6.6 kW Solar System: How Many Solar Panels?

Solar panels - 6.66kW system

6.66 kW is the largest solar system most people are allowed (without resorting to export limiters). How many panels do you need to reach the magic number?

If someone casually asks me how much solar they should install, I may simply tell them they should fill their roof with as much capacity as they reasonably can.  But after learning the details, I often recommend installing as close to 6.66 kilowatts as possible.

The reason why is fairly straightforward.  Most homes have single phase power and their Distributed Network Service Provider (DNSP) normally only allows these homes to install a maximum inverter capacity of 5 kilowatts.  Because solar panel capacity can be up to one-third larger than the inverter capacity1 the maximum solar power system size that can be installed is 6.66 kilowatts2.

Going Over 6.66 Kilowatts

There are ways around the 6.66 kilowatt limit for homes with single phase power, but they are not always permitted or practical:

  • Some DNSPs allow more inverter capacity or you can apply for special permission for a larger system.
  • Inverters can be export limited so they won’t send more than 5 kilowatts of power into the grid.  Not all DNSPs will allow this, but if export limiting is an option I suggest looking into it if you have enough roof space for a large solar system.
  • Install a solar power system that doesn’t export to the grid.  As it doesn’t send power into the grid you don’t need your DNSP’s permission to install it.  The drawback is you won’t receive a feed-in tariff for any surplus energy produced
  • Have your home upgraded to 3 phrase power.  This may only cost around $2,000 but often costs more than twice that.

Young Damien is very upset his parents are only allowed to install 6.66 kilowatts of solar. He wanted exactly one hundred times that amount. He feels quite beastly about it.

Close To 6.66 Kilowatts Is Often Practical

Given the number of solar panels that can easily be installed on a typical roof and also taking into account people’s budgets and what they expect from their solar systems, installing close to 6.66 kilowatts of panels is often the most practical option.  But while I have often recommended this, I’ve never clearly explained just how many solar panels will be required and how close to the limit you can get.

To remedy this I’ve created a table that gives:

  • Solar panel capacity in watts.
  • The maximum number of panels of that wattage that can be installed while remaining within the 6.66 kilowatt limit.
  • The total capacity of that system.

Here it is:

solar panel wattage table - maximum system size

Solar Panels From 250 to 400 Watts

The table covers panels from 250 to 400 watts.  You are very unlikely to have a solar system installed these days with 250 watt panels.  The lowest capacity on our solar panel comparison table at the moment is 255 watts.  But 250 watts seems like a good place to start.

The largest panel capacity on the table is 400 watts.  There is only one solar panel I know of larger than this and that’s a big, 72 solar cell, commercial panel from LG Solar.  You’re not likely to install these on your roof, but if you do you can work out the maths yourself.  Or you could get LG Solar to do it.  Ask Marcus from LG Solar to work it out and tell him I told you he had to do it personally.  He’ll love that.

Most panels installed these days are from 260 to 310 watts and I’ve outlined those in a pink box.  Those with higher capacity are often larger 72 cell panels that are rarely used on residential roofs.  But if you are willing to pay for a premium solar panel you can get high capacity 60 cell ones such as SunPower’s X-22, which is 360 watts.

There are bifacial solar panels that have high wattages, but they’re not suitable for normal rooftops as they perform best when they can make use of light that comes from beneath and most roofs don’t glow.  (But they can be useful as roofing for patios, carports, and sun rooms.3)

How To Use The Table

Let’s say your favorite country without kangaroos is Taiwan so you want to install Taiwanese made Winaico solar panels.  You are thinking of using their 285 watt panels and want to get as close to 6.66 kilowatts as possible.  So you check the table and:

  1. Look up 285 watts in the left hand column.
  2. Look to the right to see that the maximum number of solar panels you can install is 23.
  3. Look to the right of that and see the total capacity of the system will be 6.555 kilowatts.

For some reason I had a diabolical urge to buy 665 more of these so I’d have the number of the yeast.

Best Solar Panel Wattage For Maximum System Capacity

Looking at solar panels from 260 to 310 watts, the three best wattages for getting as close to the 6.66 kilowatt maximum are:

  • 265 watts — Maximum capacity 6.625 kilowatts
  • 275 watts — Maximum capacity 6.6 kilowatts
  • 300 watts — Maximum capacity 6.6 kilowatts

The average maximum capacity for solar panels in that range comes to 6.51 kilowatts.  So if you randomly pick from the most common capacity panels you can expect to get a system size of around 6.5 kilowatts.

