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Andrew avatar image
Andrew asked

UK regulations ESS vs Offgrid

I am looking to change my LUX ACS 3600/5kw growatt to victron but so far have been told two different things. I have a G98 allowing 5.8kw. I have28kw of pylontechs and wanted to be offgrid as much as I could but charge from it when needed. Have 6kw panels.

I want to divert excess electricity to heating/water (maybe ASHP) but am told it is not permitted to be offgrid in my scenario unless i use a genertor, as the electric can go both ways to and from the grid even though i dont want to sell the energy. Already 2/3 of my PV is going to the grid, partly due to the inflexible Lux which does not allow me to charge discharge batteries when needed - only at specific times which cannot overlap.

I dont understand other than perhaps utilities do not want self sufficiency, why this is, can anyone explain?

Also a quote for an "offgrid system" with a dual switch over consumer unit with 10k MultiPlus 48/10000/70-50 230V Battery Charger Inverter, rs450/100 mppt, with fitting and cabling, most of which is there as are battery disconnects.

Does £7,5k fitted sound a little high to replace the inverter and charge controller?

ESSoffgrid
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8 Answers
andy156 avatar image
andy156 answered ·

You can be connected to the grid and the grid will just supplement when the batteries are empty and there is no solar. This is assuming you have an inverter big enough to supply the load. I have a quattro 10000 + pylon tech stack connected to the grid and apart from the small trickle through inaccuracies I haven't used power from the grid since the 12th of May and very little in the month before that.

Who said you can't be off grid. It's a bit of vague terminology. You won't be off grid. You will just be importing close to zero in the summer months and of course still paying the standing charge for the privilege of being connected. I have a change over switch but this is in case the grid fails I can then bypass the quattro. The rest of the time I stay connected and the ESS doesn't use the grid unless it is necessary.

Truly Off grid is having the wire cut off. In which case you need a generator for the winter months.


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Andrew avatar image Andrew commented ·
thanks Andy


it seems there are so few installers who know what is possible, most want to do a grid tied system. I have managed to find just 3 installers for victron in 80mile radius and to replace inverter, charge controller to the above system is 7.5k which seems high or am I wrong?


Yes i know truly offgrid = generator and cut from the grid, but my confusion is why if charging a unit is there some problem with electricity going back, causing problems to the grid if am just charging, as i thought offgrid victron dissipates the unused PV?

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andy156 avatar image andy156 Andrew commented ·

There is no problem with electricity going back if it is under your agreed limit. If your batteries can take all the solar there will be nothing going back to the grid until they are full. Then the victron is no different to any other grid tied inverter if you have feed in enabled. At any point there is electricity going to the grid it is using the same process as any other inverter. I suspect some installer was trying to put you off going down the route of a system they didn't understand.


You would probably need to still do a G98/99/100 application depending on if the new system is capable of exporting more than you have already agreed. But this is to ensure the system is capable of limiting the export.


I think a lot of installers no nothing more than their preferred unit they have trained on. They don't understand what is possible and don't often keep up with the latest possibilities. e.g. g100 when it came in.

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ejrossouw avatar image ejrossouw commented ·

You can actually have the system "off grid" (no feedin allowed setting and no ESS ) and only connect AC as required based on AC ignore conditions. The system will then call on the grid (close the relay) when e.g. an "overload" condition occurs, but the inverter will stop when the AC relay is closed. In essence the grid will very much be used the same way a generator will be.

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h2009 avatar image
h2009 answered ·

I think you have the issues of installers not understanding the system. I don’t have DNO, I don’t export (or try not too). I have 80kw battery system and 6.8kw solar system, soon to be doubled.

My advice is speak with your supplier of equipment get them to advise on someone to do the change for you. If you need someone in the UK, let me know and I can point you in the right direction for supplier and installer



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ejrossouw avatar image ejrossouw commented ·
If you connect any power generating equipment in parallel to the grid regardless of whether exporting or not, you have a legal obligation to obtain G98/G99 etc from your DNO. With ESS your inverter is syncing and "interacting" with the grid.
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gazza avatar image
gazza answered ·

Correct me if I am wrong, however, I don't think the MultiPlus 48/10000 is ENA compliant yet for grid connection. The equivalent Quattro is however..!

Also, if you already have a G98 agreement then, as far as I know, you can connect an inverter capable of up to 3.68kW generation to the grid(not sure where your 5.8kW came from?). You may, or may not, have an additional restriction of how much export is allowed depending on your DNO.

