Consumer units for solar ...

Assuming I have a 16th edition main consumer unit (actually a split board with an RCD and a few non-RCD circuits for things like the alarm system, smoke alarms and freezer, but I digress) ... and I want to move forward to a hybrid solar inverter, infeed only, so it will be some form of hybrid inverter.

I have an incoming isolator, with SPD that feeds the existing board. The plan was to have a small board installed to 18th edition, so metal clad, grommet etc and maybe 4 ways and a doup0le pole isolator, no RCD ... 2 ways with 40A RCBOs feeding the existign electric showers, one way with an MCB feeding power to the hybrid inverter and a spare. Does that sound about right so far?

The hybrid inverter would then power the existing consumer unit. I was thinking of asking for a 2 way changeover on the input to the old consumer unit, so it could be switched back to the incoming mains (there are spare ways on the Henley blocks) if the inverter craps itself or runs off screaming. Would there we a requirement to bring the whole consumer unit up to 18th edition at the same time or can it be left as is?

Hybrid but no batteries? Import only?

Shower with no RCDs is a potential death trap.

Sounds like you've read a load of rose fertiliser on t'internet and are now confused. How about telling us exactly what you are trying to achieve, and post a few photos of your cu and incoming spd.

binky said:

Hybrid but no batteries? Import only?

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The whole explanation is a confusing mix

binky said:

Shower with no RCDs is a potential death trap.

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The OP does state 2 x 40A RCBO's for the showers

binky said:

Sounds like you've read a load of rose fertiliser on t'internet and are now confused. How about telling us exactly what you are trying to achieve, and post a few photos of your cu and incoming spd.

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I would agree, I'm not sure what the OP is trying to achieve

I absolutely *will* have significant batteries, at no point did I say no batteries, I'm not sure where you got that impression, I didn't mention batteries as a hybrid inverter with no batteries would be a complete waste of time, I thought it was self evident, but for the sale of completeness, I will have around 16 kW of panels and about 30 kWh of storage (I am wavering between 26 kWh of new LiFePO4 in two banks of 280Ah at 48V ... or 50 kWh of EV battery and the usual emulator software) The panels will be angled for optimum winter insolation, I suspect I will add additional vertically hung bifacial panels in a north/south direction at some point to catch the morning/evenign peaks.

I have no plans/interest in supplying back to the grid, I can use all I produce and then some. The costs of MCS certification would extend the payback period considerably, not worth it for me.

Anyway, I digress ... now we've got that out of the way, and the second respondent has already picked up I specifically mentioned RCBO's for the two shower feeds ... does the rest sound right?

Skipper said:

I absolutely *will* have significant batteries, at no point did I say no batteries, I'm not sure where you got that impression, I didn't mention batteries as a hybrid inverter with no batteries would be a complete waste of time,

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precisely

Skipper said:

I thought it was self evident,

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have you read some of the posts on here

Skipper said:

I will have around 16 kW of panels and about 30 kWh of storage (I am wavering between 26 kWh of new LiFePO4 in two banks of 280Ah at 48V ... or 50 kWh of EV battery and the usual emulator software) The panels will be angled for optimum winter insolation, I suspect I will add additional vertically hung bifacial panels in a north/south direction at some point to catch the morning/evenign peaks.

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OK, you will proabably need multiple inverters as I'm guessing from your description you have single phase supply. you would have a master and slave arrangement, do make sure the inverter can do this, as some cant.

Peak outputs are between 11am and 3pm same as getting sunburnt. You can get some additional morning and evening boost to the system, but outputs tend to be low. My own system will work until 10.30 in summer, but outputting a lowly 30W (OK its not really facing the right way for that, but...) So possibly better off focussing on larger array facing South and topping up batteries

Skipper said:

I have no plans/interest in supplying back to the grid, I can use all I produce and then some. The costs of MCS certification would extend the payback period considerably, not worth it for me.

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You can get export payments without MCS cert these days from the likes of Octopuss. You will need to notify DNO regardless, and your inverter will probably need export limitation, assuming single phase, - that generally needs a data cable from inverter(s) to the mains incoming point by the meter.

Skipper said:

Anyway, I digress ... now we've got that out of the way, and the second respondent has already picked up I specifically mentioned RCBO's for the two shower feeds ... does the rest sound right?

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Skim reading, my bad, but yes, given the additional loading of inverters etc, I think you would be pushing the existing board to its limits. Any particular reason for moving the showers off the old board?

Hum, octopus talk about fit without MCS but the ask for £250 to undertake your application.

Murdoch said:

Hum, octopus talk about fit without MCS but the ask for £250 to undertake your application.

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yep, but it's a lot chepaer than MCS registered contractor.

binky said:

yep, but it's a lot chepaer than MCS registered contractor.

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ah but hw long would i take me to recuperate the £250 ?

Murdoch said:

ah but hw long would i take me to recuperate the £250 ?

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Don't know, depends on the export and price paid for that.

binky said:

precisely

have you read some of the posts on here

OK, you will proabably need multiple inverters as I'm guessing from your description you have single phase supply. you would have a master and slave arrangement, do make sure the inverter can do this, as some cant.

