Sizing inverters to optimise solar panel system efficiency

The efficiency of the inverter drives the efficiency of a solar panel system because inverters convert Direct Current (DC) (as produced by the solar panels), into Alternating Current (AC) (as used by the electric grid). This leads many to wonder what effect over-sizing or under-sizing an inverter will have on overall system efficiency. This entry sheds some light on this issue, hopefully helping shoppers to make better decisions with regard to their current or future solar photovoltaic installation.

(N.b. This article was originally published in 2011. We have recently revised and updated it to reflect present best practice.)

A solar system’s inverter functions optimally within a predetermined operational ‘window’ (usually laid out in the inverter’s specifications). As the power input from the system’s solar panels goes up and down, the inverter’s ability to efficiently convert it from DC electricity to AC electricity differs. As long as the input from the panels falls with in the range of the window, the inverter can be considered to be operating optimally.

In the graph below, the red line represents an average inverter efficiency and the green arrow represents the power output from your solar panels. The grey box shows the operational window of the inverter based on the input from the solar panels and the predetermined efficiency of the inverter. In this case, an efficiency of less than about 83% would be considered ‘sub-optimal’, and ideally the system should be sized to minimise the amount of time during the day that the inverter operates within this range.

Inverter-Efficiency-Profile

Under-sizing your inverter

Using the graph above as an example, under-sizing your inverter will mean that the maximum power output of your system (in kilowatts – kW) will be dictated by the size of your inverter. Regardless of the output of the solar panels, the power output will be cut-off (‘clipped’) by the inverter so that it does not exceed the inverter’s rated capacity (e.g. 3kW, 5kW etc).

Your installer may suggest an undersized inverter if they determine that the amount of incident solar irradiation (sunlight) on your panels will be lower than expected – because of your location & climate, the orientation of your panels, or other factors.

Inverter under-sizing – sometimes referred to as ‘overclocking’ – has actually become a common and widely accepted practice in Australia – even endorsed by inverter manufacturer SMA, one of the largest and most respected names in the industry. (Read more about overclocking.)

Although the maximium power output of a solar system will be ‘clipped’ back to the inverter’s output through overclocking, there can also be gains in the overall amount of energy (kilowatt-hours – kWh) generated (see: ‘Power, energy or capacity?‘) – and slightly more energy produced in the early morning and late afternoon.

The chart below offers an illustration of how the midday losses (red) associated with an ‘under-sized’ inverter can be offset by morning and afternoon gains (green).

The rule of thumb for inverter overclocking is that solar panel capacity should not be more than roughly 30% greater than inverter capacity – e.g. no greater than 6.5kW worth of solar panels for a 5kW inverter. (Please consult an accredited installer for precise details.)

overclocking image

Over-sizing your inverter

Installing an inverter whose maximum capacity is greater than the nominal capacity of your solar panel array may be an option if you’re looking to expand your solar panel array at some point in the future, but it is not generally recommended, as the overall energy yields from your solar system may be lower than with a perfectly-sized or under-sized inverter – especially if it is significantly oversized. Although inverters are generally designed to handle lower power inputs than their nominal capacity, there are limits to this. It’s therefore important to ask your installer questions about how your system will perform in the even that an over-sized inverter is suggested – e.g. how would your overall energy yields differ over the next 5-10 years with an over-sized inverter vs a ‘right-sized’ or under-sized inverter? Balance this against the cost of the various system configurations before making your final decision.

Conclusion

Solar inverter under-sizing (or solar panel array oversizing) has a become common practice in Australia, and is generally preferential to inverter over-sizing. If an inverter is under-sized, this should happen within certain parameters – which accredited solar installers will be familiar with.

Get a free comparison of solar & battery quotes from installers who operate in your area!

© 2017 Solar Choice Pty Ltd

Comments

  1. Howdy,

    I have a 6.24 kW system with a 5 kW inverter. Does this sound right? From what I have read here it does sound right to me. Looks like from 9:45AM or so to about 1:30PM i’m peaking at 5 kW due to the inverter. So 4 to 5 hours of peak generation is hamstrung by the inverter. Looks to me though it’s just the top of the bell curve.

    Stinks to miss out on generation but if it’s for better overall generation throughout the day makes sense to me.

    What do you all think?

  2. Hi,
    I have just had a system installed that uses 2x3KW SMA Inverters. One inverter has 14 x 265KW Canadian Solar Panels on North facing roof and the other has 7 x 265KW Panels on the east and 7 x 265KW Panels on the West. I was informed that it was a 7.44KW system but having read this page it will never produce anymore than a maximum of 6KW. Can you please advise if the Inverters should have had a larger capacity as the system is hitting the 6KW and I’m assuming is being limited from producing more. I realise this is summer so will be better than the winter months but does seem a little low.
    Thanks

    1. Hi Ian,

      The maximum power output is indeed limited by inverter size – which in this case is 6kW. However, having the extra solar panels can still help to produce more energy over the course of the day (see this article about ‘overclocking’). Read more here about energy vs power in solar & batteries. In fact, oversizing of solar panel arrays relative to inverter capacity is a common and beneficial practice if done properly – and is even recommended by SMA themselves.

