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 are 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:

 

graph

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.

Capital North Facing West Facing
Adelaide 99% 100%
Brisbane 100% 100%
Canberra 100% 100%
Darwin 100% 100%
Hobart 100% 100%
Melbourne 100% 100%
Perth 100% 100%
Sydney 100% 100%

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

Many years ago now, Ronald Brakels was born in Toowoomba. He first rose to international prominence when his township took up a collection to send him to Japan, which was the furthest they could manage with the money they raised. He became passionately interested in environmental matters upon his return to Australia when the local Mayor met him at the airport and explained it was far too dangerous for him to return to Toowoomba on account of climate change and mutant attack goats. Ronald then moved to a property in the Adelaide Hills where he now lives with his horse, Tonto 23.

Comments

  1. Malmeida says:

    “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.

  2. Malmeida says:

    What SMA says: “FACTORS TO CONSIDER WHEN OVERSIZING

    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

  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,
    Neville.

  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.

    Regards
    Peter

    • 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.

        Kevin

        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.

    Cheers
    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:

          https://www.solarquotes.com.au/blog/solar-panels-on-roofs-facing-different-directions-then-you-need-to-do-this/

          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.

Trackbacks

  1. […] 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. […]

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