If you want to be spot-on 6.66 kilowatts you’ll need 370 watt panels, as 18 of them will give you that amount exactly.

Don’t Stress Out Over A Couple Hundred Watts

While it often makes sense to get as close to 6.66 kilowatts as possible, don’t panic if you are a couple hundred watts short.  Paying a few percent more for a system with a few percent more capacity is worthwhile, but your installer may not be able to easily acquire optimal wattage solar panels for you and it doesn’t make much sense to pay a heap more for them.  You may be able to use that money to make greater energy savings elsewhere, such as buying a more energy efficient appliance or buying — and using — a bicycle.4

Footnotes

  1. This is for on-grid solar systems that want to receive the STCs that lower the price of rooftop solar.  In rural areas the limits can be stricter.
  2. If you are wondering why the title of this blog post is missing a decimal point, it’s because Finn made me sacrifice it at the altar of Google – apparently most searches are for 6.6kW, not 6.66kW
  3. Kids these days don’t even know what a sun room is.  It’s a room that catches the sun in winter and so isn’t freezing.  In Toowoomba all the fleas and other insects would congregate there.
  4. You can buy a horse for like $40, but the reason why they can be so cheap is because they’re not exactly money saving devices.
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. We actually need a campaign for 10kW feed-in allowance with grid export limiting allowed across the NEM. At the moment 10kW is the norm not 5kW. Why? Because Ausgrid the biggest grid in the country offers a 10kW export limit as does United Energy and Jemena. This is about to change because the distributors want to kill or at least temper solar. Why do they want to do this? Well it just happens that they also own the nations gas distribution networks and when customers go big solar and I’m talking big ie 10-20- 52kW (on my father’s house) then those customers get rid of their gas connection. This materially harms the same owners of the electricity networks. If you are unlucky enough to have a 5kW limit (formerly Citipower Power and Ausnet but now also Evoenergy (ACTEW AGL) and SA Power Networks) then 10kW of panels with a 5kW export limit only creates a maximum of about 13% export limiting. And most likely you’ll use some of that onsite for your fridge and other appliances. We commonly see export limiting reduced to 5% in the field as not all panels are facing north on these larger systems.

  2. Hi Ronald , The real reason for max PV 6.6KW on single phase is you can’t claim STCs when PV is more than 1.333 x inverter 😉

    • Andy that is incorrect. You can install a Solaredge 10kW inverter and put 13.3kW on it and you will be able to collect STC’s on the 13.3kW. If you have 3 phase in most locations you’d be able to easily goto 40kW of panels with STCs (10kW per phase)

      • Thanks Mathew but I was referring specifically to Ronalds explanation of ” maximum inverter capacity of 5KW ” without export limitation.You are correct when referencing export limitation only.

  3. Tim Lawson says

    370W Longi Mono 72c 6.66kW Yeah!

    But you need an good installer prepared to use them.

  4. Oh well, “ to all of those who jumped on the solar ( save the world, as with it’s called c/change too ) are about to be hit even harder, for doing it NOW ! “
    Being for, all that you try to save money by that ya feed into your local grid supplies….
    Remember 🤔 when they had a offered $0.40 a unit, for all you exported is now not much more than eight (poxy) cents a unit, now….. All the whilst, they are still charging at least $0.26 plus a unit, to me, anyway on my bills ! So, who gets to POCKET the missing or disappearing 18 CENTS A UNIT you all support the power authority with ? Sad, eh….

    Now, in QLD they plan to charging solar panel OWNERS a extra $210 a year, as of soon, to that Equates to your NEEDING to provide about – 2,626 units to try breaking even 😱😱😱 Yep, “ fools and their money are seemingly still so ever easily departed, thinking they are saving the planet ! I wonder, wot will beat this scam, in our modern living lives that are ahead of us all ? “

    https://www.theaustralian.com.au/business/business-spectator/news-story/queenslands-disguised-200-hit-to-solar-owners/96490768424ff5eccb57ea6455fbb67f

  5. Oh, as with my other submitted comment made ;-

    # On needing ( at $0.08 a unit ) needing to export at least 2,626 units of your solar power to break even of these new charges … 😢😢
    # Now, just think of each & everyone who has installed solar panels in QLD will be a SLAVE in handing over 2,626 x at 0.08 is ok, in your own minds 😉 but, now consider, “ What about the OTHER $0.18 PER UNIT they will be abled to a collect from YOU & every other solar panel rooftop plebs out there, doing thy same ? “
    # so we do another bit of maths ‘ere ;-
    2,626 times by 18 cents a unit = $ 472.56 roughly out of your own solar power
    Now, “ if we total up the total amount of owners of ALL OF these solar panels just in QLD alone , is 😱😱😱 is it not ? “