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andy156 avatar image andy156 commented ·
wow, still not. I haven't followed that saga since my quattro gained its certificate. That was a nerve wracking 3-4 months for me.
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Andrew avatar image Andrew commented ·
Gazza, I might have read it wrong but was told as house east west facing I could have more panels and larger inverter. There is 8 x 2 strings of 370w, growatt 5kw and 3600 Lux acs. 4Kw is common but does not fully charge the 3 x 5000 and 3 x 3000c Pylontech batteries.
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Andrew avatar image
Andrew answered ·

@h2009 Yes please - any victron installers would be a great help as having a nightmare finding someone other than grid tied.

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daza avatar image
daza answered ·

@Andrew you will need G99 to connect any equiment like this to the grid regardless of not exporting! Anything AC over 3.68kW the DNO requires permission for. So that is what every your AC PV is kW plus the inverter say the most common used one the 48/5000 which is 4.4kW.

Lots of people are going MPPT route if you have a stringent DNO. The DNO application isn’t hard to do so don’t let that hinder you a lot of people here have done there own applications.

I’m not an installer but I’m installing mine I’ve done the Victron courses online and have background in electronics and electrical installation I couldn’t find an installer so designed with the help of this forum and seen as I’m building it I can take my time to get it right and have it how I want it.

I’ll be doing a switch on today to start programming the Multiplus2 and then final commission when I get the batteries. If you have the knowledge it’s easy enough just get a spark to go over it if need be, as I have two family members that are sparks but getting people that know Victron good luck!

my install so far just waiting on two temp sensors before tidying up the wires by the Cerbo GX. If your doing it just remember it can take up a lot of space.

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dansonamission avatar image dansonamission commented ·
We use victron in the marine market with no grid code set and they’re connected to shore power a lot of the time. At this point its affectively a battery charger connected to the grid and not a grid tied inverter. Are there different regs for connecting a yacht to the grid as you could quite easily set this up the same in a house.
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seb71 avatar image seb71 commented ·

Do not use terminators in VE.Bus in Cerbo GX (from the photo it looks like you have something in the unused VE.Bus port; but maybe it's just an empty RJ45 plug acting as a dust cap).

Use terminators only for VE.Can and BMS.Can in Cerbo GX.

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daza avatar image daza seb71 commented ·
Yes it is just an empty RJ45 as a dust cap good eyes though thanks
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Robert Boerescu avatar image Robert Boerescu commented ·
It looks like you are using an old ipad as a screen, do you use a browser and open the remote console screen to get that vew or is there an app for it? Thanks.
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daza avatar image daza Robert Boerescu commented ·
Lol no app for me this is a second gen ipad that hasn’t had updates for years, I couldn’t en even get into the VRM portal with this as it’s too old but on the local network remote console and then use the zoom function to make the screen size what it needs to be for a big screen like that just wish I had dark mode on the screen it would have looked soo good
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Andrew avatar image
Andrew answered ·

thanks Daza, that looks really neat am impressed, is that a secondary consumer unit? I suspect the money for installers is with the grid ties.

Thanks for the G99 advice. did you need justification for the DNO? The setup looks like what I was quoted 7.5k for the other week.

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daza avatar image daza commented ·

Hi mate thanks, yes it’s a duplex Hager board which is in addition to the houses 22way that ive now fully populated that big cable at the bottom is my mains routed to the garage and then retuned through the inverter back into the duplex CU back to the house complicated I know but I knew there wasn’t enough room under the stairs to house it.


Yes I had to apply for G99 and a fuse upgrade as I was looking for pos EV charging in future. As soon as the DNO replaced my fuse they granted me G99 with no restrictions. The cabling is expensive the extras that you don’t think about.

i would say look at the system design to kind of visualise what you need and where you need it this is mine others have it on the forum @sharpener is a good resource and was tremendously helpful with my design.

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Andrew avatar image Andrew daza commented ·
@Daza thanks, my solar knowledge and electrics is improving but I certainly realise my limitations, other than Victron installers, which are as common as rocking horse s**t, i am hitting a dead end.
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daza avatar image daza Andrew commented ·

@Andrew the other installers are all about profit margins and ease of install as most are all in one systems that don’t offer the flexibility like Victron. I would say find yourself a good spark. Maybe get trunking like me so it’s all layed out.