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I'm thinking a single 7.5kW will do it as far as output is concerned, I appreciate I am "over panneled" in summer, but in winter I suspect I won't have enough. I could even drop astring or two in summer of the inverter coudl not cope with the supply side of the solar .. I presumed if there was potentially more solar coming in than the maximum current the inverter could handle, it would simply current limit and let the voltage on the supply side rise, wasting available power, but that'shardly an issue in summer.

binky said:

Peak outputs are between 11am and 3pm same as getting sunburnt. You can get some additional morning and evening boost to the system, but outputs tend to be low. My own system will work until 10.30 in summer, but outputting a lowly 30W (OK its not really facing the right way for that, but...) So possibly better off focussing on larger array facing South and topping up batteries


You can get export payments without MCS cert these days from the likes of Octopuss. You will need to notify DNO regardless, and your inverter will probably need export limitation, assuming single phase, - that generally needs a data cable from inverter(s) to the mains incoming point by the meter.

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I'm sure, but I really have no interest in that, thanks all the same. I am aware of the Octopus non-MCS schemes and I am already an Octopus customer.

binky said:

Skim reading, my bad, but yes, given the additional loading of inverters etc, I think you would be pushing the existing board to its limits. Any particular reason for moving the showers off the old board?

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Moving the two showers ( both 9.5kW loads) from the old board (which will become solar/hybrid powered) to the new board (which will be fed from the incoming mains) reduces the inverter requirements considerably. These are highly intermittent loads, used once a day for 15 minutes and would need a significant investment in inverters to service them ... for a small benefit in terms of supply costs saved. For this reason, I would like to shed these loads from the "old" board as it becomes supplied by the hybrid inverter ... rather than "pushing the old board to its limits" this I think will ease the loading on the old board considerably.

The inverter will obviously be fed off the mains supplied new board.

The question is as I said, the old board being a "split" board with RCD and non-RCD sections ... the lights for example are on the non-RCD side, as the idea of plunging the entire house ito darkeness when one of the kids jams their fingers in a socket ( .. not literally!) did not appeal.Under 18th edition, lights have to be on RCDs now ... I'm just curious if I would have to bring the old 16th edition install up to 18th edition spec when the solar work is done ...

I would say get a local spark in as some of your knowledge and logic don’t add up

Being in a different board will not reduce demand on the battery/ inverter. What the inverter cannot supply will be topped from the grid. It won't damage the inverter trying to supply the showers. If you are feeling keen, install a hot water tank, heated by the silar to supply the showers - payback isn't good though .

16kw in a 7.5 inverter - it will go bang, spend lots of time just not working to self protect. How much leccy are you using a year? A standard 4 kw array, can knock out 25/30 kWh a day in summer, so 16kw is going to be around 100+ kWh even with panels optimised for winter. I'm kind of thinking you are over spending the array, so spending more money than you need to. I will also say, the best RoI is based on putting a hole in your bills rather than effectively going off grid, unless you have something like a swimming pool to dump surplus energy into.

binky said:

Being in a different board will not reduce demand on the battery/ inverter.

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Yes it will, because the shower will be connected to the incoming mains, not the inverter output.

binky said:

What the inverter cannot supply will be topped from the grid. It won't damage the inverter trying to supply the showers. If you are feeling keen, install a hot water tank, heated by the silar to supply the showers - payback isn't good though .

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I may at some point add a ground sourced heat pump, at which point, filling a hot water tank with shower water may be a thing.

binky said:

16kw in a 7.5 inverter - it will go bang, spend lots of time just not working to self protect. How much leccy are you using a year? A standard 4 kw array, can knock out 25/30 kWh a day in summer, so 16kw is going to be around 100+ kWh even with panels optimised for winter. I'm kind of thinking you are over spending the array, so spending more money than you need to. I will also say, the best RoI is based on putting a hole in your bills rather than effectively going off grid, unless you have something like a swimming pool to dump surplus energy into.

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Yes, that's why I said I am prepared to drop off strings in summer, as it is easy to have more solar than you know what to do with in summer, it is the winter you have to work for ... panels are cheap, less than £50 ... and that's when you need the most power. In the UK over a year, the average daily output is (roughly) double the panel rating ... a 16 kW array might return 60 kWh in summer when you don't need it, but you might be lucky to get 5 kWh in winter ... and that's when you would really like more to run heatpumps ... the only saving grace is cloudy days tend to be warmer thanclear days ...

Skipper said:

Yes it will, because the shower will be connected to the incoming mains, not the inverter output.

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the inverters are 'grid connected' ie wired to the mains at your board, they backfeed along this connection, and hence will back feed anything connected to the mains in your property, your boards being linked at the incoming supply, unless you want to isolate different parts of your system from the mains, but then only things connected to the UPS function of the inverter will work, and the UPS output tends to be limited to say 2/3kW not the 7.5Kw of the invetter rating

Skipper said:

Yes, that's why I said I am prepared to drop off strings in summer, as it is easy to have more solar than you know what to do with in summer, it is the winter you have to work for ... panels are cheap, less than £50 ... and that's when you need the most power. In the UK over a year, the average daily output is (roughly) double the panel rating ... a 16 kW array might return 60 kWh in summer when you don't need it, but you might be lucky to get 5 kWh in winter ... and that's when you would really like more to run heatpumps ... the only saving grace is cloudy days tend to be warmer thanclear days ...

