Where should your solar inverter go and should you worry about voltage drops?

I got a great email the other day:

“One solar installer has told me that it is best for the inverter to be as close as possible to the panels and NOT to the meter box as your checklist indicates. Is he crazy?”

Short answer. Yes – he’s crazy.

Longer answer:

As close as possible to the panels? Whatcha gonna do put it on the roof?

I get a lot of stick for this advice in one of my solar installation videos:

Solar Inverter Position

Sometimes I get heat for recommending that you put your solar inverter as close to your fusebox as possible.

The argument against this advice is basically that the voltage drop is proportional to the length of the wire and that the voltage drop between the panels and the inverter is (allegedly) more critical than the voltage drop between the inverter and the meter. Therefore you should minimise the  length of wire from the panels to the inverter at the expense of the length of wire from the inverter to the grid/meter.

I’m not sure where this argument comes from. The truth is that the voltage drop that will cause the most problems is on the 240V AC side.

If you want to be sure that your solar system will operate reliably, then the voltage drop between the inverter and your grid connection needs to be less than 1%.

Why? Here I’ll quote from a Grid Connect PV manual by GSES:

“Although not mentioned in AS/NZS 5033:2012, AC voltage drop/rise [i.e. between the inverter and the switchboard] should be kept as low as possible. The purpose of this is to keep the voltage rise to a minimum – this is to prevent voltage rise in the local grid. High levels of voltage in sections of the grid may lead to overvoltage tripping in grid connected inverters. The allowable voltage rise depends upon the local state rules that are in effect. However, under the CEC Guidelines which were effective as of the 1st of February, 2013, the new recommended AC voltage drop/rise from the inverter to the point of connection is 1%.”

Of course the best way to minimise voltage drops in your solar system – which will maximise your power output and maximise the return on investment – is to use cables that are as short and as thick as practicably possible. The thicker the cable, the lower the voltage drop across the cable. So if you absolutely need a long run of cable – you can usually compensate with thicker wire.

Typical wire thickness (measured in cross sectional area – millimetres squared) for the DC cables that run from the panels to the inverter is 1.5mm², 2.5mm², 4mm², and 6mm². If you want to minimise losses insist on at least 4mm². Believe me some of the large and super cheap solar installation companies want to save every last cent on every install and will try to get away with the 1.5mm² wire!

As for the AC cable, i.e. from the inverter to the meter, don’t go smaller than 6mm². And if you have to place your inverter more than a few metres from the meter then go  thick enough to keep the losses in that wire less than 1%.

My advice is to stipulate to your installer (in writing) that the losses in the wires (voltage drops) should be less that 2% overall for the system as a whole. After all electricity is expensive and wire is cheap!

About Finn Peacock

I'm a Chartered Electrical Engineer, Solar and Energy Efficiency nut, dad, and founder of SolarQuotes.com.au. My last "real job" was working for the CSIRO in their renewable energy division.

Comments

  1. Your response seems very logical. How about the argument that the high voltage DC last lines are a greater fire risk than AC lines? If that were true, it would argue for placing inverter closer to solar panels to more more minimize the length of DC wire run.

  2. David Maddern says

    You may explain that rationale from the fact that low to medium voltage dc has high losses over medium to long distances and ac is preferable (consistant with flow of electron vs. forward and back movement)

  3. David Colley says

    Hi Finn
    I have a test report from Photon, in PDF, of a Samil Power’s SolarLake 15000TL, 3 phase, if you are interested. You have my email & if you would like it let me know.

  4. Off grid Japan says

    Your argument makes sense for a grid tied set up, but what about an off grid array with the PVs pushing out only 24V to a battery bank and then the inverter taking its feed from there?

  5. I’m getting different STC amounts on quotes for a 3kw system in Torquay Vic. Do these vary day to day?

  6. I’m wanting to place solar panels on my shed then run a cable to my second shed about 5 meters away where I can place a supp box, then run another cable 100 meters to the house where the meter box is and supposedly where I’ll place my inverter. My question is how thick should my cable be to have a successful installation? Can I run one long cable from panels to house ? With the inverter right next to the meter box or should I go to my second shed first where I was told should be placed a meter box?

