DIY Off Grid Islanding

Discussion in 'Electricians' Talk' started by paulca, Mar 26, 2023.

  1. paulca

    paulca New Member

    About time I upgraded to 240VAC by buying an inverter. However, I went one step further and bought a hybrid "charger/inverter".

    Basically, it's an MPPT charge controller, an inverter, a battery charger and a transfer switch in a box you hang on the garage wall.

    However. While my DC system was far from the concern of the electrical standards folks, I expect due to the PEI regulations around islands there may have to be some form of inspection by a professional. Even for MY own peace of mind and that of my insurers.

    The plan is to put everything on a board, on the garage wall, neatly cabled and labelled and treat it almost like it's own little consumer unit. Correct gauge wires, henley blocks for AC, copper if I can afford it for DC.

    The point I believe any inspection will immediately look for is the disconnect from the AC in the event of the grid going down. The inverter in question has a single AC In. That AC In connects to a "latch transfer switch". Such that it can only be engaged when there is power to it. The moment power leaves that AC input the switch pops open.

    However, unlike a "roof top grid tie system" the inverter will continue to provide power on the AC Out.

    That would be the second point of concern. Does that, can that, will that ever, be connected to the grid, even accidentally.

    The answer, I believe is absolutely not. Unless it protects itself really well, that's going to let the magic smoke out of the inverter. It is not phase locked grid tied. The Inverter AC input is input only. It cannot backfeed the grid.

    The problem I might have is in adequate earthing for the panels and the inverter. I believe the house PE should be used in my case. However. The only earth connections I have in the garage are "second hand" PEs in 2.5mm cables. They are only like 1mm earth conductors.

    The inverter should really just behave like an appliance and as it's only rated 5Amp AC and will be breakered accordingly, do I absolutely need to run a 4/6mm earth conductor back to the house panel to earth the solar panels? I know there are issues with adding additional earth rods.

    It has been put to me that if I don't want plug testers to bleep madly I should also bond the inverter neutral to the PE close to the inverter as possible. It may not be in phase, but it's safe to keep it at least in the same potential.

    Any other major "DONTs" to avoid?

    Oh.. the load is just an extension cord in the garage I can run things off of. No fixed wiring, well, maybe a single extension to the office later.
     
  2. Jimbo

    Jimbo Screwfix Select

    You need a G98 or G99 approval from the DNO before commencing.
     
  3. The Happy Builder

    The Happy Builder Screwfix Select

    Three posts on this forum:
    • How to connect the electric supply to a gas hob.
    • How to install a socket in a loft
    • How to install an inverter to run in island mode.
    Are you perhaps over ambitious?
     
    Ind spark likes this.
  4. Bob Rathbone

    Bob Rathbone Screwfix Select

    Islanding is not the issue here, you need no DNO permission to disconnect their supply and connect, say, a generator to power the house, all you have to ensure is that all live conductors are disconnected from the DNO network. However, exporting or running in parallel with the DNO supply does need approvals and certification as Jimb states
     
    WH55 likes this.
  5. paulca

    paulca New Member

    This is what I thought. The ability to export is the main concern for the line workers and PEI islanding.

    If you were to approach this "inverter" from the grid side, what it will see is a battery charger. Nothing more. Nothing else is connected to the grid. A battery charger. In the event my batteries go low, or I ask it specifically, it will engage the mains charger and charge the batteries.

    The only live conductors on it's AC out will be "islanded". In that they (live phase) will not be connected to the grid by any means. (Bar the neutral and PE).

    In the event the mains goes down. My house power goes off. What will remain powered is the extension socket in the garage.

    Note. If you think it would make any such inspecting spark more comfortable, I can wire the inverter into a 13Amp plug socket with a standard british plug and a 5 amp fuse. (although the neutral/pe bond might need something less janky).
     
  6. paulca

    paulca New Member

    No. They are all complete, working and fine. The last bit of 'electrical' work I did was this, fully custom design development PCB for a DIY, custom software based digital signal processor/router and that's just 'the hobby'.
    audio_dev_circ.png

    Look at things the other way, my day job is Software Engineering and I see all manor of hobbyist's with the right idea, but making some rather grave mistakes that I know will cost them later. Granted, usually, not always, but usually there is no threat of life or fire in software. However, electronics + software + DC currents can lead to fire and I have stopped people putting code into service controlling high current DC LED lighting by explaining to them what happens if their software goes to 100% brightness on all 400 LEDs at the same time (like when it crashes). In that specific example the user was trying to control a 5 meter string of addressable 5V LEDs with a microcontroller connected to a 30A 5V power supply, he was intending on installing these light strips into foam cornices. "But they won't be on full white, the code doesn't do that.", is what I cut him off on. Two truths: "If it can happen it will happen", "Software fails."