  3. I have been quoted on a 3.9 Kw solar system with a 3.5 inverter. Is this the right size inverter or should I get a bigger size?
    Thank you
    regards

    1. Hi Vic,

      Undersizing your inverter (or oversizing the solar panel array, if you want to look at it that way) is sometimes referred to as ‘overclocking’, and it is a common and effective practice if done appropriately. In fact, SMA – the largest inverter manufacturer in the world and the leader in Australia – recommends the practice. You should of course consult with an accredited installer about the details, but there’s nothing wrong with it in principle.

      Hope this helps!

  4. I have 3kw inverter and 3 kw panels all facing north in melb.
    In mid summer the sun sets west/southwest (WSW) so can I instal a second (1.5 KW) group of panels to that same inverter? The panels would be facing that WSW direction to operate while the north facing 3kw panels are functioning at low /very low capacity late in afternoon. Facing that direction I expect the inverter to be not overloaded. Your thoughts please? (Both technically and regulatory).
    Thankyou.
    Graeme.

    1. Hi Graeme,

      The first question you need an answer to is whether your inverter has an input for a second string of panels (and associated Maximum Power Point Tracking – MPPT). If your inverter only has one string input (or the current array uses both inputs), it’s not a good idea to add more panels facing a different direction – you’ll end up losing efficiency. If there is an additional MPPT input sitting unused, however, it might be possible and even worthwhile – consult with an installer about the technical details (although I have doubts that you’d be able to add on another full 1.5kW, as 30% ‘overcapacity’ is the maximum they recommend in the Australian standards for PV installations).

      Another option would be to install a second, separate system facing west with its own dedicated inverter, but adding on to the existing system (as discussed above) would be preferable, finance-wise.

      As for the regulatory aspects, you won’t be eligible for the federal STC ‘discount’ if you add new panels, but it will apply if you add a whole second system (including inverter). Additionally, if you’re currently on a state-sponsored solar feed-in tariff then you migh forfeit it by increasing your existing system size or adding on another system – it depends on the rules in your state.

  5. I intend to put up a hybrid system which shall have dependence on solar as well as grid power. Due to space constraints I may be able to install only 1 KWp solar panels. In this scenario, is it OK if I have 1 KWp solar array but 3 KVA solar inverter (with battery bank). Any deficit in solar energy shall be met from grid.

    1. Hi Hemant,

      Probably not a good idea to undersize your solar array too much – most inverters require a certain power signal from the panels in order to ‘switch on’, so the efficiency losses could be significant. Best to speak with a certified solar installer, but my feeling is that you should opt for a smaller capacity inverter for the PV – and maybe a separate battery inverter for the battery bank.

  6. Dear Sir / Madam

    Why do you need a PV Array with a total voltage output of 600VDC supply a 380VAC; 11kW Inverter? What is the importance of the 600VDC?

    Best regards
    Fanie

    1. Hi Gabriel,

      It would depend on the time of day and where you’re located. If you’ve got a lot of sun and your panels are at peak production (about 2 hours on either side of midday) you should have enough energy to run the iron. Of course you might have problems if the sun passes behind a cloud or on days with inclement weather. Batteries could be a solution for you.

  7. I have 20 panels of 350 w each, which comes to 5000 with. Can I install 2 hybrid inverters of 5 kva each to enhance the output

    1. If your panel array’s peak output is 5kW (5000W), then you should have an inverter that is roughly classed for that figure. It’s not uncommon practice for installers to oversize a solar panel array relative to the capacity of the inverter, but it’s doubtful that many of them would recommend 2x 5kVA (~10kVA) for a 5kW solar array – an example of gross inverter oversizing – unless the plan was to eventually fit the system out with more panel capacity.

  8. Hi…I have a 3kw system with 12x250w panels and a 3.3kw inverter(panels facing north for almost all day sun,dropping off in arvo).
    the most I have ever seen it produce at once is 2.2kw (14-16kw a day)..The inverter is about 15 to 20 metres from panels and have been told this is the reason it only produces that…I am able to add on more panels (another 5 im thinking on afternoon sun only roof)as the other panels drop thes will pick up in arvo, my only worry is this going to damage inverter if it sends too much dc current to it…its only converting 2.2kw now out of 3kw panels..they told me excess would just get dumped ?
    please advise….thankyou

    1. Hi Trevor,

      You’re correct that the distance between panels and inverter and the resultant voltage drop could be the cause of the relative inefficiency of your system. We ordinarily estimate that a solar energy system is about 80% efficient from panel to socket – for a 3kW system, that translates into a peak output of about 2.4kW. The voltage drop could be further dragging it down to the 2.2kW that you’ve been witnessing – a total panel-to-socket efficiency of about 73%, which is not outlandish at all.

      Oversizing the panel array to maximise and ‘flatten’ a system’s output is a fairly common practice. This could be an option for you – especially if your inverter has a second MPPT (maximum power point tracker) input which is currently unused. I would recommend speaking to an installer or post-installation specialist (SolarSafe is one company that we know of that provides post-installation services) about exactly what your options are and what the benefits would be.

      Best of luck!

  9. Have a question, we had a company install a 4KW 16 panel system on our house last year, this is not leased. So far we have seen none of the savings they promised, per the solar company our peak usage has increased which is causing the lack of savings. We have not changed any of our daily or house utilities and we are on a set thermostat and have added, blinds, insulation and anything else. Any ideas or suggestions to debate them? Any additional suggestions are appreciated as we are not paying the same utility bill on top of paying the bill for the system.

    Thank you for you time.