    • Your CEC accredited designer can work that out in about 5 minutes. I’m not going to give you a cable size without all the details because it is a very important number to get right!

  7. Hello Finn,
    My Main Meter box located on the Far (west) wall of my shed, making it about 8-9 meters from the house west wall. There is a fuse box located inside on the West wall of the House.
    Would it be practical to locate the Inverter (SMA 5kw) inside the House next to and Conect via the Fuse Box … Is this an acceptable mounting and Connection option ?
    Or … should the inverter be loacted on the Shed with cabling back to the house and the Panels on the roof ?

    • The most important thing is that it is in a cool place. In a garage is ideal. Or a shaded external wall.

      If you have to run a longish cable to the meter, then ask the installer to tell you the voltage drop and don’t accept > 1%.

      I wouldn’t put it inside the house. They are big and ugly!

  8. Deborah Lamont-Catterall says

    Hi Finn, I have been told conflicting facts from different installers regards location of where I should place my Solax hybrid inverter and battery storage unit. Options are 5kWh panels:

    1)on house tile roof with 5kWh inverter (not so ugly in a laundry) and 4kWh batteries in laundry 5m from panels but at opposite end of house 15m from metre box;

    2) inverter beside metre box under carport 5m from panels and batteries in garden shed 5m across driveway with cables following roof beams of carport;

    3) panels on garage tin roof with inverter and batteries in garage 30 metres from mains metre box. Garage has a fuse box/sub-board but wiring too narrow for system so new trench from sub board to mains under concrete driveway required.

    In your expert opinion which is best option?From what I have been reading in your website option 2 seems the best for reduction of voltage drop. But installer assures me 6mm cable from laundry addresses that issue but insists inverter and batteries must be beside each other, not across laundry (or carport) from each other. Doesn’t the larger cable between these items address the voltage drop issue too? Is it a CEC standard that the batteries and inverter cannot be more than a metre apart? I could not find any specifics on this matter. Your advise would be appreciated.

    • Hard to say without an inspection. I’m not aware of a hard rule that says your battery to inverter cable can’t be more than 1m. Perhaps ask him which standard/guideline says that. I’d be really interested to know.

      These would be my priorities in order of importnance

      1) Batteries and inverter in a cool, shaded area with ventilation.
      2) Short as possible distance between batteries and inverter.
      3) Short as possible distance between inverter and grid meter.

      And yes – generally a thicker wire can make up for longer runs – but it should be carefully calculated to keep all voltage drops less than 3%, ideally less than 1% if practical. After all wire is cheap compared to panels and batteries!

  9. Hi Finn
    My question is how can you tell if the 240 watt solar panel is a 12V or 24v?
    Thanks,
    I appreciate it,
    Abdul Yahia

  10. Lynton & jeanette says

    Does anyone know if there is a minimum distance the inverter must be from our meter box? Our installer has placed it 3 metres away from the meter box while there is space for it to go right next to it

    • 3m should not cause any issues. Although if there was space next to the meter box, I don’t understand why your installer would not put it there, as the shorter the distance, the lower the voltage drop, and the lower the losses. But we are talking a tiny loss over 3m (assuming ice thick wire is used).

  11. Wayne and Sharee says

    Hi Finn,

    We have our 3kw panels installed on the eastern face of our shed, as it was the only place at the time, we now have a place we can install them facing north but they will be 25m from the inverter, my question is: would it be best to leave them where they are and accept the lower power generation (east) or move them and have the voltage drop over the 25m?

    • The losses from a longer cable, properly sized will be a fraction of a percent, the reduction in energy from facing east will be about 20%.

      But…

      It will be expensive to relocate.

      And…

      If you use power later in the day and are on a non-premium feed in tariff then you may save more money by having east facing panels, as they will generate more energy later in the day, increasing self consumption.

      If you have a 2nd input on your inverter, I’d consider adding a second string on the North, oversizing your inverter up to 133%.

      Or if you do not have a 2nd input, panels with micro inverters on the North may be a good idea. The current rebate will pay for most of the panel cost (but not the installation or inverter costs).