    It's the later for which I am here. To hopefully tease out those school boy errors before I make them.
     
  7. paulca

    paulca New Member

    Anyway. Back on point.

    99% of the average joe would not even come here and ask before installing such an inverter in their garage. The only reason I am here is because I understand there ARE real concerns with islanding. Or rather, it's not that they are islanded, it's proving they remain islanded in the event of a grid failure. The REAL end game there is not killing an engineering working on the grid with your inverter. In my case the particular appliance does not even support that functionality. Thus my question is more about the regulations and if they apply, how much they apply and if building control will file a claim against me to correct it ... How likely is that? Does such an install actually formally need a sign off?

    What if I just connect the inverter to a normal 13Amp plug socket. Then it's just a consumer appliance and consumer side.
     
  8. MGW

    MGW Screwfix Select

    I seem to remember seeing when my son had a narrow boat a special inverter designed for narrow boats so they could both use it when cruising, and when connected to shore power, so they could connect to a 6 amp supply and use 13 amp with the inverter making up the difference.

    It was some time ago, he sold the narrow boat when my grandson was born, so over 10 years ago, but I would suggest you join a narrow boat forum and ask your questions there, as they have over the years worked out some very crafty solutions.
     
  9. paulca

    paulca New Member

    Interesting that you say that. I got a call and the inverter I wanted is out-of-stock, seems there is a bit of a run on them with the cost of electric nearly tripling here.

    I was ordering an EPEver unit which contained everything needed in one box. Not that I need the MPPT charge controller, but still. The Victron unit however, while of higher quality and a higher standard of certification, does come with some corporate greed. It's hard to put together a solution with their material that doesn't involve you buying £1000 worth of gadgets on top of the £800 for the inverter... just to configure it how you would like.

    Tying this back to your point about narrow boats. "Out of the box" the Victron Multiplus will operate exactly as per a narrow boat or caravan. Physically unplug it (or wall switch it) and it runs as a battery inverter for a "house boat". Connect it back to the AC "shore power" and it charges the batteries and runs the loads.

    This lacks the auto-transfer nature of the previous EPEver unit, which by default supported "favour solar" mode. The Victron unit can also be more tightly configured, it's just working out what extra garbage you need to be able to configure that. Raspberry PI and an RS485 converter is cheap and an evenings work. A Vitron GX-Color controller is £500!

    Honestly though. RV mode (as I call it), will work. It will mean that I simply have a 13Amp plug to power the inverter if and when I need. That can be supplied by a 10Amp smart switch, limited to 3A as I don't trust them, and switched based on my own battery/solar monitoring software.

    The only "Anti Islanding" concerns there would be in the event the inverter was faulty and allowing inverted AC to leak onto the grid, enough to keep the smart plug relay energized. There are a lot of things to go wrong for that to happen. Again, though a simple DIN rail latch switch should fix that.

    Do RV and narrow boat electrical installations require PEI/Anti-islanding/DNO/G98/G99 inspections or sign off?
     
  10. Jimbo

    Jimbo Screwfix Select

    You cannot use the DNOs earth for island mode either. This is in scope for G98/99, depending on its output. I would suggest getting yourself a copy of the IETs “Code of Practice Electrical Energy Storage Systems” at it explains everything and with your background I think you will also find it an interesting read.

    Have a look at Solis inverters. They do exactly what you want and you can use the emergency output as a feed to a separate consumer unit for battery backup protected circuits.

    If you are choosing a unit designed to power a single outlet, that must not be used to power multiple appliances as it works on the basis of being isolated - there is no earth.
     
  11. FlyByNight

    FlyByNight Screwfix Select

    I have a Solis installed and am considering putting the "emergency" output through a CU - just as you mention. That will power just one ring final in the house - security cameras, alarm, fibre modem, network equipment and access points. Just need to look at various aspects though.
     
  12. paulca

    paulca New Member

    It's £70. No thanks.

    I did take a read through this:
    https://assets.publishing.service.g...1/domestic-battery-energy-storage-systems.pdf

    Definitely written by a sales, sorry consultancy company that sells, sorry again has experience in the industry.

    On earthing. Nice catch. Did some googling, I believe the grid connectivity part of G98/99 basically states that any conductor is considered including earths and neutrals.

    I have the older style (1960s vintage) with the lead pipe clamp earth fed from a lug on the side of the presentation unit to an earth block. At least it was it was until last year the old brown Bakelite unit, was replaced with a plastic box where all 3 go in. N, E, L. It is likely, I understand that inside that box the E and N will be bonded to the lead outer conductor of the wax/tar wrapped cable. Regardless, the earth comes out that box, then it's the DNOs earth as is everything that connects to that earthing tail.