    # Now, without being nasty here 😬 but, we CANNOT 4GET the other part of these units that flow back & forth in/out, over the rest of a year 🤔🤔🤔 your a very helpful kind of people, to fill thy COFFERS of governments & big higher a end of town doing bugger all. But collecting so MUCH OFF YOU ALL ! 🤫 but, i guess, that’s life… and, it ain’t a Sanyo at all… “

  6. That’s what Andy said …. 1.333 x Inverter capacity.

  7. Interesting you say 6.6Kw because most DNSP normally only allows these homes to install a maximum inverter capacity of 5 kilowatts – I have 3 phase and 20KW in roof with 15KW inverter

    Origin gives me 10c feed in and they say that’s because I have over a 15Kw capacity on the roof – their description actually reads “your solar PV system must be net metered and must not be larger than 10kW” yes 10KW – sooooo that just extends the range of mess/muddy waters through which I must trudge (good word) – so I gotta get past a desk jockey that is making up stuff based on unclear Ts&Cs and covering for another desk jockey that 3 months ago lead me a merry dance assuring me of the sun and the moon

    I tire of these normalised rip offs between banks lawyers accountants insurers and utility providers – I found myself starting to argue and stopped – life’s to short – Origin sold me on 18c feed in – 3 mtys after install I now get 10c – true fair or not – who cares
    I managed to dig deep into their site and found a ref only because they said it was there – I would never have found it before install based on phone calls to origin

    Point – where are they measuring you capacity / roof or inverter – only inverter matters (unless you have over rated inverter) but it’s up to “them” and the committee of “they” and they are out to get you 80(

    Drinking helps a lot in this life

    PS hard luck story above – probably best not to read …… Doh! Should have lead with that

    • I wouldn’t trust Origin as far as I could kick them. How else to you think they are going to raise the funds for their proposed Fracking project in the pristine Northern Territory. The Dollar reigns supreme again, at the expense of this beautiful country. Boy are we stupid, with Aussies willing to sell off anything that is really important, for the sake of the dollar.
      The legacy we are leaving future generations is diabolically pathetic.

      • I concur Origin are a dodgee fossil fuel company (Boral gas and oil) that just wants to frack sell gas, export gas, frack for gas. That’s the main game and Solar is actually in the way. The most solar thing about Origin is the marketing department when they’re trying to dress up their offering for retail in Australia everything else is pure fossil fuels and lobbying for fossil fuels against renewable energy. Don’t trust Origin Energy as far as you can throw them!

  8. Looking at this from a slightly different angle and shifting the discussion on Roof size. Your table above lends itself to this question.
    Given roof size is a determining factor. Do the higher rated panels provide more power for the same space.

    So my initial question is:
    Given I can only fit 24 panels on my North facing roof. (I could fit 6 on East Roof aspect too)

    I could either get:
    a. 6.6Kw using 24x 275w panels or
    b. 8.28Kw using 24x 345w panels (3phase)
    Using 290w Micro Inverters, wouldn’t the more efficient panels generate more power, enough to offset the cost difference between the 2 options?

    Is it true that the 345w panel would generate more power either side of the 290w peak limitation from the micro inverter? (side note, are there any related articles)

    • Ronald Brakels says

      Hi GLO

      A 345 watt panel with a 290 watt microinverter will have a panel capacity that is 119% that of the inverter. Its total generation should be 99% or more of what it would be if the panel had a 345 watt microinverter. So I would expect your two example systems to be almost identical in output per kilowatt of panel capacity, with the larger system producing about 25% more in total.

      If you are comparing microinverter output to string inverter output, then on an unshaded roof it might only be a few percent more.

      • Hi Ron,

        Below is a link of my house.
        A couple of installers have provided their panel fit.
        https://drive.google.com/file/d/1rCcRLcgvXz_lVc32lE1CHJGexazaCLKm/view?usp=sharing

        The last image, shows my 1.665Kw Fronius BIPV set up.

        Your comment about the 290w Micro Inverter should give me 99% or more when compared to a 345 Micro Inverter is re-assuring that I am only missing out on the’ideal peak’ unicorns that are like rainbows. Being that they only appear for a brief period.

        From the PDF, you can see that my North facing roof is approx 5degrees off North (Do installers use true North, magnetic North or Google North???)

        Anyhow, its interesting each installer has different tolerances (gaps) to fit panels.

