@Thebeeman

[sniper]

@sharpener

the quote just mentions "LUX 3600 Hybrid Inverter", I think perhaps GEN2 GivEnergy 5k is the best option price wise, they seem to have UK presence, I could not spot much about Lux. Victron EasySolar 5k doubles the price compared to Giv hmm.

Yes the system is from scratch, there is no electric cooker but new kitchen plan did have mix of gas and electric.

GivEnergy 5k + 4.8kw panels + 1x Pylon 3.5kwh to start with.

I guess if it was victron non easysolar option, it would be VICTRON MULTIPLUS-II GX 48/5000/70 + cerbo gx + MPPT minium? not sure which victron MPPT in this case.

thanks

[sharpener]

I guess if it was victron non easysolar option, it would be VICTRON MULTIPLUS-II GX 48/5000/70 + cerbo gx + MPPT minium? not sure which victron MPPT in this case.

You don't need the Cerbo, the functionality is already in the -GX multi. MPPT probably the SmartSolar 250/100 subject to voltage rating and string arrangement of the panels. 4.8kW/100A is more than the single Pylontec will take but I guess you don't want to put the scaffolding up a second time.

What do you mean by: "proper UPS capability"? If you mean "whole house backup" then that is very complex and expensive with any inverter brand.

Yes, I mean whole house backup. I disagree however, with a Victron Multi it is neither complex nor expensive, you just connect the meter tails to the "AC In" terminals via an RCD and the entire consumer unit to AC Out 1, job done. Changeover is in 20ms so TV doesn't blink, computers stay up and PV continues to generate.

If there are non-critical loads e.g. washing machine, tumble dryer you can connect those to AC Out 2 but in my case they were not easy to separate out so I didn't. The immersion heater is a special case, mine is controlled by a diverter so runs off the PV anyway, and only if there is a surplus after the batteries are fully charged.

[Stinsy]

The challenge with “whole house backup” is that you need a MUCH bigger inverter.

Even without: an electric shower, an induction hob, an electric range cooker, an EV charging point, etc., 10kW would be a sensible size, if you have any of those you’d need an even bigger inverter. Whereas if you have your lights and a sockets circuit with a few critical but low-power devices (TV, router, laptop/phone chargers, boiler, etc.) on the UPS then a 3.6kW inverter is plenty.

You also have to think about battery size and how much battery is kept in reserve for power outage. In addition, there is a whole can of worms to do with earthing and earth-neutral linkages that needs to be overcome.

It isn’t that it cannot be done, just that whole house backup is much more complex and involved that you can be forgiven for imagining, and for what benefit? We’ve had one outage in 10 years!

[nowty]

And its not just about having a bigger inverter, I have a whole house backup with an 8kW inverter which was enough in most instances in the near past. But now I've got storage heaters, heatpumps, EV chargers, there is just too much for the poor inverter to cope with so I have had to modify some of the system so that if the grid fails and the whole house backup comes on, the really high power circuits like the EV chargers remain off until the grid comes back.

[Stinsy]

And its not just about having a bigger inverter, I have a whole house backup with an 8kW inverter which was enough in most instances in the near past. But now I've got storage heaters, heatpumps, EV chargers, there is just too much for the poor inverter to cope with so I have had to modify some of the system so that if the grid fails and the whole house backup comes on, the really high power circuits like the EV chargers remain off until the grid comes back.

How do you deal with Earthing? Are you on a TT?

[nowty]

And its not just about having a bigger inverter, I have a whole house backup with an 8kW inverter which was enough in most instances in the near past. But now I've got storage heaters, heatpumps, EV chargers, there is just too much for the poor inverter to cope with so I have had to modify some of the system so that if the grid fails and the whole house backup comes on, the really high power circuits like the EV chargers remain off until the grid comes back.

How do you deal with Earthing? Are you on a TT?

I'm TNCS with grid and TT (with local earth rod) offgrid, but arguably its still a type of TN in offgrid mode as the earth connection is very close to the off grid generator. Important thing is that your RCDs still trip on a short to earth fault.

[Stinsy]

And its not just about having a bigger inverter, I have a whole house backup with an 8kW inverter which was enough in most instances in the near past. But now I've got storage heaters, heatpumps, EV chargers, there is just too much for the poor inverter to cope with so I have had to modify some of the system so that if the grid fails and the whole house backup comes on, the really high power circuits like the EV chargers remain off until the grid comes back.