    Avoiding exporting any direct (or indirect) earth or neutral conductors will require I provide the inverter with my own earth/ground reference.

    TT? That's not ideal for various reasons. Not least the other regulations about NOT having TT with outbuildings, if not needed due to those various reasons.

    Noteably in my case. I want to ensure that if I, say, plug a PC running off the solar inverter into a USB port of a device running off grid mains, that they at least share ground potential. Very little equipment will or "can" do much about ground currents finding it attractive as a route if potential exists. Electronics bench oscilloscopes are notorious for letting people find that out the hard way. I don't want any and all earth referenced equipment to become a similar liability.

    There are dark side options of course. For example. I can bend the rules around "indirect earthing" if I, say, used the underground copper heating pipe that goes to the garage as an Earth. Technically it's a copper pipe that goes at least 1 meter underground before it comes up in the house, before it may then get bonded to the DNO's PE.
     
  13. Jimbo

    Jimbo Screwfix Select

    Probably want to add some lights to that :)

    I’d suggest getting a consumer unit that has a transfer switch available (like Hager) since you will want the ability to switch “out” the inverter to have those circuits powered directly from the grid in case the inverter itself fails.

    Other that that, add an earth rod to the installation and connect at the MET and you’re good to go - the earth-neutral bond is made automatically when it switches over.
     
  14. paulca

    paulca New Member

    Going down one rabbit hole. Tell me if this is none-sense.

    Taking the bench oscilloscope as a prime example. The issue occurs if you, for example want to "scope the mains". You can connect the probe to the live no problem, but when you connect the scope ground to the neutral, not least do you create an NE fault that your trip should catch, but the scope now sinks any current required due to the potential between E and N. Night night scope. Burnt out ground track if you are lucky, blown frontend if not.

    Why does that occur? In my experience it is due to the NE potential. Even if bonded 10 meters of cable away at the presentation point, the N has current flowing on it, the E doesn't (shouldnt). Therefore there will be V=IR voltage drop (in calculus if you want RMS) on the N that is not present on the E. Therefore there will be V volts potential between them. I am not going to draw out the schematic of that and do the Kirchhoff's on it, but I'd figure if it took 3 or 5 amps to drop the 2.1V potential, it will take the scope 3 or 5 amps of current to pull it down.

    It is this scenario which would worry me about going TT between "power extensions". Yet it would not be N-E potential and NE faults, but E-E or (TT) flow faults. Not least that will drip both the RCBO and the inverter should any ground current transfer between the two.

    How likely is that scenario?
     
  15. The Happy Builder

    The Happy Builder Screwfix Select

    Say hello to Alice for me ;)
     
  16. Jimbo

    Jimbo Screwfix Select

    This is why you need to buy the book or better yet enlist the services of an electrician that knows about Electrical Energy Storage Systems (EESS) and G98.
     
  17. techie

    techie Screwfix Select

  18. paulca

    paulca New Member

    I have tried this. I got two answers.

    "We don't touch it."
    "We only do full roof grid-tie installs. Buy and install. We wont install your equipment and we are booked for the next year on installs and won't be willing to carry out any such work for you."

    FWIW:
    Here is the note pad scrawl.
    solar_island.png
     
  19. Jimbo

    Jimbo Screwfix Select

    Bear in mind that the consumer unit MCBs will do basically nothing because your potential short circuit current is going to be so limited in Island mode. However, you need 30mA RCD protection on that side if not built in to the inverter.

    The TT earth rod should be connected at the MET (not a separate system).

    The inverter must be hard wired to the installation via an MCB also (not via a 13A plug!)

    There is a definite gap in the market for solar and EESS sparks outside of solar installers.
     
    Last edited: Mar 27, 2023
  20. paulca

    paulca New Member

    MET - The main earthing terminal block at the meter "utility entry point"? Is that not the grid earth I'm meant to avoid?

    The main earth is the lead cable going out the floor.

    I have a "tame" spark who does stuff for me. He won't "sign off" on any DC stuff. It took a bit to convince him to install a 6mm DC cable between the garage and the office. He said it was a "parts and labour" job, no sign off at all. I can and usually do run my stuff via him, if and when I have some actual work for him. I'm not going to phone for advice only.

    Oh, oh, ah. Sorry, figured it out, if some installs have an earth conductor and neutral coming from the utiltiy transformer and are not terminated to ground local to the property, that would obviously constitute a risk for line workers.

    Does it matter that my local earth it local?

    EDIT: I might actually pay said spark to do the inverter install. Mostly so he can at least do all the heavy work mounting it on the wall and tidy-cabling it :)
     

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