      Hope That Helps,

      Finn

      • did you say east facing panels generate more power later in the day ?

        doesn’t the sun set in the west ?

        wouldn’t west facing panels generate more power later in the day and east more in the morning ?

        • Ronald Brakels says

          Hi Rod, Ronald here.

          I can’t see where Finn wrote that, but if he did it’s clearly just a silly mistake. East facing panels will generate more in the morning and west facing ones more in the afternoon.

  12. Hey guys,

    I have a problem with a hybrid solax 5kw inverter.
    String one keeps dropping out, I swapped the two strings and string one keeps dropping out,

    Any ideas ?

    Cheers

  13. I’m looking at getting solar, however my meter box is on a power pole about 30m from the house. Meter is an i-Credit 400 (will this do Net?). I’m on a farm and there is 3 meters in the box (2 for the sheds and one for the house). The house has the actual fuse box, with a cable running through the air from the pole to the house.
    We get a voltage drop when numerous high drain appliances are running, eg dryer, 3 AC units, kettle etc that pulls the voltage down to as low as 210V.
    I’m guessing the “house” meter would need to be moved to the house itself, otherwise a new second cable will need to be run to the pole to account for the unused solar generation? I’d prefer not to have the inverter out in the elements on the power pole, given that it likely needs to be replaced by Ausgrid soon too. I also want to be able to gather stats from it for PVOutput etc. Sounds like voltage drop issues would make placing the inverter on the power pole unavoidable?

    • Ronald Brakels says

      A minimum level of 210 volts should still be above a solar inverter’s minimum voltage cut-off, so you should be right in that respect.

      • Thanks Ronald, would I still need to run a separate cable from the inverter (bolted to the house) to the meter (bolted to a pole 30m from the house) so that unused solar generation is accounted for?

        • Ronald Brakels says

          You will have an export/import meter installed that will keep track of electricity you send into the grid.

          According to the Clean Energy Council’s installer guidelines, “The inverter shall be connected by fixed wiring to a dedicated circuit on a switchboard.” So that would be a separate cable.

  14. The switchboard (and inverter) will be 30m+ away from the meter, but the inverter and switchboard will be next to each other. The meter just records the net amount of power going in and out, maybe an additional aerial (or buried) cable is not needed then? Would save a stack of cash…

    • Ronald Brakels says

      I’m clear on what you are asking now. The inverter will be connected to the switchboard by a (short) cable and there won’t need to be an additional connection to the meter.

      • Perfect, thanks for the replies Ronald 🙂

      • All installed and working well 🙂 When the sun is up the house voltage actually improves too, which the coffee machine likes!
        We only have a 6mm core cable from the pole to the house 🙁

  15. Darryl G Hitchens says

    Can you please help with some advice. WE have a Afore Anyhome 5kw with 20 panels. the inverted was installed within 40cm from fuse box and is in direct sun light from midday on. our first inverted lasted 7 month and was replaced under warranted. at the time of installation I question the inverted being in direct sunlight and was assured its not a problem there is heaps like it. two years and seven months from the warranted inverted being installed our system is on producing half the amount of power which would be consider normal going on what its made in the past taking all variables into consideration. our System supplier tell us the reason is the slight shading ( palm frond 20 feet away) 10-15% of 1 panel but even when there is no shading.
    Reading at 10:30am 1pv=306a, vpv=281v, iac=4.2a, vac=246v and power reading was 1090w with no shading on panels at all.

    • Ronald Brakels says

      Hello Darryl. Generally I would expect 5 kilowatts of unshaded panels to be producing considerably more than 1,090 watts at 10:30 in the morning. I would check on several sunny days when the sky is clear and the sun is directly over the panels. If they aren’t producing at least close to 4 kilowatts on one of those days I’d say you have a good reason to be cranky.

      Just a very small amount of shade, even on just one panel, can have a major effect of the output of the entire system, but not when there is no shade. It is possible that there is dirt on the panels, for example bird poop, that is causing a large reduction in output. If you can visually inspect your panels you can rule this out.

      If the problem is dirt, it should improve after heavy rain, as this is often enough to clean them.