If you can look to see where you can do an earth pit it took me about 4hours to go 4.5meters deep I did want to go deeper and I knew there was nothing else below and when the mushy stuff started to come up and I couldn’t go down further as I hit a rock that would not budge. Why so deep you may ask couple of reasons I live in clay soil that likes to crack shrink and in summer you don’t want the lower part of the earth losing its connection to ground or increasing the resistance so much that it stops RCD’s RCBO’s from doing there job.

There are rules to doing earth stakes ie not around pipes or wires as that will mess it up. What I’m trying to say the more you can do the more you know the quote price should go down. FYI no spark is going to spend over 4hours doing and earth rod but my job my spare time I’ve got.

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sean avatar image sean daza commented ·
To be fair to most sparks they would likely have an earth rod driver for their SDS drill that'll drive a rod in within a couple of minutes.
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daza avatar image daza sean commented ·

@Sean you mean one of these still took over 4hours I reached 4.5meters and could go down anymore even with one of the big titan drills had to angle grind it off in the end that’s why the end isn’t threaded

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Andrew avatar image Andrew daza commented ·
4.5m deep for the earth? does that apply to offgrid Easysolar GX 2 48 3kw? I have an earth rod which is about 4ft? For the main house system currently the grid system is wired to a busbar which runs to house plumbing pipes, that was approved company, so is it different for a future system this que relates to or any?

thanks

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sharpener avatar image sharpener Andrew commented ·

Any battery system that can work in UPS/island mode needs to have an earth that is independent from the incoming supply. Equipotential bonding to pipework is not enough to satisfy the regs, you need a proper earth electrode with (for most domestic purposes) a resistance of 200ohms or less. A 4ft rod may be enough if the ground is reasonably damp earth but rock and clay are another thing altogether.

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daza avatar image daza sharpener commented ·
@Andrew as @sharpener said if you look at the pic you can see water in the pit edge its rained the day before but if you look at the clay around the pit you can see it cracking, Clay is notorious for drying out and cracking.


If it start to crack around the rod your resistance has gone to pot and risk the resistance going higher than the permitted 200ohms which is the point at which your RCD's RCBO's or if your balling AFDD's stop seeing the potential to earth, so the risk of server injury or death increases if you are that ground to earth. In clays case deeper the better i had 6 rods to sink wish i could have got them all down. But happy with the resistance we got 2.15ohms so well within the 200ohms would have liked lower but not possibly although the resistance started to go down further as the clay started to compact again.
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Craig Chamberlain avatar image Craig Chamberlain daza commented ·
Just to add another data point, the subsoil around our house is also heavy clay but remains damp beyond about 450mm deep all year round. So I only needed two rods for a total depth of 2.4m to achieve an earth fault loop impedance of around 20 ohms which is well wthin the regs. My advice is to proceed one rod at a time until you get an acceptable impedance. That said, I would start with two rods because I think a single rod at 1.2m just doesn’t get deep enough to avoid topsoil variability. This is especially worth doing if you don’t have your own loop impedance tester and don’t want to call out an electrician multiple times.

In fact, from my understanding, in an island mode scenario, the supplementary earth rod isn’t there to ensure the RCDs operate. The RCDs inside the house work just fine even without the earth rod because the inverter has a relay which links earth and neutral which effectively forms a TN-S supply to your maintained loads consumer unit. The RCDs in that consumer unit will detect an imbalance in the line & neutral in the normal way. The earth rod is simply there to ensure that no potential difference can build up between the island earth and the general mass of earth.

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Andrew avatar image
Andrew answered ·

i understand that but it is the depth of the earthing that astounds me. Friends who are builders say plumbers on building sites used to put a meter ground rod and whack it into the earth - no surround no depth of 20+ feet

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Craig Chamberlain avatar image Craig Chamberlain commented ·

With the greatest of respect for Daza, I think a 4.5m earth rod is not typical of most installations. I suspect the majority probably only have a single 1.2m rod although in many cases this will NOT be sufficient to meet the 200 ohm impedance in all conditions.

The key thing is to measure it in wet and prolonged dry conditions and add more rods if needed. For me 2.4m gave a perfectly acceptable 20ohms and that is stable regardless of weather. I didn’t measure the impedance after the first rod but I suspect it would also have been well under the 200 ohm value.

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daza avatar image daza commented ·
@Andrew yes indeed a shorter earth may have been adequate, would it have got me the lowest ohms readings no.


The kit to test the reading is expensive and I don’t own one my wife’s cousins had to come and move the mains from the house to the garage so rewire the incoming and new isolation box in the house and the big double stack in the garage they started at 9 and didn‘t finish till 2300 if the earth wasn’t done prior it would have been a two day affair even at family rates still not cheap.


