question

taddy avatar image
taddy asked

Earthing and power feed on this system...?

Intention…

My plan is to have a solar system with pylon Li batteries supplying 6 lower powered circuits in the house - lights and some socket ring circuits - with the grid charging batteries when needed. The grid will also permanently supply my higher-powered circuits such as the shower and electric cooker (the solar system will not be involved here).

Equipment

I have 3x 3.5kW pylon batteries, Multiplus II 5kw, 9 x 455W panels in 3 paralleled strings of 3 panels, 250/100 smart soar MPPT , lynx distributer and cerbo gx.

I have attached my wiring diagWiring plus poss consumer unit layout 2.pdfram for the solar system (p1) and for the consumer unit (p2). I need to get an electrician to check and wire this but just have a few questions for you guys if you can help…

Questions…

1.Is the grounding/earthing safe and correct?

2.With this set up is there any way in which I might be putting power back into the grid or is it just one way? If I am not putting anything into the grid do I still need to fill out the G98/99 applications?

3.How long could my cable runs be consumer unit to the inverter charger? I am still unsure as to whether to have the solar gear in the garage or a different room in the house or even in the loft…

Apologies if some of these questions are very basic!

wiring
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2 Answers
sharpener avatar image
sharpener answered ·

1. You don't seem to have an independent earth connection to the cases of the Pylontechs, otherwise it seems OK to me. It is allowable to connect your earth electrode to the incoming PME earth as you have done but there are also some advantages to converting your system to TT earthing and not using it (the PME earth). Too complex to discuss here, maybe Wiring Unlimited has further guidance, it is certainly worth reading anyway.

2. Yes, as discussed in your earlier thread https://community.victronenergy.com/questions/156610/ac-on-the-inverter-charger-post-rcd.html, with this setup the Multi can export (and at more than the 16A limit), even if you don't intend to, so because of this you will need to make an application to the DNO, who may impose restrictions e.g. 3.68kW max export and 3.68kW max inverter power.

3. Any reasonable length, you need to size the cable for voltage drop and check that the various impedance limits for fault protection are not exceeded. If you regard it as a power device then 5% voltage drop is permissible but IMHO it would be better to size the cables for 3% or less, in line with the limits for PV panel cables and lighting circuits and remembering that the voltage drop % is also a % efficiency loss.

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taddy avatar image taddy commented ·
Thanks again Sharpener. WRT q2 can you explain the path by which the multi feeds power back into the grid as atm I can't quite see it. Is it via the AC IN on the multi?
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ponzoa avatar image ponzoa taddy commented ·
Correct, via ACIn.
1 Like 1 ·
ponzoa avatar image
ponzoa answered ·

Don't forget you also need to earth the AC in and AC Out connections in the inverter, apart from the batteries as previously mentioned. You won't be able to double your cables from the batteries to the Lynx but 3 US3000C on a single cable set is fine and you won't have issues. If you do want to double your cables, you'll have to run the batteries individually to the Lynx or get a fourth battery and run the batteries in pairs to the Lynx. You'll need an extra Lynx distributor for that as they have 4 fused connects per Lynx Distributor.


Note: Unless you install can ET112 meter at the feed in from the grid, your shower, cooker and sock16/20 won't be powered by your solar and baterías. If you do install that meter, you can use your solar and batteries for the entire load although you'll only protect the other half of your switchboard in case of a power outage.

The ET112 is connected to the Cerbo GX USB connecter.

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sharpener avatar image sharpener commented ·
I think the OP's intention is not to power the high current loads from the batteries. But if the Multi is configured in ESS to allow export from the DC side the solar PV will nonetheless help with these loads even without the ET112 (except as you say in a power cut).


If limited to 3.7kW this should prove acceptable to the DNO and is only slightly less than the 4kW continuous rating of the Multi anyway.


BTW @Taddy I have got a full-size cooker behind my Multi 5k and it hasn't ever tripped the 50A breaker - but I wouldn't like to have an electric shower as well. So you might get away with having the cooker on the AC-Out side, then you could cook (at least up to 4.4kW total) in a power cut.


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taddy avatar image taddy sharpener commented ·
That is great news. I'll prob shift the cooker over to the solar supplied side then. I was thinking about getting a lower-powered and more efficient cooker anyway.


So from what you guys are saying, if the batteries are full and the inverter is satisfying any load demands on the AC OUT, if there is still any excess power coming in off the PVs then that will be fed into the grid via the ACIN cabling (and this is ESS mode)....? Presumably if it doesn do that then the excess would have to dissipate as heat and that is not healthy for anything.
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ponzoa avatar image ponzoa taddy commented ·
Any excess solar would go to the grid. If there is no grid, the MPPT will ramp down its power.


If you want to use solar and batteries for the cooker side of the installation while the grid is up, get a meter. Note that, in case of a power cut with your configuration, the cooker side will NOT be powered. An easier config is to put the cooker on ACout2 which will cut off in case of a power failure, here no meter will be required but you'd need to run extra cables to the switch board.

