steady Posted February 21 Share Posted February 21 afternoon all , im in the process of organising new electrical connection to a new build plot and mentioned to the connection team that i maybe doing ashp and solar panels . theve asked me what size solar inverta im thinking of installing ? its all new to me i have no idea but itll be roof mounted on a 2500 sq foot 4 bed any ideas ? Link to comment Share on other sites More sharing options...
PhilT Posted February 21 Share Posted February 21 (edited) 8 minutes ago, steady said: afternoon all , im in the process of organising new electrical connection to a new build plot and mentioned to the connection team that i maybe doing ashp and solar panels . theve asked me what size solar inverta im thinking of installing ? its all new to me i have no idea but itll be roof mounted on a 2500 sq foot 4 bed any ideas ? Depends entirely on how many solar panels you want, and their power rating, but anyway you have posted this in the Heat Pump section. Try posting to the PV (solar panel) section. Edited February 21 by PhilT Link to comment Share on other sites More sharing options...
sharpener Posted February 22 Share Posted February 22 For a 250 sq m new build you are unlikely to need 3-phase, a typical 100A supply would cope with solar panels, EV, heat pump, battery system. But some DNOs are fitting 3-phase connections now as standard as I have heard. Link to comment Share on other sites More sharing options...
SteamyTea Posted February 23 Share Posted February 23 15 hours ago, sharpener said: some DNOs are fitting 3-phase connections now as standard as I have heard. Nation Grid, which used to be Western Power are fitting 3 Phase as standard, even on an upgrade. Link to comment Share on other sites More sharing options...
Bramco Posted February 23 Share Posted February 23 2 hours ago, SteamyTea said: Nation Grid, which used to be Western Power are fitting 3 Phase as standard, even on an upgrade. That's 3 phase to the house, not necessarily a 3 phase meter Link to comment Share on other sites More sharing options...
SteamyTea Posted February 23 Share Posted February 23 7 minutes ago, Bramco said: That's 3 phase to the house, not necessarily a 3 phase meter Don't know. Was chatting to an electrician about it, but never asked about the metering. It would make sense to fit a 3 phase meter as the marginal costs are tiny compared to a meter swap. Link to comment Share on other sites More sharing options...
sharpener Posted February 23 Share Posted February 23 3 hours ago, SteamyTea said: Nation Grid, which used to be Western Power are fitting 3 Phase as standard, even on an upgrade. What kind of upgrade though? If you have an 80A supply and ask for 100 they will (subject to various checks) just change the fuse for free. I wouldn't have thought they would put in a new 3 ph cable f.o.c. Link to comment Share on other sites More sharing options...
SteamyTea Posted February 23 Share Posted February 23 1 minute ago, sharpener said: What kind of upgrade though? If you have an 80A supply and ask for 100 they will (subject to various checks) just change the fuse for free. I wouldn't have thought they would put in a new 3 ph cable f.o.c. Not sure. The case I was talking about was a small cottage in Newlyn, that had a 60A supply and it was being upgraded to a 100A. The electrician I was chatting to asked why they were putting in a 3P supply, "EC charging and HP loads" was the answer. There is no practical parking and hardly any room for an HP where that cottage is. The easy way would be to ask the local DNO what the criteria is, and what sort of upgrade is done. All speculation otherwise. Link to comment Share on other sites More sharing options...
sharpener Posted February 23 Share Posted February 23 (edited) Sounds like it might have been very old and needed a new cable, and maybe a new service head, so it kinda makes sense if you are going to dig anyway. But the original cables were quite generously proportioned, if in good condition they will happily take uprating to 80A, have had that done in the past, don't know about 100. BTW not a peep out of the OP either here or on the PV board, hope he is happy! Edited February 23 by sharpener Link to comment Share on other sites More sharing options...
Bramco Posted February 24 Share Posted February 24 On 23/02/2024 at 10:16, SteamyTea said: Don't know. Was chatting to an electrician about it, but never asked about the metering. When NG put our connection in, they told me all new connections were 3 phase as there was marginal cost to them in terms of cable. The meter isn't anything to do with them, that is supplied by the Leccy Co and AFAIK, 3 phase meters (maybe it was 3 phase smart meters) were few and far between, i.e. a long wait. Our connection was set up as 100A due to the solar PV, car chargers and ASHP etc. Simon Link to comment Share on other sites More sharing options...
steady Posted February 28 Author Share Posted February 28 thanks all ,western power quoted for single and 3 phase . ive asked them if the inverta question its important to know at this stage , no answer yet Link to comment Share on other sites More sharing options...