Did I want to risk having to worry about the earth resistance no if it was high with that distance then I would have had to make my own PME which creates it’s own issue as now you have to make sure every earth point is affective at different points of the year. YOU CAN NEVER OVER ENGINEER TODAYS PASS IS A TOMORROWS FAIL. I’m over emphasising but Regs and standards change all the time.
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Craig Chamberlain avatar image Craig Chamberlain daza commented ·
I bought a Megger MFT 1552 back in 2020 for £370 and it has been a good investment as I was able to perform a safety check on my newly purchased house wiring and resolve a bunch of issues, as well as testing things like earth impedance for my earth rod. Not meant as a replacement for a qualified electrician or EICR but a useful addition all the same.

I think the main thing to remember is that, as far as I'm aware, in island mode the purpose of the supplementary earth is not to try to replace the < 0.35ohm TN-C-S earth or the < 0.8ohm TN-S earth. It's to provide an earth reference to bleed away any build up in potential difference between the "island" and the "mainland" so to speak.

In a line to earth house equipment fault scenario, the impedance to earth is basically the same as to neutral since they are connected together by a relay inside the inverter. So the PFC will be very high and will trip overcurrent protection well within the required time to protect wiring.

In the scenario where someone touches a live wire and is either in contact with an earthed part such as an appliance, or otherwise has a sufficiently low impedance to ground, then they will activate the RCD protection which should be in place on all circuits. I can't think of any scenario where having a 2ohm, or 20ohm supplementary earth would make a significant difference compared to a 200ohm impedance. I'd love to hear from any electricians out there who disagree with that statement though. Always keen to learn! :)

I'd also love to see someone like John Ward do a deep dive on this topic to understand it more fully, but my understanding is that there is little benefit, if any, beyond obtaining a stable < 200ohm supplementary earth rod. More important is probably that you install it safely in a proper enclosure and choose the location carefully to avoid coming too close to other underground services etc. That said, if I wanted to go for a super-low impedance earth then I'd probably go with a lattice copper earth mat rather than numerous rods.

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daza avatar image
daza answered ·

@Craig Chamberlain with TT earth the lower the better you are trying to get your resistance between your property and the transformer star point low inorder for your RCD’s RCBO’s AFDD’s to function properly as myself and you have talked about before the lattice Matt requires a bigger area, dig depth and and also the cost but John Ward has https://youtube.com/watch?v=b0nLTiNwbLM&feature=share8 as it’s between him and efixx you been looking at the same videos too lol there isn’t a lot that really go Into depth with this area I might have to send Cory a message and see if he can do a video on it.

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Craig Chamberlain avatar image Craig Chamberlain commented ·

Yeah but remember, this isn't a TT earth, it's an island mode supplementary earth and in island mode the "star point" of the transformer is now inside your house and is already on a super-low impedance path. That to me is the key difference.

I do indeed watch John Ward, efixx, Cory as well as CJR Electrical, David Savery and a few others. Less so these days now that my install is done but during my learning curve period I was watching every video I could find! :)

Cheers.

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daza avatar image daza Craig Chamberlain commented ·

@Craig Chamberlain very true when in island mode but my whole install is a TT earth the DNO earth is not used in my install, as below I don’t use the grid earth for my install no metal pipe work enertering the property mine is a true TT earth, the DNO kindly labeled it when they installed the 100amp fuse, Lol David Savery is hilarious! img-3917.jpeg

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Craig Chamberlain avatar image Craig Chamberlain daza commented ·

Fair enough, but I don't think that changes the situation when in island mode where it probably becomes TN-S. Anyway, I'm not well versed in TT earthing so I'll defer to those more knowledgable than I. :)

Yeah, David S is entertaining for sure, but clearly know his stuff. Maybe you should ask him what difference a 4.5m earth rod makes compared to a 2.4m rod. I suspect the answer might be, "2.1 f***king metres!"

Joking aside, I think this conversation illustrates how we each focus on different things. For some of us it will be aesthetics, for others it will be efficiency and for others again it will be safety.

I've got 35mm2 DC cables between my 250/60 MPPTs and Lynx Distributor which are carrying 60A max when they are rated to four times that current. Why? Because I mistook the maximum size for the recommended size. 16mm2 would have been more than adequate in my case, and easier to terminate.

My 70mm2 inverter cables are also capable of 485A even though the will never see more than 200A. I think us DIY'ers have the luxury of over-engineering that commercial electricians just can't afford.

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