@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.