    1. Hi Anthony,

      Sorry to hear about your issues with your system.

      Do you have anything in place to monitor your electricity usage throughout the day? For example, a monitoring system? This would provide you with some data to present to them.

      Could you possibly switch over to a flat-rate retail tariff instead of time-of-use? Generally speaking, that is the best way to get the most out of a standard solar energy system, provided you shift your electricity usage to the sunlight hours.

  10. hello i am designing a solar station of 3kw for the load demand of 5940Kwh/ day with an autonomy of 3 days from 48V, 600Ah battery bank. is there any fault in the design? plz justify

  11. Hi,

    Hope you can spread some light on an issue that I am having. We have just connected my power monitor to our meter box after getting solar installed (approx 6months). My reason for this is we were getting massive bills after the digital meter was installed, I have been using an iPad APP to record the numbers everyday and the numbers are not making any sense. Here are some details of our setup (in basic terms..lol)

    Solar Spec:
    SMA Sunnyboy Inverter (I believe from memory is a 3.5Kw Inverter)
    24 Panels in 2 x arays (NNE and NNW) as the house is not quite N.
    Produce rought 20Kw / day (as of the last 2 weeks)

    Inverter reads: Producing – 2945W
    Monitor reads: Solar – 2867W
    : Household – 2390 (day)
    : Household – 17-23 (night)

    My issue is that with the inverter turned on and producing power our consumption goes up as well. The monitor with the solar turned off we are only using about 14W/h.

    Is this showing correct numbers or do we need to contact the installers and have them out again. Hopefully not as we made a poor choice on installers and they haven’t been the best of businesses to deal with.

    Thanks for you help.
    Merv.

  12. Hello,

    We currently have 3 x 12volt solar panel for our boat (two x 80 watts and one x 60 watts).

    We are planning to expand the solar panel by installing a 190watts solar panel. The question is, what should the size of inverter be for optimum result?

    Thanks very much

    1. Specifying the value of the panels in volts will be a bit confusing. The possibility of maintaining 12V DEPENDS ON THE KIND OF INTERCONNECTION whether series or parallel. Your current 260w panels added to 190w will be optimised if you contact your installation tech and explain to them what your expansion needs are. Thanks Maggie

  13. Hello.

    Energy Australia sold us a 3.9Kw system (15*260W panels) These were fitted with Enphase M215 inverters. I was playing around with API calls to my Envoy unit and the Enphase website, and the system reports it’s size as a 3.225Kw system. (This is exactly 15* 215W). During summer months my generation flatlines at 3.23 Kw per hour, which seems to indicate that the inverters are the limiting factors in my energy production.

    Questions:
    Should this legally be sold as a 3.9Kw system, with it having a 3.2Kw inverter, and effectively being able to only ever produce 3.2Kw?

    The inverters are rated roughly 17.5% lower than the panels. Is this a significantly large enough number to cause overheating and/or other issues with any components?

    Thanks,
    Nico

    1. Hi Nico,

      You’ve probably already read our response to Robert’s comment above – it is acceptable to have the panel array oversized to ‘flatten out’ and ‘fatten’ production, even if this means clipping peak production. The Clean Energy Council’s guidelines recommend that inverters should be rated at no less than 75% of panel capacity, and it sounds like what you have is within this limit.

      The above aside, we can see why you might not like the idea of a system being labelled as 3.9kW in capacity when it never reaches that level of power production. But hopefully the installation company knew what they were doing and sized the system as they did in order to maximise overall power output. What are the daily production numbers for your system in kWh, as opposed to kW?

    2. Hi Nico,

      I just had *installer name removed* install 8 JA Solar panels with 8 x M15 micro inverters and said my system is a 2.15kw when really it is a 1.72kw system as the inverters are rated at 215 watts. Out of curiousity how much did you pay for your system? I paid $4875.

      Cheers,

      Joseph

  14. My installer just installed a 7.6kw inverter. My system I had installed is a 9.6kw. Is this the right inverter for this size system?

    1. Hi Robert,

      We’ve just had a chat with Nigel Morris of Solar Business Services about this and here’s his response:

      Yes oversizing the array is ok in some circumstances.

      Its ok as long as the current limit of the inverter is not exceeded.

      The good part is that is can flatten out the generation curve and thus maximise production, albeit at the expense of clipping some power during the middle of the day.

      So basically, array oversizing is a common practice, but whether it’s being done correctly in your situation would depend on the specifics of your system and components. If you’re concerned, we’d recommend getting a second opinion from another installer.

      You can read more about array oversizing in this informative article from Climate Spectator.

      Best of luck with your system.

  15. I have 14 -CS6X Canadian Solar 300P Modules with a Sunny boy 3800 Inverter. This peaks early in the day and stays their for a a good while, I this to small of an Inverter ?
    Thank you,
    Joseph.

    1. Hi Joseph,

      Thanks for your comment. We’d advise you get in touch with your installer if you think there might be some kind of issue – but yes, there is a possibility that your inverter is limiting the output of your solar array.

  16. we have a 5kw system and my power bill went from $600 to $1200 and know one can tell why

    1. Hi Trevor,

      Can you describe in further detail when your bill went from $600 to $1200? Did this change happen between your last bill without a solar system and your first bill with a solar system? Or are you referring to a sudden drop in solar electricity output (and associated increased power bill) after you had the system was installed and presumably working without problems for a while?