      Unfortunately, another possibility is the panels have deteriorated. This normally doesn’t happen over such a short period of time with tier one brands, but I don’t know what kind of panels you have. Again, if you can visually inspect them and can see any imperfections such as brown spots or what look like snail trails, then one or more of your panels may be failing and dragging down the performance of the whole system.

      There could be a problem with the inverter, but they are usually an all or nothing deal and when they fail tend to stop working entirely.

      Your installer’s attitude to the inverter being in full sun is a bit lax. If might be okay for him if they normally last till the end of their warranty, but if you want to extend the life of your inverter it would probably be a good idea to put a shade above it.

  16. Darryl G Hitchens says

    Thank you for your very helpful reply. I took a reading at 2.00pm (Daylight savings)18/03
    1pv 6.2A, Vpv 252w,1ac 6.5a , Vac 243w Power Reading 1515w .
    This morning 19/03 I wash all my panels again to remove some bird poo/splatter, reading at 2.00pm Ipv 8.1a, vpv 224v ,Iac 7.7a Vac 242v, power reading 1768w. both days reading with out shadow to be found with same temp. an improvement but still approx 1/2 of what would be normal. had a really good inspection of all panels and cant find any imperfection what so ever. the panels are north facing 20x250w Schutten .I had my own very well vented cover made up for our inverter last summer but you still very hot to touch and would more than likely burn a child’s hand.
    Would you be able to recommend a Electrician with Solar System skills here in Adelaide SA who is not part of Solar and Wind Wingfield that I could contact for an independent inspections .

  17. Darryl G Hitchens says

    Greetings Finn, I was advised to contact National Renewable Group (NRG) South Australia, who came to our house and carried out a Compliance Check on our system.
    From NRG Report :OUTCOME
    One of the strings is open circuit, meaning that the system is only producing half of what it should. There are several other
    issues with the installation: the inverter has been installed on a western wall exposed to sun, the array has not been earthed
    properly, the dektites have not been sealed with silicone and the overhang on the panels is too great.
    COMMENTS
    One of the strings is not in operation. We have checked both the inverter and rooftop isolators to rule them out as the cause.
    There is no voltage at the panel side of the rooftop isolator. The bottom row of panels will need to be taken apart in order to
    find the cause of the fault.
    When I supplied this report to Solar Wind they sent out an interdependent, Nigel Griffin (GRIFFIN RENEWABLE ENERGY) who removed panel from lower string until he found a panel that had melted down part of the circuit board on the back. Still waiting on Olympic Solar/Solar Winds, Winfield .

  18. Colin Palmer says

    My solar panels keep tripping on high voltage..262 v ac.. when at full output…approx 4000 watts
    The problem appears to be that the load on my house ls low…I can stop the rise by artificially loading the board with appliances…this is a waste…what can I do..?

    • Ronald Brakels says

      Hello Colin. Sorry to hear about your inverter tripping out.

      When your inverter is at full output and the loads are low in your home, the inverter has to push the voltage higher to get the power into the grid. If it has to go too high the inverter will exceed the allowable limit and cut out. There are a couple of main things that could be causing this.

      It is possible your system could have an unusually large voltage rise. A significant voltage rise is more likely to occur if there is a long distance from your solar inverter to your grid connection. Using larger diameter cables can resolve this problem — but the cables should already by of suitable diameter for the distances involved. Still, it is possible your cables are too narrow for the job.

      Another possibility is that the grid voltage in your area is often high during the day. Informing your Distributed Network Service Provider (DNSP) of the problem may result in them fixing the problem. (Your DNSP should be on your bill.)

  19. I am possibly going solar but getting conflicting info. Solar companies want to make a sale but can’t give precise answers to some questions. My average bill is $360 per quarter and some say “do nothing”. Others want to sell me a system. 3 kwh system recommended by most agents.
    What is the most efficient position . Garage is separate from house 10.0m away with meter box only on front wall. House is 10m behind (and separated) with sub board in laundry. Collectors are on house roof facing north. Conflicting info is Inverter inside garage above meter box which gives a distance of approx 20m of run to sub board in laundry. Does this create problems with voltage drop/efficiency of the system. Collectors would be directly above the sub board. Would a new underground feed be required between garage and house (Established gardens etc to navigate)

    • Hi Ron,

      What postcode are you in? That will let me know what Feed In Rate you can get and that can make a difference to my advice re: what size system / is it worth it.

