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Hello All
I am installing a new grid connect 1.5kw Evergreen solar panel pole mounted array that is about 70m from our house. I have opted for a larger inverter that will allow up to 4kw of capacity. Eventually I would like to go higher than 4kw and here is where I am having problems understanding something the dealer has said. He stated that I should run two low voltage cables underground and have the inverter next to the switchboard on the house however my way of thinking would be to have the inverter near the arrays otherwise when and if I upgrade beyond 4kw I will have to lay more underground cable to a second inverter whereas if the inverter was mounted near the arrays then all I would have to do is add another inverter. Is there a valid reason for what the dealer stated? Provided I run large enough cable I don't see the need for the inverters to be next to the switchboard.
Also I have asked him to supply a method of monitoring the output of the array/s and he has recommended the Sunny Beam Wireless Monitor. Does anyone have any experience with this product? The Fronius inverter is capable of being networked but it appears to be a lot of extra expense.
Any help on these issued would be greatly appreciated.
Regards
Phil
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 12:51pm 25 Jan 2009
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There are many safety aspects and regulations when laying 240VAC cabling underground. Depth, protection from digging, labelling, etc etc.
Underpowering a large inverter is not efficient. Check the specs for the inverter re optimum voltages and currents to get peak inverter efficiency.
Many installers over rate the panel size to inverter. There is only a small part of the day when peak power is available, [unless a tracker is used], so the inverter can be of lower capacity than the peak panel power. The inverter I have SMA1700 is rated at 1700W. If my panels provide more than this, the inverter just limits to the 1700W. The MPP-peak is activated at this time.
Check with the enclosure type. Outside will require better sealing, and avoid plastic.
Ask the installer some questions about why this way or that.
Get a second, third opinion etc.
When I put my first system in there was not much choice, but now there is plenty.
I would do any wiring, array framing, controls for the full 4kW, and then just populate the panels later, unless you may change your mind about upgrading.
I recently had a three phase cable (4 cables) laid underground for 100m and the only specification was that it had to be (from memory) 900mm deep. There is no added safety ie sand etc. The cables are laid inside plastic conduit and are a special type of cable but from what I have been told a cable underground between an inverter and a switchboard would not even need to be double insulated.
I did not realize that would be an issue. What sort of inefficiencies are we looking at? The dealer never mentioned this when they quoted on the 4kw inverter. Would I be better off getting smaller inverters and connecting them together when I get more panels?
I was thinking about putting the inverters etc in a small shed for protection from the elements.
Did you build your own array framing or buy a premade assembly? I am getting quotes on the UniRac systems but they appear to be very pricy for what they are and I suspect that I could make a cheaper frame myself. I am a qualified mechanical engineer with experience in welding and fabrication. I have noticed that mostly aluminium is used for the framing due to it's resistance to corrosion but galvanised steel has an expected life span in excess of what the expected life span of the panels are rated at. The area the panels will be mounted does not suffer from excessive corrosion problems.
I am an electrician and a BCSE accredited installer. You should be asking your dealer to speak to their accredited designer/installer/electrician and not a salesperson because the questions that you are asking should be explaind to you properly before you start handing over any money.
1. According to AS3000 electrical cables need to have a minimum 600mm of ground cover and be run in Heavy Duty Orange PVC Conduit, it is good practise to run Orange warning tape around 300mm above the conduit.
2. I am assuming you have opted for a SB3300 or SB3800, both of these inverters have a Voltage MPPT input range of between 200 to 500 volts DC which means if you are to mount your inverter at the switchboard then the dc cable from the array to the inverter is not extra low voltage (<50V) and must be in accordance with AS3000, and be installed by a licensed electrician.
I would recommend mounting the inverter as close to the array as possible and running an AC cable large enough to minimise the voltage drop losses.
10mm2 cable 70metres long = approx 60W of losses at 4kW
16mm2 cable 70metres long = approx 40W of losses at 4kW
25mm2 cable 70metres long = approx 25W of losses at 4kW
3. According to the installation manual of the SB3300 and SB3800 inverters, when operating at 1500W output both inverters operate around 95% efficiency reducing to around 92% at full rated output.
4. The Sunny beam is a good product but it may not have the range if the inverter is 70m from the house , it is also expensive ($600-700 for sunny beam and wireless pigyback). You can get a kWhr meter for your switchboard for about $100.
5. The other point with upgrading in the future is that the panels that you upgrade with should be a match with your current panels, because the inverter only has one MPPT and panels that are different won't work as effectivily together, as panels that have the same specs. So you may be better off with a smaller inverter, and getting an additional system when required.
Hello Mick
Thanks for the reply. The inverter quoted is an SMA SB1700. If I go for the upgrade to 4kw they have quoted the Fronius IG40 which has a maximum efficiency of 94.3 percent. The MPP of the Fronius is 150-400V.
Thanks for the cable stats. I was advised by the technician that the minimum cable diameter to use would be 16mm2. I will most likely use 25mm2 depending on price. Now that I have spoken to a technician I have found the correct method of installation and that is to have the inverter as close as possible to the panels.
The price they have given me for the Sunny beam is $380.00. I have been having a look at some of the newer ampy-email meters and they are apparantly networkable so if they are suitable I might go with one of them. I could not find out if they are capable of bi-directional metering.
I am planning on upgrading the array in the next year or so. The panels I am using should still be available then. If not I will use the larger inverter for other purposes and purchase a smaller one for the current panels.
Another couple of questions that you may be able to help with.
1) The technician said I need three cables for active, neutral and earth but I thought only the active and neutral would be required and earth the panels at the array. What are your thoughts on this? We have an overhead cable run to a water pump and the electrician has only two cables to the pump and an earth at the pump switch board.
2) If I decide to run a data cable to the inverter would it be advisable to run the cable in the same trench as the power cable (in its own conduit)? Cat 6 cable is rated at a maximum length of 100m using UTP. I have heaps of UTP cat 6 cable but maybe STP cable would be more suited.
Thanks again
Regards
Phil
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 10:46am 30 Jan 2009
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I am not sure what you mean by other purposes. These units are pretty specific for an application.
If you can buy 2 inverters then funds can not really be a problem, just go and get meters that will work together with the inverters. Most grid connect inverters come with metering options.
To answer your questions the technician is correct, you will need to run active, neutral and an earth. The earth conductor will be used to earth the metal frame of the inverter. Although it is also acceptable to run two conductors (active and neutral) to a sub-board and then install an earth stake to provide an earth for the sub-board and then connect the inverter to the sub-board.
As for the data cable, if you have some unshielded cat6 cable you can try it in the same trench just be sure it is installed in white comms conduit and try to maintain about 300mm of separation and if it doesn't work you can always use it as a draw wire to pull in some shielded cable.
Hello All
Gordon
I meant to use it for more solar panels in a different array. Funds are always a problem but in my overall plan I intend on installing around 12 kilowatts of panels over the next five to ten years. Of course this depends on my not losing my job in the five to ten years and what the overall performance of the initial installation works out at.
Mick
Thanks for the information. Given the price of large cable I will most likely opt for the active and neutral and earth the inverter through a sub-board mounted with or near the inverter.
The trench will only be about 120mm wide so I would have to put it above the power cable. Would that be acceptable? Pulling a cable through seventy meters of conduit would not be a lot of fun and knowing my luck the cable or the join would break half way through. Cat6 STP is fairly cheap from Ideal so if I end up needing the cable I think I will purchase the STP.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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