      It’s hard to help you figure out what the problem might be without knowing these things!

  17. HI ,we are currently somewhat confused. We engaged a solar company to install a system with the intent of connecting stand alone battery system in a year or two, because it was indicated to us that the cost of the batteries would come down significantly due to an American company setting up for large scale production. Our average useage on our power bill was 65kwh /day, so a 15Kw system has been installed, with a ZED controller however we were not informed of the issues around export control. We are on 3 phase power and are told that the export has to be restricted to the lowest use phase. System is currently limited it seems to covering about one third of power consumption.
    The installation company has now offered to remove the installed system and install a 5Kw system instead with 5kw Ingeteam inverter and EPC control unit (more efficient they say). We are unsure now as to how to proceed, do you have any comments or advice you can offer in this regard?. Do you have any current knowledge around the quality , availabiltiy, pricing, future pricing of the stand alone/ off grid battery power storage packs?.

    1. Hi Vivette,

      Sounds like a confusing situation indeed.

      First of all – it sounds like the system was inappropriately sized from the outset. We constantly emphaise that a solar system should be sized to meet only the daytime electricity needs of a home – this is because no utility offers a reasonable rate for excess solar power these days (and in fact, utilities in Queensland actually prohibit excess solar power from being exported to the grid).

      Unless you were going to have an energy storage system installed at the same time as the panels, it really wouldn’t be worth your while to wait for batteries to become more affordable – that’s about 2+ years of ‘wasted’ excess solar power. And as of now, it is still a ‘wait and see’ game for energy storage affordability – despite lots of talk about the upcoming viability of energy storage, there aren’t many homes or businesses yet making the decision to have batteries installed.

      If they are offering to do so at no additional cost (and refund you the difference on the price between the two systems), it would probably be best for you to have them install the 5kW system in the place of the current system – unless you find an energy storage option that makes financial sense for you.

      Best of luck!

    1. Hi Mick,

      There certainly shouldn’t be anything that prevents you from having a system of this size – in fact, 4kW solar systems are quite common for domestic applications in Australia.

      Depending on where you live, you may need to install some sort of export control device. This would be if you’re in regional parts of WA or Queensland. But provided you meet the local requirements it shouldn’t be a problem to have a 4kW system installed.

      Are you running into some kind of issue?

  18. I am thinking of buying 5KW inverter for 3 KW SYSTEM, to begin with just so in future if i choose to upgrade, i have an option. My question is, does it affect the performance of panel n inverter if its not used at its full capasity??? In my case 5KW inverter bein used for 3KW system. Let me know please. Thanks.

    1. Hi Dishant,

      We generally advise against getting an oversized inverter for future expansion of your solar panel array. There will be efficiency losses when you do this, and it’s highly unlikely that most people will actually expand their system in the future. On top of this, if you do want to expand the system, you’d have to try to make sure you get exactly the same brand & output of panels–something that might be hard to do further down the line.

      Read more on this topic here.

  19. I did only read about 1/2 the above but now I really have a concern.
    3kw panels with 3kw inverter has been performing great last 3 years with max kw noticed last summer at 3900kw, all well and good, but now this summer I have suddenly noticed over 4kw with full sun on every day, I have watched when clouds have been active and kw down to 1+kw but then up to over 3 and 4 kw and staying there. I know enough about electricity to know what I don’t know and this has me confused and concerned, I don’t understand how, help please

    1. Hi Bill,

      Thanks for reading and for your comment. That does sound pretty unusual – if you only have a 3kW array you shouldn’t be producing more power than that. Your inverter is highly unlikely to be able to handle more than its rated capacity, although it would really depend on the specs of the model that you have. At the risk of sounding slightly silly (please don’t take offense), are you sure you have a 3kW system and not a 4 or 5kW system? Just taking a shot in the dark here, but usually system will not perform above their rated power output, especially for extended periods as yours appears to be doing.

      An alternative explanation might be that you’re somehow reading the DC output of the panels as opposed to the AC output of the inverter? This is also pretty unlikely, however.

      We’d recommend you get back in touch with the company that installed your system or the inverter manufacturer – they should be better equipped to address your concerns.

  20. We have a 5 k system (24 x 210w Sunpower) panels (grid tied) that was installed about 3 years ago. PVP 4800 Inverter (Advanced Energy) South facing roof mounted in San Diego. We noticed a big drop in PV production the last 3 or 4 months. We used to over produce during the winter which allowed us to use the AC during the summer. Getting an average of 2400 to 2600 watts at the inverter on a sunny day now. Electric bill no longer has us overproducing. Could it be the panels or the inverter?
    I really appreciate your website. Too bad I can’t find one in the US.

    1. Hi Don,

      Difficult to say without more information about the system–might be some new shade on your panels or perhaps a fault in one of them? Do you have any trees that could have grown tall enough to begin casting shadows recently? (Read more about partial shading & solar panels) .

      If you don’t think that’s where the problem is, the best course of action would probably be to get back in touch with the company that installed your system. If it’s new there should be some kind of performance guarantee.

  21. We have a quote for a sistem involving 15*260 JA SOlar pannels and a Goodwe GW3600-DS system (inverter has 2MPPT and supports two strings). The idea is touse both strings (7 and 8 panels, respectively) to meet the MPPT input range. The same problem bothers me, though: Can the inverter take all theoretical power of 15*260=3.9KW, although it is rated at 3.6KW (3.8 maximum) ? Should I ask for a bigger-capacity inverter ? Next in line seems to be the GW-4200-DS.

