@bobflux The 16amp per phase figure was given by the DNO as an export rate back to the grid, apologies if that wasn't clear.

Thanks for your reply, will be going with 1 phase given the costs coming in for the build and the unnecessary extra for 3 phase. I was looking at future proofing the system at this stage but cannot justify the difference.

@toodles Hi Toodles, no we are rural so no gas, water mains, or sewage pipe. We had a shock as next door farmer is on mains so saw no issues with connection until a survey showed the water meter was approx 350m away, with no way of separating it. Quote from Anglian water was around 18k to just come under the road and terminate with our own meter. We do not own the track to the plot and we would need to trench the 350m at additional cost. Borehole is now our only option.

The thinking for solar is very joined up. Solar panels produce well under their maximum output most of the time and zero at night. They produce most of their output at the same time as everyone else's solar panels so the export side isn't long term important anyway. And with a battery you can export probably 100% of that much solar down a 16A line if you really wanted too. The point of putting solar on houses is for them to have enough power that much of the time they don't need the grid not to export a load of electricity when it's least needed.

I wouldn't be the slightest surprised if the 16A limit was known well in advance in a rural location. Lots of rural stuff is long runs where it's really difficult to manage the voltage range and the DNOs have a pretty good feel for where G98 will be the limit, and where G100 will be refused too - which is a much bigger problem and the one that you really need to scope with the DNO anyway. A G98 export limit of 3.68kW (16A) is fine. A "no G100" limit means you've got to either accept a 3.68kW inverter (useless for a decent electric house) or go partly "off grid" (or more accurately grid as input only - ie grid as big generator)

On the batteries - I'd not blame any initial specs from 2 years ago. 3 years ago it was "can I afford a 5kWh battery", 2 years ago it was "5 or 10kWh", last year it was "10kWh or maybe more", this year it's "Why bother with under 16"

Except for the proprietary package pushers (who work like Apple except there really isn't a cheap alternative to scam priced add ons) battery costs have absolutely crashed, whilst the rest of the kit has been fairly flat.

@rob-of-york Lots of detail and information to go over, thank you very much. A few angles we hadn't considered, but make a lot of sense.

Again to everyone who has contributed, many thanks.

I have much to learn on our energy requirements, equipment and installation so will be back with more questions. Great forum with knowledgeable replies.

@etchedpixels I've just looked back, it was March this year we got the quote,  ASHP, battery, solar, MVHR and underfloor heating. They are a well known supplier/installer in the region, I can only assume our communication to them wasn't detailed enough. When our detailed drawings come back we will look at the situation again. 

We are looking to use hemp-lime insulation at 400mm, triple glazing etc, we should be near passivhaus standard without the certification. 

@e-a-west Sounds as though you are going to be very much off the grid then! Sounds like a very interesting project and ‘fuel’ for a number of different topics on RHH in due course. Regards, Toodles.

@etchedpixels makes a very good point about the rural location and long cable runs likely driving a 16A limitation; I'd missed that. If the DNO also won't allow a G100 compliant export limitation device, then you cannot have a grid connected inverter larger than 3.68kW. It would be wise to find out about that sooner rather than later. No G100 is a problem for running the house off batteries with a maximum draw of only 3.68kW before pulling from the grid. It's not a total show stopper, but it's not great. A 3.5kW heat pump will only draw about 1kW, so you would still have 2.5kW left for other things before going to the grid for anything more.

I come back to my earlier point about progressing slowly on this. There is a lot to be said for getting settled in and then later looking at whether solar and batteries are worthwhile given the circumstances. If you don't have an EV yet, then £9k saved on not going for 3 phase plus circa £15k saved not installing solar and a battery buys you quite a nice new EV. That would do far more for your overall CO2 emissions than the addition of some extra solar generation and battery storage. 3p per mile running costs vs 15p per mile for an economical petrol car likely also does far more for your bank balance than limited solar exports.

Your house will be so well insulated that when it needs heating, you can simply boost the temperature slightly during cheap rate electricity periods and the building's thermal capacity and insulation will ensure that it stays within a degree or so of that temperature before the next cheap rate period arrives. Most heat pump tariffs provide two or three cheap rate time slots throughout the day, so this approach will work very well for you. That way, you'll be running your heating on half price electricity even without any solar and batteries. Of course anything that also runs in the cheap rate time slots also gets to use half price electricity, for example putting the washing and dishwasher on in the afternoon 1pm to 4pm slot. Once you've had a year of actually living in the house, you'll have hard facts about your actual electricity usage and be able to properly model whether or not solar plus batteries are worth the capital outlay. It is quite possible given your somewhat unusual circumstances that they might not be and your money would be better spent elsewhere.

will be going with 1 phase given the costs coming in for the build and the unnecessary extra for 3 phase. I was looking at future proofing the system at this stage but cannot justify the difference.

If your proposed hobby room may include any 3ph machines (lathes etc) you can use a VFD to provide a usable 3ph supply from 1ph.

If theres multiple machines needing 3ph, a rotary motor, generator setup could be an option to power the workshop.

