The 18 kW/h heat pump is presumably the rated output rather than consumption? Being a little pessimistic so perhaps a COP of 3.0 meaning 6 kW/h required for the heating? I have a rather smaller drain with just over 2.5 kW/h if running flat out (rarely seen it draw more than 1.5 - 2 kW/h though). Beyond that, being all electric, we have an induction hob, immersion heater (max. 3kW/h) and one of the two microwave combination cookers runs up to about 3.5 kW/h though now that is rare as we use the air fryer for most roasting etc. We don’t have an EV, the 100 amp fuse has taken everything so far. I note that the Tesla system pulls 10 kW/h when charging plus perhaps up to 3 kW/h more for domestic draw at this time occasionally. I suppose I may have loaded the system to approx. 15kW/h at times - we are on single phase. I imagine to go three phase will be teeth suckingly expensive? Regards, Toodles. (I will be interested on the developments on this topic!)

A 100A supply will provide up to approximately 24kW, which should be more than adequate for virtually all domestic needs.

I believe that for improved battery life EV's should be charged slowly if possible.

@derek-m that should give us ample breathing room then. With the heat pump running flat out (and the house maxed out too), we're never drawing more than 5-6kW - spikes to 8kW if doing a legionnaires run. Interesting. Thank you.

@editor I did look at 3 phase, it was painful, got quoted 10k just for the DNO piece. and that was for tapping into the phases that's only 5 metres away on the street , already going to neighbours houses. Plus whatever for electrician works on my side, which I never tried to get quoted for.

I have a 100A fuse, I have a HP that pulls 6kw in worst case , only at the peak of the HW cycle. Plus 2 EV's (7kw each to charge) plus fully electric kitchen (10kw ish all maxed) plus 3 powerwalls (15kw). that does all work fine with single phase 100A. because not all are on all the time, and the batteries are bidirectional.

With 100A I can and do pull 23kw from grid during offpeak in winter for several hours if everything is charging overnight on cheap rate and the HP is running all night also. If I had less than 100A I would struggle to "download" enough cheap rate charge if both cars needed a large chunk.

Getting batteries helps as it can protect the main fuse / grid. You can tell a powerwall what the max allowed grid is, it will slow down its rate of charge (or discharge if needed, providing there is some charge in it of course) in order to protect the grid fuse.

@iancalderbank When I had the first 13.5 kW/h of Powerwall, the system was configured with ‘permissions’ from Tesla in as much that when the system was ready to go, the installers had to contact Tesla for final settings to be configured I think. At that time, I could charge the battery at 5 kW/h. When the second 13.5 kW’h of capacity was added, the installer (different company) had to finalise some settings with Tesla and the battery can now draw or discharge at a rate of 10kW/h to / from the grid. Recharges, Toodles.

I did have a 100A fuse but noticed a couple of weeks ago that it was replaced with an 80A one when the service head was replaced last year as a result of a rotting backing board.  The ASHP is still at the 'future development' stage at the moment but I do expect to have solar PV and a 6kW battery as soon as my DNO can spare the time to address my G99 application (first submitted in November, but that's another story). I already have an EV and charger. There is potentially a large power demand in the kitchen, with 2 ovens, a microwave, washing machine, dryer, dishwasher and hot tap, as the main loads.  It's most unlikely that everything will be on at the same time, but I will monitor the trends and will ask for my 100A fuse to be returned if I think there is an issue.  As a safety measure, both the EV charger and battery charger will automatically reduce demand if necessary, in any case.

@ianmk13 My G99 application took 12 weeks in 2022. Regards, Toodles.