    I appreciate any advice. Thanks.

    1. Hi Andrei,

      You’d be best to ask your installer about that-there may be aspects to the system you’re looking at that we don’t know about. However, by the sound of it, it should work fine. The actual output of your panels will rise and fall like a bell curve during the day, and only at the peak of output will they generate 3.9kW–a point they may never reach when other various derating factors are taken into account (check the specs and play with the PVWatts tool).

  22. We have a 1500w array in Far North Queensland. That we are very happy with. Output varies dramatically because of cloud and rain however on the right day it reaches just below the 1500w inverters 1600w limit. We receive a very generous feed in tariff which would be lost if we upgrade the system. It may sound silly, but if we had more panels we would even out the seasonal variations but we would need something to limit/dump the DC input to the inverter on the good days. We would still only output 1500w. Does such a device exist? Regards Bill.

    1. Hi Bill,

      There are devices that limit export of power to the grid (e.g. here and here), and are essentially required for most solar systems in Queensland these days. It’s not quite the same thing as limiting power from the inverter, though, and if you’re considering expanding your solar array you will almost certainly need a new inverter to make them worth your while–and changing the inverter is pretty clearly a no-no under QLD feed-in tariff rules. Must say to be straight, though, that installing additional panels/capacity to an existing solar array is also a technical no-no under the scheme, so tread lightly.

      Something else you could consider is getting a second system, but be advised that the federal up-front price reduction available through the Renewable Energy Target cannot be accessed more than once by for systems at a single address, so the price would be a bit higher than the market rate for you. Additionally, you’d have no feed-in tariff on it, so you’d have to make sure you use as much of the power it produces as possible.

      Whatever your eventual decision, good luck!

  23. I have a 5000 growatt inverter operating with 20 250 watt panels can I add more panels to overload this setup safely

    Thank you
    Les

    1. Hi Les,

      We generally advise against installing more solar panel capacity than your inverter can handle. You have (20 x 250W =) 5000W (5kW) of solar panel capacity, and the inverter is also 5kW. If you want to add more panels it would be best to get another inverter sized to match the new array.

  24. Regarding Solar Output appearing to be Low.

    The major factor affecting the output of solar cells is the position of the sun in the sky – ie the angle of incidence of the sunlight on the solar cells.
    For maximum output the sunlight needs to hit the solar cell at 90 degrees.
    Unfortunatley, this only happens for a very short time during the day – (around Noon in winter).

    Hence solar system outputs can only reach full power for a short period during the day.

    To simplify this – you will only get the RMS value of the rated output on average throughout the day.

    This is due to the solar angle of incidence on the cells – best output is between 10:00 and 14:00 – where the sunlight enters the cells at around 70 – 90 degrees.

    So – dont be disheartened if your system hardly peaks at its rated output – it is operating normally.

    You need to derate the power output by the RMS value as this is a result of how the sun moves through the sky during the day (appears to move)

    ie – a 5 Kw system will average out to about 3.5kW over the whole day – due to the apparent movement of the sun angle of incidence

    If you have the opportunity – watch your power meter
    write down the output in bright sunshine only – during the day – and guess what – it will average out to be the rms value of the solar panels rated output.

    So realistically, you are starting with an average of 74% output – all other system inefficiencies (inverters etc) will reduce the output further.

    Have fun!

    NB

  25. Hello All,

    We have recently installed a Solar system (1KW panels, 3.5KVA/48V inverter, and 48V/150ah battery) in a petrol station to operate two pumps of 0.75hp each. The panels are connected 4in series (125W each) to match inverter voltage of 48Vwith 2rows. The system worked well by sharing solar, batteries and mains power. The reason to chose 3.5KVA was to meet the initial load of motor.

    However, now only one pump at a time working as the owner rewinded one of the motor and it is consuming high current. The owner has few bucks to spend on the system.

    We planned to increase the inverter size initially, but higher capacity inverters, for example 5KVA is available in 72V only. My question is- Shall i use the 5KVA/72V inverter successfully within the existing 48V (panels and batteries) system?

    Does the inverter V should be matched with panels and batteries?

    Please help me.

    Best,
    Satish

    1. Hi Satish,

      Thanks for the comment. Unfortunately I am not confident giving you too much detailed advice about this situation given its technical nature (and the involvement of batteries). Have you tried contacting the person who installed the system, or did you install it yourselves?

  26. Hi solsar choice,

    I have a 1.6KW system consisting of 9 X 170Watt Dragon Panels and an Eversol 1500TL-AS inverter installed on my house in Perth, the roof faces NW and sits approx. 30 degree angle (tiled). I have had this system installed for almost 2 years now so I have had some time to assess it over several seasons. I am currently generating approx. 8.4 KWH per day during the summer months and around 5.0 plus in the winter months-on good days of course.
    I would like to add a panel or two to the system as I feel there is room for the inverter to handle it – during observations at peak generating time I only see about 1250 watts momentarily on the inverter panel readout, most time it seems to run about 1000watts during the peak generating time of between 11am to 2pm (give or take). I would have liked to put a couple of panels on the opposite side of the peak of roof to the panels existing location to get more morning sun but note your comments to keep the new panels (matched if possible-same internal resistance??) on the same side next to existing panels for which there is space to add them.
    I had concerns about overloading the inverter but feel it can probably handle it given that most of the time it is producing output as per above-I’m not sure if this inverter has no, single or dual mppt input that would allow me to run a separate string?? Your comments about adding extra capacity will void my current rebate for those KHW sent to the grid currently standing about 48.8 Cents-are the suppliers/installers of the extra panels obliged to let Synergy/Western Power know of the additions? Any suggestions as to pros and cons of this potential upgrade?

