Ron,

        Is there any issue to install 6kw inverter on the 6.6kw panel (being in Sydney)? I understand there will be 5kw capping on export to grid. Is there anything I need to be aware of?


        • Ronald Brakels says

          If you are in the Endeavour Distributed Network Service provider area, you will be limited to a 5 kilowatt cap on solar exports if you have single phase power, which most homes do. (If you are in the Ausgrid area, which covers eastern Sydney, single phase homes can install up to 10 kilowatts of inverter capacity which a cap on solar exports.)

          If you are considering getting a 6 kilowatt inverter and export limiting it to 5 kilowatts, then I would suggest putting up to 8 kilowatts of panels on your roof provided they will fit. While you will lose some output due to being export limited, solar panels very rarely function at their full capacity, so the amount lost will not be great. If there are people at home during the day using electricity the losses will be even less.

  28. Hello!
    Hey, just letting you know that your hyperlink for “Pwatts” in the section “Performance Comparison Using PVwatts” is referencing to a random videoclip.

    • Ronald Brakels says

      That’s my fault. It’s actually a little joke. A very little joke. The correct link to PVWatts is earlier in that section while the second one is a link to the performer P. Watts. It’s not a very funny joke, I admit. But apparently, at the time, I couldn’t resist making it.

  29. Alan Parkes says

    Hi – I do understand the benefits of oversizing. I do just want to confirm that as stated all inverters can easily handle 133% oversizing. How does this relate to an inverter’s technical specs of maximum recommended DC Power input. For example the Solax X1 3.3-T-N specs has AC 3300W and specs say maximum recommended

    • Alan Parkes says

      Oops – sorry somehow managed to cut off end of sentence. The solax 3.3 has max recommended DC inout power of 3500W. So is it still ok to have 4400W of panels (133%). Or even more? I’m in NZ so don’t have the 133% limit for your STC scheme. Thanks

      • Ronald Brakels says

        Hi Alan

        Manufacturer’s guidelines must be followed, so not all inverters will be able to accept a panel capacity that is 133% of inverter capacity. However, the maximum panel capacity isn’t the same as maximum DC input power and a solar designer will be able to determine how much panel capacity an inverter can accept. If you’d like to look at an online tool that let’s you see different array sizes a manufacturer will allow, Fronis has an online configurator for their inverters here:


  30. Hi Solar quotes team.
    I have 6.480kW of panels and a Fronius 5kW Primo inverter. When first installed my peak output would reach over 5.6kW/h during the middle of the day. I was happy with this. As winter progressed (I live in Darwin so call it dry and hot instead of wet and hot) I experienced over voltage issues from the grid. This was fixed by my installer’s engineers. I have since not been able to get more than 5.05kW/h. I notified my installers and they are telling me that the 5.6kW/h I was seeing was caused by the extra power demand of the inverter, to run cooling fans and circuit boards etc. and my 5kW inverter will never exceed 5kW/h exported or consumed. Does this sound right. Even on 43 degree days in October I didn’t exceed 5.05kW/h, yet the fan was cranking. Doesn’t make sense to me. Keen to hear your thoughts.

    • Ronald Brakels says

      Hi Dion

      While a 5 kilowatt inverter should never average more than 5 kilowatts of AC output, it is possible for them to briefly go over this amount. However, a figure of 5.6 kilowatts is definitely unusual. I’m not sure why it would be that high and I’m afraid you can’t expect it to return to that. While Fronius inverters will use more energy to power their fans when it’s hot this won’t increase the inverter’s output, so the explanation doesn’t make sense to me.

  31. Nikhilesh says

    Hi Solar Quotes team,

    I am in powercor area in Victoria, having a single phase and hence limited to 5Kw upload limit.

    I am looking to see if I should go and settle-down with the the standard 6.6kw system or go with 8.2Kw inverter & 10KW panels with feed limited to 5KW.

    Reason I’m looking for a larger system is, my consumption (mostly during night time) is more due to reverse cycle ducted electrical cooling & heating system.
    Hence looking for a better solar solution than the standard suggestions for a single phase , which is 6.6KW system.

    I want to know if there is any value with going for a larger inverter system, yet feed limiting it to 5KW as per powercor mandate.