The solar is baked in by the building regulations these days, it's also last time I looked at it about the same cost to put a tiled roof on a house as in roof solar (although arguably the on roof stuff is a shade better). The in roof hardware is much more expensive but the labour and time is way lower than the strange British obsession with nailing little rectangles together.

No G100 limits your grid tied not grid connected inverter to 3.68kW. That's a really important distinction and plenty of farms for example have really big grid connected but not grid tie inverters. There are ways and means to work around this, either by just not exporting in the first place (grid connected inverter only - effectively offgrid but with the grid as a generaotr input), and splitting things between a 3.68kW grid tie inverter that's fielding your exports and a big non grid tie inverter that's running the house. That does add a lot of complexity though.

Agree with Rob on the battery to some extent but you would still need to plan all the stuff that matters with battery in advance and you've then got to pick a hybrid inverter that supports batteries but can run without them - which narrows the field somewhat. The battery location rules are complicated and they really determine where the inverter goes. If you want to do house backup you'd also want to wire once so that you've got the essential loads split from things like the EV charger, power showers, oven etc.

Certainly battery prices seem to be on the down and everyone is predicting they'll continue to fall in price and improve.

This is way more complex than I had hoped. I have contacted a local ASHP company who seem to be aligned with Vaillant, they come recommended but looks like they do not provide other services. Ideally I would prefer a complete package, ASHP, PV, battery etc, so that they all align. I'll see what they have to say.

If, in the meantime, anyone has suggestions of highly regarded suppliers/installers in the Suffolk area please let me know, or possibly point me in the right direction on the Forum.

 "A little knowledge is a dangerous thing" springs to mind with where I was at with it all before joining here. Thank you all for your very detailed input. I shall be back with more questions no doubt.

Posted by: @e-a-west

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We will need new post and transformer at either 3phase 100kVA at £25k or 1 phase 25kVA at £16k.

Note if you have a PV inverter and either sun or charged batteries, and the electricity provider is limited to 25kVA, your actual limit before it trips is 25kVA + whatever the inverter can output. That requires a bit of thinking about the panel, since the distribution must be sized to carry the whole current.

Also consider a smart EV charging station that will exploit PV and also monitor total VA drawn from the grid and reduce charging power to avoid tripping when needed. This is a basic function, most of them do it, but Rule #1 of PV is "nothing is compatible with anything" so you must check first before painting yourself into a corner. Some of these "smart" devices will not even charge the car if the internet is down, a process known as "enshittification".

It goes without saying that the EVSE will want its own smartmeter, which will be incompatible with the smartmeter your PV inverter is married to, both being extremely overpriced variants of the exact same product you can get for very low cost on aliexpress, but with slight protocol variations to make sure your money becomes their money. 

Most "smart" EVSEs are ridiculously dumb and require manufacturer cloud access for even the most basic functions like timed charge or PV optimized charge which means it will no longer work when the manufacturer unplugs the servers, or they will decide to charge a monthly fee at some point. If you do not want to waste money on a garbage product, please check https://evcc.io/ and pick an EVSE that can be controlled locally using ethernet or modbus. They you can use evcc or home assistant or anything else.

Put a conduit of the correct size plus one between the panel and the EVSE, then another for control, then another just in case.

With a near passive house new build, consider ducted air to air heat pump. It also does cooling and air conditioning, which is nice when PV delivers "free" power in the summer, and heating COP is excellent. Ducted is problematic when the required heating power is huge because that requires moving an equally huge amount of air through ducts, which means enormous ducts and/or noisy fans. But with your low heating power requirements, there is no such drawback as long as the cooling power requirement is also reasonably low (shading, protection against sun on windows, etc).

Given current climate trends, in a well insulated house, cooling requires more power than heating, so the heat pump ends up sized for cooling and oversized for heating.

Posted by: @e-a-west

Ideally I would prefer a complete package, ASHP, PV, battery etc, so that they all align.

It might be worth taking a look at the Octopus zero bills initiative. I think your house would easily qualify in terms of the level of insulation that you have planned.

As its says in their PR,

"A Zero Bills home is a regular house with good insulation to make it energy-efficient, and it's then fitted with solar panels, a heat pump, and a home battery. These technologies work together to power the home, and our tech platform, Kraken, manages it all to make sure the energy is used in the smartest way possible."

"Residents do not pay a penny for the energy their home uses and there are no standing charges, for at least 5 (but usually 10) years. There is a generous fair use allowance, which is the amount of energy usage included in the guarantee (set at roughly double the average household usage). The only exception is that electric vehicle charging is billed separately at our super low Intelligent Octopus Go rate, which automatically charges your car at the cheapest rates, creating a complete clean energy ecosystem."

https://octopus.energy/blog/explore-zero-bills-home-customer-interview/ and many other pages that you will easily find via google.

I have no experience of this myself. Rather, I am mentioning it because it seems to fit the bill in terms of integration and easy of use. In theory, it would be fit and forget. Nothing for you to manage once installed and zero energy bills for ten years, plus EV charging at very competitive rates.