    1. Hi Peter,

      Thanks for commenting.

      To answer the 2 key parts of your enquiry:

      -As you are aware, you cannot expand your system size and retain your current feed-in tariff. The WA government has been clear about this. While you might be able to get away with installing 2 extra panels without your network company noticing, we would of course have to officially recommend not doing this. If you were found out, you’d risk losing a very generous incentive–the current rate is only a fraction of the 48.8c/kWh you are currently receiving.

      -In any case, it is against the Australian standard for solar PV installations to install more panel capacity than inverter capacity, so no upstanding installer will do this. It would also most likely void the inverter’s warranty, which could land you in a tough position down the line if you start having problems with it.

      I hope this information is useful. Best of luck with your system!

  27. Hi There,

    I live in 20km north of Perth. I have 3 kw SLK-3000 solar king inverter and 8 off 190kw mono crystalline (Total 1520kw) panes in a single raw. I want to add more panes to get more production from solar energy.

    Can you please assist that how many more similar panes I can add to get more production at best performance efficiency of Solar king inverter? How many Optimum panes?

    What is the actual efficiency of the inverter? How many maximum panes we can add?

    I cannot add more panels in the same raw. Is it possible with this inverter to connect 2 raws of panels?

    In a really good day I am getting only maximum 10KW production in a day with the current set up. Is it fair or average? How much I will produce in average after getting more optimum number of additional panels?

    Also, how long our Feed-in-tariff rates remain same with western power? My upgrade of panels harms any current rate?

    This section gives me a lot good info and proper understanding. Thanks in advance for your expert advice.

    1. Hi Nisarg,

      Thanks for the comment. First of all, I thought it would be pertinent to point out that if you are receiving the feed-in tariff in WA expanding your system could change your eligibility–i.e. you might lose your feed-in tariff if you add more panels.

      For the technical questions, I would recommend first consulting the inverter and panel manufacturers, or possibly the company that did your installation. You can also read more about inverter sizing and solar panel array sizing in this article: “Optimising solar system efficiency through inverter sizing“.

      To briefly answer your other questions:

      Can you please assist that how many more similar panes I can add to get more production at best performance efficiency of Solar king inverter? How many Optimum panes?

      Any new panels you add should be of the same brand and have the same specifications as the ones already installed, unless your inverter has dual maximum power point tracking (MPPT), in which case you may be able to have a separate string of panels. Please refer to the inverter and panel specs.

      What is the actual efficiency of the inverter? How many maximum panes we can add?

      Again, please refer to the panel and inverter specifications.

      I cannot add more panels in the same row. Is it possible with this inverter to connect 2 rows of panels?

      If your inverter has dual MPPT, it is possible to add a second row of panels. Even if it is only single MPPT or no MPPT, the inverter might have a dual input–but in this case it is key that all the panels are matched in brand and specifications (and as much as possible, age as well). If possible, you’ll also want all the panels to be facing the same direction, at the same angle without dual MPPT.

      In a really good day I am getting only maximum 10KW production in a day with the current set up. Is it fair or average? How much I will produce in average after getting more optimum number of additional panels?

      I am guessing that you mean 10kWh per day here (kWh is the measure of energy produced, kW is capacity), and I assume this is the system’s summer output.

      Typically, a 3kW system in Perth will produce on average 4kWh of power per day (averaged across the year), equaling about 12kWh/day. This figure could be about 15kWh in summer if you had panels to match the capacity of your inverter.

      Also, how long our Feed-in-tariff rates remain same with western power? My upgrade of panels harms any current rate?

      As mentioned above, increasing your system size would invalidate your eligibility for the state’s feed-in tariff. It’s up to you whether the costs associated with upgrading your system and the benefits of the increased system output are worth losing the feed-in tariff. With electricity prices rising in WA, this may end up being the case, but it ultimately depends on your power use habits (timing, energy efficiency, etc).

      Hope this helps. Best of luck with your system.

  28. Hi
    I’ve received a quote for setting up a 2.5kW solar system at home (10 x CMS 250 panels). The inverter quoted is a Eversolar 2000 – I think because it should be a generous system for my usage. Still, is it ok undersize the inverter? The guy said it may run more efficiently, but I’m concerned about your comments of overheating.

    Many thanks.

    1. Hi Andrea,

      I believe you can slightly undersize your inverter as, at its best, your system will work at about 90% efficiency and each inverter has a different range. However, our in house solar experts advise that consistently going over the kW capability of your inverter can damage it and this leads to fire risks.

      If you would like to get a second opinion, feel free to complete the Solar Quote Comparison to the right of the page. You’ll receive quotes for up to 7 installers operating within your local area and we’ll allocate a Solar Broker to you to help you make a well informed decision. Our service is free of charge and impartial, so there is no pushy sales pitch.

      Hope that helped and we look forward to helping you soon

  29. I have just had a solar system installed with 13 x 250watt panels and a 3kw macsolar inverter. 6panels facing west on one string and 7 facing north on another.

    is this ok to be running 3.25kw of panels on a 3kw inverter?

