When our battery is charging at 10 kW and the DHW is also taking 3 kW, the heat pump is taking 2 kW whilst the house ‘background load’ may be up to a further kW, we are totting up a 16 kW (or slightly more!) load to a single phase of the grid. I don’t know the main fuse rating though 🤨. Must be close to limit I feel. Regards, Toodles.

@toodles I wouldn't worry unduly about exceeding the supply fuse rating occasionally, although I suspect it could affect the 'life' of the fuse eventually.  I'm more concerned about contributing to the risk of unbalancing the 3-phase supply at my neighbourhood sub-station.

@ianmk13 Hence my mentioning of ‘single phase’; I understand about phase imbalance and I have no idea if my local substation is monitored in such a way that the balance is known or not by those who need to know. As far as I can tell, there are very few roofs adorned with PV panels in this area, there are very few heat pumps visible or known of either. I think there may be a few EV’s in the area but again, not many to my knowledge. Regards, Toodles.

@toodles If you were to be making an LCT application today (which you're not), your Total Household Demand would need to be calculated.
If that were found to be around 16kW, then your home is a borderline case for being moved to 3-phase.

The guideline figure most commonly used by DNOs is 60A current demand from a single-phase.

But there are many variables involved in the calculation:

• the size of the 3-phase cable "in the road" from which your house is supplied
• the cable length between you and the local substation transformer
• the number of houses between you and the transformer which are supplied from the same phase as you
• the 'available demand capacity' of the substation
• the total export to that substation from other houses which have solar/wind generation
• the number of houses on that substation feed with heat-pumps and/or EV chargers

I have access to that data for substations in the four regions for which NGED is the DNO.

But I don't have the algorithm which is then applied, so I still couldn't arrive at the same answer as the Network Planner for the area.

In the case of @ianmk13 (who doesn't live in post-code MK13, in case you wondered!) I did previously supply him with substation data (Nov'23), prior to the installation of his GivEnergy All-in-One storage battery.

There have obviously been changes to the loading of his substation since then, and I'm happy to share some of the current details with forum members by way of illustration:

• Transformer size: 500kVA with four 'Feeds' at 440v
• Daytime max. demand: 237kVA
• Night-time max. demand: 519kVA (3.8% overload)
• Connected properties: 269
• EV chargers: 25 (assumed to be 7½kW each)
• Heat pumps: 3
• Solar generation: 31 properties, contributing a total of 136kW (which is why daytime demand is lower)
• Storage batteries: 5 properties

Ian's location on the Feed which supplies him from that substation is significant, but I'm withholding that level of detail.

Ian - you are right to observe that the GivEnergy AIO inverter is the sticking point should you wish to (or need to) have a 3ph connection for a heat-pump.
But I don't know what version of the AIO kit you have, so I'm loathe to make any suggestion at this stage.

Thank you for that information @transparent, my G99 application for 8.96kWp. was processed (took some 12 weeks) without a query and I have not personally dealt with them since. The ASHP was installed later and any contact with my DNO was handled by the installer if it was required. I am very unlikely to be requesting an EV charging facility so I suppose I just leave well alone - though it would be nice to know if the phases are being treated nicely locally! Regards, Toodles.

Posted by: @transparent

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In the case of @ianmk13 (who doesn't live in post-code MK13, in case you wondered!)

You're giving my secrets away!  I'd wager that it's more than likely that you're not as transparent as your moniker would suggest. 😉 

My AIO is a 13.5kWh model with a gateway. If I remember correctly, the recently-announced version is also a single-phase unit.

I'm not aware of there having been any supply failures on my substation, but I frequently hear of faults within a mile or two. I would like to 'do the right thing' but I feel that I am between a rock and a hard place.  It would have been preferable had I been aware of a 3-phase upgrade option before I spent £14k last year and I could have given it some thought then. I am not too averse to my equipment being controlled by a third party: my car and battery charging benefit from the Octopus IOG tariff, but I expect that charging slots are based solely on half-hourly wholesale prices, with no consideration of grid loads. Notwithstanding the potential risk of 'bad actors', it's unfortunate that there doesn't seem to be a practicable way for a community to come together to share information for their mutual benefit to protect the security of their supply.

Is your GivEnergy AIO this one?

If so, then it's a high-voltage model.

Once you have a storage battery which operates above 75v then I'm afraid it requires a qualified electrician to delve inside.

If it had been a set of 52v batteries, then you could've re-used them in a different set-up,
connected to a 3ph inverter.

@transparent

As I thought - Rock and a hard place 😕 

I believe there are 2 variants of GivEnergy's Version 1 All-In-One product. Both have the high voltage battery but with different size inverters. I think they will have caught a lot of early-adopters off-guard by changing their design strategy.

I don't know their product history well enough.

I know that the separate inverter and battery combinations used 52v LiFePO4 battery packs.
Perhaps all the AIO units were always higher voltage.

GivEnergy had to change.

Their inverters were only capable of delivering 50% of the rated power when drawing from the battery,
and they couldn't operate in parallel to increase power output.

A new design engineer, Mick, joined them about a year ago.
That's what's brought about the radical change.

Your future direction rather depends on the size of heat-pump you're going to need.

If its power rating takes you in the direction of a 3ph supply to the house (using NGED calculations),
then it's probably more viable to sell on the GivEnergy unit.

Instead, buy a 3-phase inverter with adequate power to run the house (incl the heat-pump) in an 'off-grid' mode,
ensuring that it can be configured for Zero Export, and is approved for that on the ENA database.

Then add as many Fogstar self-assembly cabinets as you require.
Each will have a capacity of around 14 - 16kWh (depending on your choice of cells), and operate at 52v.

Posted by: @transparent

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If its power rating takes you in the direction of a 3ph supply to the house (using NGED calculations),
then it's probably more viable to sell on the GivEnergy unit.

Yes, that's what I was thinking.  That would be a shame as I otherwise like the product and the company.  In retrospect, I haven't found the accompanying App and Portal as essential as I had expected. Control via Home Assistant and 'community-provided automations' has been more than adequate.

I've been exchanging DMs with @old_scientist during the past day.

In his case the house is very close to the local substation.
That means he is unlikely to be permitted to export more than the usual 16A (3.68kW).

Being close to your local substation means that there are fewer houses between you and the transformer.
Anything you export is less likely to be used within the area served by that substation,
so there's a greater chance of it causing losses at the transformer due to phase-imbalance and harmonics.

The greater the distance between the house and the substation, the lower will be the mains voltage.

Every cable has a small, but finite, resistance.
That creates a voltage drop along the cable length.

To export to the grid, the inverter must raise its output voltage:

The higher the voltage difference between the inverter and the grid, the more current will flow.

However, the maximum voltage must not exceed 253v.
That's the statutory limit imposed by Section 27 of the The Electricity Safety, Quality and Continuity Regulations (2002).

The G98 certification for devices which can export to the grid enforces this rule.
If the grid voltage rises to 253v, then the inverter must cease operating, and effectively detach itself from the grid.

When applying to the DNO for G99, and requesting export above 16A (per phase),
the further you are from the transformer, the more likely it is that you will be permitted a higher level of export.

A significant proportion of what you export will be taken by houses between you and the substation.