Dillsue Posted February 28 Share Posted February 28 If you mark up the area where the panels will be mounted with typical panels, you'll have a fair idea of what you likely max output will be. You can then tell them that figure and they can move the supply design forward with a bit more certainty. In your shoes I'd be using figures of 450watt/panel with the panels 1150 wide x 1800 tall which includes gaps between them. Otherwise get a local installer to size thing up off your drawings Link to comment Share on other sites More sharing options...
sharpener Posted February 28 Share Posted February 28 (edited) 1 hour ago, steady said: thanks all ,western power quoted for single and 3 phase . ive asked them if the inverta question its important to know at this stage , no answer yet If you are planning on fitting the max panels as per @Dillsue's reply then the advantage of 3 phase is that you will automatically be allowed 3.68 kW export per phase. This is much better than arguing with the DNO to be allowed to export more than 3.68kW on a single phase supply. For comparison I have a 200 sq m barn with a S facing roof in two sections, 3.68 and 3.24 kW respectively. So you might well get 10kW off 2500 sq ft at which point this becomes significant. There is a free-to-use roof planner for solar PV on the Midsummer Wholesale website. Edited February 28 by sharpener 1 Link to comment Share on other sites More sharing options...
jack Posted February 28 Share Posted February 28 I'd at least run the cabling for three phase. It's orders of magnitude more work to go back and add it later. Link to comment Share on other sites More sharing options...
sharpener Posted February 28 Share Posted February 28 (edited) 22 min jack changed the title to Solar inverter I rather liked the distinctive title, it made this thread easier to spot! Edited February 28 by sharpener Link to comment Share on other sites More sharing options...
jack Posted February 28 Share Posted February 28 1 hour ago, sharpener said: 22 min jack changed the title to Solar inverter I rather liked the distinctive title, it made this thread easier to spot! Fair enough. I rarely change titles, but someone searching for information about inverters ought to be able to find this thread! Link to comment Share on other sites More sharing options...
matth76 Posted March 1 Share Posted March 1 (edited) A normal 100amp single phase connection is more than fine for a heat pump and solar, and a even a couple of EVs if you choose to (most modern EVs can only charge up to a max of 11 or 12kw on AC charging - most home chargers only provide AC-charging and the biggest I have seen is 7.4kw so not far off). We have all of these and very rarely get to even a fraction of even half of what our mains fuse capacity is (and that would only be on xmas day when everything is running and it is sub-zero outside - which is very rare and even then not even close to our limit and most heat pumps run at a lot less than their advertised size). The size of solar inverter shouldn't be an issue if it is a "hybrid" inverter which will be DC-coupled. The only thing I can think of is they want to make sure any excess solar generated that is sent back to the grid can be coped with - however a single phase hybrid inverter is normally only sized up to a certain size anyway so all single phase connections should be able to cope (the biggest solar hybrid inverter I have ever seen on single phase is 16kw - but generally they are all around 8kw or less). We have a 7.5kw single phase hybrid solar inverter with whole house backup and large battery storage, air source heat pump and EV. We run our whole house including running the heat pump 24 hours a day off our solar batteries (which charge up from the mains grid during the winter at off-peak tariff prices and from the sun at all other times of the year). We have 21kwh usable storage. The sizing of our solar inverter was something I researched a lot and I sourced all of my solar equipment myself with a trade account I have, and had our electrician fit it all. I sized ours according to what our peak loads in our house might potentially be, as my main objective was to be less reliant on the grid and run entirely off our battery storage. I had to fill in a G99 application form (never done one before but was fairly straight forward) as my potential hybrid inverter was going to be over 3.68kw. And the DNO approved us for a limit of 8kw export, meaning my 7.5kw inverter was allowed. You have to get G99 approval first before anything is installed over 3.68kw (unless the law has changed since I did my application). Each solar inverter will have something called a maximum continuous discharge rate, which ultimately tells you how much load in your house it can handle before the grid cuts in. Normally the smaller the advertised size of the inverter the smaller the max continuous discharge rate - the discharge rate is not always the same as the advertised "size" of the inverter (it is sometimes smaller) and it is not always the "max continuous rate" (as it may only last for 10 seconds. We have the Solax single phase hybrid inverter which allows a maximum continuous discharge rate of 7.5kw - you also need enough battery storage to get to the max potential discharge rate. You have to look in the specifications or small print to find the discharge rate but that is ultimately how I sized and sourced my inverter (a professional installer will normally do this all for you) - as well as being able to handle the size and number of PV panels on our roof - all of this you are very unlikely to know at the point of building your house. It is a bit different when you come to older more traditional solar inverters which are AC-coupled single phase string inverters (an example of this is a string inverter connected with a Tesla Powerwall) where the battery storage is also exposed to the grid. But again all of this can and should be able to be handled by all modern 100amp fuses and cabling to the local transformer. One thing the DNO may try and do is quote you for a three phase connection which is often an astronomical price compared to the more common 100a single phase connections (hence why they like to quote it as it is a lot more money for them). We had a new 100a single phase connection put in for our self-build and it was about £6k, which included all new cabling to the nearest transformer (I did all the labour for the trenches for the cables) and the new cabling is also three phase compatible so if we ever wanted three phase in the future it is only the transformer which would need replacing. But three phase was going to be over £12k total to get and not needed as we don't run heavy load any workshop tools etc. This ended up being quite a long post. In summary, I don't think I would really know what size solar inverter you are likely to want at this stage but I also don't think it will have much of a bearing on your connection (as described). In my opinion the regular 100amp single phase is far more than ample for most modern fully electric houses (like ours) but three phase is great if the quote is reasonable, so as to future proof any needs in the future. Edited March 1 by matth76 Link to comment Share on other sites More sharing options...
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