What size of MIC (kVa) for new build house for EV

The charger we got installed came with a smart energy monitor on the mains supply. We've an air to water heat pump on a 32 amp breaker. So far we've not gone over 3kw usage at any one time. Feels like there is loads of head room for 7kw charging without the upgrade, though the upgrade is easier now that the main fuse board is in the meter cabinet.

That's fair enough, most of our appliances are A+++ rated (except the dryer). It might be spiking up when we turn on the kettle or the like, but our steady state seems pretty low.

^ This

There is lots wrong in your post and understanding of the HP and EVs and fuses etc.

The 16kVA connection will suffice. I’ll write you a full explanation tomorrow.

Another factor in calculations is what is daily commute. I used to do 110km a day which worked out average 20kWh energy needed per car per day, so in less than 3 hours car would be refilled at 6/7kW charging rate. If you have a 9 hour night rate it should be possible to charge 2 cars on typical commute. It would be rare both cars would need a full charge and need to be 100% full the next day. You can set one charger to be priority over the other one to ensure one car can get more. Even just starting charging with priority car first should do that.

As said dishwashers and washing machine only use high power while heating water which may only be 10 minutes of the wash cycle.

We may be forced into smart meters with 2 hour low night pricing typical. Will you be forced smart meter on new build?

You may want to consider solar during planning. You would need massive solar to power heat pump in winter from sun during daytime. However solar is relatively cheap compared to long term bills.

Do you know the annual cost difference on different supplies?

Personally I would be worried about cost of heat pump. Electricity is crazy expensive now. I would want my house ideally passive rated (using sun through windows to warm house) and have house a+++ rated.

You need to look up "electrical diversity".

All of your post is calculating based on everything being on and drawing max power at the same time. In reality it wont happen. Thats not to say you dont need to take some precautions (load balancing etc) but the point is you dont calculate your MIC based on everything being on at the same time.

The ESB fuse could be 100A. It could also be 80A but I think they are installing 100A now. It gives you access to 80A at your consumer unit either way. Note also that the ESB fuse wont just pop at 80A. They are designed to last beyond 80A to account for load spikes when things like HP's turn on and very short bursts.

Thats a rather large heat pump for a new build. Unless its a massive house (400m²+) it looks like overkill to me. Somewhere between 6-12kW would be more normal, particularly for a modern A rated build.

Its unlikely you would wake up to an uncharged car unless you are doing huge mileage every day in both cars. In reality you will be charging them a couple of times a week and on random days. On the rare occasion where both need a big topup on the one night let the load balancing do its thing and you will still get 100kWh+ into the 2 cars over the 9hr night rate. e.g. You have an 80A fuse, 60A used by the 2 cars for 9hrs, so that's 124kWh. Thats two long range cars charged from 0-100% and you still had 20A to spare for the HP so the cars might ramp down by a few amps to just keep you under 80A. It wont change the end result much and its unlikely you would be going from 0-100% on both anyway.

Those appliances are pulling 10A for a tiny portion of their full 1-2hr cycle. Im not sure they would even pull 10A. When they are rinsing, spinning etc they use very small amount of power. When they are heating the water for a few minutes they peak, but that's only minutes, not hours (i.e. electrical diversity). So, those appliances wont materially affect your ability to have a charged car in the morning.

I'd say closer to 50A in reality.

The costs are likely to be much higher for the 29kVA but very much dependent on your local grid supply. The key thing in the ESB charges document is where it says "+ MV Network Charges". Those MV charges could be many thousands if they have to run extra supply specifically for you. The only way you would know is by asking them to give you a quote for it and they would visit your site and match that to the grid. I'd be willing to bet it will be thousands, particularly if you are in a rural setting with not much grid around you.

Yes, you should definitely be looking at that. My 12kW HP is rated for 20A but some are variable rather than a set rate whenever its running so its not drawing 20A all the time and it will also be cycling on/off as required.

Again, diversity... will the shower be running while the cars are charging? And a shower will only be running for minutes anyway so again, not a big deal. The cars will rate down while the shower is running if it happens to coincide..... rating down for 5,10,20mins over a 9hr period is just background noise.

I doubt your PC is taking anything close to 10A. Unless you are crypto mining with it or something! Again, diversity will be at play here, the PC wont be doing much at night, presumably.

16kVA will cut it.

I have all of what you have described above. It works fine on 16kVA. I do occasionally hit the limit and the charge points rate down as required. Plenty to spare over the 9hr night rate.

If you are still a bit unsure and want to future proof what you could do is wire the house to take the next step up (20kVA) but only get 16kVA from the ESB. If you find you have issues you can then relatively easily upgrade the ESB side without having to upgrade the house "tails" and consumer unit etc. Thats a discussion you'd need to have with your electrician.

Thanks so much to all for the answers, HUGELY helpful. And @ECO_Mental if a picture is worth a 1000 words, that graph of yours surely is. If I can ask how did you generate it and what are you (and anyone else who cares to comment) using to monitor your consumption like this?

Hey @ECO_Mental did you have any issues with installing multiple ShellyEM units on the one home network?

Well based on that I've bought 3 of them in prep for solar installation. I've the EV coming off the meter, so going to bang on out there on the sub board and the other two for monitoring solar, the heat pump and the cylinder. Last I'll use for the kitchen maybe or the utility.

I saw they support up to WiFi 4 and the main consumer unit sits above the router.