1 Like 1 ·
sharpener avatar image sharpener taddy commented ·

Using just the internal current sensor in the Multi then the priority order for solar PV will be as you correctly say

  • Loads on the AC-Out
  • Battery
  • Loads on AC-In (Cooker/shower) - the Multi thinks it is exporting to the grid but the company meter just sees a smaller demand
  • Grid

OTOH if you fit an external current sensor on the meter tails (CT clamp wired to the Multi) the order will be

  • Loads on AC-Out
  • Loads on AC-In (Cooker/shower) - the Multi now knows they are your loads and they will show up correctly on the dashboard
  • Battery
  • Grid

An ET112 wired to the GX device is an alternative but there will be a slower response and more overshoot, because there is now more software in the control loop. I can't see any particular advantage in using AC-Out 2 either especially if the inverter is in a distant location.

I have spent some time looking for lower-powered cooking options for when there are just the two of us, particularly as many evening meals use the top oven which takes 2kW.

The smallest useful size of oven which would take two escalopes or ready meals or two pizza halves (e.g. https://www.amazon.co.uk/Tefal-OF445840-Capacity-Rotisserie-Stainless/dp/B077PSKF8F/) still consumes 1380W and would cost over £70, I estimated the payback time as 480 meals! Better to make sure you turn the oven off and rely on its residual heat while you boil the veg etc etc.

Do post here if you have found a better compromise in a small counter-top type cooker!

Also for small hotel-type 1 litre kettles, they are cheap in boxes of 8 to the trade but I haven't found one that doesn't have a steep delivery charge as a one-off.


-1 Like -1 ·
taddy avatar image taddy sharpener commented ·
Thanks so much for all that info. It's good to know that if it had excess power the multi might actually be assisting with the 'upstream' cooker/shower load and saving a bit of money. I didn't realise that was how it worked. I'll let you know if I find anything better cooker-wise. At the mo I'm still waiting for the Pylon batteries as they keep getting delayed and delayed. Seems there is a national shortage atm.
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sharpener avatar image sharpener taddy commented ·
Yes, the concept of power being able to flow out of the "In" is confusing. A further complication is where to connect the PV if like ours it is on the AC side, it can go on either the In or the Out with differing ramifications. We have it so its power flows in to the "Out" (!) so it will work in a power cut.


I too need an extra Pylontech module and I have been quoted December at the earliest. Best of luck with your system.

1 Like 1 ·
taddy avatar image taddy sharpener commented ·

They told me October 10th (BimbleSolar) but every time we approach a given date they put it back. I can't seem to find them anywhere else in the UK either. I've been considering shipping them in from Holland or elsewhere in Europe but I'm not sure if that's going to incur some kind of VAT/duties fee on arrival.

When you said "further complication is where to connect the PV if like ours it is on the AC side, it can go on either the In or the Out ..." - do you mean PV as in Photovoltaic cells? You connect them to the AC terminals on your system???


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taddy avatar image taddy commented ·
Thanks for the answer. It's strange because the company that supplied me this kit checked my diagram which originally only had one positive and one negative cable from the batteries to the lynx and they said I needed to double up (apparently two cable-battery sets are in the kit for this purpose but I haven't received these or the batteries yet). The mutliplus documentation seems to recommend 70mm2 for the 48/5000/70 which is even bigger than 2x25mm2 pylon cables! Is it that 2 lugs wouldn't fit on the lynx terminals?

Also I thought that with the multiplus I thought the chassis ground is continuous with the ACIN and ACOUT ground so wouldn't earth cables on ACIN and OUT just be going to the same place anyway? Sorry, if my questions are very basic!


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sharpener avatar image sharpener taddy commented ·
Yes, one earth cable is sufficient.


Can't help much with the battery cables as my Pylon Force L2 has only a single cable from the BMS for up to 4 x 3.55kWh modules (I have two). This cable is rated at 100A (AFAIR this is limited by the temperature rating of the plug-in connectors). The cable gets slightly warm to the touch with 74A so I would guess it's good for 100A which is the max o/p from your MPPT anyway.


There are 2 x 2kW inverters between my panels and the AC-Out if that is what you were querying. So they work in a power cut, the neat bit is if they are generating too much for the Multi to cope with it shuts them down by raising the system frequency slightly, then it runs off battery for 5 mins and tries again.

Have at last found the notes I was looking for about ovens:

The smallest I have been able to find that claims to take a 10in pizza is this, https://www.amazon.co.uk/dp/B09HKBKL4P 1400 W (presumably 700W grill only), there is a slightly larger one in black also 1400W which one reviewer says is what you actually need for a 10in pizza. Air frying capability as well would be good to have but they are bigger and use even more power. So no good answer.

The smallest overall is this https://www.amazon.co.uk/dp/B09J4G35X9, only 650W, it will do fish and chips or one ready meal or maybe two slices of pizza. The reviews are a bit mixed (though better than the equivalent Netta or Belaco product) so might be worth a punt at £40! That would buy 120kWh at peak rate even at present prices, so saving say 500W x 1/2 hour will pay for itself in 480 meals(!)
1 Like 1 ·
ponzoa avatar image ponzoa taddy commented ·
For up to 3 batteries, the supplied cables by Pylontech are fine. If you get more batteries, you'll have to run more of these cables to your lynx distributor where you fuse your battery runs. From the Lynx to the Multi you can use the larger cables so you have room to grow your battery bank. Your MPPT should also go to your Lynx. If you need more than 4 connections to your Lynx, you can add another one so make sure that when you install the lynx distributor, you leave room to add another one.


Good luck.

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