    1. Hi Adrian,

      If the system is running at optimum efficiency, the output of the panels will still be around the 90% mark. This means that the 3kW inverter will be able to handle your everyday base load plus the occasional production of over 3kW, in addition to this all inverters have a range that they can work at – details should be in the manufacturers handbook.

      Hope this puts your mind at rest.

      1. thanks for that. in the hand book it states the rated input is 3000watts and the max input is 3300watts.

        my installers advised me that all my panels would not fit north hence why i have some west. i have measured it myself and it is possible to have all panels north.

        on a good day im generating 19kwh.

        since it is possible to have all my panels facing north. do you think i would see any gain or would i get too close to maxing my inverter out.

        my setup now is good as i get a good range from the north and west. but will i gain from having higher peak power from all panels north?

        1. Hi Adrian,

          19kWh on a good sounds like a good figure. Over the course of the year we normally advise that you should average at 4kWh for each kilowatt of solar you have installed.

          Installers may have looked at your available roof space, for example there is a minimum distance from the pitch of the roof that has to be observed and there may be other features that have a space requirement around them. If you’re not happy with this you can ask the installer to clarify why there wasn’t enough space and explain the rules that they worked with.

          You would get a little more peak power from having them all your panels on the north, but as long as the north and west panels are on different strings being fed into a dual inverter you’ll be getting the optimum output from each array. If you have some panels on the west you’ll get slightly longer day time generation and can substitute your day time energy needs for longer, therefore reducing your reliance on the grid and your energy bills.

  30. This is another one from the UK.

    I’m looking at installing 4Kw, (12 Panels) of Sunpower E20 333 and the company I’ve talked to have recommended Samil Power’s SolarRiver SR4K4TLA1 inverter. I’ve read that Samil have a good reputation and have been recommended by Photon Lab as a ‘serious competitor’ to the top supplier’s inverters, but would you recommend this inverter with Sunpower panels or should I look at either SMA, Power 1 or Fronius as a better option?

    N.B. I’ve really enjoyed reading the letters and appreciate your expert knowledge.

    Thanks. Glenn

    1. Hi Glenn,

      All the inverters you’ve mentioned have a good reputation. One of our installers gave us some positive feedback about Samil inverters, however, they haven’t been in business long enough to really prove their longevity.

      If you’ve been working with our UK office, Solar Selections, you can contact your Solar Broker directly. They will be able to talk you through your quotes and the components offered and help you make an informed decision.

      Hope this helps

  31. I am trying to get feedback about panels made by GESOLAR as well.Is it a tier 1 brand and would you recommend it?Thanks in advance.

    1. Hi Cherry,

      As we’re an impartial service we can’t recommend one manufacturer or installer over another, and without knowing your circumstances it’s difficult to know what set up would be right for you.

      You can fill in our FREE, impartial Solar Quote Comparison and receive an instant quote for up to 7 installers who operate in your area. This will give you a rough guide to what’s on the market and if any quotes you’ve been sent so far are good or over priced, we also allocate you with your own personal Solar Broker who can talk you though your quote and provide advice and information about the set up of your system.

      Alternatively you can contact us directly on 1300 78 72 73, a member of our team can with you to assess your needs and generate a personalised solar quote.

      We look forward to helping you soon.

  32. Thanks again for your comprehensive reply.Much appreciated.
    One final question is regarding SMA and Aurora inverters.
    SMA5000TL, I understand, will operate without performance derating up to 30 to 40 degrees internal temperature (50 to 60 for Aurora) and
    Will operate without performance derating in environments up to 60% to 70% humidity (100% for Aurora).Inverter efficiency is 97% for SMA and 96% for SMA.
    Based on these facts and figures how does one choose between either of them?
    What are the feedback from customers with real life experience.
    Look forward to hearing from you soon.

    1. Hi George,

      Wow, it looks like you’ve really been doing your homework! I both the SMA and Aurora inverters have good reputations, SMA is probably the best inverter on the market. Looking at the figures you’ve quoted if you live in the Territory or Far North Queensland you might be better going with the Aurora to help as it looks better for the extreme heat and the humidity you get up there.

      Other than that, because they are so close together specification wise it would probably be a matter of cost that makes the decision, but whatever you chose you won’t go far wrong.

      If they same installer is offering both you could ask their advice, if you have two different installers you are considering you might look at what future support and warranties they are offering to help you choose.

      Good luck.

  33. Thanks for the informative reply based on which we will stick to 20 panels!Could we also know if polycrystalline panels are more suited for QLD than mono panels?We have read about Suntech being in financial difficulty.If they go bankrupt and into administration what happens to our warranty?Look forward to hearing from you soon.

    1. Hi Cherry,

      Monocrystalliane used to be the ‘big’ thing in solar and when some of the newer panel manufacturers launched their polycrystalline models they marketed them as being the future of solar and told people mono was out of date, in reality there is no real difference in performance. With regards to SunTech, their demise has been greatly exaggerated, we had a visit from the SunTech team a couple of weeks ago who advised us that it’s business as usual for the company. There has been wide spread misreporting regarding a court case in Italy, SunTech is not part of that court case but a company they hold a majority shareholding in is. SunTech is fully expecting a positive outcome and this case isn’t affecting their everyday finances.