    • Ronald Brakels says

      Hi Nikhilesh

      The good news is it can definitely make sense to go with a 10 kilowatt system that is export limited to 5 kilowatts. This is because the solar panels will rarely operate at their full rated output, especially in Melbourne, so little solar energy is lost due to export limiting.

      Looking at a worse case scenario where you home uses zero kilowatt-hours during the day the difference in annual production will be:

      10 kilowatts north facing solar with no export limit: 13,700 kilowatt-hours
      10 kilowatts north facing solar with 5 kilowatt export limit: 12,000 kilowatt-hours

      So even in a worse case situation only 12% of solar production will be lost by exporting the system to 5 kilowatts. Because things like refrigeration run through the day it will be better than this and it is also fairly easy to set electric hot water systems and appliances to run during the middle of the day.

  32. Martin Usher says

    I have a 3kW inverter with 2kW of panels. The open circuit voltage of the panels is 450V. The maximum DC input of the inverter is 550V. So how can I even upgrade the system to 3kW without going over the maximum input, let alone go to 133% (4kW) as suggested by the article ‘Why Oversizing Solar Panel Arrays is a smart move”?

    • Ronald Brakels says

      Hi Martin.

      Adding solar panels to an existing solar system is expensive and almost never a good option compared to either installing a second separate system or removing the old system and replacing it with one large new one. The new system can be oversized. Someone in your situation is likely to be better off replacing the old system with one large new one, but it comes down to your individual circumstances and preferences.

      • Martin Usher says

        Thanks for the reply. This situation occurred because the original 2kW inverter died a year or so ago (well out of warranty) and the electrician replaced it with a 3kW. I didn’t get more panels to avoid losing my feed in tarriff. But that still leaves the question of how the new one could ever generate its full capacity when adding more panels would exceed it maximum input voltage.

  33. I need to replace my 2kw system but need the new system to be 2kw no more to keep my 60c feed in tariff which remains till 2028. With a 2kw inverter can I have panels installed that are 30% more than 2kw and still retain my 60c feed in tariff? Thank you

    • Ronald Brakels says

      Hi Frank

      I’m not sure where you are, but I’m guessing South Australia. Generally, to keep your high feed-in tariff, it’s only possible to repair your system and not expand it or replace it with a new one. Because your system is only 2 kilowatts there’s a good chance you’ll be better off replacing it with a large new system and losing the old high feed-in tariff, but what’s best will depend on your individual situation and preferences.

  34. We have a Fronius Primo 5.0 kw connected 6.6 kw panels via two strings, when first installed (Jun. 2021) both strings were restricted when then inverter reached max. Recently only one string is being restricted and the other running to capacity, the net overall result is still order ie. below 5.0 kw.
    Should both strings be restricted when generation reaches max. or is it in order to restrict just one string?

  35. Hi, I’m installing two (2) systems using 2 x Primo Fronius 5kW. There’s two (2) spec sheets that I can find, one being a 5kW and the other (Aus) being a 5kVA (nominal 4.6kW). Ergon’s limit is 10kVA however I’m paying for ‘overclocking’ based on 4/3rds of 10 (13.3kW panels).
    Q: Have you got any write-ups on STC issues relating to the kVA rating being used for ‘overclocking’? Or do the STC rules assume a PF of 1 for this purpose?
    The quote uses 2 x 5kW Fronius and 184 STCs.
    Regards, Terry.

    • Ronald Brakels says

      Hi Terry

      Your STCs will be based on the total solar panel capacity installed and this is not allowed to be more than one-third larger than the inverter capacity. So if you install 13.3 kilowatts of panels with 10 kilowatts of inverter capacity your STCs will be based on the full 13.3 kilowatt panel capacity.

      If you have 13.32 kilowatts of panels then 184 STCs is the correct number.

  36. Thanks for the prompt reply Ronald but the query was about the inverter being rated in kVA rather than kW. The Fronius Aus spec sheet for a Fronius 5.0 says 5kVA. I’m using 2 of these to stay in Ergon’s 10kVA limit and was trying to get an understanding of how the one third rule applies to a kVA rating.

