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

ECO_Mental wrote: »

Hi,

Building a new house out in the country and am I just looking to get my ESB connection. What size of MIC should I get to be some way future proofed for EV charging, I don't have an EV yet but planning to in the next year or two.

My house will have Air Source HP, MHRV and I will be putting in solar PV, 3KWp min but probably as much as I can.

Looking as the ESB site 16 kVa I think is the new minimum I think I should get if I am planning to get an EV. But ESB have 20 kVa or 29 kVa options. There isn't a 3 Phase line near me but can I get 20 kVa or 29 kVa on a single phase, but again are these over kill but I want to be future proofed as best as possible.

I have this cross posted in the Electrical forum but then though the EV charging will be the main consumer of power in the house into the future so I posted here as well. many thanks

KCross wrote: »

Are you specifically referring to 3ph there?
I have a 1ph 16kVA connection and it has an 80A fuse. A standard 12kVA connection typically has a 60A fuse and the 100A fuse is for 20kVA+

The kVA in is somewhat meaningless, it's more about the conductor size going into your unit. I have an old 8A supply in the city centre but it's fed by 25mm square conductors with an 80A main fuse.

That 8A supply pulls 40kW in the winter no problem. I rang ESB Networks after an ECIR about this a while ago and was basically told if the main fuse has not blown there is no problem.

More kVA means more ability to draw more power. The weak link is the 80A fuse. ESB Networks will replace it once but will complain the second time according to a spark I spoke to.

I have a 16kVA connection with 6kW heat pump and 2 EVs with 2 chargers

It isn't an issue for us because the chargers have load balancing built in, or rather one of them does

The chargers share the same 40A fuse. The Leaf only charges at 16A so the Zappi will monitor the load on that circuit and slow down the charging speed of the ID.4 so as not to overload the circuit

Similarly the Zappi monitors the house's usage and will slow down if the heat pump is drawing a lot of power

When we replace the Leaf the next car will probably draw 7kW, so we'll probably replace the EO with another Zappi as they can do better load balancing that way. The EO can also do load balancing but the version we have is too old for that

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You're right, a lot of it comes down to resource management. The load balancing can slow down the charging, a bit, but it's very rare that we need to charge both cars at the same time anyway

Even still, if we push up to the 40A limit for the circuit, that's 9.2kW. Over the 9 hours of night rate, that's 82kWh. On average that's probably around 435km of range

Divided between both cars that's still 200km per car per night. If you regular daily commute for both cars is more than this, then you'll need more power

Even then, you can charge a couple of hours at the day rate if needed, it's worth balancing the costs against the cost of upgrading your supply

The heat pump might not have a major impact depending on the power draw. Ours is a 6kW output so pulls around 1.5kW of electricity. I think with the immersion or backup heater it's closer to 3kW for short bursts

We haven't had any issues of overloading with the Leaf. We'll see how it goes this winter with both cars but I don't forsee any issues

I've found the folks on the ESBN customer help aren't really knowledgeable about the engineering involved and can't help with any technical stuff. They told me I need a new meter when switching to a Day/Night meter, even though I've a newer digital meter which can do all of the readings already

My house has an 80A fuse in the meter and 63A on the CU as well. Not sure what the logic behind that was, might be standard but could also be that the electrician probably had a box of 63A MCBs in the van

It does mean I'm limited to 63A, but if the meter tails support it I also have the possibility to increasing this to 80A if needed (or a but less, since I assume I'll want some buffer between the CU fuse and the ESB one)

That sounds a bit dodgy. If correct it means you can pull more than the ESB fuse and hence easily blow it. Either your electrician put in the wrong fuse or that ESB person on the phone hadnt a clue what they were talking about and you actually have an 80A meter fuse.

Do NOT do this!

^ 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.