      I wouldn’t want to give you advice on where to put the panels or inverter without seeing your site.

      Finn

  20. What danger is there from the DC wiring and is there any benefit to keeping it high and out of child reach? It will be covered by conduit so I’m thinking it probably doesn’t matter. Just wanted to check as it seems the most shaded location for our inverter could be under a deck (two storey house), so the DC cable would run down from the roof past the level of the deck where people can reach it.

  21. Michael Jakob says

    Hi Finn.

    We have been doing the rounds with our solar installer for 6 months and the system is still tripping out.
    Our installer put in an 8.7 kW system on a single phase solaredge SE7300 inverter. It was connected in series with an much older 2 kW system. Never worked properly.
    I then had a 3 phase net meter put in to get full use of the 3 phase power to the board which was set up and always used as a single phase installation. The we put the old 2 kW system and the new 8.7 kw system on different phases. No change!
    I am now wondering if a 3 phase inverter is going to solve the over voltage issue. Are you aware if this would drop the voltage rise by about 3V or not as this is what we would need to be out of trouble?
    Of course the installer who failed to do a site check or any calculations is kicking and screaming it is not his fault as he does not want to bear the cost of fixing his mess.
    I suspect we need regulations to be upgraded so that consumers are not left high and dry by this issue…..which is from what I understand a significant issue for many of us trying to do the right thing by generating clean energy.
    Any help greatly appreciated. Thanks for your help and useful articles.

  22. Owen Johnsen says

    I want to relocate my solar panels to a position that actually receives maximum sunlight. At present they only receive light for a few hours a day. However, when relocated they will be 100 meters from the inverter. I am intending to install batteries between the solar panel and the inverter. This way I can use my power generated during the day and night and still have some to send to the grid. What size cabling would be best and is it possible.

    • Ronald Brakels says

      Hi Owen

      That is feasible, but unusual. Your installer would have to do the calculations and work out the cabling required for your particular system. If you have a 3 phase inverter it may be easier to move that closer to the panels and use AC cabling. Note with DC current you’ll need a circuit and most solar systems have 2 strings of panels, so with 2 strings you’ll need 4 times the length of cabling as with an AC connection.

      The cabling for most battery systems is very thick and so they need to be located close to the inverter.

      It is possible you would be better off installing more panels in a poor location than putting a smaller number in an optimal location.

  23. Khurram Iftikhar says

    HI, I am designing a 27KW (70- 395W lgs ) with 2 solar edge string inverter(11.4 kw). ground mount.
    The closest 400 amp electrical service is 500 feet away … or i could connect directly to a utility pole which is also 500 feet away .
    My main concern is should i put the inverters closer to the PV array or the electrical service/utility pole ?
    if i put the inverter close to the array, voltage drop gets high, and if i keep it close to the electrical service/utility pole we have 500 feet of dc running. i dont know which is better.
    would appreciate some insights.

    • Ronald Brakels says

      Generally it is easier to keep the solar inverter close to the solar panels and have a longer length of AC cable to the grid connection. But 500 feet is around 160 meters so with 3 phase power and a 20 kilowatt inverter the cable from the inverter to the grid connection would need a cross section of about 50 square millimeters to keep voltage rise to under 1%. It may be easier to locate the panels closer to the grid connection. Your installer will be able to advise you on your options.

      Wait a minute — Let me use my internet spy powers on you… Are you in Canada? The North American grid is different from ours and I don’t know how that will affect things.

  24. Hi Finn,
    Im just in the planning stages for installing a sub-board in my shed. Eventually I will be getting Solar installed onto the shed as its perfectly positioned. The run between the shed and the main switchboard is 45m. Do you recommend the inverter mounted at the main switchboard,or Inside the shed and separate 240V cables into the Main Switchboard or can it be connected via the sub-board in the shed if the wiring is large enough for minimal Vd? Just trying to understand which will be cheaper and to know the electrician has the right idea as well. A battery bank behind the shed is an option too if they become cheaper in the future.
    Thanks alot, Kyle.