        Naturally the 24 panel north facing array appeals to me. Giving me 9.945Kw across 2x arrays (West 1.665Kw BIPV Fronius and North 8.28Kw Panel)

        I have no North aspect shading issues, but like the appeal of the Enphase IQ7+ micro inverter tied in with Solar Analytics to monitor consumption/usage and solar generation from 2 systems.

        It looks like Micro Inverters may cost an extra $2-2.5K over 24 panels.
        Trying to work out the Peace of Mind by increasing the upfront cost by this difference.

        • Ronald Brakels says

          That will be true north as that’s what’s important when working out where the sunshine is coming from.

  9. Sean Wright says

    Would be great to add a column for panel size, so I could work out how many panels for a given wattage would fit on my roof. I’m fairly space constrained so would want to go for higher wattage panels, as long as they aren’t too big.

  10. Bret Busby says

    “Have your home upgraded to 3 phrase power.”

    Hmm.

    One phrase for the system retailer, one phrase for the authorising institution, and, one phrase for the STC people….

    Sounds like keeping different sets of books for different purposes….

    🙂

  11. Bret Busby says

    What about the Jinko 315W “Mono Perc Black Frame” panels?

    Are they standard or larger size panels?

    Some retailers in Perth are offering 6.6 kW systems with those panels, for around $3000 to $4500, and, that capacity panel has the advantage that only 21 panels are required to get total panels capacity of 6.615kW.

    • Ronald Brakels says

      Jinko has standard sized (165cm x 99cm) 60 cell panels up to 320 watts, so I presume their black frame ones are of that size.

  12. This info is basically out of date. Sunpower Maxeon 400W are the most energy dense panels and it will take 16 of them to cover a roof. They are in residential 1.7sqm format

  13. Bret Busby says

    Matthew Wright – How is the information “basically out of date”, regarding your information?

    At 400W per panel (my roof currently has 20 x 250W panels, on two of its faces, so, 16 panels would not cover those two faces, let alone the other faces of the roof, so, “it will take 16 of them to cover a roof” may cover the roof of a “tiny house”, but, not the roof of a grownup house with more than one or two bedrooms and a laundry and a full size lounge), 16 panels gives total generating capacity of 6.4kW (16×400=6400).

    A problem with 400W panels, in the context of the article above, is that no integer multiple of 400, is closer to the limit of 6.66 kW, specified as the limit of total panels capacity allowed for a 5kW single phase inverter, than lesser capacity panels, such as my previous example of 21x315W=6615W, or, the three examples in the article, for panels 300W and less, that gave total capacity (in multiplying by integers) of 6.6 to 6.625kW.

    So, again, in the context of the theme and content of the article, in terms of how to get the highest total panels generating capacity less than or equal to 6.66kW, how is the article content “basically out of date”, given that it already, in the bottom line of the table, includes 400W capacity panels, to which you referred?

    • Geoff Miell says

      Bret Busby,

      I draw your attention to the published specifications for the Sunpower Maxeon 3 solar-PV panels.
      See: https://www.sunpower.com.au/sites/default/files/max3-400-390-370-au_0.pdf

      I note the “SPR-MAX3-400” has a nominal capacity rating of 400 W, but the power tolerance is +5% / -0%. Thus, 105% of 400 W equals 420 W.

      That means the individual panels (when new) have an actual maximum power output capacity that can range between 400 to 420 W.

      So, that means that 16x Sunpower SPR-MAX3-400 panels (when new), can provide a maximum combined power output ranging between 6,400 to 6,720 W, subject to the variations in manufacture of the individual panels.

      I note Sunpower also provide a 25-year Combined Power and Product Warranty. You get the quality and performance you pay for.

      The Sunpower Maxeon 3 400 W panels are more energy dense, enabling restricted rooftop spaces producing more energy, compared with other lower power capacity panels.

      IMO, rather than looking at the nominal ratings, you should be looking at the tolerance ranges. Unless you are unlucky, it’s likely the 16x Sunpower Maxeon 3 panels would likely be on average producing more than the nominal rated output under optimum conditions.

  14. Bret Busby, my parents have a grown up house at 127 panels 51kW using Sunpower’s new Maxeon 400W. Now that’s covering your roof for the equivalent of a Tesla solar roof but at a cheaper price and much higher efficiency too.

    • Ronald Brakels says

      Now that’s a big residential system.

      • That’s what they said about my 10 panel 1.65kW BP Solar system back in 2000.

        Today it’s a tiny system.

        This system on my father’s house has been return on investment than that BP Solar system and that includes having panels in all directions and verticals.