How do you deal with Earthing? Are you on a TT?

I'm TNCS with grid and TT (with local earth rod) offgrid, but arguably its still a type of TN in offgrid mode as the earth connection is very close to the off grid generator. Important thing is that your RCDs still trip on a short to earth fault.

My understanding is that the supplier’s earth is unreliable in the event of an outage. If the combined earth-neutral conductor is broken (on its own or in addition to the line conductor) you’d have no earth in off-grid mode.

A convenient PME spike, or your own earth rod solves this. However up until very recently the regs explicitly forbade your own earth spike in addition to the supplier’s TN earth (it was an “either-or” situation). The latest set of regs are unclear, they seem to REQUIRE your own earth spike in addition the the supplier’s TN earth, Guidance Note 8 will hopefully clarify.

[sharpener]

The challenge with “whole house backup” is that you need a MUCH bigger inverter.

Even without: an electric shower, an induction hob, an electric range cooker, an EV charging point, etc., 10kW would be a sensible size, if you have any of those you’d need an even bigger inverter. Whereas if you have your lights and a sockets circuit with a few critical but low-power devices (TV, router, laptop/phone chargers, boiler, etc.) on the UPS then a 3.6kW inverter is plenty.

You also have to think about battery size and how much battery is kept in reserve for power outage. In addition, there is a whole can of worms to do with earthing and earth-neutral linkages that needs to be overcome.

It isn’t that it cannot be done, just that whole house backup is much more complex and involved that you can be forgiven for imagining, and for what benefit? We’ve had one outage in 10 years!

I still disagree, and believe me I have been into this in a great deal of detail and have read the IET Code of Practice for EESS from cover to cover.

The size of inverter I needed was defined by its 50A passthrough capability, which is enough to supply the whole house including an electric cooker. After that its 4.4kW (9kW peak) UPS/backup capability comes essentially for free, including all the required loss-of-mains detection and automatic neutral-earth bonding relay you refer to.

I looked at segregating the critical load circuits but this would involve rewiring the kitchen, utility room and office as our predecessors had put them all on the one circuit, this would have been very disruptive to do (and expensive if I had it done by a contractor). The existing PV stays generating during an outage so that potentially adds another 3.7kW to the inverter's rating.

The battery is sized to last from sundown until the cheap rate starts at 2300 GMT, then I give it a boost charge as there is a bizarre peak rate period from 0000 to 0100, finally before the cheap rate ends at 0700 I give it another boost to cook breakfast with. My cost-benefit analysis showed it was not worthwhile having a battery that would last all night. I have not set any capacity aside specifically to cover outages as I agree with you they are not frequent enough to warrant it.

Because it makes no sense to discharge one battery to charge up another, as and when I get an EV charger I will switch the garage circuits over to the grid manually (with the big changeover switch that is already installed), meanwhile it stays on the UPS side as there is a pump and water treatment plant that needs to be available 24/7.

I had a TT supply already and it was a simple matter to check that its resistance was less than 200 ohms. For sure the supplier's earth is not to be relied on, so having your own earth electrode is non-optional. Definitive guidance on the earthing requirements is here:

https://electrical.theiet.org/wiring-ma ... e-systems/

[cojmh]

The existing PV stays generating during an outage so that potentially adds another 3.7kW to the inverter's rating.

I am interested in this part of what you said.

My understanding of my own hybrid inverter (which might not be the case with other inverters) is that the grid down inverter limit is set to a maximum of what can be supplied by the battery side of the system and even if the PV is generating the output is still limited to a maximum of what the batteries could supply.

So for example in EPS mode my inverter will supply a maximum of 2.5KW even though the system is able to do 5KW when the grid is up.

So if grid is down and PV is generating the full 5KW from the panels I would still be limited to 2.5KW maximum

If the grid is available then there is no issue as the system will supply up to 5KW from the batteries and the PV combined if it is available.

I thought the logic of this was simply that power from the PV cannot be guaranteed at any given time so it was limited to battery discharge capability in the event that the grid was not there to fall back on to.

I could be totally wrong and am interested to know if I am misunderstanding this as I find the 2.5KW limit a little annoying!

[rogeriko]

If you have a seperate Grid Tied Inverter then the AC output power from that can be added to the off grid inverter output power. An all in one hybrid inverter will not do this.