  25. DONALD MERCER says

    Anyone familiar with Solar River inverters? I have a 5000TL that suddenly kicked up a “DC reverse” alarm #15, which my manual says is a fan fault…..I changed the fan, still getting it.It won’t allow the AC to run, it says dc reverse, then goes to “no utility” even tho’ the menu shows 240v. Anyone have a clue? It’s still under warranty, but Samil seems to be ignoring all warranty work, so I’m desperately hoping to avoid a new inverter.

    thanks
    Don

    • Ronald Brakels says

      I don’t know anything about the inverter but you may want to contact a consumer affairs organization in your state to get Samil to either repair it or replace it. If they are not doing anything they are clearly in the wrong.

  26. I want to install a 6.6kw solar system with a 5kw inverter . I have a 10mm 3phase cable underground hooked to a 3 phase import /export meter. solar panels and inverter will be installed at a shed 150m away from import/export meter and the meter is 30m from pole on the street connected with16mm 3 phase cable. Is it possible

    • Ronald Brakels says

      Hi Sam.

      I’m afraid for a 5 kilowatt 3 phase inverter the maximum distance that can be covered with 10 square mm cross section 3 phase cable is 143m. To keep voltage rise within the acceptable 1% limit the cable would need to be replaced with one with 16 square mm cross section which will allow a distance of 227m. Because of the high cost of replacing the cable you may want to consider installing solar on ground mounts closer to your import/export meter.

  27. Peter McDonald says

    Problem, NEDAP Power Router 5 KW inverter at house and transformer about 500 Metres away. I-credit 500 meter at pole and transformer where a bore pump also runs from. Before solar installed in 2014 there was a meter in the box at the house where the inverter connects to the grid but was removed and the only meter is the one on the pole all that distance away. Since 2014 only about 5,000 KW is shown as exported to the grid and the LED on the inverter shows a”soft grid error” all the time. Since installation it appears the system hasn’t worked properly. An engineer friend tells me the distance between the inverter connection at the box at the house and the transformer/meter pole is most likely the problem. It appears to me the solar installers removed the old meter at the house and should have replaced it with a new Net type but just relied on the one at the distant transformer pole which was there originally to meter the bore. My engineer friend advises that there should be a meter where the original was in the box at the house next to the inverter.
    NEDAP have gone belly up and the original installer wants nothing to do with it.
    HELP please with any suggestions.

    • Ronald Brakels says

      Hello Peter

      According to the Australian Standard AS4777.1 a solar installer must ensure there is no more that a 2% voltage rise from the inverter to the point of supply. If your point of supply to the grid is 500m away then it is not plausible that the voltage rise would be 2% or less. If this is the case, your installer would not have followed the Australian Standard when installing your system as they are required to do. I am not a lawyer, but my understanding is they should not have gone ahead with your solar installation and — provided my interpretation of what has happened is correct — they are required to provide a remedy. I suggest contacting consumer affairs and getting advice on how to proceed.

  28. Hi Finn and Ronald,

    I’m getting a 6.6kW system with a 5kW inverter installed on my house which was built in the 1970’s. My preference would be for the inverter to be mounted in the garage rather than next to the power box which would result in an extra 11m of cabling each way to and from the inverter (i.e. 11m DC in and 11 AC out). My installers have said that the extra distance may cause some issues with voltage because the mains wiring of the power box has smaller wires than what would be used in modern day houses.

    I would have thought that provided the wires used are thick enough going into the power box, it would not make a difference. What are your thoughts?

    • Ronald Brakels says

      Hi Nicolas

      Even if heavy duty copper cable with a 25 mm cross section is used from the inverter to the switchboard, over 11m it can still result in a modest voltage rise. It is possible this could be enough to cause a voltage rise issue when combined with old wiring your home has. You will also lose a little energy on the DC side and need to pay for extra cabling. Note the DC side will require two extra lengths of cable.

      You could ask the installer if the voltage rise would be acceptable if heavy duty cabling was used and get a quote for the system with that extra cost. Then you can decide if it is worthwhile.

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