        Buildings clad in solar material will become the norm. Cheaper commodity panels will soon be 400W (ie 2-3 years time) and in 20 years we’ll be talking 800W multi layer panels so my dad’s house redone would be 100kW

  15. Trisha Drioli says

    Hello, I’m adding to an existing system. I have 3.5 kW and want to add another 6 kW (I have 3 phase power). Is it correct that I won’t get the solar credits for augmenting my existing system?

    • Ronald Brakels says

      Hi Trisha

      You can get the STCs that lower the cost of solar for new capacity. If you are replacing panels in an existing system that have already received STCs then you won’t receive them. Note it will be easier to add a second new 6 kilowatt solar system than increase the size of an existing 3.5 kilowatt system.

  16. ron jones says

    I have a 11kw system with 3 phase connected. I get a 20 cent feed in tarrif from AGL. Could not be happier.

  17. Bret Busby says

    Matthew Wright –

    1. The 127 panels on your parents’ roof, shows that your claim that it only takes 16 panels to cover their roof, is wrong.

    2. The 51kW total panels capacity is far greater than the 6.66 kW total panels capacity allowance for a single phase grid connected system, which is to what the article referred; “6.6 kW Solar System: How Many Solar Panels?”, and so, is irrelevant to discussion of the article. So, Malcolm Turnbull’s palace had about 10kW of panels capacity (even though he did not believe that domestic rooftop photovoltaic systems are of any benefit), but, that is equally irrelevant to the article. It is like the Texan who said that his ranch is so big, that he can start at one side, and drive all day, and not reach the other side, to which, the Australian replies “Yeah, I got a car like that, too.”. Interesting, but, irrelevant to the discussion of the article.

    Read the title of the article.

  18. Bret Busby,

    That’s because of the delay in getting replies up here is stuffing things around.

    Firstly most grid companies offer export limiting.

    10kW inverter limit is more common than 5kW

    So most people off the bat can get 13.3kW of panels on 10kW inverter on a single phase connection. Most of the rest of people can get 6.66kW on 5kW of inverter.

    Most of the people who can get 10kW or 5kW of inverter capacity approved for as an export limit can also install additional inverter on their side of the meter with an export limiting device such as Fronius smart meter of Solaredge Modbus meter.

    So for a single phase system most people ie those living in Sydney, Melbourne United or Jemena, or with export limiting in Citipower, Powercor, Essential, Evo can have 33 400W Sunpower maxeon on their roof. But because the export limiting is unlimitted in many networks much higher which is wortwhile in many instances if you have a battery. 20kW of solar PV with a 10kW export limit only results in about 12.5% of energy max lost to export limiting with that number reduced with onsite consumption.

  19. Bret Busby says

    Matthew Wright –


    Firstly most grid companies offer export limiting.

    10kW inverter limit is more common than 5kW

    So most people off the bat can get 13.3kW of panels on 10kW inverter on a single phase connection. Most of the rest of people can get 6.66kW on 5kW of inverter.

    Most of the people who can get 10kW or 5kW of inverter capacity approved for as an export limit can also install additional inverter on their side of the meter with an export limiting device such as Fronius smart meter of Solaredge Modbus meter.

    So for a single phase system most people ie those living in Sydney, Melbourne United or Jemena, or with export limiting in Citipower, Powercor, Essential, Evo can have 33 400W Sunpower maxeon on their roof. But because the export limiting is unlimitted in many networks much higher which is wortwhile in many instances if you have a battery. 20kW of solar PV with a 10kW export limit only results in about 12.5% of energy max lost to export limiting with that number reduced with onsite consumption.

    Okay – I am in Western Australia; the remote community that is not regarded as part of Australia, by the east coast of Australia.

    In the Perth metropolitan area, which, I believe, is part of the SWIS, export limiting (at least, on single phase grid connections) is not allowed. Maximum inverter output capacity allowed for single phase grid connections, is the 5kW as referenced in the article.

    So, for where I am; in the Perth suburbs, in the remote community of Western Australia (when the wind is blowing the right way, we can get ABC television – about 1-10 days each year, and only SBS and the seven television networks, are relatively stable, here), the 5kW single phase grid connection inverter limit, and, total panels generating capacity, as both referenced in the article, apply – that is, for single phase grid connections.

    Storage batteries, for domestic rooftop photovoltaic systems, here, appear to be a figment of someone’s imagination.

    And, we will probably be getting the 5G cellphone network, here, by about the end of the century, if the camels carrying the towers and equipment, survive the journey from Sydney.

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