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Before any PV panel gets going, the are in a stalled condition, whereby they will be at Voc ie max volts, so you will have to be careful with your string voltages even in winter. The Mppts will also have limits on their inputs. Now personally I wouldn't want to be messing about with the strings, so you could have a single hybrid inverter with your batteries, and a standard solar inverter to save money. The inverters have a 'export limitation' function, so if you aren't using the energy, they will automatically limit power generation without the need to mess about with the strings. Given summers are likely to be warmer but wetter, there's plenty of scope for using energy, like charging your EV, batteries, tumble driers etc etc. And heat pumps can often be used as air con, for when we get a heat wave. I think there's a free version of PVGis to help design your system.

Ah, I think I see the confusion, I will be using *hybrid* inverters NOT grid tied inverters ... let me see if I can paste a typical diagram and annotate it ... this was the SolaX X1 hybrid, which was my probable choice if I go the "high voltage" battery route. So the new board in red will power the showers and the input to the hybrid inverter ... the blue board is the old baord and will be fed from the inverter only.

Hybrid isn't 'off grid' it just means it's possible to use it as a standalone AC battery system with no solar connected or as battery and solar inverter. I see what you are trying to do with the UPS function, just double check it's man enough to run the rest of the house. Unless you suffer regular power cuts, I wouldn't worry about the UPS function, it has potentially nasty earthing issues which are hard to explain - no standards really exist for this, and it's ok as a temporary supply, but as a permanent thing it's debatable. Also when the inverter fails you will lose the house, or have to do some quick rewiring. You could install a changeover switch to mitigate that , and in theory the inverter should be good for 15 years or so. You don't need to use the UPS for the old board, it will get back fed via the meter tails. In short the inverter monitors grid voltage and outputs a voltage roughly 5V higher, so like water at a higher level, it flows first, preventing taking power from the grid connection. Hope that makes sense.

Yes, I am aware of the risks of inverter failure ... I did mention a chnageover switch, I have designed "a few" switch-mode PSUs in the past, up to the 10kW so I do understand the way these things go pop when most inconvenient.

But yes ... having dug through the actual user manual for this one, rather than the shortform blurb, you are right, it can supply energy back out the "input" so it is still grid tied ... lightbulb moment!

Hmm that changes things! Thanks for the heads-up on that, that makes a lot more sense now ... it can do the full 7.5kW on that output and can be set up in an off-grid mode apparently, but it would make a lot more sense to just put the lights and freezer on it. I'll have to investigate the earthing. If it is floating or whether the neutral carries through ... we are T-N-CS here, so the earth obviously needs to be continuous across both sides as it always was ... I guess it is no different to running the lights/fridge off an isolation transformer if the UPS side is floating ... but it would be nice to know if there was not a possibility for a DC offset ... at least the PSSC on that output should be low.

It's beginning to sound like a small board on the UPS side for lights and freezer and smoke alarms might be the ways to go ... I shall go away and research the various inverters, I can see I shall have to actually RTFM very carefully before deciding exactly which one to go for.

With tn-c-s your earth is linked to the neutral supply, so if you lose the grid for some reason, there's a chance you will also lose your earthing. To avoid such possible issues, safestest thing is to convert to TT system using earth rods, but that can also have issues. So as a UPS, I would only want to be powering essential items like fridge and freezer. Inverter manufactures instructions for the UPS function are also rather vague with regards to earthing, so I'm not a fan of using it. If you have a scan through the solar section in here, there's a long discussion about this in one of the threads. Don't ask me which one coz I've forgotten

In theory, even if you lose the entirety of the incoming supply (phase and neutral) it is irrelevant in a T-N-CS system, as everything in the house is still bonded to the same point, this is a the "faraday cage" principle behind equipotential bonding. Remember in a T-N-CS system, a fault can (and sometimes does) result in the neutral being pulled to a voltage well away from local "earth" without danger as the entire house simply fllws the neutral/earth ...

I'd struggle to get anything like a reasonable T-T system working, we are on very sandy soil, ground conductivity values are crap!

but your bonding is connected to the main incoming earth, and that is linked to neutral in the main cutout head, so loss of neutral means voltages can rise on the earth bonding. Soyeas voltages would rise equally, but if you stepped out the house on a rainy day and happend to be touching say a radiator, you could get belted. Unlikely I know, but not so much if you have an EV. If you have steel water or gas pipes that will form an earth rod as such, but that can be unreliable. T-N-CS in theory has multiple earth spikes along the length of the cable back to the nearest transformer, but you can't rely on the fault not being between you and the nearest rod.

True story from a DNO friend of mine. They lost neutral in the centre of Truro shopping centre. First reports were of gas appliances going haywire, so gas called out intially. By the time DNO got there, the gas pipe, when they dug down to find the electrical fault was glowing red hot!