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Whoa enthusiasts.

Keep in mind 3 phase is NOT standard for UK domestic so you will encounter some additional costs even once you have DNO bit done (metering, wiring, switchgear etc) If it's just an ordinary urban house and a large rural property/mansion, I seriously doubt there is any real justification.
What additional costs are there? I didn't look that far into it, but i'm curious of the implications.
 

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What additional costs are there? I didn't look that far into it, but i'm curious of the implications.
Instead of one consumer unit for the peak supply and one consumer unit for the off-peak supply, I now have a 3-phase distribution board feeding three on-peak and three off-peak consumer units distributed round the house (plus a separate consumer unit in the garage). OK it is overkill, but it gives me flexibility. I also needed a 63A 3-phase contactor installed for switching the supplies to the off-peak consumer units.

Having put in a 4-core SWA cable to the garage (in case I wanted off-peak power in a 'garden store' room) it became easy to use two of those cores to feed the charging point direct from the main distribution board.
 

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For three phase, you will have a lot bigger DISTRIBUTION board and almost all the metering and switchgear stuff will NOT be bog standard cheap domestic stuff.
 

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To be fair, I haven't measured single day power consumption recently, but annual consumption from the grid had gone down from about 27000kWh to about 9500kWh or so. That was before installing better controls on the heat pumps - so they basically just ran almost continuously controlled by the thermostat (except for warmer days in summer). I now have WiFi enabled controllers connected to them all, so expect slightly lower usage during winter. We have also added an EV in the meantime, which will add a few thousand kWh to the total (mostly on cheap rate overnight).

One advantage of knowing the ~135kWh figure was that I was fairly confident that we didn't need much more than 5kW of continuous heat input even in pretty cold weather - which can easily be supplied by the heat pumps.

We're hoping to soon install a Sunamp phase change thermal store along with an 'Eddi' controller to monitor all three phases so that we can make better use of our PV production (and get mains pressure hot water, yay!) - at the moment we have an old fashioned hot water tank, with the immerser controlled by a 'Solar iBoost' which can only monitor one phase, so we don't make the best use of our PV generation to provide hot water - you could consider that another potential downside os a three phase supply: it's harder to use devices such as smart meters and solar diverters because they're almost all designed for single phase.
With the overall 3 fold gross reduction in daily max consumption????, it would theoretically possible to achieve the same COST saving by using night storage and Octopus Go. OK not not nearly as flexible as your setup.

The phase change heat storage, no doubt heated electrically on an off peak tariff, sounds like a great system.
 

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We're hoping to soon install a Sunamp phase change thermal store along with an 'Eddi' controller to monitor all three phases so that we can make better use of our PV production (and get mains pressure hot water, yay!) - at the moment we have an old fashioned hot water tank, with the immerser controlled by a 'Solar iBoost' which can only monitor one phase, so we don't make the best use of our PV generation to provide hot water - you could consider that another potential downside os a three phase supply: it's harder to use devices such as smart meters and solar diverters because they're almost all designed for single phase.
Out of interest, what's the purchase cost of the Sunamp system looking like?
 

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My parents just have 3 normal consumer units on their 3 phase. Two units are just used fro night time heating with the 3rd unit doing all the rest. Unless the cost is a lot more to install I would always get 3 phase installed, even if only one phase is connected to a consumer unit.
 

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It's vacuum insulated, so much lower standing losses help justify higher cost.

Plus usual heat store advantagrs ( legonnaires risk, safety inspections, multiple heat sources)
 

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I would only consider one if the home was insulated to passive home standards and had a high risk of overheating along with not being on mains gas. Partly due to exporting excess PV power and importing gas being better for CO2.
 

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A very high cost compared to a normal mains pressure hot water tank and PV dirverter.
That's including installation and an "Eddi" and "Harvi". The unit itself is just over £2k. It has the advantage of being about a quarter the size of a mains pressure hot water tank, not being pressurised (so no regular maintenance inspections required) and being rectangular can actually fit into spaces you couldn't put a cylindrical tank anyway. It has equivalent energy storage to a 280L cylinder (though as noted above, with much lower standing losses).
 

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That's including installation and an "Eddi" and "Harvi". The unit itself is just over £2k. It has the advantage of being about a quarter the size of a mains pressure hot water tank, not being pressurised (so no regular maintenance inspections required) and being rectangular can actually fit into spaces you couldn't put a cylindrical tank anyway. It has equivalent energy storage to a 280L cylinder (though as noted above, with much lower standing losses).
Yep, that's the reason I'm investigating it. My apartment is quite small, so losing the 210ltr cylinder from the utility room would add a meaningful amount of floor space. The added efficiency benefits are almost just a bonus rather than a key motivator.
 
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