      Suntech is one of the best solar PV manufacturers on the market, the warranty you mentioned is for 25 years and in the last ten years they have had a 0.06% claim rate. When you consider they have over 7GW of panels installed globally that’s a pretty good figure!

      Enjoy your solar panels and if any of your friends or neighbours are looking to go solar send them our way, we’d love to help!

  34. We are planning to install 20x250w Suntech panels with a 5kw Aurora inverter.We are told this inverter can take up to 5.75kw or in other words 3x250w more panels.Is this recommended?We have secured 44cents feed in tariff.Will this in any way result in us being disqualified for the FIT?Thanks

    1. Hi Cherry,

      Although inverters have the ability to cope with additional energy periodically, constantly operating your inverter over it’s capacity will significantly reduce the life of the inverter and may lead to a potentially dangerous overheating scenario. If the installer has recommended 5kW of panels and a 5kW inverter, under optimum conditions you should be operating at around 90% efficiency.

      Adding panels to your existing system can disqualify you from the existing FiT, I believe your installer would be in the best position to advise you. If you haven’t signed a contract or are still in the cooling off period you can check you’re getting the best deal by filling in our FREE Solar Quote Comparison, you’ll receive quotes from up to 7 installers who operate in your area. We also allocate customers with a personal Solar Broker who can answer your questions and, with the Solar Choice Discount, you can get a better deal than going to the installer direct.

      Good luck with your system.

  35. Hi Guys. I am currently running 14 LPK 250W Solar Panels on a Xantrex GT5.0 Inverter. I have been realy happy with it’s performance and am looking at adding extra panels. How many should I add? I know that 6 new panels (to make 20 panels total) takes it to a 5kW array, but I have been told adding 8 would be fine too. What are your thoughts??

    1. Hi Leigh,

      It’s great to hear you’re getting on so well with your current system and want to expand. There are a few things you have to take into consideration when adding panels to your current system. If you installed your system a while ago and are benefitting from one of the Premium feed-in tariffs adding panels may mean that you are no longer eligible to receive the Premium rate.

      If you do decide to proceed you will need to purchase panels that match your current set up (ideally the same panels you have now). Normally we would advise that your panels match the output of your inverter, so adding 6 woud take you to 5kW, this is because the inverter is not designed to cope with power generation above its capacity on an ongoing basis, overloading on a regular basis is actually detrimental to the system and can cause a fire hazard.

      It may be that you have been advised that 8 panels would be ok due to the loss in performance of your existing system so adding 8 may mean that the maximum you would generate would be 5kW (your system will only perform as well as the worst panel so any new panels will perform as through you had installed them at the same time as the originals).

      If you are looking to increase your energy generation to help you further offset your bills, the best option may be to install the extra panels on a separate inverter ensuring you get the maximum power from your new system.

      We hope this information helps.

      1. Thanks guys. Really helpful. Will go with 6. My system was approved up to 5kW so it won’t affect FIT. Your advice and website is great. Thanks.

  36. Hi I live in South Yorkshire, England, and wonder if you could assist. I have 14 X 250 watt sharp solar panels fitted with an SMA3000TL inverter. On checking the spec of the inverter it states that max input power is 3200w and the nominal power available is 3000w, is this acceptable as to my mind the panels are, or should be producing more power than the max input allowed, i.e. 3500 watt should be produced by the panels. Is the inverter adequate for me to obtain max performance from the system or should it have a larger one such as the SMA 3600, for example. Also I have noticed that 2 of the panels look different from the others. Could they be of a lower output than the others in order to make the system compliant with the max input for the inverter. Any comments would be appreciated, prior to contacting the installer. Thanks.

    1. Hi Ade,

      Our UK office might be better placed to answer this for you, http://www.solarselections.co.uk.

      In Australia the inverter size has to be larger that the kW outage of your panels, but this could be different in the UK. We also haven’t heard of any instances where two different types of panels are installed and I’d definitely query this with the installer, if you contact our UK office they should be abe to give you the correct advice.

      We hope you get it all sorted!

  37. Hi we have a system installed 20 x BLD 190w modules and a JSI 5kw inverter. The system does not seem to be producing what we expected average 14.7 kw per day over last 91 days. Located in Canberra with system in full sun north facing position 17.5 degree pitch. Could the inverter be oversized? or we’re our expectations too great? Thanks for your help.

    1. Hi Chris,

      We would expect an average of 15kWh per day over the past 3 months, due to the shortened winter daylight hours, so it sounds like your system is doing really well. As we’re going into summer with longer hours of strong sunlight you’re system should start producing more energy and this might be more in line with what you’re expecting.

      If you are basing your calculations on a 5kW system, as this is the size of your inverter, that might be where the difference between the expected generation and the actual figures arises. The the system size is actually 3.8kW (20 x 190w modules), we normally advise that a system will produce 4kWh per 1kW averaged throughout the year.

      We hope this helps.

    1. Hi TJ. You’re right–SB1700 does not have dual MPPT. It has 2 inputs for the one MPPT. Thanks for pointing that out.

  38. Great information on this page, I have 8 x 190w panels connected to a MacSolar 1.5 facing NNE in Perth, looking at the specs for this inverter I see that it has a max input of 1800, would you recommend adding an additional 1 or 2 panels to this system? I have room for more panels but assume I would lose the RECS if I upgrade my inverter.

    Thanks in advance