    • Ronald Brakels says

      Sorry about that. Technically speaking, 5kVA is the same as 5 kilowatts. So if there is a 10kVA export limit then up to 10 kilowatts of solar power can be exported to the grid. But it can get confusing because the capacity of an inverter is its “AC nominal output” which is given in watts or kilowatts but its “Maximum output power” — which is different — can be given in kVA and can be higher. So a 4.6 kilowatt inverter with a 5kVA maximum output power is a 4.6 kilowatt inverter and two of them will add up to 9.2 kilowatts. If you want to install 13.3 kilowatts of panels you will need a total of 10 kilowatts of AC nominal output. This could be one 10 kilowatt inverter or, as you are planning, two 5 kilowatt ones.

  37. Hi, my agreement with Energex limits me to a generation capacity of 3.6 kilowatts. Does that wording “generation capacity” refer to the inverter or the panels? I’m hoping it means my inverter can’t be more than 3.6 kilowatts but I could have a third more panel capacity attached i.e. 4.8 kilowatts of panels on a 3.6 kilowatt inverter.

    • Ronald Brakels says

      Hi Steve

      You’ll have to give me the exact wording for me to be certain, but it sounds like is your home will be export limited to 3.6 kilowatts. This means you can install a 5 kilowatt solar inverter with up to 6.66 kilowatts of solar panels, but your inverter will be export limited so it can’t send more than 3.6 kilowatts of solar power into the grid at any time. This is not a major problem because most of the time your solar system will produce under 3.6 kilowatts and because your home will normally consume some of the power first. So if your solar inverter was producing 5 kilowatts of power in the middle of a sunny day, provided your home was consuming 1.4 kilowatts of power or more, no solar energy would go to waste. If there is normally no one at home during the day you can do things such as put an electric hot water system and/or other devices on a timer so it switches on in the middle of the day. While it would be better not to be export limited at all, with a 3.6 kilowatt export limit there will be little difference to how much your electricity bills are reduced.

      • Hi Ronald, thanks very much for your reply. The wording in my agreement is:
        “Maximum allowed generation capacity: 3.6 kilowatts”

        I already have 2 kilowatts of panels and I’m looking at adding more panels and replacing the inverter with a new one (to qualify for STCs on the new panels) to take the system up to the allowed maximum to get the most I can out of the QLD Gov Solar Bonus Scheme FIT between now and 2028 when it expires.

  38. Hi Ronald,
    We currently have a 10.7kw Canadian panel system (29 panels) with a 8.25kw Solaredge inverter, 10kw Solaredge battery and now a new Solaredge ev home charging station.
    I’ve heard we can expand on the 10.7kw panel system since we have a battery and ev charging station but how much can we expand?
    We live in the eastern suburbs of Sydney.

    • Ronald Brakels says

      The bad news is you can’t really add panels to your existing solar inverter because if it’s a SolarEdge 8.25kW inverter then it’s likely to be only able to accept a maximum of 11.135kW of panels. But what you can do is add a second, separate solar system. If you are in the Ausgrid and you have three phase power – which is very likely given your current inverter – then you can install up to 40kW of solar panels. As that’s far more than what will fit on any normal roof, you can fill your roof with solar panels if you wish. Filling your roof can mean facing panels south, but this is not a real problem. While they’ll produce less energy than north facing panels, they can definitely still be worthwhile.

  39. Francesco Pagliarella says

    Hello Ron. I have 15kW of panels feeding into a 10kW 3 phase inverter plus 15kW of battery storage capacity. Most days, the oversizing means the batteries are full at 9.30am, at which point power clipping (at the 10kW inverter limit) occurs each day, between 9.30am to 3.30pm. If the panel efficiency is 85%, the panels are generating 12.75kW – which means 2.75Kw is foregone power. I’m thinking of tapping-off this power at the inverter input, and feeding it into a 2.4kW element of an electric storage HWS service. Is this feasible? And if so, do you know how best to achieve this? I’d appreciate your comments. Francesco.


  1. August 12, 2016: Sustainable House Day 2016 | The Greeny Flat Experience says:

    […] This article from Solar Quotes about why it can be a good idea to oversize the number of solar panels relative to the size of your inverter. Basically it’s can be a clever way to get around restrictions on the size of inverters that can be connected to the grid. […]

Speak Your Mind

Please keep the SolarQuotes blog constructive and useful with these 5 rules:

1. Real names are preferred - you should be happy to put your name to your comments.
2. Put down your weapons.
3. Assume positive intention.
4. If you are in the solar industry - try to get to the truth, not the sale.
5. Please stay on topic.

Please solve: 14 + 9 

Get The SolarQuotes Weekly Newsletter